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UNIVERSITY OF OULU P .O. Box 8000 F I -90014 UNIVERSITY OF OULU FINLAND
A C T A U N I V E R S I T A T I S O U L U E N S I S
Professor Esa Hohtola
University Lecturer Santeri Palviainen
Postdoctoral research fellow Sanna Taskila
Professor Olli Vuolteenaho
University Lecturer Veli-Matti Ulvinen
Director Sinikka Eskelinen
Professor Jari Juga
University Lecturer Anu Soikkeli
Professor Olli Vuolteenaho
Publications Editor Kirsti Nurkkala
ISBN 978-952-62-1336-1 (Paperback)ISBN 978-952-62-1337-8 (PDF)ISSN 0355-3191 (Print)ISSN 1796-220X (Online)
U N I V E R S I TAT I S O U L U E N S I SACTAA
SCIENTIAE RERUM NATURALIUM
U N I V E R S I TAT I S O U L U E N S I SACTAA
SCIENTIAE RERUM NATURALIUM
OULU 2016
A 680
Janne Pesonen
PHYSICOCHEMICAL STUDIES REGARDING THE UTILIZATION OF WOOD- AND PEAT-BASED FLY ASH
UNIVERSITY OF OULU GRADUATE SCHOOL;UNIVERSITY OF OULU,FACULTY OF SCIENCE
A 680
ACTA
Janne Pesonen
A C T A U N I V E R S I T A T I S O U L U E N S I SA S c i e n t i a e R e r u m N a t u r a l i u m 6 8 0
JANNE PESONEN
PHYSICOCHEMICAL STUDIES REGARDING THE UTILIZATION OF WOOD- AND PEAT-BASED FLY ASH
Academic dissertation to be presented with the assent ofthe Doctoral Training Committee of Technology andNatural Sciences of the University of Oulu for publicdefence in the OP auditorium (L10), Linnanmaa, on 21October 2016, at 12 noon
UNIVERSITY OF OULU, OULU 2016
Copyright © 2016Acta Univ. Oul. A 680, 2016
Supervised byDocent Toivo KuokkanenProfessor Mirja IllikainenProfessor Ulla Lassi
Reviewed byDoctor Eloy Asensio de LucasDoctor Maria Letizia Ruello
ISBN 978-952-62-1336-1 (Paperback)ISBN 978-952-62-1337-8 (PDF)
ISSN 0355-3191 (Printed)ISSN 1796-220X (Online)
Cover DesignRaimo Ahonen
JUVENES PRINTTAMPERE 2016
OpponentProfessor Raimo Alén
Pesonen, Janne, Physicochemical studies regarding the utilization of wood- andpeat-based fly ash. University of Oulu Graduate School; University of Oulu, Faculty of ScienceActa Univ. Oul. A 680, 2016University of Oulu, P.O. Box 8000, FI-90014 University of Oulu, Finland
Abstract
The main aim of the European Union’s waste legislation and the corresponding Finnish wastelegislation is to reduce the production of waste. Further, the aims of the European Union’s growthstrategy are to reduce the production of greenhouse gases, increase the use of renewable energy,and improve energy efficiency. According to the renewed Waste Tax Act, a waste tax has to bepaid on all fly ashes that are deposited in landfills in Finland.
A large amount of wood- and peat-based fly ashes are formed annually in Finland, and theamount is likely to increase in the future due to the increasing use of renewable energy. Previously,these ashes have mainly been deposited in industrial landfills, but the need to utilize the fly asheshas increased recently due to changes in waste legislation.
In this thesis, several issues related to the utilization of wood- and peat-based fly ash werestudied, with the general objective of improving the utilization potential of such ashes.
As the first stage of this research, the suitability of willow ash for use as a fertilizer was studied.Willow ash would be well suited for use as a fertilizer due to its very high nutrient content.However, cadmium, a heavy metal, was found to be enriched in the ashes of the studied willowspecies. Due to this, special attention should be paid when choosing willow species for energyproduction.
In the second stage of the research, the possibility of improving the strength development ofwood- and peat-based fly ashes, as well as the possibility of stabilizing fly ash containing highamounts of heavy metals via the addition of cement and/or alkali activation, was investigated.Strength development was found to be dependent on the amount of reactive calcium and the ratiobetween that amount of reactive calcium and the sum of the reactive silicon, aluminum, and sulfur(Ca/(Si + Al + S)). The studied methods performed well in terms of stabilizing barium, copper,lead, and zinc.
During the next stage, the effect of different chemical digestion methods, which are regulatedby the Finnish waste legislation, on the utilization potential of fly ash was studied. The digestionmethod had a significant impact on the results of the potassium content analysis, which couldaffect the possibility of using fly ash as a fertilizer.
As the final stage of the research, the co-granulation of ash with sewage sludge and lime wasstudied. From a technical point of view, the co-granulation was successful, although thecompressive strength of the granules was low. Additionally, an insufficient nitrogen content wasachieved with a sludge addition of 20-40 weight%.
Keywords: ash fertilizers, fertilizer legislation, fly ash, geopolymers, granulation, heavymetals, peat ash, recycled fuels, sludge, solubility, stabilization, willow, wood ash
Pesonen, Janne, Puu- ja turveperäisen lentotuhkan hyödyntämiseen tähtääviäfysikaalis-kemiallisia tutkimuksia. Oulun yliopiston tutkijakoulu; Oulun yliopisto, Luonnontieteellinen tiedekuntaActa Univ. Oul. A 680, 2016Oulun yliopisto, PL 8000, 90014 Oulun yliopisto
Tiivistelmä
Euroopan unionin jätelainsäädännön ja sitä vastaavan suomalaisen lainsäädännön tavoitteena onehkäistä jätteiden muodostumista. Euroopan Unionin kasvustrategian tavoitteena on vähentääkasvihuonekaasupäästöjä, lisätä uusiutuvan energian käyttöä ja parantaa energiatehokkuutta.Uudistetun jäteverolain mukaan kaikista kaato-paikoille sijoitetuista lentotuhkista tulee Suomes-sa maksaa jäteveroa.
Suomessa puu- ja turveperäisiä lentotuhkia muodostuu vuosittain suuria määriä ja määrätulee vielä kasvamaan uusiutuvan energiankäytön lisääntyessä. Aiemmin nämä tuhkat ovat pää-tyneet pääasiassa läjitykseen teollisuuden kaatopaikoille, mutta muuttuneen jätelainsäädännönseurauksena tarve hyödyntää lentotuhkia on lisääntynyt.
Tässä väitöstyössä tutkittiin puu- ja turveperäisten tuhkien hyödyntämiseen liittyviä kysy-myksiä. Työn yleistavoitteena oli parantaa tuhkien hyödyntämis-mahdollisuuksia.
Tutkimuksen ensimmäisessä vaiheessa tutkittiin pajutuhkan soveltuvuutta lannoitteeksi.Pajutuhka soveltuisi hyvin lannoitteeksi erittäin hyvien ravinne-pitoisuuksien ansiosta. Raskas-metalleista kadmiumin havaittiin kuitenkin rikastuvan tutkittujen pajulajien tuhkiin. Tähän tulisikiinnittää erityishuomiota, kun pajulajeja valitaan energiantuotantoa varten.
Tutkimuksen toisessa vaiheessa selvitettiin mahdollisuutta parantaa turpeen ja puun lentotuh-kien lujittumista sekä raskasmetallipitoisen lentotuhkan stabiloimista sementtilisäyksen ja/taialkaliaktivoinnin avulla. Lujuuden kehitys riippui reaktiivisen kalsiumin määrästä sekä reaktiivi-sen kalsiumin määrän ja reaktiivisten piin, alumiinin ja rikin määrien summan välisestä suhtees-ta (Ca/(Si + Al + S)). Tutkitut menetelmät toimivat hyvin bariumin, kuparin, lyijyn ja sinkin sta-biloinnissa.
Seuraavassa vaiheessa selvitettiin Suomen lainsäädännössä määritettyjen kemiallisten hajo-tusmenetelmien vaikutusta tuhkan hyödyntämispotentiaaliin. Hajotusmenetelmällä oli suuri mer-kitys kaliumin pitoisuutta määritettäessä, mikä voi vaikuttaa lentotuhkan hyödynnettävyyteenlannoitteena.
Viimeisessä vaiheessa tutkittiin tuhkan yhteisrakeistusta lietteen ja kalkin kanssa. Teknisestiyhteisrakeistus onnistui hyvin, mutta rakeiden puristuslujuus oli alhainen. Lisäksi 20 - 40 pai-no% lietelisäyksellä ei rakeisiin saatu riittävän korkeaa typpipitoisuutta.
Asiasanat: geopolymeerit, kierrätyspolttoaineet, lannoitelainsäädäntö, lentotuhka, liete,liukoisuus, paju, puutuhka, rakeistus, raskasmetallit, stabilointi, tuhkalannoitteet,turvetuhka
For the loved ones who are no longer with us.
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Acknowledgements
This research was primarily conducted in the Research Unit of Sustainable
Chemistry at the University of Oulu, although some parts of the research were
conducted in the Research Unit of Fibre and Particle Engineering at the University
of Oulu. I greatly acknowledge the “Development of tree plantations for tailings
dumps afforestation and phytoremediation in Finland and Russia” project
(European Neighborhood and Partnership Instrument Cross Border Cooperation
funding), the GEOPO project “Stabilization of hazardous ashes in inorganic
polymeric materials” (Finnish Funding Agency for Technology and Innovation
funding), the TUULI project “Sustainable utilization of ash, slag and pyrolysis
residuals” (Finnish Funding Agency for Technology and Innovation funding), and
the Biotuhka project “Biotuhkapohjaisten materiaalien hyödyntäminen
metsämaiden lannoitteina” (European Regional Development Fund funding), as
well as the companies involved, for their financial and technical support. The Oulu
University Scholarship Foundation, Tauno Tönning Foundation and Oulun läänin
talousseuran maataloussäätiö are acknowledged for providing financial support for
this work. The University of Oulu Graduate School, the Riitta and Jorma J. Takanen
Foundation, and the Kerttu Saalasti foundation are all acknowledged for awarding
conference travel grants.
I would like to thank my supervisors, Adjunctive Professor Toivo Kuokkanen,
Professor Mirja Illikainen, and Professor Ulla Lassi, for their guidance and support.
Toivo was the person who first introduced me to the topic of fly ash utilization
during my master’s degree studies and even after his retirement a couple of years
ago, he has been actively involved in my research. Without Toivo’s contribution
and his belief in my skills, this doctoral study would not have been possible. Both
Mirja and Ulla welcomed me warmly as a full member of their research teams from
the first day I stepped into their offices, and I always felt that they gave me the best
possible help and guidance.
Adjunctive Professor Jaakko Rämö and Professor Osmo Hormi are
acknowledged for the support and guidance they provided in the doctoral training
follow-up group. The official reviewers of this thesis, Maria Letizia Ruello (PhD)
from Marche Polytechnic University and Eloy Asensio de Lucas (PhD) from Eduardo Torroja Institute for construction Science, are to be thanked for their
valuable commentary. I also wish to thank all my co-authors for their valued
contributions to the articles. I wish to thank all my colleagues in the research
projects, especially Aki Villa (PhD), Juho Yliniemi (MSc), and Ville Kuokkanen
10
(PhD). My gratitude also goes to the entire staff of the Research Unit of Sustainable
Chemistry.
Special thanks must go to all my friends, since there is not enough sarcasm in my
life without their contributions. My deepest gratitude goes to my family for all their
support and encouragement over the years. Finally, thank you Tuula for always
being there for me.
Oulu, August 2016 Janne Pesonen
11
Abbreviations
AA alkali activator
CSH calcium silicate hydrate
EU European Union
FA fly ash
FBC fluidized bed combustion
ICP-OES inductively coupled plasma optical emission spectrometry
L lime
L/S liquid-to-solid ratio
NASH amorphous alkaline aluminosilicate hydrate
PC Portland cement
PCC pulverized coal combustion
REACH Registration, Evaluation, Authorisation and Restriction of
Chemicals
REF recovered fuel
S sludge
S/S stabilization and solidification
XRD X-ray diffraction
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List of original publications
This thesis is based on the following publications, which are referred throughout
the text by their Roman numerals:
I Pesonen J, Kuokkanen T, Kaipiainen E, Koskela J, Jerkku I, Pappinen A & Villa A (2014) Chemical and physical properties of short rotation tree species. European Journal of wood and wood products 72(6): 669–777.
II Pesonen J, Yliniemi J, Kuokkanen T, Ohenoja K & Illikainen M (2016) Improving the hardening of fly ash from fluidized-bed combustion of peat and wood with the addition of alkaline activator and Portland cement. Romanian Journal of Materials 46(1): 82–88.
III Pesonen J, Yliniemi J, Illikainen M, Kuokkanen T & Lassi U (2016) Stabilization/solidification of fly ash from fluidized bed combustion of recovered fuel and biofuel using alkali activation and cement addition. Journal of Environmental Chemical Engineering 4(2): 1759–1768.
IV Pesonen J, Kaakinen J, Kuokkanen T, Välimäki I & Illikainen M (2016) Comparison of standard methods for evaluating the metal concentrations in bio ash, Manuscript.
V Pesonen J, Kuokkanen V, Kuokkanen T & Illikainen M (2016) Co-granulation of bio-ash with sewage sludge and lime for fertilizer use. Journal of Environmental Chemical Engineering, In press.
The author of this thesis was the primary author of papers I–V and he has written
the first draft of all papers. He has mainly designed, conducted, and analyzed the
results of all the experiments related to these publications, with the help from the
other authors.
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15
Contents
Abstract
Tiivistelmä
Acknowledgements 9 Abbreviations 11 List of original publications 13 Contents 15 1 Introduction 17
1.1 Background ............................................................................................. 17 1.2 Scope and objectives ............................................................................... 18
2 Finnish legislation regarding fly ash utilization 21 2.1 Environmental Protection Act ................................................................. 21 2.2 Waste Act and Waste Tax Act .................................................................. 22 2.3 Landfill Decree ....................................................................................... 24 2.4 Earth Construction Decree ...................................................................... 26 2.5 Fertilizer Product Act and Decree ........................................................... 29 2.6 REACH Regulation ................................................................................. 31 2.7 Summary of the chemical digestion methods regulated by
Finnish authorities ................................................................................... 31 3 Composition and reactivity of fly ash 35
3.1 Combustion techniques and the composition of fly ash .......................... 35 3.2 Improvement of the hardening of fly ash ................................................ 36 3.3 Granulation of fly ash ............................................................................. 38 3.4 Stabilization and solidification ................................................................ 39
3.4.1 Leaching tests ............................................................................... 40 4 Materials and methods 43
4.1 Biomass samples (Paper I) ...................................................................... 43 4.2 Fly ash samples (Papers II–V) ................................................................ 43 4.3 Preparation of fly ash mortars (Papers II and III) ................................... 44 4.4 Preparation of fly ash granules (Paper V) ............................................... 46 4.5 Analytical methods ................................................................................. 48
4.5.1 Elemental analysis ........................................................................ 48 4.5.2 Compressive strength (Papers II and V) ....................................... 48 4.5.3 X-ray diffraction (Paper II) ........................................................... 49 4.5.4 Leaching tests (Paper III) ............................................................. 49 4.5.5 Neutralizing values (Paper V) ...................................................... 50
16
5 Results and discussion 51 5.1 Willow samples (Paper I) ........................................................................ 51 5.2 Fly ash Mortars ....................................................................................... 52
5.2.1 Improvement of the hardening of fly ash (Paper II) ..................... 52 5.2.2 Stabilization/solidification (Paper III) .......................................... 58
5.3 Comparison of digestion methods (Paper IV) ......................................... 64 5.3.1 Comparison of the digestion methods mandated by the
Finnish authorities for fertilizer use .............................................. 64 5.3.2 Comparison of the digestion methods mandated by the
Finnish authorities for earth construction use ............................... 65 5.4 Fly ash granules (Paper V) ...................................................................... 66
5.4.1 Compressive strengths .................................................................. 66 5.4.2 Element contents .......................................................................... 67 5.4.3 Neutralizing values ....................................................................... 70
6 Conclusions 71 References 73 List of original publications 81
17
1 Introduction
1.1 Background
The European Union’s (EU) Europe 2020 growth strategy aims to reduce
greenhouse gas emissions by 20%, increase the use of renewable energy to 20%,
and improve energy efficiency by 20% compared to the levels in 1990 by the year
2020 (European Commission 2016b). In Finland, the renewable energy target is set
higher at 38%. The aims of the EU’s circular economy strategy are to increase
recycling and the re-use of products and waste materials (European Commission
2016a), while the main aims of the EU’s waste legislation and the corresponding
Finnish waste legislation are to prevent the generation of waste and increase the
utilization of waste materials in accordance with the waste hierarchy (European
Commission 2008, Finnish Ministry of the Environment 2016a). In addition, a new
Finnish Waste Tax Act 1126/2010 (Finnish Ministry of Finance 2016) came into
force in 2011. According to the Waste Tax Act, a waste tax has to be paid on all
combustion ashes that are deposited in industrial landfills (Finnish Ministry of
Finance 2016).
In the forest-rich Nordic countries, such as Finland and Sweden, biomass
combustion is responsible for a considerable amount of the total energy production
and recent changes to the EU’s energy policies mean that the share of bioenergy in
the total energy production will continue to grow. Previously, ashes generated by
the combustion of wood and peat have mainly been disposed of in industrial
landfills, but the changes to waste legislation and the EU’s new circular economy
strategy have increased the need to utilize combustion ashes rather than disposing
of them, as well as the need to develop new ash-based products.
Ash is the inorganic, incombustible part of the fuel that is left behind after
combustion. It is usually classified as either bottom or fly ash (FA). Bottom ash is
the coarse part of the ash that is removed through the bottom of the combustion
chamber, whereas FA is the fine part of the ash, which exits the combustion
chamber together with the combustion gases and is then collected using
electrostatic precipitators. The combustion technique and the fuel that is used both
have a significant impact on the chemical composition and physical properties of
the FA.
Possible targets for the use of wood- and peat-based FA include fertilizers
(Huotari et al. 2007, Saarsalmi et al. 2012, Saarsalmi et al. 2014), earth
18
construction (Huttunen & Kujala 2000), soil stabilization (van Ejik & Obernberger,
I., Supancic, K. 2012), wastewater purification (Laohaprapanon et al. 2010), and
alkali-activated materials (Yliniemi et al. 2015). In order to utilize FA for the
abovementioned targets, the FA has to fulfill both the material requirements of the
utilization target, as well as meeting the requirements of the relevant legislation. In
practice, a good understanding of the physicochemical and mechanical properties
of the FA in question is necessary in order to meet those requirements.
1.2 Scope and objectives
In this thesis, several issues related to the utilization of wood- and peat-based FA
were studied, with the general objective being to improve the utilization potential
of such ashes.
Short rotation tree species, such as willows, are generally well suited for energy
production, although in some cases they can contain high amounts of heavy metals,
especially cadmium. Due to this, the FA from willow combustion could actually be
considered a form of hazardous waste. As the first stage of this research, the
potential of willow ash for use as a fertilizer was studied (Paper I).
Portland cement (PC) and alkali activation have been used to stabilize different
types of hazardous waste. During this stage of the research, the question of whether
or not the strength development of FA from wood and peat combustion can be
improved using PC and/or alkali activation, as well as the potential of this type of
treatment for use in stabilizing FA containing high amounts of heavy metal, was
studied (Papers II and III).
The chemical digestion method used affects the results of element content
analyses. According to the Finnish legislation concerning the utilization of FA,
several standardized digestion methods can be used in element content analyses. At
this stage of the research, the possibility of the utilized chemical digestion method
affecting the elemental analysis of FA to such an extent that it could reduce the
utilization potential of the FA was investigated (Paper IV).
Although in some cases the high heavy metal content of FA can reduce the
possibility of utilizing it, FA, especially that generated by wood combustion, is
actually a very good forest fertilizer. However, FA does not contain any nitrogen,
which is released into the atmosphere during combustion. In the final stage of the
research, whether or not the fertilizing properties of FA granules could be increased
via the addition of sewage sludge and lime was studied, as well as how these
19
additions affect other properties of the granules, such as the compressive strength
and heavy metal content (Paper V).
20
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2 Finnish legislation regarding fly ash utilization
The most important pieces of Finnish legislation concerning FA utilization are the
Environmental Protection Act 527/2014 (Finnish Ministry of the Environment
2016b), the Environmental Protection Decree 713/2014 (Finnish Ministry of the
Environment 2015c), the Waste Act 646/2011 (Finnish Ministry of the
Environment 2016a), the Waste Decree 591/2006 (Finnish Ministry of the
Environment 2015a), the Waste Tax Act 1126/2010 (Finnish Ministry of Finance
2016), and the Landfill Decree 331/2013 (Finnish Ministry of the Environment
2015b). Ash fertilizers are regulated by the Fertilizer Product Act 539/2006
(Finnish Ministry of Agriculture and Forestry 2015a) and the Fertilizer Product
Decree 24/2011 (Finnish Ministry of Agriculture and Forestry 2015b), while the
utilization of ash in earthworks is controlled by the Earth Construction Decree
591/2006 (Finnish Ministry of the Environment 2010). If a particular ash fulfills
the conditions defined by the Waste Act (Finnish Ministry of the Environment
2016a) and is therefore classified as an industrial by-product, then registration
under the EU’s REACH (Registration, Evaluation, Authorisation and Restriction of
Chemicals) Regulation 1907/2007 (European Commission 2006) is required.
In the spring of 2016, the European Commission released a proposal for the
revision of the EU’s fertilizer legislation (European Commission 2016c). One aim
of the renewed Fertilizer Regulation is to ease the launching of new organic
fertilizers into the EU market. The initiative also includes limit values for heavy
metals. However, the revision will certainly affect Finnish fertilizer legislation. At
the moment, in addition to Finland, Denmark is the only EU country that has a
specific decree designed to control ash fertilizers (Danish Ministry of the
Environment 2008). In Sweden, there is no ash fertilizer legislation, although the
Swedish Forest Agency has provided recommendations concerning the use of ash
fertilizers (Swedish Forest Agency 2008).
2.1 Environmental Protection Act
The purpose of the Environmental Protection Act 547/2014 (Finnish Ministry of
the Environment 2016b) is to prevent and reduce the risk of environmental
pollution, prevent and reduce emissions, remove the adverse effects of pollution,
and prevent environmental damage. The Environmental Protection Act further aims
to safeguard a healthy, pleasant, and ecologically diverse and sustainable
22
environment, support sustainable development, and prevent climate change. The
Environmental Protection Act is also intended to promote the sustainable use of
natural resources, reduce the amount and harmfulness of waste, and prevent the
harmful effects of waste. The Environmental Protection Act applies to industrial
and other activities that cause or can cause environmental pollution. It also applies
to waste management and activities that produce waste. According to the
Environmental Protection Act, an environmental permit is needed to conduct the
abovementioned activities. However, an environmental permit is not needed when
harmless ash is used as a fertilizer. Then, the Fertilizer Product Act 24/2011 is
applied (Finnish Ministry of Agriculture and Forestry 2015a). In addition, an
environmental permit is not required when ash is used in earthworks according to
the Earth Construction Decree 591/2006 (Finnish Ministry of the Environment
2010). The application procedure for an environmental permit is regulated by the
Environmental Protection Decree 713/2014 (Finnish Ministry of the Environment
2015c).
2.2 Waste Act and Waste Tax Act
The Waste Act 646/2011 (Finnish Ministry of the Environment 2016a) has recently
been renewed to coincide with the EU’s Waste Directive 2008/98/EC (European
Commission 2008, Finnish Ministry of the Environment 2016a). The purpose of
the Waste Act is to prevent the hazards and harm to human health and the
environment posed by waste and waste management, reduce the amount and
harmfulness of waste, promote the sustainable use of natural resources, ensure
functioning waste management, and prevent littering. The Waste Act includes a
five-step waste hierarchy, which describes the different options available for
dealing with waste. The most popular option for dealing with waste is, according
to the waste hierarchy, preventing the formation of waste streams and reducing
their harmfulness. If this is not possible, the next step down in the hierarchy is the
preparation of waste for re-use, followed by recycling, other recovery (e.g., energy
recovery), and finally, if none of the first four steps are feasible, waste should be
disposed of using ecologically beneficial methods. (Finnish Ministry of the
Environment 2016a).
The Waste Act also includes the so-called End-of-Waste criteria, which
describe how a material can be classified as an industrial by-product instead of
waste. A substance or object is not waste but rather a by-product so long as it results
23
from a production process wherein the primary aim is not the production of that
substance or object and:
1. further use of the substance or object is certain;
2. the substance or object can be used directly as is, or without any further
processing other than normal industrial practice;
3. the substance or object is produced as an integral part of a production process;
and
4. the substance or object fulfils all relevant product requirements and
requirements for the protection of the environment and human health for the
specific use thereof and, when assessed overall, its use would pose no hazard
or harm to human health or the environment. (Finnish Ministry of the
Environment 2016a).
Additionally, a substance or object is no longer waste if:
1. the substance or object has undergone a recovery operation;
2. the substance or object is commonly used for a specific purpose;
3. a market or demand exists for the substance or object;
4. the substance or object fulfils technical requirements for specific purposes and
meets the existing regulations applicable to similar products; and
5. the use thereof will not, assessed overall, pose any hazard or harm to human
health or the environment. (Finnish Ministry of the Environment 2016a).
Further, the Waste Degree 179/2012 (Finnish Ministry of the Environment 2015a)
specifies the regulations of the Waste Act (e.g., general requirements for organizing
waste management) (Finnish Ministry of the Environment 2016a).
The aim of the Waste Tax Act 1126/2010 (Finnish Ministry of Finance 2016)
is to increase waste utilization and reduce the disposal of waste in landfills. All
waste materials (including combustion ashes) for which utilization with
environmentally friendly methods is possible that are deposited into landfills are
included within the degree. Additionally, private and industrial landfills are
included within the decree. Previously, for example, combustion ashes were
exempted from the waste tax, but now a waste tax of 70 €/ton has to be paid for all
waste materials that are deposited in landfills. (Finnish Ministry of Finance 2016).
24
2.3 Landfill Decree
The purpose of the Landfill Decree 331/2013 (Finnish Ministry of the Environment
2015b) is to prevent surface and ground water, soil, and air pollution, as well as
climate change and many other environmental hazards, by controlling all aspects
of landfill design, use, closure, and post-closure care in such a way that the wastes
deposited in landfills do not cause any danger to humans or the environment over
long periods of time. (Finnish Ministry of the Environment 2015b). Landfills are classified into three types: dangerous waste landfill, non-
hazardous waste landfill, and inert waste landfill. The limit values for the different
landfill waste classes are listed in Tables 1 and 2. The two permitted methods for
the solubility measurement of harmful substances according to Landfill Decree are
the up-flow percolation test CEN/TS 14405 (2004) and the two-stage batch test
SFS-EN 12457-3 (2012). (Finnish Ministry of the Environment 2015b).
25
Table 1. Limit values for the solubility of harmful substances from waste materials for
inert waste, non-hazardous waste, and hazardous waste landfills according to the
Landfill Decree 331/2013 (Finnish Ministry of the Environment 2015b).
Element/variable Inert waste landfill
mg kg-1 dry matter
(L S-1 = 10 l kg-1)
Non-hazardous waste landfill
mg kg-1 dry matter
(L S-1 = 10 l kg-1)
Hazardous waste landfill
mg kg-1 dry matter
(L S-1 = 10 l kg-1)
As 0.5 2 25
Ba 20 100 300
Cd 0.04 1 5
Crtot 0.5 10 70
Cu 2 50 100
Hg 0.01 0.2 2
Mo 0.5 10 30
Ni 0.4 10 40
Pb 0.5 10 50
Sb 0.06 0.7 5
Se 0.1 0.5 7
Zn 4 50 200
Cl- 800 15000 25000
F- 10 150 500
SO42- 10001 20000 50000
Phenol index 1
Dissolved
organic carbon
(DOC)2
500 800 1000
Total dissolved
solids (TDS)3
4000 60000 100000
1) Waste material also fulfills the qualification requirement if the sulfate content does not exceed the
following limit values: 1,500 mg l-1 (first extract of percolation test, L S-1 = 0.1 l kg-1) and 6,000 mg kg-1 (L
S-1 = 10 l kg-1); a percolation test has to be used for content determination at L S-1 = 0.1 l kg-1; and a
batch or percolation test can be used for the content determination at L S-1 = 10 l kg-1. 2) Testing can be performed at pH 7.5–8.0 (L S-1 = 10 l kg-1) if the limit value for the DOC is exceeded in
the natural pH value of the waste material. 3) The TDS value can be used instead of the limit values for sulfate and chloride.
26
Table 2. Other requirements for waste materials deposited in inert waste, non-
hazardous waste, and hazardous waste landfills according to the Landfill Decree
331/2013 (Finnish Ministry of the Environment 2015b).
Element/variable Inert waste landfill, mg
kg-1
Non-hazardous waste
landfill
Hazardous waste landfill
Total dissolved carbon
(TOC)
30000 (3%) 5%3) 6%3,4
Benzene, toluene, ethyl
benzene, and xylenes
(BTEX)
6
Polychlorinated biphenyls
(PCB)1
1
Mineral oil (C10–C40) 500
Polyaromatic
hydrocarbons (PAH)2
40
pH ≥6.0
Neutralizing value Has to be measured and
evaluated
Has to be measured and
evaluated
Loss on ignition (LOI)4 10%
1) Total amount of congenerics 28, 52, 101, 118, 138, 153, and 180. 2) Total amount of compounds (anthracene, acenaphthene, acenaphthylene, benzo(a)anthracene,
benzo(a)pyrene, chrysene, benzo(b)fluoranthene, benzo(g,h,i)perylene, benzo(k)fluoranthene,
dibenzo(a,h)anthracene, phenanthrene, fluoranthene, fluorene, indeno(1,2,3-cd)pyrene, naphthalene,
pyrene). 3) Calculated per dry-matter. 4) The limit value for either TOC or LOI has to be applied.
2.4 Earth Construction Decree
The purpose of the Earth Construction Decree 591/2006 (Finnish Ministry of the
Environment 2010) is to promote the utilization of crushed concrete waste and fly
and bottom ashes from the combustion of coal, peat, and wood. These waste
materials can be utilized in earth construction without the need for an
environmental permit if they fulfill the criteria set by the Earth Construction Decree.
The Decree is applicable for the following earth construction purposes:
1. Public roads, streets, bicycle lanes, pavements, and areas directly connected to
these, necessary for road maintenance or traffic, excluding noise barriers;
2. Parking areas;
3. Sports grounds and routes in recreational and sports areas;
27
4. Railway yards as well as storage fields and roads in industrial areas, waste
processing areas and air traffic areas. (Finnish Ministry of the Environment
2010).
The Decree does not apply in groundwater areas that are suitable for water supply.
The wastes used in earthworks have to be either covered or paved. Covering refers
to protecting a structure containing waste with a layer of natural rock, the minimum
thickness of which is 10 cm, in order to prevent the spread of waste. Paving refers
to protecting a structure containing waste with asphalt with a maximum void of 5%,
or another material with which a corresponding level of protection can be achieved,
in order to reduce the seepage of rainwater. The limit values for the content and
solubility of harmful substances in waste are listed in Table 3. The permissible
methods for the solubility measurement of harmful substances according to Earth
Construction Decree are the up-flow percolation test CEN/TS 14405 (2004) and
the two-stage batch test SFS-EN 12457-3 (2012). The contents of harmful
substances should be determined using the SFS-EN 13656 (2003) or SFS-EN
13657 (2003) standards. (Finnish Ministry of the Environment 2010).
28
Table 3. Limit values for the content and solubility of harmful substances from fly and
bottom ashes generated by coal, peat, and wood combustion according to the Earth
Construction Decree 591/2006 (Finnish Ministry of the Environment 2010).
Harmful substance Limit value, mg kg-1 dry matter
Basic characterizations
Limit value, mg kg-1 dry matter
Quality control investigations
Content Leaching (L S-
1 = 10 l kg-1)
Covered
structure
Leaching (L
S-1 = 10 l kg-1)
Paved
structure
Content Leaching (L S-
1 = 10 l kg-1)
Covered
structure
Leaching (L S-
1 = 10 l kg-1)
Paved
structure
Polychlorinated
biphenyls (PCB)1
1.0
Polyaromatic
hydrocarbons (PAH)2
20/403
Dissolved organic
carbon (DOC)
500 500
As 50 0.5 1.5 50
Ba 3000 20 60 3000
Cd 15 0.04 0.04 15
Cr 400 0.5 3.0 400 0.5 3.0
Cu 400 2.0 6.0 400
Hg 0.01 0.01
Mo 50 0.5 6.0 50 0.5 6.0
Ni 0.4 1.2
Pb 300 0.5 1.5 300 0.5 1.5
Se 0.1 0.5 0.1 0.5
Sb 0.06 0.18
V 400 2.0 3.0 400 2.0 3.0
Zn 2000 4.0 12 2000
F- 10 50 10 50
SO42- 1000 10000 1000 10000
Cl- 800 2400 800 2400
1) Total quantity of congenerics 28, 52, 101, 118, 138, 153, and 180. 2) Polyaromatic hydrocarbons, total amount of compounds (anthracene, acenaphthene, acenaphthylene,
benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(g,h,i)perylene, benzo(k)fluoranthene,
dibenzo(a,h)anthracene, phenanthrene, fluoranthene, fluorene, indeno(1,2,3-c,d)pyrene, naphthalene,
pyrene, chrysene). 3) Covered structure/paved structure.
29
2.5 Fertilizer Product Act and Decree
The objective of the Fertilizer Product Act 539/2006 (Finnish Ministry of
Agriculture and Forestry 2015a) is, in order to ensure the quality of plant protection,
foodstuffs, and the environment, to promote the supply of safe fertilizer products
that are of good quality and suitable for plant production, utilization of by-products
suitable for use as such, as well as provision of sufficient information on fertilizer
products to their buyers and users. According to the Act, the term “fertilizer product”
refers to fertilizers, liming materials, soil conditioners, substrates, microbe products,
and by-products used as fertilizer products. Only fertilizer products with a type
designation that is included in either the national type designation list of fertilizer
products (Evira 2016) or, in the case of EC (European Community) fertilizers, the
type designation list of EC fertilizers published as an Annex to the Fertilizer
Regulation (European Commission 2003) may be imported, placed on the market,
or manufactured for placing on the market. (Finnish Ministry of Agriculture and
Forestry 2015a).
Peat-, wood-, and field biomass-based ashes are listed in the national type
designation list of fertilizer products (Evira 2016) as by-products used as fertilizer
products. There are also other attributes listed for fertilizers in the national type
designation list, including the minimum contents of key ingredients and the
analysis methods for nutrient and heavy metal contents for each fertilizer type. The
contents of heavy metals in ash fertilizers should be determined according to the
EPA 3050B (1996), EPA 3051A (2007), or CEN/TS 15411 (2006) standards. The
nutrient contents can be determined using either the EPA 3050B (1996), EPA
3051A (2007), CEN/TS 15290 (2006), or CEN/TS 15410 (2006) standards. (Evira
2016).
The quality requirements for fertilizers, such as the limit values for heavy
metals and nutrients, are found in the Fertilizer Product Decree 24/2011 (Finnish
Ministry of Agriculture and Forestry 2015b) (Table 4). These limit values do not
apply if the fertilizer products are used for the landscaping of landfills or other
enclosed areas.
30
Table 4. Limit values for heavy metals (HNO3 extraction for inorganic fertilizers and
HNO3-HCl digestion for organic fertilizers) and nutrients from ash fertilizers according
to the Fertilizer Product Decree 24/2011 (Finnish Ministry of Agriculture and Forestry
2015b).
Element/variable Unit Field fertilizers Forest fertilizers
As mg kg-1 25 40
Hg1 mg kg-1 1.0 1.0
Cd mg kg-1 2.5 25
Cr mg kg-1 300 300
Cu mg kg-1 600 700
Pb mg kg-1 100 150
Ni mg kg-1 100 150
Zn2 mg kg-1 1500 4500
P + K % ≥2
Ca % ≥6
Neutralizing value % (Ca) ≥10
1) Measured using the EPA 743 method. 2 ) The limit value can be exceeded in the case of a Cu or Zn deficiency of the soil. The limit value of Zn
for forest fertilizers can only be exceeded in peatland forests if a Zn deficiency is measured using soil,
leaf, or needle analysis; then, the maximum amount of Zn is 6000 mg kg-1 ha-1.
There are also other demands concerning cadmium and arsenic contained in the
Fertilizer Product Decree. If the phosphorus content of the fertilizer is at least 2.2%
(5% P2O5), then the cadmium content of the fertilizer may not exceed 50 mg per kg
of phosphorus (22 mg Cd / kg P2O5). In addition, the average maximum load of
cadmium should not exceed 1.5 g ha-1 a-1. In forestry, this means a maximum of
100 g ha-1 of cadmium over a 60-year time period, while in agriculture and
horticulture, the maximum is 7.5 g ha-1 over a five-year time period. The maximum
arsenic load resulting from the use of ash fertilizers in forestry should not exceed
2.65 g ha-1 a-1. The maximum arsenic load is therefore 160 g ha-1 over a 60-year
time period. (Finnish Ministry of Agriculture and Forestry 2015b).
The ash must be processed so that dusting is minimized. In practice, this means
the granulation of the ash. Only inorganic fertilizer products can be added to
granulated ash in order to increase its usefulness, or meet the minimum
requirements of the Fertilizer Product Decree. Ash fertilizers with added boron may
not be used in groundwater or nature conservation areas. (Finnish Ministry of
Agriculture and Forestry 2015b).
31
2.6 REACH Regulation
The purpose of the EU’s REACH (European Commission 2006) Regulation is to
protect human health and the environment. The REACH Regulation is applied to
the registration, evaluation, authorization, and restriction of chemicals. REACH
requires all companies to register all chemical substances that they manufacture or
import at least one ton of per year. The REACH Regulation does not apply to ash
or other wastes, which are included in the EU’s waste legislation. However, if
wastes are classified as industrial by-products, i.e., they fulfill the End-of-Waste
criteria of the Waste Act (Finnish Ministry of the Environment 2016a), they fall
within the remit of the REACH Regulation and so have to be registered. (European
Commission 2006).
2.7 Summary of the chemical digestion methods regulated by
Finnish authorities
The chemical digestion method used for the element content analysis regulated by
the Finnish Earth Construction Decree 591/2006 (Finnish Ministry of the
Environment 2010), the Finnish Fertilizer Product Decree 24/2011 (Finnish
Ministry of Agriculture and Forestry 2015b), and the national type designation list
of fertilizer products (Evira 2016) are presented in Table 5. The leaching tests are
discussed in section 3.4.1.
The Earth Construction Decree allows the use of two different chemical
digestion methods for the analysis of heavy metals: the SFS-EN 13656 standard
(2003) and the SFS-EN 13657 standard (2003). The SFS-EN 13656 standard is a
total digestion method intended to dissolve the entire sample, while the SFS-EN
13657 standard is a partial digestion method intended to digest the portion of the
elements that could become environmentally available over time. The Fertilizer
Product Decree and the national type designation list of fertilizer products allow
the use of five different chemical digestion methods for the analysis of nutrients
and/or heavy metals: the CEN/TS 15290 standard (2006), the CEN/TS 15410
standard (2006), the EPA 3050B standard (1996), the EPA 3051A standard (2007),
and the CEN/TS 15411 standard (2006). The CEN/TS 15290 (2006), CEN/TS
15410 (2006), and CEN/TS 15411 (2006) standards are total digestion methods,
while the EPA 3050B (1996) and EPA 3051A (2007) standards are partial digestion
methods. It is interesting to note that the limit values for heavy metals in inorganic
fertilizers, including FA, found in the Fertilizer Product Decree are for HNO3
32
digestion, a partial digestion method. However, according to the type designation
list of fertilizer products, total digestion can also be used for the analysis of heavy
metals.
In practice, the results of the element content analysis are higher if they are
determined with the help of total digestion rather than partial digestion. If the
results of the partial and total digestion methods are remarkably different from one
another, then simply by choosing partial digestion instead of total digestion, or vice
versa, the utilization potential of FA in a given application can be either increased
or decreased. This issue is discussed in Paper IV.
33
Table 5. The chemical digestion methods used for the element content analysis
regulated by the Finnish Earth Construction Decree 591/2006 (Finnish Ministry of the
Environment 2010), the Finnish Fertilizer Product Decree 24/2011 (Finnish Ministry of
Agriculture and Forestry 2015b), and the national type designation list of fertilizer
products (Evira 2016).
Decree Standard Elements Description
Earth Construction
Decree 591/2006
SFS-EN 13656
(2003)
Heavy metals: As, Ba, Cd,
Cr, Cu, Mo, Pb, V, Zn
Microwave-assisted digestion (HF
+ HNO3 + HCl)
SFS-EN 13657
(2003)
Heavy metals: As, Ba, Cd,
Cr, Cu, Mo, Pb, V, Zn
Microwave-assisted digestion or
thermal heating digestion (HCl +
HNO3)
Fertilizer Product Decree
24/2011 and national
type designation list of
fertilizer products
CEN/TS 15290
(2006)
Nutrients: P, K, Ca
Microwave-assisted digestion
(HNO3 + H2O2 + HF)
CEN/TS 15410
(2006)
Nutrients: P, K, Ca
Microwave-assisted digestion or
hot water bath digestion (HF +
HNO3 + HCl) or oven digestion
(HNO3 + HClO4)
EPA 3050B
(1996)
Heavy metals: As, Cd, Cr,
Cu, Pb, Ni, Zn; Nutrients:
P, K, Ca
Thermal heating digestion (HNO3
+ H2O2 + HCl)
EPA 3051A
(2007)
Heavy metals: As, Cd, Cr,
Cu, Pb, Ni, Zn; Nutrients:
P, K, Ca
Microwave-assisted digestion
(HNO3 or HNO3 + HCl)
CEN/TS 15411
(2006)
Heavy metals: As, Cd, Cr,
Cu, Pb, Ni, Zn
Microwave-assisted or hot water
bath digestion (HF + HNO3 + HCl)
or oven digestion (HNO3 + HClO4)
34
35
3 Composition and reactivity of fly ash
3.1 Combustion techniques and the composition of fly ash
The chemical composition and properties of FA are strongly dependent on the
combustion technique and the ash composition of the fuel being used. Coal is
traditionally combusted using the pulverized coal combustion (PCC) technique,
which takes place at high temperatures (1200–1300ºC) (Marx & Morin 2008, Raiko
et al. 2002). Together with a fast cooling process, this causes the FA to have a high
chemical reactivity (i.e., pozzolanic reactivity) (Xu et al. 2010). Wood and peat are
most often combusted using the fluidized bed combustion (FBC) technique
(Koornneef et al. 2007, Raiko et al. 2002). In fluidized bed combustion, an inert
bed material (typically sand) is heated between 800 and 1000ºC and then suspended
by air flow. The fluidized bed acts as a heat buffer, thereby enabling high heat
transfer between the fuel particles. FBC is less sensitive than PCC to moisture
content variations and it is therefore better suited for the combustion of wood and
peat. However, due to the lower combustion temperature, FBC FA are less reactive
than PCC FA. (Iribarne et al. 2001, Koornneef et al. 2007, Raiko et al. 2002).
The main components of wood FA are Ca, K, Mg, and P, whereas the main
components of peat and coal FA are Si, Al, and Fe. The heavy metal contents of
wood and peat FA are usually rather low. However, in some cases, the Cd content
of willow FA in particular can be quite high due to the fact that some willow species
are metal accumulators, which can be used for the phytoremediation of heavy
metals from soil (Meers et al. 2007, Mleczek et al. 2010). The accumulation of Cd
in willow ash is discussed in Paper I. (Alakangas 2000, Harding 2008).
The composition of wood ash makes it a good fertilizer for fields and forests,
since it contains all the main nutrients that plants need in almost the correct
proportions, excluding nitrogen, which is released into the atmosphere during
combustion (Karltun et al. 2008, Vesterinen 2003). This means that wood ash is
suitable for use as a fertilizer in peat lands, which contain high amounts of nitrogen
but lack phosphorus and potassium (Huotari et al. 2007). However, in nitrogen-
poor heath forests, if only an ash fertilizer is applied, an additional nitrogen source
is needed (Saarsalmi et al. 2012, Saarsalmi et al. 2014). This issue is discussed in
Paper V.
36
3.2 Improvement of the hardening of fly ash
The high pozzolanic reactivity means that PCC FA is well suited for concrete
structures, and it has long been used as a partial substitute for cement in concrete
(Kuroda et al. 2000, Mehta & Monteiro 1993). The basis of the pozzolanic
reactivity is the pozzolanic reaction, in which amorphous silicon dioxide (SiO2)
from the FA reacts with calcium hydroxide (Ca(OH)2) according to the following
reaction (Massazza 1998, Mehta 1987):
2 SiO2 + 3 Ca(OH)2 → Ca2Si2·3H2O (1)
The product of this reaction is calcium silicate hydrate (CSH), which is also the
main reaction product of cement hardening. CSH is almost solely responsible for
the final strength of concrete. In PC, CSH is formed in the hydration reactions of
calcium silicates. Additionally, the calcium hydroxide needed for the pozzolanic
reaction is formed in the hydration reactions. The main constituent of PC,
tricalcium silicate (Ca3SiO5), forms CSH and calcium hydroxide according to the
following reaction (Odler 1998):
2 Ca3SiO5 + 6 H2O → Ca3Si2O6·3H2O + 3 Ca(OH)2 (2)
Dicalcium silicate (Ca2SiO4) is the other important constituent of PC, which forms
the same CSH and calcium hydroxide during its hydration reaction as the tricalcium
silicate (Odler 1998):
2 Ca2SiO4 + 4 H2O → Ca3Si2O6·3H2O + Ca(OH)2 (3)
It is also possible to create strong structures via the alkali activation (also known
as geopolymerization) of coal FA (Fernández-Jiménez & Palomo 2005, Álvarez-
Ayuso et al. 2008). In alkali activation, a solid aluminosilicate precursor, for
example, coal FA, is dissolved in an alkali (usually Na or K) hydroxide or silicate
solution to produce a three-dimensional, amorphous alkaline aluminosilicate
hydrate (NASH) network structure (Provis & van Deventer 2007), which can have
properties comparable to hardened Portland cement. The formed material is known
as an alkali-activated material or geopolymer. The network structure is highly
disordered and the Si/Al ratio of the precursor materials affects the reaction
pathway of the polymerization reaction and the structure of the geopolymer
network; therefore, neither the pathway nor the network structure are yet fully
understood (Barbosa et al. 2000, Provis & van Deventer 2007, Rowles M.R. et al. 2007). However, the fundamental network consists of AlO4 and SiO4 tetrahedra.
37
The net negative charge imbalance caused by the valency difference between Si
and Al is compensated for by the alkali cations (Na+ or K+) (Barbosa et al. 2000,
Rowles M.R. et al. 2007). A semi-schematic presentation of the Na-polysialate
geopolymer as suggested by Barbosa et al. (2000) is presented in Figure 1.
Fig. 1. Semi-schematic presentation of the Na-polysialate geopolymer as suggested by
Barbosa et al. (Barbosa et al. 2000).
Recently, the alkali activation of coal FA and PC blends has also been studied
(Palomo et al. 2013). The products of ordinary PC reactions and alkaline activation
reactions do not form as separate gels, but instead interact and change in structure
and composition during the process, thereby causing the structure to be complex
(García-Lodeiro et al. 2012). The high pH (over 13) and the presence of aqueous
aluminate modifies the CSH towards calcium aluminosilicate (CASH) (García
Lodeiro et al. 2010). Likewise, the aqueous calcium modifies the NASH gel as
sodium is partly replaced by calcium to form (N,C)ASH gel (García-Lodeiro et al. 2010). Studies using synthetic samples have shown that at pH values of over 12,
the formation of calcium aluminosilicate CASH is favored instead of NASH, so
long as a sufficient amount of calcium is available (García-Lodeiro et al. 2011).
Wood- and peat-based FA from FBC are not well suited for high strength concrete
or alkali-activated structures, even if they contained high amounts of Si and Al,
because of the low pozzolanic reactivity (Iribarne et al. 2001, Koornneerf et al.
38
2007). However, wood FA in particular possesses self-hardening properties, mainly
because of the high calcium content (Illikainen et al. 2014, Ohenoja et al. 2016).
The self-hardening begins with the hydration of calcium oxide (CaO) into calcium
hydroxide Ca(OH)2 (Isännäinen et al. 1997):
CaO + H2O → Ca(OH)2 (4)
Calcium hydroxide gradually reacts with carbon dioxide (CO2) to form calcium
carbonate (CaCO3) (Isännäinen et al. 1997):
Ca(OH)2 + CO2 → CaCO3 + H2O (5)
If S and Al are available, then ettringite can also be formed (Illikainen et al. 2014):
Ca3Al2O6 + 3 CaSO4·2H2O + 26 H2O → Ca6Al2(SO4)3(OH)12·26H2O (6)
A common application of self-hardening is the granulation of FA to reduce dust
formation and improve the handling of ash fertilizers. Peat FA contain less calcium
than wood FA, and the self-hardening properties of peat-wood FA are generally
weaker than those of wood FA, while low-Ca ashes do not necessarily self-harden
at all (Illikainen et al. 2014). However, with alkali activation or the addition of PC,
the strength development of even low-Ca FA can be improved. These types of low-
strength materials could be used in applications where high strength is not needed,
such as soil stabilization (Kolias et al. 2005) or earthworks. The improvement of
the hardening of peat and wood FA is discussed in Paper II.
3.3 Granulation of fly ash
Granulation techniques are widely used in many applications in the pharmaceutical,
agrochemical, and mining industries (Reynolds et al. 2007, Walker 2007). The
granulation of FA is a routine treatment for FA fertilizers in Finland, although there
are only a few national research reports on the subject (Isännäinen et al. 1997,
Korpilahti 2003) and no previous scientific publications. In this thesis, the co-
granulation of FA with sewage sludge and lime was studied in Paper V.
The granulation of peat and wood FA for fertilization purposes is based on the
self-hardening reactions (4)–(6) presented in section 3.1. The most commonly used
granulator types are the rotary drum granulator and the pan granulator (Korpilahti
2003). Both granulators are based on a sloping, rotating plane along which the
wetted FA rolls. The collisions of the moist FA particles involved in a rolling motion
39
lead to the enlargement of the particles (granule nuclei). Further granule growth
takes place due to layering of FA onto these nuclei. (Walker 2007).
Granulation can also be used for the manufacturing of lightweight aggregates
from FA, which can be utilized, for example, in lightweight concrete or earthworks.
In the production of lightweight aggregates, Portland cement or alkali activation is
used to improve the hardening of the FA. (Yliniemi et al. 2016).
3.4 Stabilization and solidification
Stabilization and solidification (S/S) techniques have been widely used for the
treatment of different wastes. The main applications of S/S technology are: 1)
treatment of wastes prior to landfill disposal, 2) remediation of contaminated soils,
and 3) solidification of non-hazardous, unstable wastes such as sludges. (Conner &
Hoeffner 1998, LaGrega et al. 1994).
Using stabilization techniques, the contaminants of a waste material are
converted into less soluble, mobile, or toxic forms through chemical processes,
although stabilization does not necessarily change the physical characteristics of
the waste (Conner & Hoeffner 1998). Solidification results in the waste material
being encapsulated in a solid monolithic block. The contaminants do not
necessarily interact chemically with the solidifying reagent. Instead, they are
embedded in the solidified matrix by physical processes. In solidification, the
strength of the waste material is increased, while the compressibility and
permeability are reduced. The distinction between chemical and physical
immobilization is frequently not clear, and both mechanisms operate
simultaneously. Briefly, chemical immobilization occurs at an atomic scale,
whereas physical immobilization takes place at a micron scale. (Glasser 1997,
LaGrega et al. 1994).
The chemical immobilization of metals in S/S systems is usually achieved
through precipitation as hydroxides, carbonates, sulfates, or silicates, with the most
common being the precipitation as hydroxides. Most metal hydroxides have a
minimum solubility at some specific pH in the alkaline region. The solubility
increases as the pH moves in either direction from this point (amphoteric behavior).
For a mixture of metals, the pH control is always a compromise, since the optimum
pH is different for different metal hydroxides. Other common metal compounds in
S/S systems are less sensitive to pH than hydroxides. Additionally, the minimum
solubility of a specific metal is usually not required if the solubility is below the
regulatory limits. Metals such as Cr and Mo are oxyanionic elements. Thus, in
40
environments with a high pH, their oxidation state can be negative. Oxyanions
cannot be precipitated in this way because they cannot neutralize the negative
charge of hydroxide, carbonate, sulfate, or silicate ions. These characteristics of
oxyanions are the main reason why some elements are poorly immobilized in high
pH S/S systems (Chen et al. 2009, Conner & Hoeffner 1998).
Many types of binder materials can be used for S/S processes (Glasser 1997,
LaGrega et al. 1994). The most commonly used binder is PC. Other binder
materials include lime and different pozzolanic materials such as coal FA. Recently,
promising S/S results have also been obtained with the alkali activation of coal FA
(Guo et al. 2013, Nikolić et al. 2014, Zhang et al. 2008). In Paper III, as a new S/S
technique, the simultaneous use of Portland cement and alkali activation was
studied. The paper also deals with the possible mechanism of FA S/S.
3.4.1 Leaching tests
The effectiveness of an S/S treatment can be tested by measuring different physical,
mechanical, or chemical properties (Chen et al. 2009, LaGrega et al. 1994).
Commonly studied physical properties include moisture content, particle size,
rheology, and microstructure (X-ray diffraction). Mechanical studies include
strength, compressibility, and permeability measurements. Since the primary goal
of the S/S treatment is to reduce the release of contaminants into the environment,
chemical leaching tests provide the most useful information regarding how
successful the S/S treatment has been. Experimental conditions such as the pH, type
of leachant, leaching time, amount of leachant, and particle size of the studied
material affect the concentration of contaminants in the leachate. Therefore, results
obtained from different solubility tests cannot be compared and different types of
tests are used for different purposes. (LaGrega et al. 1994).
The solubility tests can be roughly divided into three groups: 1) regulatory tests,
2) predictive tests, and 3) investigatory tests (LaGrega et al. 1994). The first group
of tests are used in regulatory decision-making processes (environmental permits),
where the result of the test is compared to the limit values determined by the
appropriate authorities. For example, in Finland the two-stage batch test (SFS-EN
12457-3 2012) is used as a quality control test to assess whether waste materials
fulfill the regulatory requirements determined by the Earth Construction Decree
and the Landfill Decree (Finnish Ministry of the Environment 2010, Finnish
Ministry of the Environment 2015b). The extraction fluid used in the two-stage
batch test is water.
41
Predictive tests are used for modeling real world contaminant migration in the long-
term. An example of this type of test is the static diffusion test NEN 7375 (2004).
The purpose of the static diffusion test is to simulate the leaching of inorganic
components into water from monolithic materials under aerobic conditions as a
function of time. With this test, it is possible to determine the leaching mechanism
(diffusion, dissolution, depletion, or surface wash-off) of inorganic components.
Investigatory tests such as sequential extraction are used to study the binding
mechanisms of contaminants. In sequential extraction, various types of chemical
reagents are applied to the samples in a series, with each successive treatment being
more drastic than the previous one. In four-step sequential leaching, the leachable
elements are divided into four fractions: i) a water-soluble fraction, ii) an acid-
soluble fraction, iii) a reducible fraction, and iv) an oxidizable fraction
(Nurmesniemi et al. 2005, Rauret et al. 1999). In theory, the first fraction should
contain water-soluble ions, while the second fraction should contain metals bonded
electrostatically, metals bonded with weak covalent bonds, or metals bonded to
carbonates. The third fraction should contain metals bonded to Mn and Fe oxides,
while the fourth fraction should contain metals bonded to organic matter or to
different sulfides and oxides. However, sequential leaching was originally designed
for the fractionating of sediments. Therefore, the bonding of different metals that
originate from matrixes that differ notably from sediments, such as FA, cannot be
precisely deduced from sequential extraction results. For example, FA is quite basic
and the acetic acid used in the second step of sequential extraction is not strong
enough to acidify the sample matrix. Thus, even if the FA matrix did contain some
carbonates, they would not dissolve. Still, even when the bonding of metals cannot
be deduced from sequential extraction data, it nevertheless provides a good
estimate of the solubility of metals in real environmental conditions. (Rauret et al. 1999, Tessier et al. 1979).
42
43
4 Materials and methods
4.1 Biomass samples (Paper I)
The studied willow species were Salix myrsinifolia and Salix schwerinii. The
willow samples were collected from a plantation in Joensuu, Finland. The willows
had been growing for four years. Two samples of both species were studied: one
sample containing only stem wood (S) and one sample containing both stem wood
and bark (SB). The samples were incinerated according to standard CEN/TS 14775
(2004) protocol. The dry weighed samples were placed in a cold oven (Nabertherm
Controller P 320) and the temperature was increased to 250°C for 1 hour. The
temperature was then increased further to 550°C for 24 hours. The incinerated
samples were named after the corresponding willow species as S. myrsinifolia S, S. myrsinifolia SB, S. schwerinii S, and S. schwerinii SB.
4.2 Fly ash samples (Papers II–V)
In total, six different FA samples were studied in this thesis (Papers II–V). Detailed
information regarding the samples is given in Table 5. All the FA samples were
obtained from Finnish power plants that use the FBC technique. Sample FA3 was
the result of the co-combustion of recovered fuel (REF) and biomass fuel, while
the other samples were the result of the co-combustion of peat and wood. The
recovered fuel was packing material waste such as plastic (not PVC), carton, paper,
and wood that was collected from industrial and retail outlets. The FA samples were
collected from either ash silos or the first field of the electrostatic precipitators.
44
Table 6. Details concerning the origin of the fly ash (FA) samples studied in this thesis.
Property FA1 FA2 FA3 FA4 FA5 FA6
Boiler type Bubbling
fluidized bed
Circulating
fluidized bed
Bubbling
fluidized bed
Circulating
fluidized bed
Circulating
fluidized bed
Circulating
fluidized bed
Boiler
capacity
246 MW 96 MW 194 MW 315 MW 55 MW 96 MW
Sample
collection
Electrostatic
precipitator
Electrostatic
precipitator
Electrostatic
precipitator
Silo Silo Silo
Sample type Incremental Incremental Incremental Aggregate Aggregate Incremental
Approximate
fuel mixture
70% wood
30% peat
70% peat
30% wood
50% REF
50% biomass
(mainly bark)
61% peat
39% wood
67% peat
25% wood
8% other fuels
(process gas,
coal, and oil)
50–60%
wood
30–40% peat
4.3 Preparation of fly ash mortars (Papers II and III)
The chemical composition and average particle size of the FA1–FA3 and PC used
in the mortars are presented in Table 6. The hydraulic reactivities of FA1 and FA2
were assessed using a selective dissolution method in order to determine the
fraction of each component that is available for short-term hardening reactions. The
reactive calcium, silica, and aluminum were determined as the amounts found to
be soluble in an ethylenediaminetetraacetic acid and triethanolamine solution with
a pH of 11.6 ± 0.1. The Ca, Si, and Al contents of the solution were determined
using the inductively coupled plasma (ICP) technique. (Dyson et al. 2007, Haha et al. 2010, Luke & Glasser 1987).
The formulae for the mortars prepared and studied in Papers II and III are
presented in Table 7. A mixture of sodium silicate (Zeopol® 25, Huber, or Merck
KGaA, Germany) and NaOH solutions (5 M or 10 M) was used as an alkali
activator (AA). NaOH solutions were prepared from NaOH pellets (p.a. ≥99%
Merck KGaA, Germany) and deionized water. The cement used in the mortars was
white Portland cement (CEM I; Finnsementti, Finland).
The mortars were prepared by first mixing the dry matter thoroughly. This dry
mixture was then slowly added to the liquid AA solution while stirring. In order to
obtain good workability of the mortars, some deionized water was added to the
mixture. Stirring was continued for 3–5 minutes. Directly after mixing, the mortars
were packed into cubic molds (35 x 35 x 35 mm), which were then placed in airtight
plastic bags for 24 hours (T = 22ºC). The samples were then removed from the
45
molds and stored in the plastic bags (T = 22ºC) until they were tested. Some
examples of the mortars are presented in Figure 2.
Table 7. Chemical compositions and average particle sizes of the fly ash (FA1–FA3) and
Portland cement (PC) samples.
Property FA1 FA2 FA3 PC
d50 (µm) 21.2 18.6 29.0 9.8
CaO (%) 25.8 9.7 27.7 68.1
SiO2 (%) 29.5 47.9 32.8 23.7
Al2O3 (%) 11.6 9.7 12.1 2.0
Fe2O3 (%) 16.6 24.2 5.9 0.4
Na2O (%) 1.9 1.1 2.7 0.2
K2O (%) 2.0 1.3 1.7 0.1
MgO (%) 3.2 1.7 2.6 0.6
P2O5 (%) 3.6 2.5 1.5 0.2
TiO2 (%) 0.3 0.2 1.8 0.0
SO3 (%) 3.9 1.6 5.5 2.1
Reactive Si (%) 2.2 1.5 11.1
Reactive Al (%) 0.8 0.3 0.5
Reactive Ca (%) 14.4 3.1 48.6
Table 8. Formulae for the fly ash FA1–FA3 mortars. The abbreviations used are: FA = fly
ash; PC = Portland cement; and AA = alkali activator.
Sample FA (%) PC (%) AA Water/binder ratio
FA1(100)AA 100 0 Yes 0.45
FA1(80)PC(20)AA 80 20 Yes 0.45
FA1(70)PC(30)AA 70 30 Yes 0.45
FA1(80)PC(20) 80 20 No 0.47
FA2(100)AA 100 0 Yes 0.58
FA2(80)PC(20)AA 80 20 Yes 0.58
FA2(70)PC(30)AA 70 30 Yes 0.58
FA2(80)PC(20) 80 20 No 0.62
FA3(80)PC(20) 80 20 No 0.28
FA3(80)PC(20)AA 80 20 Yes 0.31
FA3(70)PC(30)AA 70 30 Yes 0.31
FA3(100)AA 100 0 Yes 0.31
46
Fig. 2. Some examples of the fly ash mortars (Papers II and III). Mortar FA1(80)PC(20)AA
is on the left and mortar FA3(80)PC(20)AA is on the right.
4.4 Preparation of fly ash granules (Paper V)
The compositions and sample names of the FA granules prepared and studied in
Paper V are presented in Table 8. The hygienized sewage sludge was obtained from
a local municipal wastewater treatment plant that uses the commercial KemiCond
(Kemira 2014) method of hygienization. The lime was commercial (Biolan,
Finland) calcium hydroxide (Ca(OH)2). The FA, sewage sludge, and lime were
weighed and then mixed thoroughly using a ribbon blade agitator. While agitating
the mixture, a small amount of water was added to the dry materials until small
aggregates started to form in the paste. The pastes were granulated using a simple
rotary drum granulator (Fig. 3). The granulator consists of an angle adjustable
sloping drum that is rotated by an electric motor. After granulation, the granules
were dried at room temperature (21ºC) in open vessels in a laboratory fume hood
for 28 days. The granules in the vessels were mixed daily in order to reduce mold
growth and speed up drying. Some examples of the FA granules are presented in
Figure 4.
47
Table 9. Compositions and sample names of the fly ash FA6 granules. The
abbreviations used are: FA = fly ash; S = sludge; and L = lime.
Sample FA (%) Sludge (%) Lime (%) Water/dry matter
ratio
FA6(100) 100 0 0 0.46
FA6(80)S(20) 80 20 0 0.54
FA6(60)S(40) 60 40 0 0.78
FA6(60)S(30)L(10) 60 30 10 0.57
FA6(50)S(30)L(20) 50 30 20 0.59
FA6(40)S(30)L(30) 40 30 30 0.58
Fig. 3. The experimental rotary drum granulator used in Paper V.
Fig. 4. Some examples of the fly ash FA6 granules (Paper V). From left to right: FA6(100),
FA6(60)S(40), and FA6(50)S(30)L(20).
48
4.5 Analytical methods
Detailed descriptions of the most important analysis methods used in this research
are provided in the following subsections.
4.5.1 Elemental analysis
The standardized digestion methods used in the element content characterization
are listed in Table 9. The element contents were analyzed using inductively coupled
plasma optical emission spectrometry (ICP-OES) at an accredited test laboratory,
Ahma Ympäristö Ltd, or at the Trace Element Laboratory at the University of Oulu.
Table 10. Chemical digestion methods used in this thesis.
Digestion
method no.
Paper
no.
Standard Reagents Sample
(g)
1 IV ISO 11466 (2007) Soil quality - Extraction of trace
elements in aqua regia.
21 ml HCl
7 ml HNO3
3.0
2 I, IV, V EPA Method 3051A (2007) Microwave-assisted acid
digestion of sediments, sludges, soils, and oils.
10 ml HNO3 0.5
3 II, III, IV EPA Method 3051A (2007) Microwave-assisted acid
digestion of sediments, sludges, soils, and oils.
9 ml HNO3
3 ml HCl
0.5
4 IV SFS-EN 13656 (2003) Characterization of waste.
Microwave-assisted digestion with hydrofluoric (HF),
nitric (HNO3) and hydrochloric (HCl) acid mixture for
subsequent determination of elements.
6 ml HCl
2 ml HNO3
1 ml HF
0.5
4.5.2 Compressive strength (Papers II and V)
The compressive strengths of the FA granules and FA mortars were measured using
a Zwick Z100 Roell testing machine with TestXpert II software. The compressive
strengths of the FA granules were measured by placing a granule in a steady
position between two horizontal steel plates. A granule size of 10 mm (sieved to
this size) in diameter was used. The granule was then loaded under a constant
deformation rate of 0.01 mm/s. For each batch, the compressive strengths of 3–6
granules were measured after 28 days of curing, and their average values and
standard deviations were calculated. The compressive strengths of the FA mortars
were measured according to the European cement standard EN 196-1 (2005) after
49
14 or 28 days of curing. The average of three individual measurements was taken
in each case and the standard deviations were calculated.
4.5.3 X-ray diffraction (Paper II)
The main crystalline phases of the powdered ash mortars were identified with a
Siemens 5000 X-ray diffractometer using CuKaα radiation (40 mA and 40kV) and
a graphite monochromator. The step interval, integration time, and angle interval
used were 0.04°/step, 2.5 s/step, and 10–60°, respectively. The X-ray diffraction
(XRD) analysis was performed on the starting materials and on the ash mortars
after 14 or 28 days of curing. The International Centre for Diffraction Data database
was used to identify the crystalline phases (The International centre for diffraction
data 2006). All measurements were conducted at the Center of Microscopy and
Nanotechnology at the University of Oulu.
4.5.4 Leaching tests (Paper III)
The leaching of heavy metals was studied using three different methods: 1) a two-
stage batch test (SFS-EN 12457-3 2012); 2) a static diffusion test for monolithic
materials (NEN 7375:2004 2004); and 3) a four-step sequential leaching procedure
(Nurmesniemi et al. 2005, Rauret et al. 1999).
In the two-stage batch test SFS-EN 12457-3 (2012), the samples were crushed
and sieved to a particle size <4 mm and then mixed for 6 hours (step 1) with
deionized water (liquid-to-solid ratio; L/S = 2) on a mechanical end-over-end
tumbler. In the second step, the residue from step one was mixed for 18 hours with
deionized water (L/S = 8). The eluates from both steps were filtered (1 µm filter
paper retention) and analyzed according to the ICP-OES method. The cumulative
release (L/S = 10) was then calculated.
In the static diffusion test NEN 7375 (2004), the solid cubic mortar samples
were subjected to leaching in closed tanks using of deionized water as the leachant
(Vwater/Vsample = 4.7). The water was replaced eight times during the test (at 0.25, 1,
2.25, 6, 9, 16, 35, and 65 days). The eluates were then filtered (1 µm filter paper
retention), and the filtrates were collected and analyzed according to the ICP-OES
method. Cumulative leaching was then calculated.
In the four-step sequential leaching procedure (see Table 11), the sample
mortars were first crushed and sieved to a particle size <0.5 mm. In the first step a
50
sample size of 1.0 g was used. The eluates from each step were filtered (1 µm filter
paper retention) and then analyzed according to the ICP-OES method.
Table 11. Four-step sequential leaching procedure (Nurmesniemi et al. 2005, Rauret et al. 1999).
Step Fraction Extractant Experimental conditions
F1 Water soluble 40 ml H2O at pH 4 (with HNO3) 16 h at 22 ± 5°C, constant shaking
F2 Exchangeable and
acid soluble
40 ml HOAc 0.11 mol l-1 16 h at 22 ± 5°C, constant shaking
F3 Reducible 40 ml NH2OH·HCl 0.5 mol l-1
at pH 1.5 (with HNO3)
16 h at 22 ± 5°C, constant shaking
F4 Oxidizable 10 ml H2O2 30% w/v
10 ml H2O2 30% w/v
50 ml NH4OAc 1 mol l-1 at pH 2
(with HNO3)
1 h at 22 ± 5°C, occasional manual
shaking, then 1 h 85 ± 2°C. Reduce the
volume to less than 3 ml
1 h at 85 ± 2°C. Reduce the volume to
about 1 ml
16 h at 22 ± 5°C
4.5.5 Neutralizing values (Paper V)
The neutralizing values of the FA granules were determined according to European
standard EN 12945 (2014). The dried and crushed granules (2 g) were extracted
with 0.5 M HCl (50 ml), and the mixtures were boiled on a hot plate for 10 min.
The excess acid in the mixtures was titrated with 0.25 M NaOH solutions. The
mixtures were stirred with a magnetic stirrer during titration. The neutralizing
values were calculated based on the consumption of NaOH.
51
5 Results and discussion
5.1 Willow samples (Paper I)
The element contents of the S. myrsinifolia and S. schwerinii ash samples are
presented in Table 11. The nutrient contents of the willow ash samples were at a
good level, and they were several times higher than the minimum requirements (Ca
≥ 60000 mg kg-1 and K + P ≥ 20000 mg kg-1) for forest fertilizers stipulated by
Finnish legislation (Finnish Ministry of Agriculture and Forestry 2015b). Therefore,
these willow ashes would be well suited for use as a fertilizer.
However, the Cd contents of the ashes were 4–8 times higher than the Finnish
limit value for forest fertilizers (25 mg kg-1). In practice, this means that these ashes
could not be used as a forest fertilizer due to their high cadmium content. Even
though the Cd contents were below the detection limits in the soil (<0.4 mg kg-1),
Cd still accumulated in the willows. The accumulation of Cd is explained by the
fact that certain willow species have been found to be metal accumulators, which
can hence be used for the phytoremediation of heavy metals from soil (Meers et al. 2007, Mleczek et al. 2010). Cd accumulation and metal accumulation in general
can hamper the use of willow in energy production, especially if the amount of
soluble Cd increases together with the increasing total Cd content. In such a case,
it is possible that the ash from willow combustion may even be classified as
hazardous waste. To prevent this, special attention should be paid to choosing
willow species for energy production that are not metal accumulators.
The element contents were usually higher in the bark-free samples (2S). The
reason for this was the different ash content in the SB and S samples. The Cd
contents were also notably high in the samples containing bark (SB).
52
Table 12. Element contents in the S. myrsinifolia and S. schwerinii ash samples and the
Finnish limit values for forest fertilizers (Finnish Ministry of Agriculture and Forestry
2015b). Samples with the notation SB contain both stem wood and bark, while samples
with the notation S contain only stem wood.
Element unit S. myrsinifolia
SB
S. myrsinifolia
S
S. schwerinii
SB
S. schwerinii
S
Limit value
Ca mg kg-1 275000 209000 266000 188000 ≥60000
K mg kg-1 107000 149000 119000 135000
P mg kg-1 42000 70000 38000 63000
K + P mg kg-1 149000 219000 157000 198000 ≥20000
Mg mg kg-1 33000 48000 34000 51000
S mg kg-1 12000 14000 11000 20000
As mg kg-1 <40 <40 <40 <40 40
Cd mg kg-1 95 137 127 213 25
Cr mg kg-1 <40 <40 <40 <40 300
Cu mg kg-1 300 600 300 700 700
Ni mg kg-1 35 32 46 49 150
Pb mg kg-1 <40 <40 <40 <40 150
Zn mg kg-1 4165 3854 4797 4286 4500
5.2 Fly ash Mortars
5.2.1 Improvement of the hardening of fly ash (Paper II)
Compressive strength
The 14-day compressive strengths of the FA mortars are shown in Figure 5. Better
compressive strengths were achieved with FA1, which contained significantly more
Ca than FA2. The FA2 ash did not harden at all without the addition of PC
(FA2(100)AA).
These compressive strengths were significantly lower than the typical values
for coal FA (20 MPa and over) (García-Lodeiro et al. 2013, Palomo et al. 2013,
Temuujin et al. 2009), which was expected because peat and wood FA obtained
from FBC combustion are generally considered to have less pozzolanic activity
than coal ash obtained from PCC (Iribarne et al. 2001, Koornneef et al. 2007). The
compressive strengths of the self-hardened samples prepared from the same type
of FA were much lower in a previous study: 2.6 MPa for the FA1 type ash, while
53
the FA2 type ash barely hardened at all, so significant improvements were obtained
when cement addition and alkali activation were used (Illikainen et al. 2014).
Fig. 5. Compressive strengths of the FA1 and FA2 sample mortars (Paper II).
A very strong positive correlation between the compressive strength and the
amount of reactive Ca and a strong positive correlation between the compressive
strength and the ratio between reactive Ca and the sum of the reactive (Al + Si + S)
(Fig. 6) were found. Hence, the compressive strengths increased as the amount of
54
reactive Ca increased compared to the other reactive components. There is probably
some optimum value for this ratio, after which the compressive strength starts to
decrease. In PC, this ratio is close to 4, and here the ratio in the highest compressive
strength mortar (FA1(80)PC(20)) was close to 3.5. However, the total sum of the
reactive components also influences the strength development of the mortars in
addition to the ratio between the reactive components. For example, the one clearly
abnormal result (FA2(80)PC(20)) in Figure 6 is explained by the low sum of the
reactive components in the mortar. So, in addition to having the reactive
components in the correct proportions, there have to be enough of the reactive
components in the mortars.
The mortars studied here are very complex, since the reactive components
come from three very different sources (FA, PC, and AA) and it is difficult to
predict how these precursors interact with each other and which reaction products
are formed during the hardening process. Still, the strength development of the
mortars can be explained, at least to some extent, with these simple correlation plots.
It should be noted that the AA solution used was highly basic (pH over 14) when
compared to the pH of 11.6 of the solvents used for the reactive component
determinations. Due to the high alkalinity, the AA solution most likely dissolves
more Ca, Al, and Si than is indicated by the reactive component determinations,
which could have some effect on these correlation plots.
55
Fig. 6. Compressive strengths (14 days) of the FA1 and FA2 sample mortars (Paper II)
as a function of the reactive CaO and of the ratio (Ca/(Al + Si + S)).
56
XRD analysis
Some examples of the XRD diffractograms are shown in Figure 7. The anhydrite,
lime, and alite had mainly been consumed from the FA1 mortars after 14 days of
curing. In mortar FA1(80)PC(20), sodium aluminum sulfate and some form of
hydrated calcium aluminate were detected. A broadly distributed halo between 26°
and 37° was detected in all the FA1 sample mortars. The NASH gel in geopolymers
is usually detected as a broad halo between 20° and 40°, whereas in cement the
CSH signal is a broad peak at 30° (García-Lodeiro et al. 2011, Lecomte et al. 2006,
Pangdaeng et al. 2014). No clear CSH signal was found in the FA1 mortars,
although the broad halos indicated that some amorphous phases were formed.
Most of the anhydrite and alite phases were consumed from the FA2 mortars
after 14 days of curing. No crystalline product signals were detected in the alkali-
activated mortar FA2(80)PC(20)AA. Ettringite and portlandite were detected in
mortar FA2(80)PC(20). A visible halo between 25° and 38° could be detected in all
the FA2 sample mortars, indicating amorphous phases.
Ettringite and portlandite were only detected in the mortars that did not contain
any AA. These phases usually form during both the self-hardening of the FA and
cement hydration (Illikainen et al. 2014, Mehta & Monteiro 1993, Steenari &
Lindqvist 1997, Taylor 1997). Their absence in the mortars containing AA suggests
that the presence of the AA prevents their formation. Martinez-Ramirez and Palomo
(2001) concluded that highly alkaline media retard normal PC reactions.
Additionally, mainly amorphous phases were detected when simultaneous AA and
PC addition to coal FA was studied (García-Lodeiro et al. 2013, Palomo et al. 2013).
It should be noted that the mortars based on the FBC ashes differ significantly from
the PCC FA-based mortars, which consist almost entirely of reactive components.
In this study, all the added PC and AA increased the amount of reactive components
in the mortars, thereby increasing the strength. Due to this, remarks made regarding
those reactive precursors do not necessarily apply to the less reactive FBC ashes
studied here. In any case, the main strength increasing component in PC is the CSH
gel, while in geopolymers it is the NASH gel, which are both poorly recognizable
in XRD diffractograms. NASH gel does not include any Ca, which, according to
the compressive strength data, should play a significant role in the strength
development of the studied mortars. This means that amorphous CSH gel or other
amorphous phases (such as CASH) containing Ca should be produced even though
they cannot be recognized from the diffractograms.
57
Fig. 7. XRD diffraction data for the fly ash FA1 and FA2 and Portland cement (PC) mixes
and the sample mortars after 14 days of curing (Paper II): 1 = quartz, 2 = anorthite, 3 =
maghemite, 4 = lime, 5 = alite 6 = anhydrite, 7 = sodium aluminum sulfate, 8 = hydrated
calcium aluminate, 9 = ettringite, and 10 = portlandite.
58
5.2.2 Stabilization/solidification (Paper III)
Solubility tests
Figure 8 shows the theoretical leaching of Ba, Cr, Mo, Pb, Sb, V, and Zn versus the
determined leaching from the FA3 and FA3 mortars, as well as the limits permitted
by the Finnish government (Finnish Ministry of the Environment 2010) for heavy
metal leaching from the FA used in earthworks. The theoretical leaching was
calculated by identifying the leachable metals in the precursors and then
multiplying the leachable content by the precursor weight percentages in the final
mortars.
The leached amounts of Cr, Mo, Pb, and Zn from the FA3 mortar exceeded
Finnish limits. It is possible that the leached amount of Sb exceeded the legal limits
as well, but its concentration was below the detection limit. The leaching of Pb, Zn,
and Ba had clearly decreased in all the sample mortars. Good immobilization of
these metals has been reported before (Anastasiadou et al. 2012, Bankowski et al. 2004a, Bankowski et al. 2004b, Bie et al., Guo et al. 2013, Izquierdo et al. 2009,
Izquierdo et al. 2010, Luna Galiano et al. 2011, Minaríková & Škvára 2006,
Ogundiran et al. 2013, Xu et al. 2006, Álvarez-Ayuso et al. 2008, Škvára et al. 2009).
The leaching of Cr increased in all the mortars, while the leaching of Mo
increased in all the mortars, except FA3(80)PC(20), where it decreased. Both the
increased solubility of Cr (Izquierdo et al. 2010, Álvarez-Ayuso et al. 2008, Škvára et al. 2009) and the immobilization of Cr have been reported (Bie et al., Guo et al. 2013, Izquierdo et al. 2009, Luna Galiano et al. 2011, Xu et al. 2006). Increased
leaching of Mo has been reported from alkali-activated ash (Bankowski et al. 2004a, Izquierdo et al. 2009, Luna Galiano et al. 2011, Ogundiran et al. 2013, Álvarez-
Ayuso et al. 2008).
The leaching of Sb was below the detection limit in the FA3 mortar and in all
the cement-containing mortars, whereas it was increased in the alkali-activated
mortar FA3(100)AA. Higher leaching of Sb was reported when the ash was
stabilized/solidified with an AA than when S/S was achieved with cement (Luna
Galiano et al. 2011).
Research has suggested that the main mode of stabilization for alkali-activated
FA is precipitation as metal hydroxides (Izquierdo et al. 2009). In this study, the pH
value of the leachates was approximately the same before and after alkali activation
and/or cement addition. The leaching of all the metals would have been the same
59
before and after alkali activation and/or cement addition if the pH alone was a key
factor. The fact that it was not contradicts the idea that hydroxide precipitation is
the main mode of stabilization. The same observation has been made previously
(Ogundiran et al. 2013, Yliniemi et al. 2015).
Compared to the FA3, the solubilities of Pb and Zn were below the Finnish
Earth Construction Decree 591/2006 (Finnish Ministry of the Environment 2010)
limits (for FA used in earthworks) after alkali activation and/or cement addition,
although the solubility of Cr and Mo in all the mortars exceeded the limits, with
even higher values than in the FA3 (especially the FA3(100)AA). Additionally, the
solubility of Sb exceeded the legal limit in the FA3(100)AA mortar. Due to the high
levels of leaching of Cr, Mo, and Sb from the FA3(100)AA mortar, alkali activation
alone seemed to be the worst S/S method of all the S/S procedures studied here.
Furthermore, although the immobilization of Zn and Pb was good with all the S/S
methods, the increased leaching of Cr and Mo means that the performance of none
of the S/S methods was completely satisfactory. It is not possible to deduce from
these results whether the immobilization of Zn and Pb was chemical or physical
because the sample mortars were only ground to a particle size of <4 mm. Therefore,
it is possible that these metals were only physically encapsulated in the solidified
matrix.
60
Fig. 8. Theoretical leaching vs. determined leaching from the fly ash FA3 mortars (Paper
III) according to the EN-12457-3 (2012) standard and the limit values of the Earth
Construction Decree 591/2006 (Finnish Ministry of the Environment 2010). The dashed
line column (marked with M*) represents the calculated leaching of a metal if the
leachability was unaffected by the alkali activation and/or cement addition. The black
column presents the determined leaching concentration. The symbol X denotes that the
leachable concentration was below the detection limit.
61
The cumulative leaching results derived from the static diffusion test NEN 7375
(2004) are presented in Table 12. Overall, the results were in good agreement with
the results of the two-stage batch test, which is most likely due to the similar pH
conditions used in both tests. As the leaching of heavy metals was mostly below
the detection limit (<0.05 mg l-1), the leaching mechanism could not be determined.
However, according to the standard, if conductivities at stages 7–8 (35 and 65 days)
are less than two-times higher than conductivities at stages 5–6 (9 and 16 days), the
sample matrix is not soluble. Conductivities at stages 7–8 were on the same level
as in the stages 5–6 (5.5–7 mS), indicating that the matrix of the sample mortars
did not dissolve during the test period. This, together with the leaching data,
indicates that the sample mortars were stable and that the heavy metals were, for
the most part, immobilized well in the sample mortars, at least by the physical
encapsulation mechanism. The exceptions were the relatively high solubilities of
Cr and Mo from the alkali-activated mortar FA3(100)AA and the solubility of Ba
from the cement-containing mortar FA3(80)PC(20).
Table 13. Cumulative leaching results for the fly ash FA3 mortars (65 days) derived from
the static diffusion test NEN 7375 (2004).
Mortar Unit As Ba Cd Cr Cu Mo Ni Pb Sb V Zn
FA3(80)PC(20) mg kg-1 <1.0 5.8 <1.0 <2.3 <1.0 <1.4 <1.0 <1.0 <1.0 <1.0 <1.0
FA3(80)PC(20)A
A
mg kg-1 <1.1 <2.0 <1.1 <1.9 <1.1 2.3 <1.1 <1.1 <2.5 <1.1 <1.1
FA3(70)PC(30)A
A
mg kg-1 <1.1 <3.4 <1.1 <1.2 <1.1 <1.5 <1.1 <1.1 <1.1 <1.1 <1.1
FA3(100)AA mg kg-1 <1.2 <1.4 <1.2 5.3 <1.2 6.0 <1.2 <1.2 2.2 <1.2 <1.2
The results of the four-step sequential leaching procedure for Ba, Cu, Cr, Pb, V, and
Zn are presented in Figure 9. As explained in section 3.4.1, sequential leaching was
originally designed for the fractionating of a sediment matrix (Rauret et al. 1999,
Tessier et al. 1979), which is very different from the FA-based matrix studied here.
Therefore, the bonding of different metals cannot be precisely deduced from these
results. Nevertheless, it is clear that the first two fractions (F1 and F2) contain the
most readily bioavailable metals. Here, the first two fractions (F1 and F2) are
referred to as easily bioavailable fractions, while total bioavailability refers to the
sum of all the fractions (F1–F4) (Kaakinen et al. 2012).
The total bioavailability of Sb was clearly decreased in all the mortars, while
the total bioavailability of Zn and Cu was decreased in the FA3(80)PC(20) and
62
FA3(70)PC(30)AA mortars. The total bioavailability of Ba, Cr, and Pb was
increased in all the mortars when the dilution effect caused by the addition of
cement and AA was taken into account.
The increase in the total bioavailability after the S/S treatments suggests that
encapsulation is more likely to be a physical process than a chemical process.
However, if the sum of the easily bioavailable fractions (F1 and F2) is considered,
it can be seen that the easily bioavailable amount of Zn and Cu was decreased
considerably in the mortars containing cement (FA3(80)PC(20),
FA3(80)PC(20)AA, and FA3(70)PC(30)AA). Thus, these elements seem to be
subject to some level of chemical stabilization in addition to the physical
stabilization (encapsulation). As the leaching of these elements was increased in
the FA3(100)AA mortar (no PC), chemical stabilization likely involves reaction
products produced during cement hardening. As stated earlier, the precipitation of
heavy metals as hydroxide is unlikely. Yet, precipitation as carbonate, sulfate, or
silicate could be a possible immobilization mechanism (Chen et al. 2009). As
silicates are generally only very slightly soluble, precipitation as carbonate or
sulfate is more likely.
The total bioavailability of Ba, Cu, Cr, Pb, and Zn was highest in the alkali-
activated FA3(100)AA mortar. In addition, the amount of easily bioavailable Zn
and Cu was the highest in this mortar. Thus, the results confirm that alkali activation
alone seems to be the worst S/S method of all the S/S procedures studied here.
63
Fig. 9. Results of the four-step sequential leaching for the fly ash FA3 mortars (Paper
III). F1 = water-soluble fraction; F2 = acid-soluble fraction; F3 = reducible fraction; and
F4 = oxidizable fraction.
64
5.3 Comparison of digestion methods (Paper IV)
5.3.1 Comparison of the digestion methods mandated by the Finnish authorities for fertilizer use
As discussed in section 2.7, the permissible pre-treatment methods for determining
the concentration of heavy metals according to the Finnish Fertilizer Product
Decree 24/2011 (Finnish Ministry of Agriculture and Forestry 2015b) and the
national type designation list of fertilizer products (Evira 2016) include HNO3
extraction (method 2; Table 9) for inorganic fertilizers (including FA) and HNO3-
HCl extraction for organic fertilizers (method 3; Table 9) as described by the EPA
3051A (2007) standard. Additionally, three acid digestion (HNO3 + HCl + HF)
according to the CEN/TS 15290 (2006) standard or CEN/TS 15410 (2006)
standard can be used for nutrient content studies. The last two are total digestion
methods similar to method 4 (Table 9). EPA 3051A (2007) (methods 2 and 3) is
intended to digest the samples almost completely, except for those elements that
are tightly bound to silicate or alumina mineral fractions, rendering them non-
mobile. (Evira 2016, Finnish Ministry of Agriculture and Forestry 2015b).
In this study, the heavy metal (Cd, Cu, Ni, Pb, and Zn) contents of FA4 were
quite low, clearly lower in fact than the limits set by the Finnish authorities (Table
13). However, the As content exceeded the Finnish limit for field fertilizers. The
stronger digestion conditions of method 3 provided somewhat higher results for Zn,
Cr, Co, and Ni than those obtained by method 2. Still, the overall recoveries with
method 2 were quite good (78.4–100%). Similar behavior was observed with Ca
and P, with the recoveries of method 2 being 83.4% for Ca and 91.3% for P. The
largest differences were seen with K. For FA4, method 3 gave just over 20% higher
results than method 2. Compared to the total concentration (method 4), only 34.6%
(method 2) to 42.1% (method 3) of the K was obtained with methods 2 and 3. An
even larger difference for K was found with FA5. Method 3 gave over 30% higher
results than method 2, and the recovery percentage for method 2 was only 22.7%.
The sum of the P and K contents was below the minimum requirements of the
Finnish Fertilizer Product Decree with methods 2 and 3. However, method 4
showed that the sample met the requirements. Additionally, the Ca concentration
determined by method 2 was slightly below the minimum requirement set by the
decree, although the requirements were met with methods 3 and 4. All the methods
(2–4) are permitted by the Finnish environmental administration for nutrient
analysis, even though the use of HNO3 digestion (method 2) is recommended. In
65
practice, these results demonstrate that total digestion, as in method 4, is the
preferred method when the nutrient contents of FA fertilizers are analyzed. In the
worst case scenario, the use of nitric acid digestion can either prevent the use of ash
as a fertilizer, or lead to significant extra costs, for instance, requiring the addition
of potassium to meet the minimum requirements of the Fertilizer Product Decree.
Table 14. Heavy metal and nutrient concentrations in fly ashes FA4 and FA5 based on
three digestion methods, and a comparison with Finnish limit values (Finnish Ministry
of Agriculture and Forestry 2015b).
Sample Element Limit
value1
(mg kg-1)
Method 22
HNO3
(mg kg-1)
Recovery3
(%)
Method 32
HNO3 + HCl
(mg kg-1)
Recovery3
(%)
Method 42
HCl + HNO3 +
HF (mg kg-1)
FA4
As 25/40 33.2 (± 1.4) 94.9 34.4 (± 0.6) 98.3 35.0 (± 0.4)
Cd 2.5/25 2.2 (± 0.03) 100.0 2.2 (± 0.1) 100.0 2.2 (± 0.1)
Cr 300 116 (± 3) 78.4 136 (± 2) 91.9 148 (± 3)
Cu 600/700 104 (± 1) 81.3 108 (± 1) 84.4 128 (± 2)
Ni 100/150 51.4 (± 0.2) 87.9 53.5 (± 0.4) 91.5 58.5 (± 1.6)
Pb 100/150 42.9 (± 1.0) 80.8 44.2 (± 1.2) 83.2 53.1 (± 0.7)
Zn 1500/4500 269 (± 6) 85.7 299 (± 4) 95.2 314 (± 7)
Ca 60000 57810 (± 541) 83.4 60593 (± 629) 87.4 69290 (± 705)
K K + P
20000
6305 (± 191) 34.6 7677 (± 180) 42.1 18227 (± 363)
P 8607 (± 130) 91.3 9188 (± 51) 97.4 9429 (± 160)
FA5 K 2893 (± 133) 22.7 3874 (± 37) 30.3 12767 (± 445)
1) Field fertilizers/Forest fertilizers. 2) Mean result (± standard deviation). 3) Recovery % = (measured value)/(measured value with digestion method 4= x 100.
5.3.2 Comparison of the digestion methods mandated by the Finnish authorities for earth construction use
The digestion methods permitted by the Earth Construction Decree (Finnish
Ministry of the Environment 2010) are three acid digestion SFS-EN 13656 (2003)
(method 4) and aqua regia digestion SFS-EN 13657 (2003), which is comparable
to method 1.
All the results for FA4 obtained with methods 1 and 4 (Table 14) were clearly
below the limits of the Finnish Earth Construction Decree (Finnish Ministry of the
Environment 2010). The recoveries obtained with method 1 were mainly good
(over 80%), except for Pb (60.8%) and Ba (45.6%). Since the Finnish authorities
66
accept both these methods, method 1 should be used for the digestion in order to
minimize the heavy metal content analysis results and therefore maximize the
utilization potential in earthworks. However, it should be noted that the final
decision is made based on leaching tests instead of these content analyses. If the
heavy metal contents exceed the limit values of the decree, but the results of the
leaching tests are below their corresponding limits, then utilization in earthworks
is still possible (without an environmental permit), although in the opposite
situation such a use is not possible.
Table 15. The Finnish Earth Construction Decree limits and the heavy metal
concentrations in fly ash FA4 yielded by the two digestion methods (Finnish Ministry of
the Environment 2010).
Element Limit value
(mg kg-1)
Method 11
HCl + HNO3
(mg kg-1)
Recovery2
(%)
Method 41
HCl + HNO3 + HF
(mg kg-1)
As 50 33.6 (± 0.4) 96.0 35.0 (± 0.4)
Ba 3000 627 (± 10) 45.6 1375 (± 28)
Cd 15 1.9 (± 0.02) 86.4 2.2 (± 0.1)
Cr 400 131(± 3) 88.5 148 (± 3)
Cu 400 114 (± 3) 89.1 128 (± 2)
Mo 50 6.6 (± 0.06) 81.5 8.1 (± 0.3)
Pb 300 32.3 (± 0.2) 60.8 53.1 (± 0.7)
V 400 272 (± 5) 91.9 296 (± 3)
Zn 2000 293 (± 5) 93.3 314 (± 7)
1) Mean result ± standard deviation. 2) Recovery % = (measured value)/(measured value with digestion method 4) x 100.
5.4 Fly ash granules (Paper V)
5.4.1 Compressive strengths
The compressive strength results for the FA granules are presented in Figure 10.
The compressive strengths were reduced by up to 90% after the addition of sludge
when compared to the control granule FA6(100). The granules containing sludge
were so weak that they could easily be crushed with bare fingers, and it is likely
that they would not be able to withstand various processing stages, transportation,
67
and application to the forest. However, the optimum strength of the FA granules is
quite a complicated issue. FA is generally used for forest fertilization because of its
very long-lasting (over 20 years) fertilizing effect (Saarsalmi et al. 2012). The
granules should be hard enough to promote the gradual transfer of nutrients to the
forest soil over several years. On the other hand, too high a compressive strength
can retard and possibly prevent the leaching of nutrients.
The self-hardening reactions of the FA were presented in section 3.2 (reactions
(4) – (6)). Self-hardening begins with the hydration of calcium oxide (CaO) into
calcium hydroxide (Ca(OH)2, which gradually reacts with CO2 to form calcium
carbonate (CaCO3). Ca can also form other strength-providing products such as
ettringite (Eq. 6). One possible reason for the low strength is that the large,
unreactive sludge particles physically blocked the reactive ash and lime particles
from reaching one another. However, further studies with, for example, an electron
microscope are needed to determine the reason(s) for the low strength of the sludge-
ash granules.
Fig. 10. Compressive strengths of the fly ash FA6 granules (Paper IV).
5.4.2 Element contents
The element contents of the FA granules are presented in Table 15. The N content
of the granules remained quite low (approximately 0.1–0.3%) after the addition of
sludge, which can be explained by the relatively low dry matter content of the
sludge. At least some of the N was volatilized during granulation, which was
68
noticed as a smell of ammonia. However, the N content was in line with the relative
portion of the sludge in the granules. The typical N nutrient needs of Finnish heath
forests ranges between 120 and 200 kg ha-1, and to achieve this level, at least 45 t
ha-1 of the granule FA6(60)S(40) containing the highest concentration of N would
need to be spread in a forest. In practice, the N content of the studied granules is
too low for N-poor heath forests and thus granules with a higher sludge portion
appear to be needed.
A general observation from Table 15 is that when the concentration of one
nutrient increased, the concentration of another nutrient decreased, which makes it
difficult to determine the most suitable nutrient mix for the granules (for any given
application). The sum of the K + P contents in the granules FA6(50)S(30)L(20) and
FA6(40)S(30)L(30) fell below the minimum limit value of Finnish legislation
(Finnish Ministry of Agriculture and Forestry 2015b). However, P or K deficiency
is usually not a major problem in Finnish heath forests. In addition, the value of the
K content is strongly dependent on the digestion method used in the analysis, as
discussed in Paper IV. The heavy metal content of the granules was quite low and
the addition of sludge and lime, in particular, decreased the heavy metal content
further in all samples. All the studied granules would be suitable for use as forest
fertilizer and only the Cd content exceeded the Finnish limit for field fertilizers
(Finnish Ministry of Agriculture and Forestry 2015b). However, in samples
FA6(50)S(30)L(20) and FA6(40)S(30)L(30), the amount by which it exceeded the
limit value was within the measurement uncertainty (±18%) of the analysis method.
Thus, in practice, these two samples fulfil the requirements of Finnish legislation
concerning field fertilizers.
69
Ta
ble
16
. N
utr
ien
t an
d h
ea
vy
me
tal
co
nte
nts
of
the
fly
as
h F
A6
gra
nu
les
an
d t
he
Fin
nis
h l
imit
va
lue
s f
or
fie
ld/f
ore
st
fert
iliz
ers
(Fin
nis
h M
inis
try
of
Ag
ricu
ltu
re a
nd
Fo
restr
y 2
01
5b
).
Sa
mp
le
Unit
N
Ca
K
P
M
g
S
As
Cd
C
r C
u
Pb
Ni
Zn
FA
6(1
00
) m
g k
g-1
120
149000
13000
12000
16000
16500
10
5
98
140
39
72
540
FA
6(8
0)S
(20
) m
g k
g-1
1270
136000
11700
11800
14700
14900
8.9
4.4
90
130
34
67
500
FA
6(6
0)S
(40
) m
g k
g-1
2690
133000
11400
12800
14300
16200
9.3
4.3
86
140
33
65
490
FA
6(6
0)S
(30
)L(1
0)
mg
kg
-1
1910
154000
10600
11300
18700
14200
8.4
3.8
80
120
30
59
450
FA
6(5
0)S
(30
)L(2
0)
mg
kg
-1
2440
167000
8820
9610
22700
11900
7.4
3.1
66
100
25
51
400
FA
6(4
0)S
(30
)L(3
0)
m
g k
g-1
2050
191000
7400
8400
27100
10500
6.5
2.6
55
92
20
43
340
Lim
it va
lue
1)
mg k
g-1
-/≥6
00
00
K
+ P
-/≥
20000
25/4
0
2.5
/25
300
600/
700
100/
150
100/
150
1500/4
500
1) F
ield
/fo
rest
fe
rtili
zer
70
5.4.3 Neutralizing values
The neutralizing values of the FA6 granules are presented in Table 16. All the
granules exceeded the minimum neutralizing value (10% Ca) set by the Finnish
Fertilizer Decree (Finnish Ministry of Agriculture and Forestry 2015b). The
neutralizing value increased together with an increase in the lime content, while it
decreased slightly as the sludge content of the granules increased. In practice, the
neutralizing ability of the ash-sludge granules was high enough to enable the pH
adjustment of acidic soil, even without any addition of lime, due to the relatively
high Ca content of the FA (Table 15). However, the addition of lime clearly
improves the ability of the granules to raise the pH of acidic soil. As a comparison,
the neutralizing value of commercial lime is on average 32% Ca (Käytännön
maamies 2013).
Table 17. Neutralizing values of the fly ash FA6 granules and the Finnish limit values for
field fertilizers (Finnish Ministry of Agriculture and Forestry 2015b).
Sample Neutralizing value (% Ca)
FA6(100) 12.8
FA6(80)S(20) 12.4
FA6(60)S(40) 11.4
FA6(60)S(30)L(10) 14.4
FA6(50)S(30)L(20) 17.2
FA6(40)S(30)L(30) 19.3
Field fertilizers >10
71
6 Conclusions
In this work, various issues related to the utilization of wood- and peat-based FA
were studied, with the general objective of improving the utilization potential of
such FA. At first, the suitability of willow ash for use as a fertilizer was studied.
After this, the possibility of improving the strength development of FA obtained
from wood and peat combustion with the addition of PC and/or alkali activation,
as well as the possibility of using this type of treatment to stabilize FA containing
high amounts of heavy metals, was investigated. Then, the effects of the different
chemical digestion methods that are regulated by Finnish legislation on the
utilization potential of FA were studied. Lastly, the co-granulation of ash with
sewage sludge and lime was studied. The main findings of this thesis are:
– Willow ash would be well suited for use as a fertilizer due to its very good
nutrient contents. However, special attention should be paid to choosing willow
species for energy production that are not metal accumulators, since Cd
accumulation in particular can hamper the use of willow in energy production
if high amounts of Cd are enriched into the FA.
– The hardening properties of peat-wood FA can be improved with PC and/or
alkali activation. The strength development of the peat-wood FA-based mortars
is dependent on the amount of reactive Ca, as well as the ratio between the
amounts of reactive Ca and reactive Si + Al + S.
– Very good immobilization results can be achieved for metals such as Ba, Cu,
Pb, and Zn using PC- and/or alkali activation-based S/S of REF-biomass FA.
In general, PC-based S/S seems to perform better than alkali activation-based
S/S alone. These S/S processes are not suitable for the immobilization of
oxyanionic elements such as Cr.
– Finnish authorities allow the use of several different digestion methods for the
concentration analysis of nutrients from ash fertilizers. The measured K
content is strongly dependent on the digestion method used. Total digestion
using, for example, a mixture of three acids (HF + HCl + HNO3) would be the
preferred method when the nutrient contents of FA fertilizers are analyzed. The
use of nitric acid digestion could, in the worst case scenario, either prevent the
use of FA as a fertilizer, or lead to significant extra costs, for instance, requiring
the addition of K to meet the minimum requirements of the Fertilizer Product
Decree.
72
– From a technical point of view, FA can be co-granulated with sludge and lime
without any problems, although the addition of sludge considerably lowers the
compressive strength of the granules. Therefore, it is likely that ash-sludge
granules would not be able to withstand various processing stages,
transportation, and application to the forest as such. Additionally, a sludge
addition of 20–40% is not high enough to enable ash-sludge granules to be used
as a fertilizer in N-poor heath forests.
73
References
Alakangas E (2000) Suomessa käytettävien polttoaineiden ominaisuuksia (in Finnish). VTT Research notes 2045. Espoo, Valtion teknillinen tutkimuskeskus.
Álvarez-Ayuso E, Querol X, Plana F, Alastuey A, Moreno N, Izquierdo M, Font O, Moreno T, Diez S, Vázquez E & Barra M (2008) Environmental, physical and structural characterisation of geopolymer matrixes synthesised from coal (co-)combustion fly ashes. J Hazard Mater 154(1–3): 175–183.
Anastasiadou K, Christopoulos K, Mousios E & Gidarakos E (2012) Solidification/stabilization of fly and bottom ash from medical waste incineration facility. J Hazard Mater 207–208: 165–170.
Bankowski P, Zou L & Hodges R (2004a) Reduction of metal leaching in brown coal fly ash using geopolymers. J Hazard Mater 114: 59–67.
Bankowski P, Zou L & Hodges R (2004b) Using inorganic polymer to reduce leach rates of metals from brown coal fly ash. Minerals Eng 17: 159–166.
Barbosa V, MacKenzie K & Thaumaturgo C (2000) Synthesis and characterisation of materials based on inorganic polymers of alumina and silica: sodium polysialate polymers. Int J Inorg Mater 2: 309–317.
Bie R, Chen P, Song X & Ji X (2015) Characteristics of municipal solid waste incineration fly ash with cement solidification treatment. J Inst Energ, In press.
CEN/TS 14405 (2004) Characterization of waste. Leaching behaviour tests. Up-flow percolation test (under specified conditions). Brussels: European Committee for Standardization.
CEN/TS 14775 (2004) Solid biofuels. Method for the determination of ash content. Brussels: European Committee for Standardization.
CEN/TS 15290 (2006) Solid biofuels. Determination of major elements. Al, Ca, Fe, Mg, P, K, Si, Na and Ti. Brussels: European Committee for Standardization.
CEN/TS 15410 (2006) Solid recovered fuels. Method for the determination of the content of major elements (Al, Ca, Fe, K, Mg, Na, P, Si, Ti). Brussels: European Committee for Standardization.
CEN/TS 15411 (2006) Solid recovered fuels. Methods for the determination of the content of trace elements (As, Ba, Be, Cd, Co, Cr, Cu, Hg, Mo, Mn, Ni, Pb, Sb, Se, Tl, V and Zn). Brussels: European Committee for Standardization.
Chen QY, Tyrer M, Hills CD, Yang XM & Carey P (2009) Immobilisation of heavy metal in cement-based solidification/stabilisation: A review. Waste Manage 29: 390-403.
Conner JR & Hoeffner SL (1998) A critical review of stabilization/solidification technology. Crit Rev Environ Sci Technol 28: 397–462.
Danish Ministry of the Environment (2008) Lovtidende A. Nr. 818. Bekendtgørelse om anvendelse af bioaske til jordbrugsformål (Bioaskebekendtgørelsen) (in Danish).
Dyson HM, Richardson IG & Brough AR (2007) A Combined 29Si MAS NMR and Selective Dissolution Technique for the Quantitative Evaluation of Hydrated Blast Furnace Slag Cement Blends. J Am Ceram Soc 90: 598–602.
74
EN 12945 (2014) Liming materials. Determination of neutralizing value. Titrimetric methods. Brussels: European Committee for Standardization.
EPA Method 3050B (1996) Acid digestion of sediments, sludges, and soils. United States Environmental Protection Agency, 12.
EPA Method 3051A (2007) Microwave assisted acid digestion of sediments, sludges, soils and oils. United States Environmental Protection Agency, 25.
European Commission (2003) Regulation (EC) No 2003/2003 of the European parliament and of the council of 13 October 2003 relating to fertilisers.
European Commission (2006) Regulation (EC) No 1907/2006 of the European parliament and of the council of 18 December 2006 concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH). Off J Eur Union 49: 1–849.
European Commission (2008) Directive 2008/98/EC of the European parliament and of the council of 19 November 2008 on waste and repealing certain directives. Off J Eur Union 51(1): 3–30.
European Commission (2016a) Circular Economy Strategy. URI: http://ec.europa.eu/environment/circular-economy/index_en.htm. Cited 17.3.2016.
European Commission (2016b) Europe 2020 - Europe´s growth strategy. URI: http://ec.europa.eu/europe2020/index_en.htm. Cited 8.1.2016.
European Commission (2016) Circular Economy Package. Proposal for a Regulation of the European Parliament and of the Council laying down rules on the making available on the market of CE marked fertilising products and amending Regulations (EC) No 1069/2009 and (EC) No 1107/2009 URI: https://ec.europa.eu/transparency/regdoc/rep/1/2016/EN/1-2016-157-EN-F1-1.PDF Cited 17.8.2016.
Evira (2016) Kansallinen lannoitevalmisteiden tyyppinimiluettelo (in Finnish). Fernández-Jiménez A & Palomo A (2005) Composition and microstructure of alkali
activated fly ash binder: Effect of the activator. Cem Concr Res 35: 1984–1992. Finnish Ministry of Agriculture and Forestry (2015a) Lannoitevalmistelaki 539/2006 (in
Finnish). URI: http://www.finlex.fi/fi/laki/ajantasa/2006/20060539. Cited 31.3.2016. Finnish Ministry of Agriculture and Forestry (2015b) Maa- ja metsätalousministeriön asetus
lannoitevalmisteista 24/11 (in Finnish). URI: http://www.finlex.fi/data/normit/37638-11024fi.pdf. Cited 25.11.2015.
Finnish Ministry of Finance (2016) Jäteverolaki 1126/2010 (in Finnish). URI: http://www.finlex.fi/fi/laki/ajantasa/2010/20101126. Cited 8.1.2016.
Finnish Ministry of the Environment (2010) Valtioneuvoston asetus eräiden jätteiden hyödyntämisestä maarakentamisessa 591/2006 (in Finnish). URI: http://finlex.fi/fi/laki/ajantasa/2006/20060591. Cited 7.1.2016.
Finnish Ministry of the Environment (2015a) Valtioneuvoston asetus jätteistä 179/2012 (in Finnish). URI: http://www.finlex.fi/fi/laki/ajantasa/2012/20120179. Cited 31.3.2016.
Finnish Ministry of the Environment (2015b) Valtioneuvoston asetus kaatopaikoista 331/2013 (in Finnish). URI: http://www.finlex.fi/fi/laki/alkup/2013/20130331. Cited 7.1.2016.
75
Finnish Ministry of the Environment (2015c) Valtioneuvoston asetus ympäristönsuojelusta 713/2014 (in Finnish). URI: http://www.finlex.fi/fi/laki/ajantasa/2014/20140713. Cited 31.3.2016.
Finnish Ministry of the Environment (2016a) Jätelaki 646/2011 (in Finnish). URI: http://www.finlex.fi/fi/laki/ajantasa/2011/20110646. Cited 8.1.2016.
Finnish Ministry of the Environment (2016b) Ympäristönsuojelulaki 527/2014 (in Finnish). URI: http://www.finlex.fi/fi/laki/ajantasa/2014/20140527. Cited 31.3.2016.
García Lodeiro I, Fernández-Jimenez A, Palomo A & Macphee DE (2010) Effect on fresh C-S-H gels of the simultaneous addition of alkali and aluminium. Cem Concr Res 40: 27–32.
García-Lodeiro I, Maltseva O, Palomo A & Fernández-Jiménez A (2012) Hybrid alkaline cements. Part I: Fundamentals. Rev Rom Mater Rom J Mater 42: 330–335.
García-Lodeiro I, Fernández-Jiménez A & Palomo A (2013) Variation in hybrid cements over time. Alkaline activation of fly ash–portland cement blends. Cem Concr Res 52: 112–122.
García-Lodeiro I, Palomo A, Fernández-Jiménez A & Macphee DE (2011) Compatibility studies between N-A-S-H and C-A-S-H gels. Study in the ternary diagram Na2O–CaO–Al2O3–SiO2–H2O. Cem Concr Res 41: 923–931.
García-Lodeiro I, Fernández-Jiménez A, Palomo A & Macphee DE (2010) Effect of Calcium Additions on N–A–S–H Cementitious Gels. J Am Ceram Soc 93: 1934–1940.
Glasser FP (1997) Fundamental aspects of cement solidification and stabilisation. J Hazard Mater 52: 151–170.
Guo X, Shi H & Xu M (2013) Static and dynamic leaching experiments of heavy metals from fly ash-based geopolymers. J Wuhan Univ Technol Mater Sci Ed 28: 938–943.
Haha MB, De Weerdt K & Lothenbach B (2010) Quantification of the degree of reaction of fly ash. Cem Concr Res 40: 1620–1629.
Harding NS (2008) Characteristics of Alternative Fuels. In: Tillman BGMA (ed) Combustion Engineering Issues for Solid Fuel Systems. Burlington, Academic Press: 83–131.
Huotari N, Tillman-Sutela E, Kauppi A & Kubin E (2007) Fertilization ensures rapid formation of ground vegetation on cut-away peatlands. Can J For Res 37: 874–883.
Huttunen E & Kujala K (2000) The use of peat ash in earth construction International conference on practical applications in environmental geotechnology. Espoo, Geological Survey of Finland: 83–91.
Illikainen M, Tanskanen P, Kinnunen P, Körkkö M, Peltosaari O, Wigren V, Österbacka J, Talling B & Niinimäki J (2014) Reactivity and self-hardening of fly ash from the fluidized bed combustion of wood and peat. Fuel 135: 69–75.
Iribarne J, Iribarne A, Blondin J & Anthony EJ (2001) Hydration of combustion ashes — a chemical and physical study. Fuel 80: 773–784.
Isännäinen S, Huotari SH & Mursunen H (1997) Lentotuhkan itsekovetus (in Finnish). Helsinki, Metsäteho.
ISO 11466 (2007) Soil quality – Extraction of trace elements in aqua regia. Geneva: International Organization for Standardization.
76
Izquierdo M, Querol X, Davidovits J, Antenucci D, Nugteren H & Fernández-Pereira C (2009) Coal fly ash-slag-based geopolymers: Microstructure and metal leaching. J Hazard Mater 166: 561–566.
Izquierdo M, Querol X, Phillipart C, Antenucci D & Towler M (2010) The role of open and closed curing conditions on the leaching properties of fly ash-slag-based geopolymers. J Hazard Mater 176: 623–628.
Kaakinen J, Kuokkanen T, Kujala K, Välimäki I & Jokinen H (2012) The use of a five-stage sequential leaching procedure for risk assessment of heavy metals in waste rock utilized in railway ballast. Soil Sedim Contam 21: 322–334.
Karltun E, Saarsalmi A, Ingerslev M, Mandre M, Andersson S, Gaitnieks T, Ozolincius R & Varnagiryte-Kabasinskiene I (2008) Wood Ash Recycling – Possibilities And Risks. In: Röser D, Asikainen A, Raulund-Rasmussen K & Stupak I (eds) Sustainable Use of Forest Biomass for Energy: A Synthesis with Focus on the Baltic and Nordic Region. Dordrecht, Springer Netherlands: 79-108.
Käytännön maamies (2013) Kalkkitaulukko, nopeavaikutteinen (in Finnish). URI: http://kaytannonmaamiesfi.virtualserver27.hosting.fi/wp-content/uploads/2013/12/nopeavaikutteinen_2012.pdf. Cited 31.3.2016.
Kemira (2014) KemicondTM - vähemmän lietettä, desinfiointi, hajunpoisto (In Finnish). Kolias S, Kasselouri-Rigopoulou V & Karahalios A (2005) Stabilisation of clayey soils with
high calcium fly ash and cement. Cem Concr Comp 27: 301–313. Koornneef J, Junginger M & Faaij A (2007) Development of fluidized bed combustion–An
overview of trends, performance and cost. Prog Energy Comb Sci 33: 19–55. Korpilahti A (2003) Tuhkan esikäsittely metsäkäyttöä varten (in Finnish). Metsätehon
raportti 143 . Kuroda M, Watanabe T & Terashi N (2000) Increase of bond strength at interfacial transition
zone by the use of fly ash. Cem Concr Res 30: 253–258. LaGrega M, Buckingham P & Evans J (1994) Hazardous Waste Management. New York,
McGraw-Hill Inc. Laohaprapanon S, Marques M & Hogland W (2010) Removal of organic pollutants from
wastewater using wood fly ash as a low-cost sorbent. Clean Soil Air Water 38: 1055–1061.
Lecomte I, Henrist C, Liégeois M, Maseri F, Rulmont A & Cloots R (2006) (Micro)-structural comparison between geopolymers, alkali-activated slag cement and Portland cement. J Eur Ceram Soc 26: 3789–3797.
Luke K & Glasser FP (1987) Selective dissolution of hydrated blast furnace slag cements. Cem Concr Res 17: 273–282.
Luna Galiano Y, Fernández Pereira C & Vale J (2011) Stabilization/solidification of a municipal solid waste incineration residue using fly ash-based geopolymers. J Hazard Mater 185: 373–381.
Martinez-Ramirez S & Palomo A (2001) Microstructure studies on Portland cement pastes obtained in highly alkaline environments. Cem Concr Res 31: 1581–1585.
77
Marx P & Morin J (2008) Chapter 7 – Conventional Firing Systems. In: Tillman BGMA (ed) Combustion Engineering Issues for Solid Fuel Systems. Burlington, Academic Press: 241–274.
Massazza F (1998) Pozzolana and pozzolanic cements. In: Hewlett PC (ed) Lea's Chemistry of Cement and Concrete (Fourth Edition). Oxford, Butterworth-Heinemann: 471–635.
Meers E, Vandecasteele B, Ruttens A, Vangronsveld J & Tack FMG (2007) Potential of five willow species (Salix spp.) for phytoextraction of heavy metals. Environ Exp Bot 60: 57–68.
Mehta PK (1987) Natural Pozzolans: Supplementary Cementing Materials in Concrete. Ottawa, CANMET Special Publication.
Mehta PK & Monteiro JM (1993) Concrete: Microstructure, Properties, and Materials. New York, Inkwell Publishing Services.
Minaríková M & Škvára F (2006) Fixation of heavy metals in geopolymeric materials based on brown coal fly ash. Ceram Silikaty 50: 200–207.
Mleczek M, Rutkowski P, Rissmann I, Kaczmarek Z, Golinski P, Szentner K, Strażyńska K & Stachowiak A (2010) Biomass productivity and phytoremediation potential of Salix alba and Salix viminalis. Biomass Bioenerg 34: 1410–1418.
NEN 7375:2004 (2004) Leaching characteristics - Determination of the leaching of inorganic components from moulded or monolitic materials with a diffusion test - Solid earthy and stony materials. Netherlands Standardization Institute, 39.
Nikolić V, Komljenović M, Marjanović N, Baščarević Z & Petrović R (2014) Lead immobilization by geopolymers based on mechanically activated fly ash. Ceram Int 40: 8479–8488.
Nurmesniemi H, Pöykiö R, Perämäki P & Kuokkanen T (2005) The use of a sequential leaching procedure for heavy metal fractionation in green liquor dregs from a causticizing process at a pulp mill. Chemosphere 61: 1475–1484.
Odler I (1998) Hydration, Setting and Hardening of Portland Cement. In: Hewlett PC (ed) Lea's Chemistry of Cement and Concrete (Fourth Edition). Oxford, Butterworth-Heinemann: 241–297.
Ogundiran MB, Nugteren HW & Witkamp GJ (2013) Immobilisation of lead smelting slag within spent aluminate–fly ash based geopolymers. J Hazard Mater 248–249: 29-36.
Ohenoja K, Tanskanen P, Wigren V, Kinnunen P, Körkkö M, Peltosaari O, Österbacka J & Illikainen M (2016) Self-hardening of fly ashes from a bubbling fluidized bed combustion of peat, forest industry residuals, and wastes. Fuel 165: 440–446.
Palomo A, Maltseva O, García-Lodeiro I & Fernández-Jiménez A (2013) Hybrid alkaline cements. Part II: The clinker factor. Rev Rom Mater Rom J Mater 43: 74–80.
Pangdaeng S, Phoo-ngernkham T, Sata V & Chindaprasirt P (2014) Influence of curing conditions on properties of high calcium fly ash geopolymer containing Portland cement as additive. Mater Des 53: 269–274.
Provis JL & van Deventer JS (2007) Geopolymers - Structures, Processing, Properties and Industrial Applications. Cambridge, Woodhead Publishing.
Raiko R, Saastamoinen J, Hupa M & Kurki-Suonio I (eds) (2002) Poltto ja Palaminen (in Finnish). Helsinki, International Flame Research Foundation.
78
Rauret G, López-Sánchez JF, Sahuquillo A, Rubio R, Davidson C, Ure A & Quevauviller P (1999) Improvement of the BCR three step sequential extraction procedure prior to the certification of new sediment and soil reference materials. J Environ Monit 1: 57–61.
Reynolds GK, Le PK & Nilpawar AM (2007) High shear granulation. In: Salman A, Hounslow M & Seville J (eds) Handbook of Powder Technology. Elsevier Science: 3–19.
Rowles M.R., Hanna J.V., Pike K.J., Smith M.E. & O'Connor B.H. (2007) 29Si, 27Al, 1H and 23Na MAS NMR study of the bonding character in aluminosilicate inorganic polymers. Appl Magn Reson 32: 663–689.
Saarsalmi A, Smolander A, Kukkola M, Moilanen M & Saramäki J (2012) 30-Year effects of wood ash and nitrogen fertilization on soil chemical properties, soil microbial processes and stand growth in a Scots pine stand. For Ecol Manage 278: 63–70.
Saarsalmi A, Smolander A, Moilanen M & Kukkola M (2014) Wood ash in boreal, low-productive pine stands on upland and peatland sites: Long-term effects on stand growth and soil properties. For Ecol Manage 327: 86–95.
SFS-EN 12457-3 (2012) Characterisation of waste. Leaching. Compliance test for leaching of granular waste materials and sludges. Part 3: Two stage batch test at a liquid to solid ratio of 2 l/kg and 8 l/kg for materials with high solid content and with particle size below4 mm (without or with size reduction). Helsinki: Finnish Standards Association.
SFS-EN 13656 (2003) Characterization of waste. Microwave assisted digestion with hydrofluoric (HF), nitric (HNO3) and hydrochloric (HCl) acid mixture for subsequent determination of elements. Helsinki: Finnish Standards Association.
SFS-EN 13657 (2003) Characterization of waste. Digestion for subsequent determination of aqua regia soluble portion of elements. Helsinki: Finnish Standards Association.
SFS-EN 196-1:en (2005) Methods of testing cement. Part 1: Determination of strength. Helsinki: Finnish Standards Association.
Škvára F, Kopecký L, Šmilauer V & Bittnar Z (2009) Material and structural characterization of alkali activated low-calcium brown coal fly ash. J Hazard Mater 168: 711–720.
Steenari B- & Lindqvist O (1997) Stabilisation of biofuel ashes for recycling to forest soil. Biomass Bioenergy 13: 39–50.
Swedish Forest Agency (2008) Rekommendationer vid uttag av avverkningsrester och askåterföring (in Swedish).
Taylor HFW (1997) Cement Chemistry. London, Academic Press Ltd. Temuujin J, van Riessen A & Williams R (2009) Influence of calcium compounds on the
mechanical properties of fly ash geopolymer pastes. J Hazard Mater 167: 82–88. Tessier A, Campbell PGC & Blsson M (1979) Sequential extraction procedure for the
speciation of particulate trace metals. Anal Chem 51: 844–851. The International centre for diffraction data (2006) The powder diffraction file. van Ejik RJ & Obernberger, I., Supancic, K. (2012) IEA Bioenergy Task 32. Options for
increased utilization of ash from biomass combustion and co-firing. Arnhem, Kema Nederland.
79
Vesterinen P (2003) Wood ash recycling - State of the art in Finland and Sweden. VTT Research Report PRO2/6107/03 .
Walker GM (2007) Drum Granulation Processes. In: Salman A, Hounslow M & Seville J (eds) Handbook of Powder Technology. , Elsevier Science B.V.: 219–254.
Xu H, Li Q, Shen L, Zhang M & Zhai J (2010) Low-reactive circulating fluidized bed combustion (CFBC) fly ashes as source material for geopolymer synthesis. Waste Manage 30: 57–62.
Xu JZ, Zhou YL, Chang Q & Qu HQ (2006) Study on the factors of affecting the immobilization of heavy metals in fly ash-based geopolymers. Mater Lett 60: 820–822.
Yliniemi J, Nugteren H, Illikainen M, Tiainen M, Weststrate R & Niinimäki J (2016) Lightweight aggregates produced by granulation of peat-wood fly ash with alkali activator. Int J Miner Process 149: 42–49.
Yliniemi J, Pesonen J, Tiainen M & Illikainen M (2015) Alkali activation of recovered fuel–biofuel fly ash from fluidised-bed combustion: Stabilisation/solidification of heavy metals. Waste Manage 43: 273–282.
Zhang J, Provis JL, Feng D & van Deventer JSJ (2008) Geopolymers for immobilization of Cr6+, Cd2+, and Pb2+. J Hazard Mater 157: 587–598.
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List of original publications
I Pesonen J, Kuokkanen T, Kaipiainen E, Koskela J, Jerkku I, Pappinen A & Villa A (2014) Chemical and physical properties of short rotation tree species. European Journal of wood and wood products 72(6): 669–777.
II Pesonen J, Yliniemi J, Kuokkanen T, Ohenoja K & Illikainen M (2016) Improving the hardening of fly ash from fluidized-bed combustion of peat and wood with the addition of alkaline activator and Portland cement. Romanian Journal of Materials 46(1): 82–88.
III Pesonen J, Yliniemi J, Illikainen M, Kuokkanen T & Lassi U (2016) Stabilization/solidification of fly ash from fluidized bed combustion of recovered fuel and biofuel using alkali activation and cement addition. Journal of Environmental Chemical Engineering 4(2): 1759–1768.
IV Pesonen J, Kaakinen J, Kuokkanen T, Välimäki I & Illikainen M (2016) Comparison of standard methods for evaluating the metal concentrations in bio ash, Manuscript.
V Pesonen J, Kuokkanen V, Kuokkanen T & Illikainen M (2016) Co-granulation of bio-ash with sewage sludge and lime for fertilizer use. Journal of Environmental Chemical Engineering, In press.
Reprinted with permission from Springer (Paper I), Serban Solacolu Foundation
(Paper II), and Elsevier (Papers III and V).
Original publications are not included in the electronic version of the dissertation.
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665. Varanka, Sanna (2016) Multiscale influence of environmental factors on waterquality in boreal rivers : application of spatial-based statistical modelling
666. Luukkonen, Tero (2016) New adsorption and oxidation-based approaches forwater and wastewater treatment : studies regarding organic peracids, boiler-water treatment, and geopolymers
667. Tolkkinen, Mari (2016) Multi-stressor effects in boreal streams : disentangling theroles of natural and land use disturbance to stream communities
668. Kaakinen, Juhani (2016) Öljyllä ja raskasmetalleilla pilaantuneita maita koskevanympäristölainsäädännön ja lupamenettelyn edistäminen kemiallisella tutkimuksella
669. Huttunen, Kaisa-Leena (2016) Biodiversity through time : coherence, stability andspecies turnover in boreal stream communities
670. Rönkä, Nelli (2016) Phylogeography and conservation genetics of waders
671. Fucci, Davide (2016) The role of process conformance and developers' skills inthe context of test-driven development
672. Manninen, Outi (2016) The resilience of understorey vegetation and soil toincreasing nitrogen and disturbances in boreal forests and the subarctic ecosystem
673. Pentinsaari, Mikko (2016) Utility of DNA barcodes in identification anddelimitation of beetle species, with insights into COI protein structure across theanimal kingdom
674. Lassila, Toni (2016) In vitro methods in the study of reactive drug metaboliteswith liquid chromatography / mass spectrometry
675. Koskimäki, Janne (2016) The interaction between the intracellular endophyticbacterium, Methylobacterium extorquens DSM13060, and Scots pine (Pinussylvestris L.)
676. Ronkainen, Katri (2016) Polyandry, multiple mating and sexual conflict in a waterstrider, Aquarius paludum
677. Pulkkinen, Elina (2016) Chemical modification of single-walled carbon nanotubesvia alkali metal reduction
678. Runtti, Hanna (2016) Utilisation of industrial by-products in water treatment :carbon-and silicate-based materials as adsorbents for metals and sulphate removal
679. Suoranta, Terhi (2016) Advanced analytical methods for platinum group elements :applications in the research of catalyst materials, recycling and environmental issues
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PHYSICOCHEMICAL STUDIES REGARDING THE UTILIZATION OF WOOD- AND PEAT-BASED FLY ASH
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