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Valorization of Rice Husk Ash (RHA) assilica precursor for the obtainment of clay
bricks and deflocculating additives
Fernanda Andreola, L. Barbieri, I. Lancellotti
Department of Engineering “Enzo Ferrari”
University of Modena and Reggio Emilia, Italy
5th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
ATHENS2017
25th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
AIM
Valorize RHA in ceramic field taking advantage ofits feature as amorphous silica source
Obtain ceramic bricks by substitution of clayedmaterials with different percentages of RHA,following the typical brickmaking process
Study an environmental friendly route tosynthesize (from the rice husk ash) sodiumsilicate solutions and check their deflocculantcapability for ceramic bodies.
35th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
Burnt outLHV: 15 MJ/kg
Worldwide rice production: 717 million tons/year (Italy: 1.50 million tons/year)
Total global RHA amount : ≈35 million tons/year
Rice husk Rice husk ash (RHA)
UTILIZED AS BIOMASS FUEL: in the rice Parboiling process, cement and brick kilns
IT IS NOT A WASTE: sold and used as a pozzolanic, insulating, waterproofing
and fertilizer material
WHY USE RHA?
22% from milled paddy 25% is generated
45th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
RHA CHARACTERIZATION
Rietveld‐R.I.R.Quantitative analysis
Agreement AgreementAgreement indices
Cristobalite 11,5% Rwp = 6,33
Rp = 4,51
χ2 = 5,82Tridymite 2,8%
Amorphous silica 85,7%
SEM microstructureRietveld-RIR analysis
Position [°2Theta]
10 20 30 40 50 60 70
0
100
400
900
1600
RHATQ.RD
C,T
C C
Crystobalite
Trydimite
N C H S
0.18% 9.95% 0.47% 0.48%
Elemental analysis
Bondioli F., Andreola, F., Barbieri, L., Manfredini, T., Ferrari, A.M.:Effect of Rice Husk Ash (RHA) in the Synthesis of (Pr,Zr)SiO4 Ceramic Pigment, J. Euro. Ceram. Soc., 27, 3483-3488 (2007)
5
CURRENT INDUSTRIAL PROCESSES• MELTING PROCESS (OR VETRIFICATION) WITH DISSOLUTION:
• Calcination of a mixture of sodium carbonate (Na2CO3) and natural quartz sand (SiO2) in suitable furnaces at 1400-1500 °C, according to the reaction:
Na2CO3 + m SiO2 Na2O mSiO2 + CO2 Formation of anhydrous sodium silicate (Na2OmSiO2) in molten state (magma).
• Dissolution of the "solid glass" obtained in the previous step, in water, in special autoclaves under high pressure and temperature, according to the reaction:Na2O mSiO2 + n H2O Na2O.SiO2 n H2O + SiO2
• HYDROTHERMAL PROCESSBased on the reaction of silica with a caustic soda solution in autoclave under high pressure and temperature conditions, according to the reaction:
2NaOH + m SiO2 + (n -1 ) H2O Na2O mSiO2 nH2O
5th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
6
Slz. NaOH1M, 1.5M, 2M, 3M
Alkaline attack in hermetic teflon vessel using thermostatic bath
SOLID/LIQUID RATIO 1:5
OPERATIVE CONDITIONS
•Molar concent. NaOH(aq):1‐3 M
•Contact time: 1,3,5 hs
•T=80°C; P=1 atm.
•Particle size : <180 , <63 m
Separation of soluble silicates by Filtration
Filter Whatman n° 54 + 52
Ground to improve reactivity
EXPERIMENTAL PROCEDURE
RHA
5th International Conference on Sustainable Solid Waste Management,21-24 June 2017 - Athens, Greece
Ramman
Tritation by HCl 1M
Deflocculating capability tests by
Rotational Reometry
XRD
SEM/EDS
Separation of soluble silicates by Filtration
Filter Whatman n° 54 + 52
CARACTERIZATION NA-SIL SOLUTIONSRaman Spectroscopy
cm⁻¹
Inte
nsità
(arb
itrar
y un
it)
cm⁻¹ λ caracteristic of Si‐O(Na)molecolar lattice
Raman confirmed that the
synthetized Slz are Na‐silicates
Slz.obtained from synthesis
RHA
Commercial Products
SiO2/Na2O = 1:2SiO2/Na2O = 1:1
D. Fortnum and JO. Edwards, J. lnorg. NucI. Chem. 2 (1956) 264.
J.E. Earley, D. Fortnum, A. Wojcicki and JO. Edwards, J. of Am. Chem. Soc. 81 (1959) 1295.
5th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
5th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
SOLUBLE NA-SILICATES SOLUTION
High reactivity of ash , different ponderal ratio as a function of molar [NaOH] used
Determination SiO2% and Na2O% by titriation method(HCl 1M, methyl red as indicator) based on ISO 2124-1972
1M 1,5M 2M 3M
3.05
2.64
2.241.64
00.5
11.5
22.5
33.5
[NaOH]
Rp (SiO2/Na2O)
after 3 hs
<63 m
95th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
Commercial Silicates. Clay 65wt%
The best commercial deflocculant Na-SIL 2:1, the optimum amount is 0.5 wt%
DEFLOCCULANT CAPABILITY
105th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
The rheological measures conducted using the same amount ofthe commercial and synthesized solutions (0.5%) highlightedthat all of synthesized solutions have a better performancerespect to the commercial one.
050
100150200250300350400450500
CommercialNa‐SIL. 2:1
Silicatefrom RHANaOH1M
Silicatefrom RHANaOH 1.5M
Silicatefrom RHANaOH 2M
η [m
Pa s]
shear rate 30s‐1
shear rate 200s‐
DEFLOCCULANT CAPABILITY
BRICKMAKING PROCESSRHA (5-20 wt%)
Italian production:
5.2 million ton/y Font: Report ANDIL (2015)
5th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
11
125th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
ExperimentalRaw materials:
Clay mixture /rice husk ash (5-20 wt%)
Mixing Paste(20-27%moisture)
Wet Extrusion
(P=8-9 bar)
Drying (Troom=3hs; 100°C,48 hs)
Firing ind.cycle(960°C,24 hours with 6
hours of soaking temperature)
L.Srinkage, Naphta Absorption, carbonates,
Loss Weigth
L.Srinkage, Water Absorption (24 h), Flexural Strength,
Loss Weigth
SEM, XRD
135th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
BRICKS CHARACTERIZATIONAfter drying After firing
2.22
2.95
2.382.19
2.65
0
0.5
1
1.5
2
2.5
3
3.5
0 5 10 15 20 RHA (wt%)
Lin
ear
Sri
nka
ge
(%)
12.06
14.6915.66
18.57
9.68
0
5
10
15
20
25
0 5 10 15 20
RHA (wt%)
N.A
(%
)
RHA (wt%) WA% LS%
0 17.00 0.02
5 19.58 0.06
10 23.00 0.05
15 26.42 0.04
20 32.05 0.04
145th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
This image cannot currently be displayed.
5%
20%
SEM/XRD ANALYSIS
10%
0%
Q: SiO2; Ak: Ca2MgSi2O7; G: Ca 2 Al(AlSi)O 7
CONCLUSIONS RHA acts as raw material for brick products due to a high silica
content which have mainly plasticity reducing effect on the brickbodies. Contributes to reduce the linear shrinkage during dryingand firing steps.
With substitutions up to 5 wt% into the bricks bodies, the mainproperties tested are in accordance to the recommended valuesfor roofing bricks. Upper amounts of RHA contributes to increasefinal porosity lightweight bricks
The tests conducted using an environmental friendly route permitto obtain solutions with ponderal ratio SiO2/Na2O 2:1 typical ofcommercial silicates used in ceramic industry as deflocculants.
Rheological measures confirmed that the silicate solutions obtainedare suitable to use as defloculanting additives and showed a betterperformance respect to commercial ones.
5th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
THANK YOU FOR YOUR ATTENTION !!!
165th International Conference on Sustainable Solid Waste Management,
21-24 June 2017 - Athens, Greece
The authors acknowledge Eng. Nicole Bagnoli and Eng. E. Guidetti for the thesis projects
175th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
Caracterization of ashes after treatmentX-Ray Diffraction
0 20 40 60 80
Arbitrary Unit
2θ
Ceneretq
TQ
1M
4M
It is verified that the alkaline treatment attacks amorphous silica and alsocristobalite crystalline phase decreases intensity.
3 hs 5 hs
<63 μm <180 μm <63 μm <180 μm
% Si % C % Si % C % Si % C % Si % C
RHA tq 41.4 16.0 41.4 16.0 41.4 16.0 41.4 16.0
1 M 30.7 30.0 38.3 30.3 36.3 29.1 38.9 31.7
2 M 31.5 40.0 36.6 44.5 31.0 44.0 32.4 35.1
4M**(1 h) 23.2 52.6 29.6 61.6
Caracterization of ashes after treatmentSEM/EDS
• Using EDS is observed a decrease ofthe Si content after alkaline attack
• The reactivity is high using fine ash• It is not necessary increases to 5 hs
the contact time
5th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
195th International Conference on Sustainable Solid Waste Management, 21-24 June 2017 - Athens, Greece
OXIDE (wt%) YELLOW CLAY GREY CLAY
SiO2 52,67 50,41Al2O3 11,02 12,16TiO2 0,58 0,61Fe2O3 4,30 4,32CaO 11,96 11,96MgO 2,44 3,12K2O 2,44 3,12Na2O 0,54 0,72ZnO - -PO4 - -SO4 - -MnO - -
L.O.I (1100°C) 13,06 13,77CaCO3 (CALCIMETRY) 18,5 19,5
YELLOW CLAY Illite-mica, Smectite, Kaolinite and Chlorite (traces) , Quartz, K-Feldspars, Carbonate ( calcite and dolomite)
GREY CLAY Illite-mica, Smectite, Kaolinite and Chlorite (traces) , Quartz, K-Feldspars, Carbonate, Hematite in tracce
CLAYS CHARACTERIZATION
LE SOSPENSIONI DEVONO PRESENTARE DETERMINATE
CARATTERISTICHE:
BUONA CAPACITA’ DI SCORRIMENTO
BASSA PERCENTUALE DI ACQUA
AGGIUNTA DI UN DEFLOCCULANTE
AZIONE DISPERDENTE
AZIONE FLUIDIFICANTE
PRINCIPALI MECCANISMI DI AZIONE DEI DEFLOCCULANTI
•Spostamento del pH verso valori basici con immissione di OH-•Sostituzione con cationi alcalini degli altri cationi presenti nel doppio strato;•Aumento della carica negativa delle micelle per adsorbimento di alcuni anioni (TPF, PPA;)•Aggiunta di un colloide protettore che sottrae le particelle all’azione di ioni flocculanti (SIL);
Na2O. nSiO2+H2O nSiO2 +2Na++OH-