MODIFIED CLAY AS SOIL AMENDMENT FOR REMEDIATION: STUDIES OF LEACHING AND SORPTION KINETICS

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MODIFIED CLAY AS SOIL AMENDMENT FOR REMEDIATION: STUDIES OF

LEACHING AND SORPTION KINETICS

M.Sc. Juris BurlakovsDr. Zane Vincevica-GaileB.Sc. Mara StapkevicaProf. Dr. Maris KlavinsDepartment of Environmental Science, University of Latvia,Latvia

ABSTRACTSoil contamination with metals and metalloids is seriousenvironmental problem nowadays, caused mainly by intensiveanthropogenic activities such as industry, traffic ormining. Soil remediation regarding metals and metalloids inpolluted sites includes methodologies based on chemicalprecipitation, ion exchange, carbon adsorption, membranefiltration, adsorption and co-precipitation. Soilamendments that affect metal immobilization can be used forremediation of soil. Use of clay, natural (raw) ormodified, as a soil amendment is one of the mostperspective soil remediation methodologies due to theefficiency and cost effectiveness. Clay consists ofcrystalline-hydrated aluminosilicates and it has highexchange capacity that is important property for theprocess of binding of metals and metalloids.Efficiency of clay as an immobilization agent for metalbinding was tested by sorption and batch leaching tests.Sorption capacity for raw and modified clay samples wasexperimentally tested under various pH and temperatureconditions. Samples of modified clay as a sorbent weretested for sorption of Pb as monocontaminant and at complexcontamination of metals. Clay modification was done byusing Ca and Na salts, HNO3 (protonated forms), Fe-oxyhydroxide, hydroxyapatite. Higher sorption capacity wasobserved for clay modified with hydroxyapatite and Casalts. Sorption capacity increased with a rise of

14th International Multidisciplinary Scientific GeoConference SGEM 2014

temperature at the optimum pH 5.0-5.5. Immobilization ofmetals with cheap soil amendments such as clay in situ iseffective method for reduction of environmental hazardswith low and medium target concentrations of metals ormetalloids at relatively stable environment. Increasedefficiency can be reached by using clay modified withhydroxyapatite as soil amendment.Keywords: modified clay, soil amendments, soil remediation,sorption kinetics

INTRODUCTIONQuality of soil and groundwater is fundamentally important,and different technologies are used for the remediation ofdiffuse and point pollution sources generated by industrialas well as natural contamination. Toxic heavy metal ionsare non-biodegradable and tend to accumulate in livingorganisms, causing severe disorders and diseases.Overexposure of metals promotes development of manyoccupational illnesses [1]. Development of soil andgroundwater remediation technologies is a matter of a greatimportance with the target to eliminate historically andrecently contaminated sites as contamination causes loss ofland as a valuable resource [2].Several physiochemical methods can be applicable for theremoval of metal ions from environement, including chemicalprecipitation, reverse osmosis, filtration, solventextraction, electrodeposition, electrodialysis, ionexchange, and adsorption etc. [3]. Application of soilamendments can be used often as one of the in situtechnologies for the regeneration process of contaminatedsoil. Use of natural zeolites is not as efficient as use ofsynthetic ones, but clay minerals in many cases can beapplied as suitable sorbents for the removal of metals.However, wastewater can be treated much cheaper with a goodefficiency as the zeolite (clay) is among the alkalineporous aluminoo-silicate materials with a negative charge[4].Nowadays the research trends are concentrated toinvestigate zeolites and modified clays, especially,

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organoclays, as effective treatment agents. Application andefficiency of different type of natural clay and claycomposites has achieved wide attention recently forpossible use as adsorbents of metal ions from aqueousmedium because of their effortless availability andcomparatively low costs in removing of various metals andmetalloids like As, Cd, Cr, Fe, Mn, Pb, Se, U, V and Zn[5].Current paper describes the main results obtained in Latviaafter clay modification with Fe-oxyhydroxide, nitric acid,Ca and Na salts, and hydroxyapatite considering the ionexchange mechanism. Pb was selected as a model pollutantfor the experiments of sorption kinetics as Pb salts areused in many industrial applications and it is well knownenvironmental pollutant. Also other metals (e.g., Cu, Zn)and metalloids (e.g., As) were analyzed in the leachingexperiment. The aim of this work was to evaluate the use ofmodified clay, which can be possibly applicable forremediation of water (sewage or groundwater) and soilcontaminated with metals and metalloids. Improvement ofmodified clay sorption properties in aquatic phase canreveal the potential and efficiency of innovative materialsusable in remediation industry as soil amendments.

PERSPECTIVES IN USE OF CLAY AS SOIL AMENDMENTContaminated soils can be ameliorated using amendments suchas zeolites, lime, phosphates and organic matter. Additionof lime in soil reduces bioavailability of metals, whilezeolites can be used as molecular sieves. Adsorption isconsidered as an effective method for metal ion removalfrom aqueous solutions due to its cost-effectiveness andhigh efficiency [1], [6]. Zeolites are studied widelybecause they can reduce solubility and thus the biologicalavailability of metals incorporated in salts and complexes,also oxides and metal-carbonate precipitates can be formed[7]. Importance of layer silicate clays in remediationcommonly is illustrated by cation exchange capacity (CEC).Permanent negative charged particles in clay minerals avoidleaching of elements from soils but still keep them


available as nutrients for plants. Smectites are clayswhich mostly are of small particle size, but vermiculiteand zeolite are coarser and have very strong negativecharge [8]. Particles of zeolite are very strongly chargedand size of tunnels between the particles is limiting andcontrolling selectivity of different ion passages throughthem [9].Clay minerals are used for wastewater treatment as they areamong the cheap, easy available and efficient materials.M.F. De Boodt (1991) has examined the application of heat-treated clay used together with Al(OH)3 coatings forremoval of both, anionic and cationic contaminants, fromwastewater and soil [10]. Also, the possibility of Hgcontaminated Wabigoon-English-Winnipeg River systemremediation by use of uncontaminated mass of clay and silthas been suggested [11]. Theoretically, detritus would betransported by river system and laid down on contaminatedsediments, which are older and formed down before; besides,contaminated material is diluted and microbial methylatingactivity should be inhibited.Clay minerals are capable in sorbing and desorbing cationsand anions as well as uncharged metal species, andparticipate in exchange reactions. Capacity and energy ofbinding are varying greatly depending on the type of clayas capacity is the function of specific surface area.Sorption of trace elements by colloids includes a lot ofbinding sites regarding trace element species, andmechanisms of binding are variable. Anions and cations arefreely held by surface charge, but more strongly by bindingsites with ligands. Bonds between the ions and sorptionplaces can be from ionic to covalent; van der Waals forcesand other dipole effects play significant role in sorptionof uncharged species. Sorption is a relatively rapidprocess; nevertheless, it takes a while for species toinvade the interlamellar structures [12].

SOIL AMENDMENT EFFICIENCY TESTSLeaching tests for soil amendment efficiency in contaminated soils

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In order to test the efficiency of multicontaminantimmobilization in sandy soil (sand content 89%), the soilsamples were spiked with selected metals (Cu, Pb, Zn). Thespiking was achieved with following concentration ofmetals: 200 mg/kg of Pb, 300 mg/kg of Zn and 100 mg/kg ofCu. Different clay samples were used as soil amendmentsadding them at rate 10% of dry weight. Leaching tests wereperformed by stirring the samples for 24 h, and the resultsare summarized in Table 1. Measurements of elementconcentration were performed by atomic absorptionspectrometry (AAS).Leaching experiment was performed in order to simulateprocesses in widely distributed soils in Latvia undernatural conditions in batch mode without impacts of heavyrains or acid precipitation. Results from leachingexperiment after clay modification with Fe-oxyhydroxide,hydroxyapatite, Ca, Na salts and protonation by HNO3 incomparison with data of raw clay material revealed thatsorption capacity (immobilization) is higher for the soilamendments. Cation base saturation for modified samples wasalso increased higher by 1.5 to 2-fold times, if comparedto unmodified clay samples. Increased immobilization of Pbions (10-30%) was observed in soil samples if modified claywas added. In case of Devonian clay, when Fe-oxyhydroxidewas added comparably to non-amended, no significant changeof immobilization efficiency if quantitatively more than10% of dry weight content Fe-oxyhydroxide is applied in theclay [13], [14]. Most effective immobilization of Pb, Zn and Cu can beachieved if soil is amended with clay modified usinghydroxyapatite or Ca salts as it was observed for modifiedQuaternary Lielauce clay. Use of raw clay as the soilamendment is feasible; however, if higher concentration ofmetals on polluted site is supposedpredicted, theimmobilization by raw clay material can be insufficient.Lower efficiency of immobilization was achieved by usingvarved clays from Zeiļu Lake (Latvia) and Borovichi(Russia).


Table 1. Leaching intensity of Pb, Zn and Cu from sandysoil after addition of different clay material as soilamendment

Clay materialdescription

Extractionsite Raw / Modified

Elementconcentration ineluate*, mg/kg

Pb Zn CuDevonian clay -illitic with significant content of kaolinite

Lode quarry, Priekuļi region, Latvia

Raw 89.5 223.0 51.3

Modified withFe-oxyhydroxide 11.1 56.9 15.6

Quaternary clay- mainly illitic

Sātiņi quarry, Saldus region, Latvia

Raw 29.2 115.7 54.9


Lielauce quarry, Auce region, Latvia

Raw 29.3 124.4 54.8Modified with

Ca salts<0.02 12.4 7.9

Modified Nasalts 1.4 12.5 11.2

Modified withprotonation by

HNO3

8.6 89.5 19.4

Modified withhydroxyapatite

<0.02 7.3 0.3


Apriķi quarry, Aizpute region, Latvia

Raw 32.1 89.9 58.2


Prometejs quarry, Talsi region, Latvia

Raw 38.6 100.5 61.5


Laža quarry, Liepāja region, Latvia

Raw 40.5 114.7 47.2

Quaternary glaciolacustrine clay - illitic, silt content up to

Zeiļu Lake,Ludza region, Latvia

Raw 112.7

204.7 80.0

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30%Quaternary glaciolacutstrine varved clay - illitic, structure varved, summer layers with significant silt amount

Borovichi, Novgorod Oblast, Russia

Raw 131.5 231.6 89.3

Sandy soil, without amendment 187.9 269.0 84.5

* Standard deviation for AAS measurements varied in range 0.5-17.2%

Tests of sorption kinetics

Experimental tests of sorption kinetics were designed inorder to evaluate the sorption of Pb by using solution ofPbNO3 in concentration of Pb at 50, 100 and 300 mg/L,respectively. Quaternary Lielauce clay modified with Ca andNa salts, and protonated by HNO3 was were used in forcomparison of with clay modified with hydroxyapatite as wellas raw clay material. Some results of sorption kinetics,where spiked solution with 100 mg/L of Pb was was used,respectively, using 30 ml of Pb solution and 0.015 g ofsorbent, are shown in Figure 1. Measurements of Pbconcentration were performed by atomic absorptionspectrometry (AAS). Maximum efficiency was reached in 2-4 hof continuos agitation after the initial contact of sorbentand sorbate., and after continuous agitation.


Figure 1. Pb sorption kinetics tested by Quaternary Lielauceclay (raw and modified)

Sorption kinetics for modified clay if compared with rawclay was more efficient in all cases, but the most effectiveresults were derived regarding use of clay modified by Casalts or hydroxyapatite. Modification of clay material withCa salts or hydroxyapatite is reasonable as thoseey can bechosen as effective sorption agents for wastewater treatmentor in polluted soil stabilization applications. However,further analysis of feasibility in different environmentalconditions of modified clays should be performedare welcome.The scanning electron microscope (SEM) picture approved theincreasing crystalline complexity of the structure withinhydroxylapatite crystals on the surface of modified clay(Figure 2).

Figure 2. Surface of Quaternary Lielauce clay samplemodified by hydroxyapatite; the circle shows thehydroxyapatite crystallites on the surface.

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In terms of sorption efficiencyefficiency, the mosteffective results were derived from hydroxyapatite modifiedclay with higher equimolar concentration of Ca/P 1.667.These crystals can support the ion exchange at microporelevel by ability to add metal or metalloid ions. X-raydiffraction (XRD) patterns also improved the formation ofnew hydroxyapatite minerals on the clay surface, thusincreasing the surface for sorption.

CLAY FOR “GENTLE REMEDIATION” – PERSPECTIVES IN LATVIAOverall assessment of efficiency of natural and modifiedclays from different extraction sites and of differentgeological age was studied and compared. Modification ofQuaternary and Devonian clay material was done by Fe-oxyhydroxide, hydroxyapatite, Ca and Na salts as describedpreviously in this paper. Devonian clay material wasextracted at the Lode quarry in the northern part ofLatvia; this kind of clay consists of illite withsignificant content of kaolinite. Quaternary clay materialwas extracted at several places over the territory ofLatvia: Lielauce, Sātiņi, Apriķi, Laža, Prometejs quarriesand Zeiļu Lake as well as at Borovichi varved clay quarryin Russia. Table 2 and Table 3 summarize the utility ofclay material, both raw and modified, for possible use assoil amendment for immobilization of metals and metalloids.

Table 2. Description of raw clay material applicable forthe use as soil amendment (authors’ workout after [13],[14], [15], [16])

Clay materialtype Description

Devonian clay from Lode quarry, Latvia

Easy extraction Applicable as soil amendment in unmodified way

but effective only for Pb immobilization Modification recommended in order to increase

sorption capacity Potential use as “gentle remediation” agent

disputable as efficiency low, target areas


located far from extraction sites

Quaternary clayfrom Sātiņi, Lielauce, Apriķi, Prometejs, Lažaquarries, Latvia

Easy and cheap extraction, huge amount available Applicable as soil amendment in unmodified way

but effective only for Pb immobilization Modification recommended in order to increase

sorption capacity Potential use as “gentle remediation” agent

disputable due to low efficiency, target areas located far from extraction sites

Frequently used for cover layers in closed landfills and dump sites, recommended for the use as confining layer in geotechniques

Glaciolacustrine clay from Zeiļu Lake, Latvia

No extraction planned Tested for the pilot study

Glaciolacustrine clay from Borovichi quarry, Russia

Easy and cheap extraction None soil remediation market in Novgorod Oblast

currently, no export available Applicable for cover layers of landfills and

dump sites

CONCLUDING REMARKS Clay is well known immobilizing agent applicable for

metal contaminants; however, increased efficiency can bereached by use of modified clay material as soilamendment. Calcium salts and hydroxyapatite can beassessed as the most appropriate substances for claymodification.

Immobilization of metals using inexpensive soilamendments in situ such as clay is effective method forthe reduction of environmental hazards with low andmedium target concentrations of metals and metalloids atrelatively stable environment.

Advanced studies of clay modification opportunities forwastewater treatment and soil applications should beperformedare welcome.

“Gentle remediation” for contaminated sites with low andmedium target concentrations of metals and metalloidsare methodology with great potential to develop in thefuture.

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Implementation of remediation methods and technologiesis dependent mostly from specific national legislation,economic situation and full environmental cost-benefitstructure.

Table 3. Description of modified clay material applicablefor the use as soil amendment (authors’ workout after [13],[14], [15], [16])

Clay materialtype Description

Devonian clay from Lode quarry modifiedwith Fe-oxyhydroxide

Good perspectives for the use of As removal in contaminated areas (co-precipitation with Fe)

Extraction far from reality, only one contaminated site in Latvia with As is economically active

Modification with Fe-oxyhydroxide relatively cheap

Legislation on “gentle remediation” application as remediation technology must be implemented

Applicable as sorbent for industrial wastewater treatment

Quaternary Lielauce clay modified with Ca and Na salts, protonated by HNO3

Good perspectives for use in remediation of cationic species of metals in contaminated areas(immobilization efficiency relatively high for Pb, Cu, Ni, Zn)

Extraction far from reality, no economic evaluation performed

Modification with Ca and Na salts relatively cheap

Legislation on “gentle remediation” application as remediation technology must be implemented

Pilot testing in progress, modification with Ca salts showed better results comparing to modification with Na salts and protonation by HNO3

Quaternary Lielauce clay modified with hydroxyapatite

Detected highest efficiency in cases of multicontamination

Immobilization efficiency higher for Pb and Ni Most advisable as “gentle remediation” technique

as soil amendment Applicable as a sorbent for industrial

wastewater treatment

ACKNOWLEDGEMENTS


This study has been supported by the European Social Fundwithin the project “Interdisciplinary Team of YoungScientists for Assessment and Restoration of Soil Qualityand Usage Potential in Latvia”(No.2013/0020/1DP/1.1.1.2.0./13/APIA/ VIAA/066).

REFERENCES[1] Lee S.M. & Tiwari D. Organo and inorgano-organo-modified clays in the remediation of aqueous solutions: Anoverview. Applied Clay Science, 59-60, pp 84-102, 2012.[2] Directive 2008/1/EC of the European Parliament and ofthe Council of 15 January 2008 concerning integratedpollution prevention and control. Official Journal of the EuropeanUnion, L 24, pp 8-29, 2008.[3] Wu Y.H., Wen Y.J., Zhou J.X., Cao J.L., Jin,Y.P. & WuY.Y. Comparative and competitive adsorption of Cr(VI),As(III), and Ni(II) onto coconut charcoal. EnvironmentalScience & Pollution Research International, 20/4, pp 2210-2219, 2013.[4] Mohamed M.M. Heat capacities, phase transitions andstructural properties of cation-exchanged H-mordenitezeolites. Thermochimica Acta, 372/1-2, pp 75-83, 2001.[5] Bhattacharyya K.G. & Gupta S.S. Adsorption of a fewheavy metals on natural and modified kaolinite andmontmorillonite: A review. Advances in Colloid & Interface Science,140/2, pp 114-131, 2008.[6] Wang X.J., Liang X., Wang Y., Wang X., Liu M., YinD.Q., Xia S.Q., Zhao J.F. & Zhang Y.L. Adsorption ofcopper(II) onto activated carbons from sewage sludge bymicrowave-induced phosphoric acid and zinc chlorideactivation. Desalination, 278/1-3, pp 231-237, 2011.[7] Querol X., Alastuey A., Moreno N., Alvarez-Ayuso E.,Garcia-Sanchez A., Cama J., Ayora C. & Simon M.Immobilization of heavy metals in polluted soils by theaddition of zeolite material synthesized from coal fly ash.Chemosphere, 62/2, pp 171-180, 2006.[8] Dixon J.B. Roles of clay and oxide minerals in soils.In: Environmental Interactions of Clays. Parker A. & Rae J.E.

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(eds.), Springer-Verlag, pp 37-53, 1998.[9] Ming D.W. & Mumpton F.A. Zeolites in soils. In: Mineralsin Soil Environments Dixon J.B. & Weed S.B. (eds.), Soil ScienceSociety of America, pp 873-911, 1987.[10] De Boodt M.F. Application of sorption theory toeliminate heavy metals from waste waters and contaminatedsoils In: Interactions at the Soil Colloid-Solution Interface Bolt G.H.,de Boodt M.F., Hayes M.H.B., McBride M.B. & de StrooperE.B.A. (eds.), Springer-Verlag, pp 293-320, 1991.[11] Parks J.W. & Hamilton A.L. Accelerating recovery ofmercury-contaminated Wabigoon/English River system.Hydrobiologia, 149, pp 159-188, 1987.[12] Jackson T.A. The biogeochemical and ecologicalsignificance of interactions. In: Environmental Interactions ofClays. Parker A. & Rae J.E.. (eds.), Springer-Verlag, pp 93-206, 1998.[13] Burlakovs J., Karasa J. & Klavins M. Devonian claymodification for the improvement of heavy metal sorptionproperties. Scientific Journal of Riga Technical University, Series:Environmental & Climate Technologies, 3, pp 22-26, 2013c.[14] Burlakovs J., Karklina A., Karpovics A. & Klavins M.Different type clay amendments for lead immobilization incontaminated soils. Scientific Journal of Riga Technical University, Series:Material Science and Applied Chemistry, 29, pp 137-141, 2013d.[15] Burlakovs J., Klavins M. & Karklina A. Remediation ofsoil contamination with heavy metals by using zeolite andhumic acid additives. Latvian Journal of Chemistry, 51/4, pp 336-341, 2012b.[16] Burlakovs J. & Vircavs M. Heavy metal remediationtechnologies in Latvia: Possible applications andpreliminary case study results. Ecological Chemistry &Engineering S, 19/4, pp 533-547, 2012.

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MODIFIED CLAY AS SOIL AMENDMENT FOR REMEDIATION: STUDIES OF LEACHING AND SORPTION KINETICS