Thiocyanate-induced labilization of schwertmannite: Impacts and mechanisms
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摘要
Schwertmannite is an amorphous iron(III)-oxyhydroxysulfate that forms in acid mine drainage(AMD) environments. The characteristic of high heavy metal adsorption capability makes schwertmannite a potentially useful, environmentally friendly material in wastewater treatment. Unstable schwertmannite is prone to recrystallization.Understanding the mechanisms that induce schwertmannite labilization and affect its capacity to remove heavy metals are of great environmental and geochemical significance.Thiocyanate(SCNˉ) is a hazardous pseudohalide that is also normally found in AMD.However, little is known about the impact of Fe(III)-binding ligand SCNˉ on schwertmannite stability and its subsequent capacity to bind trace elements. Here, we investigated the adsorption of SCNˉ on schwertmannite and subsequent mineral transformation to characterize this little-known process. The appearance of Fe2+indicated that the interactions between schwertmannite and SCNˉ may involve complexation and reduction reactions. Results showed that the majority of the adsorbed-SCNˉ was immobilized on schwertmannite during the 60-days transformation. The transformation rates of schwertmannite increased with increasing concentrations of SCNˉ. Goethite was detected as the dominant transformation product with or without SCNˉ. The mechanisms of SCNˉ-promoted dissolution of schwertmannite can be described as follows:(1) formation of Fe(III)–NCS complexes on the schwertmannite surface and in solution, a process which increases the reactivity of solid phase Fe(III);(2) the extraction of Fe(III) from schwertmannite by SCNˉ and subsequent schwertmannite dissolution; and(3) the formation of secondary minerals from extracted Fe(III). These findings may improve AMD treatment strategies and provide insight into the use and potential reuse of schwertmannite as a trace element sorbent.
Schwertmannite is an amorphous iron(III)-oxyhydroxysulfate that forms in acid mine drainage(AMD) environments. The characteristic of high heavy metal adsorption capability makes schwertmannite a potentially useful, environmentally friendly material in wastewater treatment. Unstable schwertmannite is prone to recrystallization.Understanding the mechanisms that induce schwertmannite labilization and affect its capacity to remove heavy metals are of great environmental and geochemical significance.Thiocyanate(SCNˉ) is a hazardous pseudohalide that is also normally found in AMD.However, little is known about the impact of Fe(III)-binding ligand SCNˉ on schwertmannite stability and its subsequent capacity to bind trace elements. Here, we investigated the adsorption of SCNˉ on schwertmannite and subsequent mineral transformation to characterize this little-known process. The appearance of Fe2+indicated that the interactions between schwertmannite and SCNˉ may involve complexation and reduction reactions. Results showed that the majority of the adsorbed-SCNˉ was immobilized on schwertmannite during the 60-days transformation. The transformation rates of schwertmannite increased with increasing concentrations of SCNˉ. Goethite was detected as the dominant transformation product with or without SCNˉ. The mechanisms of SCNˉ-promoted dissolution of schwertmannite can be described as follows:(1) formation of Fe(III)–NCS complexes on the schwertmannite surface and in solution, a process which increases the reactivity of solid phase Fe(III);(2) the extraction of Fe(III) from schwertmannite by SCNˉ and subsequent schwertmannite dissolution; and(3) the formation of secondary minerals from extracted Fe(III). These findings may improve AMD treatment strategies and provide insight into the use and potential reuse of schwertmannite as a trace element sorbent.
Schwertmannite is an amorphous iron(III)-oxyhydroxysulfate that forms in acid mine drainage(AMD) environments. The characteristic of high heavy metal adsorption capability makes schwertmannite a potentially useful, environmentally friendly material in wastewater treatment. Unstable schwertmannite is prone to recrystallization.Understanding the mechanisms that induce schwertmannite labilization and affect its capacity to remove heavy metals are of great environmental and geochemical significance.Thiocyanate(SCNˉ) is a hazardous pseudohalide that is also normally found in AMD.However, little is known about the impact of Fe(III)-binding ligand SCNˉ on schwertmannite stability and its subsequent capacity to bind trace elements. Here, we investigated the adsorption of SCNˉ on schwertmannite and subsequent mineral transformation to characterize this little-known process. The appearance of Fe2+indicated that the interactions between schwertmannite and SCNˉ may involve complexation and reduction reactions. Results showed that the majority of the adsorbed-SCNˉ was immobilized on schwertmannite during the 60-days transformation. The transformation rates of schwertmannite increased with increasing concentrations of SCNˉ. Goethite was detected as the dominant transformation product with or without SCNˉ. The mechanisms of SCNˉ-promoted dissolution of schwertmannite can be described as follows:(1) formation of Fe(III)–NCS complexes on the schwertmannite surface and in solution, a process which increases the reactivity of solid phase Fe(III);(2) the extraction of Fe(III) from schwertmannite by SCNˉ and subsequent schwertmannite dissolution; and(3) the formation of secondary minerals from extracted Fe(III). These findings may improve AMD treatment strategies and provide insight into the use and potential reuse of schwertmannite as a trace element sorbent.
引文
Acero,P.,Ayora,C.,Torrentó,C.,Nieto,J.M.,2006.The behavior of trace elements during schwertmannite precipitation and subsequent transformation into goethite and jarosite.Geochim.Cosmochim.Acta 70(16),4130-4139.
Antelo,J.,Fiol,S.,Gondar,D.,Pérez,C.,López,R.,Arce,F.,2013.Cu(II)incorporation to schwertmannite:effect on stability and reactivity under AMD conditions.Geochim.Cosmochim.Acta119,149-163.
Baltrusaitis,J.,Cwiertny,D.M.,Grassian,V.H.,2007.Adsorption of sulfur dioxide on hematite and goethite particle surfaces.Phys.Chem.Chem.Phys.9(41),5542-5554.
Bao,Y.P.,Guo,C.L.,Lu,G.N.,Yi,X.Y.,Wang,H.,Dang,Z.,2018.Role of microbial activity in Fe(III)hydroxysulfate mineral transformations in an acid mine drainage-impacted site from the Dabaoshan Mine.Sci.Total Environ.616-617,647-657.
Bigham,J.,Schwertmann,U.,Carlson,L.,Murad,E.,1990.A poorly crystallized oxyhydroxysulfate of iron formed by bacterial oxidation of Fe(II)in acid mine waters.Geochim.Cosmochim.Acta 54(10),2743-2758.
Bigham,J.M.,Schwertmann,U.,Traina,S.J.,Winland,R.L.,Wolf,M.,1996.Schwertmannite and the chemical modeling of iron in acid sulfate waters.Geochim.Cosmochim.Acta 60(12),2111-2121.
Boening,D.W.,Chew,C.M.,1999.A critical review:General toxicity and environmental fate of three aqueous cyanide ions and associated ligands.Water Air Soil Pollut.109(1-4),67-79.
Boily,J.F.,Gassman,P.L.,Peretyazhko,T.,Szanyi,J.,Zachara,J.M.,2010.FTIR spectral components of schwertmannite.Environ.Sci.Technol.44(4),1185-1190.
Bonnissel-Gissinger,P.,Alnot,M.,Ehrhardt,J.J.,Behra,P.,1998.Surface oxidation of pyrite as a function of pH.Environ.Sci.Technol.32(19),2839-2845.
Burton,E.D.,Johnston,S.G.,2012.Impact of silica on the reductive transformation of schwertmannite and the mobilization of arsenic.Geochim.Cosmochim.Acta 96,134-153.
Burton,E.D.,Bush,R.T.,Sullivan,L.A.,2007a.Schwertmannite reduction and iron(II)-monosulfide formation in acidified coastal lowlands:iron-sulfur geochemistry and implications for water quality.Geochim.Cosmochim.Acta 71(15),A135.
Burton,E.D.,Bush,R.T.,Sullivan,L.A.,Mitchell,D.R.G.,2007b.Reductive transformation of iron and sulfur in schwertmannite-rich accumulations associated with acidified coastal lowlands.Geochim.Cosmochim.Acta 71(18),4456-4473.
Burton,E.D.,Bush,R.T.,Sullivan,L.A.,Mitchell,D.R.G.,2008.Schwertmannite transformation to goethite via the Fe(II)pathway:reaction rates and implications for iron-sulfide formation.Geochim.Cosmochim.Acta 72(18),4551-4564.
Chen,M.Q.,Lu,G.N.,Guo,C.L.,Yang,C.F.,Wu,J.X.,Huang,W.L.,et al.,2015.Sulfate migration in a river affected by acid mine drainage from the Dabaoshan mining area,South China.Chemosphere 119,734-743.
Cornell,R.M.,Schwertmann,U.,1996.The Iron Oxides.VCHVerlagsgesellschaft,Weinheim,New York.
Espana,J.S.,Pamo,E.L.,Santofimia,E.,Aduvire,O.,Reyes,J.,Barettino,D.,2005.Acid mine drainage in the Iberian Pyrite Belt(Odiel river watershed,Huelva,SW Spain):geochemistry,mineralogy and environmental implications.Appl.Geochem.20(7),1320-1356.
Fan,C.,Guo,C.L.,Chen,M.Q.,Huang,W.L.,Wan,J.J.,Reinfelder,J.R.,et al.,2018.Transformation of cadmium-associated schwertmannite and subsequent element repartitioning behaviors.Environ.Sci.Pollut.Res.26(1),617-627.https://doi.org/10.1007/s11356-018-3441-9.
Gan,M.,Sun,S.J.,Zheng,Z.H.,Tang,H.J.,Sheng,J.R.,Zhu,J.Y.,et al.,2015a.Adsorption of Cr(VI)and Cu(II)by AlPO4modified biosynthetic schwertmannite.Appl.Surf.Sci.356,986-997.
Gan,M.,Zheng,Z.H.,Sun,S.J.,Zhu,J.Y.,Liu,X.X.,2015b.The influence of aluminum chloride on biosynthetic schwertmannite and Cu(ii)/Cr(vi)adsorption.RSC Adv.5(114),94500-94512.
Gould,W.D.,King,M.,Mohapatra,B.R.,Cameron,R.A.,Kapoor,A.,Koren,D.W.,2012.A critical review on destruction of thiocyanate in mining effluents.Miner.Eng.34,38-47.
Knorr,K.-H.,Blodau,C.,2007.Controls on schwertmannite transformation rates and products.Appl.Geochem.22(9),2006-2015.
Kumpulainen,S.,Raisanen,M.L.,Von Der Kammer,F.,Hofmann,T.,2008.Ageing of synthetic and natural schwertmannites at pH 2-8.Clay Miner.43(3),437-448.
Lanno,R.P.,Dixon,D.G.,1994.Chronic toxicity of waterborne thiocyanate to the fathead minnow(pimephales promelas):a partial life-cycle study.Environ.Toxicol.Chem.13(9),1423-1432.
Liao,Y.H.,Liang,J.R.,Zhou,L.X.,2011.Adsorptive removal of As(III)by biogenic schwertmannite from simulated Ascontaminated groundwater.Chemosphere 83(3),295-301.
Miller,F.A.,Wilkins,C.H.,1952.Infrared spectra and characteristic frequencies of inorganic ions.Anal.Chem.24(8),1253-1294.
Namasivayam,C.,Sureshkumar,M.V.,2007.Modelling thiocyanate adsorption onto surfactant-modified coir pith,an agricultural solid'waste.Process Saf.Environ.Protect.85(B6),521-525.
Paikaray,S.,Peiffer,S.,2010.Dissolution kinetics of sulfate from schwertmannite under variable pH conditions.Mine Water Environ.29(4),263-269.
Paikaray,S.,Peiffer,S.,2012.Abiotic schwertmannite transformation kinetics and the role of sorbed As(III).Appl.Geochem.27(3),590-597.
Paikaray,S.,Schr?der,C.,Peiffer,S.,2017.Schwertmannite stability in anoxic Fe(II)-rich aqueous solution.Geochim.Cosmochim.Acta 217,292-305.
Peine,A.,Trischler,A.,Küsel,K.,Peiffer,S.,2000.Electron flow in an iron-rich acidic sediment-evidence for an acidity-driven iron cycle.Limnol.Oceanogr.45(5),1077-1087.
Regazzoni,A.E.,Blesa,M.A.,1991.Reactivity of surface iron(III)-thiocyanate complexes characterized by the dissolution of hematite in acidic thiocyanate solutions.Langmuir 7(3),473-478.
Regenspurg,S.,Peiffer,S.,2005.Arsenate and chromate incorporation in schwertmannite.Appl.Geochem.20(6),1226-1239.
Regenspurg,S.,Brand,A.,Peiffer,S.,2004.Formation and stability of schwertmannite in acidic mining lakes.Geochim.Cosmochim.Acta 68(6),1185-1197.
Stookey,L.L.,1970.Ferrozine-a new spectrophotometric reagent for iron.Anal.Chem.42(7),779-781.
Suter,D.,Siffert,C.,Sulzberger,B.,Stumm,W.,1988.Catalytic dissolution of iron(III)(hydr)oxides by Oxalic acid in the presence of Fe(II).Naturwissenschaften 75,571-573.
Vithana,C.L.,Sullivan,L.A.,Burton,E.D.,Bush,R.T.,2014.Liberation of acidity and arsenic from schwertmannite:effect of fulvic acid.Chem.Geol.372,1-11.
Vu,H.P.,Moreau,J.W.,2015.Thiocyanate adsorption on ferrihydrite and its fate during ferrihydrite transformation to hematite and goethite.Chemosphere 119,987-993.
Wang,H.,Bigham,J.M.,Tuovinen,O.H.,2006.Formation of schwertmannite and its transformation to jarosite in the presence of acidophilic iron-oxidizing microorganisms.Mater.Sci.Eng.C-Biomimetic Supramol.Syst.26(4),588-592.
Wang,Z.M.,Schenkeveld,W.D.,Kraemer,S.M.,Giammar,D.E.,2015.Synergistic effect of reductive and ligand-promoted dissolution of goethite.Environ.Sci.Technol.49(12),7236-7244.
Williams,A.G.B.,Scherer,M.M.,2004.Spectroscopic evidence for Fe(II)-Fe(III)electron transfer at the iron oxide-water interface.Environ.Sci.Technol.38(18),4782-4790.
Xie,F.F.,Borowiec,J.,Zhang,J.D.,2013.Synthesis of AgCl nanoparticles-loaded hydrotalcite as highly efficient adsorbent for removal of thiocyanate.Chem.Eng.J.223,584-591.
Xie,Y.Y.,Lu,G.N.,Ye,H.,Yang,C.F.,Xia,D.,Yi,X.Y.,et al.,2017.Fulvic acid induced the liberation of chromium from CrO42--substituted schwertmannite.Chem.Geol.475,52-61.
Zeng,Y.F.,Wang,H.,Guo,C.L.,Wan,J.J.,Fan,C.,Reinfelder,J.R.,et al.,2018.Schwertmannite transformation via direct or indirect electron transfer by a sulfate reducing enrichment culture.Environ.Pollut.242,738-748 Pt A.
Zhang,S.L.,Jia,S.Y.,Yu,B.,Liu,Y.,Wu,S.H.,Han,X.,2016.Sulfidization of As(V)-containing schwertmannite and itsimpact on arsenic mobilization.Chem.Geol.420,270-279.
Antelo,J.,Fiol,S.,Gondar,D.,Pérez,C.,López,R.,Arce,F.,2013.Cu(II)incorporation to schwertmannite:effect on stability and reactivity under AMD conditions.Geochim.Cosmochim.Acta119,149-163.
Baltrusaitis,J.,Cwiertny,D.M.,Grassian,V.H.,2007.Adsorption of sulfur dioxide on hematite and goethite particle surfaces.Phys.Chem.Chem.Phys.9(41),5542-5554.
Bao,Y.P.,Guo,C.L.,Lu,G.N.,Yi,X.Y.,Wang,H.,Dang,Z.,2018.Role of microbial activity in Fe(III)hydroxysulfate mineral transformations in an acid mine drainage-impacted site from the Dabaoshan Mine.Sci.Total Environ.616-617,647-657.
Bigham,J.,Schwertmann,U.,Carlson,L.,Murad,E.,1990.A poorly crystallized oxyhydroxysulfate of iron formed by bacterial oxidation of Fe(II)in acid mine waters.Geochim.Cosmochim.Acta 54(10),2743-2758.
Bigham,J.M.,Schwertmann,U.,Traina,S.J.,Winland,R.L.,Wolf,M.,1996.Schwertmannite and the chemical modeling of iron in acid sulfate waters.Geochim.Cosmochim.Acta 60(12),2111-2121.
Boening,D.W.,Chew,C.M.,1999.A critical review:General toxicity and environmental fate of three aqueous cyanide ions and associated ligands.Water Air Soil Pollut.109(1-4),67-79.
Boily,J.F.,Gassman,P.L.,Peretyazhko,T.,Szanyi,J.,Zachara,J.M.,2010.FTIR spectral components of schwertmannite.Environ.Sci.Technol.44(4),1185-1190.
Bonnissel-Gissinger,P.,Alnot,M.,Ehrhardt,J.J.,Behra,P.,1998.Surface oxidation of pyrite as a function of pH.Environ.Sci.Technol.32(19),2839-2845.
Burton,E.D.,Johnston,S.G.,2012.Impact of silica on the reductive transformation of schwertmannite and the mobilization of arsenic.Geochim.Cosmochim.Acta 96,134-153.
Burton,E.D.,Bush,R.T.,Sullivan,L.A.,2007a.Schwertmannite reduction and iron(II)-monosulfide formation in acidified coastal lowlands:iron-sulfur geochemistry and implications for water quality.Geochim.Cosmochim.Acta 71(15),A135.
Burton,E.D.,Bush,R.T.,Sullivan,L.A.,Mitchell,D.R.G.,2007b.Reductive transformation of iron and sulfur in schwertmannite-rich accumulations associated with acidified coastal lowlands.Geochim.Cosmochim.Acta 71(18),4456-4473.
Burton,E.D.,Bush,R.T.,Sullivan,L.A.,Mitchell,D.R.G.,2008.Schwertmannite transformation to goethite via the Fe(II)pathway:reaction rates and implications for iron-sulfide formation.Geochim.Cosmochim.Acta 72(18),4551-4564.
Chen,M.Q.,Lu,G.N.,Guo,C.L.,Yang,C.F.,Wu,J.X.,Huang,W.L.,et al.,2015.Sulfate migration in a river affected by acid mine drainage from the Dabaoshan mining area,South China.Chemosphere 119,734-743.
Cornell,R.M.,Schwertmann,U.,1996.The Iron Oxides.VCHVerlagsgesellschaft,Weinheim,New York.
Espana,J.S.,Pamo,E.L.,Santofimia,E.,Aduvire,O.,Reyes,J.,Barettino,D.,2005.Acid mine drainage in the Iberian Pyrite Belt(Odiel river watershed,Huelva,SW Spain):geochemistry,mineralogy and environmental implications.Appl.Geochem.20(7),1320-1356.
Fan,C.,Guo,C.L.,Chen,M.Q.,Huang,W.L.,Wan,J.J.,Reinfelder,J.R.,et al.,2018.Transformation of cadmium-associated schwertmannite and subsequent element repartitioning behaviors.Environ.Sci.Pollut.Res.26(1),617-627.https://doi.org/10.1007/s11356-018-3441-9.
Gan,M.,Sun,S.J.,Zheng,Z.H.,Tang,H.J.,Sheng,J.R.,Zhu,J.Y.,et al.,2015a.Adsorption of Cr(VI)and Cu(II)by AlPO4modified biosynthetic schwertmannite.Appl.Surf.Sci.356,986-997.
Gan,M.,Zheng,Z.H.,Sun,S.J.,Zhu,J.Y.,Liu,X.X.,2015b.The influence of aluminum chloride on biosynthetic schwertmannite and Cu(ii)/Cr(vi)adsorption.RSC Adv.5(114),94500-94512.
Gould,W.D.,King,M.,Mohapatra,B.R.,Cameron,R.A.,Kapoor,A.,Koren,D.W.,2012.A critical review on destruction of thiocyanate in mining effluents.Miner.Eng.34,38-47.
Knorr,K.-H.,Blodau,C.,2007.Controls on schwertmannite transformation rates and products.Appl.Geochem.22(9),2006-2015.
Kumpulainen,S.,Raisanen,M.L.,Von Der Kammer,F.,Hofmann,T.,2008.Ageing of synthetic and natural schwertmannites at pH 2-8.Clay Miner.43(3),437-448.
Lanno,R.P.,Dixon,D.G.,1994.Chronic toxicity of waterborne thiocyanate to the fathead minnow(pimephales promelas):a partial life-cycle study.Environ.Toxicol.Chem.13(9),1423-1432.
Liao,Y.H.,Liang,J.R.,Zhou,L.X.,2011.Adsorptive removal of As(III)by biogenic schwertmannite from simulated Ascontaminated groundwater.Chemosphere 83(3),295-301.
Miller,F.A.,Wilkins,C.H.,1952.Infrared spectra and characteristic frequencies of inorganic ions.Anal.Chem.24(8),1253-1294.
Namasivayam,C.,Sureshkumar,M.V.,2007.Modelling thiocyanate adsorption onto surfactant-modified coir pith,an agricultural solid'waste.Process Saf.Environ.Protect.85(B6),521-525.
Paikaray,S.,Peiffer,S.,2010.Dissolution kinetics of sulfate from schwertmannite under variable pH conditions.Mine Water Environ.29(4),263-269.
Paikaray,S.,Peiffer,S.,2012.Abiotic schwertmannite transformation kinetics and the role of sorbed As(III).Appl.Geochem.27(3),590-597.
Paikaray,S.,Schr?der,C.,Peiffer,S.,2017.Schwertmannite stability in anoxic Fe(II)-rich aqueous solution.Geochim.Cosmochim.Acta 217,292-305.
Peine,A.,Trischler,A.,Küsel,K.,Peiffer,S.,2000.Electron flow in an iron-rich acidic sediment-evidence for an acidity-driven iron cycle.Limnol.Oceanogr.45(5),1077-1087.
Regazzoni,A.E.,Blesa,M.A.,1991.Reactivity of surface iron(III)-thiocyanate complexes characterized by the dissolution of hematite in acidic thiocyanate solutions.Langmuir 7(3),473-478.
Regenspurg,S.,Peiffer,S.,2005.Arsenate and chromate incorporation in schwertmannite.Appl.Geochem.20(6),1226-1239.
Regenspurg,S.,Brand,A.,Peiffer,S.,2004.Formation and stability of schwertmannite in acidic mining lakes.Geochim.Cosmochim.Acta 68(6),1185-1197.
Stookey,L.L.,1970.Ferrozine-a new spectrophotometric reagent for iron.Anal.Chem.42(7),779-781.
Suter,D.,Siffert,C.,Sulzberger,B.,Stumm,W.,1988.Catalytic dissolution of iron(III)(hydr)oxides by Oxalic acid in the presence of Fe(II).Naturwissenschaften 75,571-573.
Vithana,C.L.,Sullivan,L.A.,Burton,E.D.,Bush,R.T.,2014.Liberation of acidity and arsenic from schwertmannite:effect of fulvic acid.Chem.Geol.372,1-11.
Vu,H.P.,Moreau,J.W.,2015.Thiocyanate adsorption on ferrihydrite and its fate during ferrihydrite transformation to hematite and goethite.Chemosphere 119,987-993.
Wang,H.,Bigham,J.M.,Tuovinen,O.H.,2006.Formation of schwertmannite and its transformation to jarosite in the presence of acidophilic iron-oxidizing microorganisms.Mater.Sci.Eng.C-Biomimetic Supramol.Syst.26(4),588-592.
Wang,Z.M.,Schenkeveld,W.D.,Kraemer,S.M.,Giammar,D.E.,2015.Synergistic effect of reductive and ligand-promoted dissolution of goethite.Environ.Sci.Technol.49(12),7236-7244.
Williams,A.G.B.,Scherer,M.M.,2004.Spectroscopic evidence for Fe(II)-Fe(III)electron transfer at the iron oxide-water interface.Environ.Sci.Technol.38(18),4782-4790.
Xie,F.F.,Borowiec,J.,Zhang,J.D.,2013.Synthesis of AgCl nanoparticles-loaded hydrotalcite as highly efficient adsorbent for removal of thiocyanate.Chem.Eng.J.223,584-591.
Xie,Y.Y.,Lu,G.N.,Ye,H.,Yang,C.F.,Xia,D.,Yi,X.Y.,et al.,2017.Fulvic acid induced the liberation of chromium from CrO42--substituted schwertmannite.Chem.Geol.475,52-61.
Zeng,Y.F.,Wang,H.,Guo,C.L.,Wan,J.J.,Fan,C.,Reinfelder,J.R.,et al.,2018.Schwertmannite transformation via direct or indirect electron transfer by a sulfate reducing enrichment culture.Environ.Pollut.242,738-748 Pt A.
Zhang,S.L.,Jia,S.Y.,Yu,B.,Liu,Y.,Wu,S.H.,Han,X.,2016.Sulfidization of As(V)-containing schwertmannite and itsimpact on arsenic mobilization.Chem.Geol.420,270-279.