title: Biomineralization of arsenate to arsenic sulfides is greatly enhanced at mildly acidic conditions.
abstract: Arsenic (As) is an important water contaminant due to its high toxicity and widespread occurrence. Arsenic-sulfide minerals (ASM) are formed during microbial reduction of arsenate (As(V)) and sulfate (SO4(2-)). The objective of this research is to study the effect of the pH on the removal of As due to the formation of ASM in an iron-poor system. A series of batch experiments was used to study the reduction of SO4(2-) and As(V) by an anaerobic biofilm mixed culture in a range of pH conditions (6.1-7.2), using ethanol as the electron donor. Total soluble concentrations and speciation of S and As were monitored. Solid phase speciation of arsenic was characterized by x-ray adsorption spectroscopy (XAS). A marked decrease of the total aqueous concentrations of As and S was observed in the inoculated treatments amended with ethanol, but not in the non-inoculated controls, indicating that the As-removal was biologically mediated. The pH dramatically affected the extent and rate of As removal, as well as the stoichiometric composition of the precipitate. The amount of As removed was 2-fold higher and the rate of the As removal was up to 17-fold greater at pH 6.1 than at pH 7.2. Stoichiometric analysis and XAS results confirmed the precipitate was composed of a mixture of orpiment and realgar, and the proportion of orpiment in the sample increased with increasing pH. The results taken as a whole suggest that ASM formation is greatly enhanced at mildly acidic pH conditions.
authors.affiliation: Department of Chemical and Environmental Engineering, The University of Arizona, P.O. Box 210011, Tucson, AZ, USA. Electronic address: luciar@email.arizona.edu.
authors.forename: Lucia
authors.initials: L
authors.lastname: Rodriguez-Freire
authors.affiliation: Department of Chemical and Environmental Engineering, The University of Arizona, P.O. Box 210011, Tucson, AZ, USA.
authors.forename: Reyes
authors.initials: R
authors.lastname: Sierra-Alvarez
authors.affiliation: Department of Soil, Water and Environmental Science, The University of Arizona, P.O. Box 210038, Tucson, AZ, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Root
authors.affiliation: Department of Soil, Water and Environmental Science, The University of Arizona, P.O. Box 210038, Tucson, AZ, USA.
authors.forename: Jon
authors.initials: J
authors.lastname: Chorover
authors.affiliation: Department of Chemical and Environmental Engineering, The University of Arizona, P.O. Box 210011, Tucson, AZ, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Field
mesh_terms: D000327:Adsorption; D001149:Arsenates / Q000737:chemistry*; D001151:Arsenic / Q000737:chemistry*; D001152:Arsenicals / Q000737:chemistry*; D001419:Bacteria / Q000378:metabolism; D001673:Biodegradation, Environmental; D019149:Bioreactors; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D008903:Minerals / Q000737:chemistry; D013431:Sulfates / Q000737:chemistry; D013440:Sulfides / Q000737:chemistry*; D014867:Water; D014874:Water Pollutants, Chemical / Q000032:analysis; D018508:Water Purification / Q000379:methods*
chemical_list: D001149:Arsenates; D001152:Arsenicals; D008903:Minerals; D013431:Sulfates; D013440:Sulfides; D014874:Water Pollutants, Chemical; D014867:Water; C045816:arsenic trisulfide; C058317:arsenic disulfide; D001151:Arsenic; C025657:arsenic acid
keywords: Arsenate reduction; Biomineralization; Bioprecipitation; Orpiment; Realgar; Sulfate reduction