title: Effect of ferrous iron on arsenate sorption to amorphous ferric hydroxide.
abstract: Amorphous ferric hydroxide (AFH) sorbents are commonly used for removal of arsenate from water. When disposed in microbially active, reducing environments, such as landfills, Fe(II) will be generated by reductive dissolution of the AFH surface and arsenate will be desorbed. However, the observed ratio of arsenate (and, in fact, total arsenic) to total iron in the leachate is not consistent with the original ratio of arsenate to iron on the AFH. Work to determine if ferrous iron re-adsorption to the AFH can partially explain this inconsistency is described. As pH increases above 7, Fe(II) increasingly sorbs onto the AFH surface. This sorption is largely independent of ionic strength and somewhat irreversible at high pH. In contrast, arsenate partitioning to AFH decreases with increasing pH. However, over the pH range from 5 to 9, the presence of Fe(II) sorbed to the AFH surface increases the capacity for arsenate sorption. In addition, when no Fe(II) is present, arsenate binding is largely to surface sites inaccessible to Fe(II) binding. The results are also consistent with Fe(II) sorption to AFH sites, otherwise unfavorable to arsenate binding and transformation of those sites into arsenate-amenable binding sites.
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, Tucson, Arizona, USA.
authors.forename: Muhammed
authors.initials: M
authors.lastname: Mukiibi
authors.forename: Wendell P
authors.initials: WP
authors.lastname: Ela
authors.forename: A Eduardo
authors.initials: AE
authors.lastname: Sáez
mesh_terms: D000327:Adsorption; D001149:Arsenates / Q000737:chemistry*; D001151:Arsenic / Q000032:analysis*; D018053:Arsenites / Q000737:chemistry; D002623:Chemistry Techniques, Analytical / Q000295:instrumentation* / Q000379:methods; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions; D007501:Iron / Q000737:chemistry / Q000494:pharmacology*; D014867:Water / Q000737:chemistry; D018508:Water Purification
chemical_list: D001149:Arsenates; D018053:Arsenites; D005290:Ferric Compounds; D007477:Ions; D014867:Water; C021024:ferric hydroxide; D007501:Iron; D001151:Arsenic