title: Model predictions of realgar precipitation by reaction of As(III) with synthetic Mackinawite under anoxic conditions.
abstract: This study investigates the removal of As(III) from solution using mackinawite, a nanoparticulate reduced iron sulfide. Mackinawite suspensions (0.1-40 g/L) effectively lower initial concentrations of 1.3 x 10(-5) M As(III) from pH 5-10, with maximum removal occurring under acidic conditions. Based on Eh measurements, it was found that the redox state of the system depended on the mackinawite solids concentration and pH. Higher initial mackinawite concentrations and alkaline pH resulted in a more reducing redox condition. Given this, the pH edge data were modeled thermodynamically using pe (-log[e(-)]) as a fitting parameter and linear pe-pH relationships within the range of measured Eh values as a function of pH and mackinawite concentration. The model predicts removal of As(III) from solution by precipitation of realgar with the formation of secondary oxidation products, greigite or a mixed-valence iron oxide phase, depending on pH. This study demonstrates that mackinawite is an effective sequestration agent for As(III) and highlights the importance of incorporating redox into models describing the As-Fe-S-H2O system.
authors.affiliation: University of Michigan, Department of Civil and Environmental Engineering, 181 EWRE, 1351 Beal Avenue, Ann Arbor, Michigan 48109, USA.
authors.forename: Tanya J
authors.initials: TJ
authors.lastname: Gallegos
authors.forename: Young-Soo
authors.initials: YS
authors.lastname: Han
authors.forename: Kim F
authors.initials: KF
authors.lastname: Hayes
mesh_terms: D000693:Anaerobiosis; D001151:Arsenic / Q000737:chemistry* / Q000302:isolation & purification; D001152:Arsenicals / Q000737:chemistry*; D011232:Chemical Precipitation; D004777:Environment; D005296:Ferrous Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D010084:Oxidation-Reduction; D013440:Sulfides / Q000737:chemistry*; D013455:Sulfur / Q000302:isolation & purification
chemical_list: D001152:Arsenicals; D005296:Ferrous Compounds; D013440:Sulfides; C058317:arsenic disulfide; D013455:Sulfur; D001151:Arsenic; C022597:ferrous sulfide