title: Dependence of particle concentration effect on pH and redox for arsenic removal by FeS-coated sand under anoxic conditions.
abstract: FeS has been recognized as a good scavenger for arsenic under anoxic conditions. To create a suitable adsorbent for flow-through reactors such as permeable reactive barriers, it has been suggested that this material may be coated onto sand. However, previous work on FeS-coated sand has focused on batch reactors, while flow-through reactors usually have higher solid-solution ratios. To ascertain whether differences in the solid-solution ratio (SSR) are important in this system, batch sorption experiments were conducted as a function of pH using As(III) and FeS-coated sands at various solid-solution ratios. The results showed little variation in the distribution coefficient with SSR at pH 7 and 9. However, at pH 5, the results showed lower values of the distribution coefficient at lower SSRs, the reverse of typically reported SSR effects. Measured pe values showed a dependence on SSR, which, when coupled with chemical modeling of the Fe-As-S-H2O system, suggested a change in the removal mechanism with SSR, from adsorption to a reduced Fe(II) oxyhydroxide phase (represented by Fe2(OH)5) to precipitation as As2S3 or AsS. On the other hand, at pH 7 and 9, arsenite adsorption is the most probable removal mechanism regardless of the pe. Thus, this study identified variations in pH and redox conditions, and the removal mechanisms that these parameters govern, as the reason for the apparent SSR effect.
authors.affiliation: Korea Institute of Geoscience and Mineral Resources, Daejeon, Republic of Korea. Electronic address: yshan@kigam.re.kr.
authors.forename: Young-Soo
authors.initials: YS
authors.lastname: Han
authors.affiliation: Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, United States. Electronic address: averyd@umich.edu.
authors.forename: Avery H
authors.initials: AH
authors.lastname: Demond
authors.affiliation: U.S. Geological Survey, Denver, CO, United States. Electronic address: tgallegos@usgs.gov.
authors.forename: Tanya J
authors.initials: TJ
authors.lastname: Gallegos
authors.affiliation: Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, United States. Electronic address: ford@umich.edu.
authors.forename: Kim F
authors.initials: KF
authors.lastname: Hayes
mesh_terms: D000327:Adsorption; D001151:Arsenic / Q000737:chemistry*; D018053:Arsenites / Q000737:chemistry; D004566:Electrodes; D005296:Ferrous Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D012822:Silicon Dioxide; D013696:Temperature; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D018053:Arsenites; D005296:Ferrous Compounds; D014874:Water Pollutants, Chemical; D012822:Silicon Dioxide; C015001:arsenite; D001151:Arsenic; D010100:Oxygen; C022597:ferrous sulfide
keywords: Arsenic; FeS; Particle concentration effect; Redox; Solid-solution ratio; Sorption