title: Sorption mechanisms of arsenate during coprecipitation with ferrihydrite in aqueous solution.
abstract: Dilute arsenate (As(V)) coprecipitation by ferrihydrite was investigated to determine if treatment of acid mine drainage containing dilute As(V) using coprecipitation is feasible. The sorption density obtained at pH 5 and 7 was nearly identical when As(V) was coprecipitated with ferrihydrite, while it was higher at pH 5 when As(V) was adsorbed on the ferrihydrite. The high sorption density of As(V) to ferrihydrite in coprecipitation with 1-h reaction time suggested that coprecipitation occurs via both adsorption and precipitation. Furthermore, the relationship between residual As(V) and sorption density revealed a BET-type isotherm, with a transition point from a low residual As(V) concentration to a high residual As(V) concentration being observed for all initial As(V) concentrations between 0.15 and 0.44 mmol/dm(3) when the initial molar ratio was 0.56 at pH 5 and 7. X-ray diffraction and the zeta potential revealed that the transition point from surface complexation to precipitation was obtained when the initial As/Fe ratio was 0.4 or 0.5. When dilute As(V) was coprecipitated with ferrihydrite at pH 5 and 7, it was primarily adsorbed as a surface complex when the initial molar ratio was As/Fe < 0.4, while a ferric arsenate and surface complex was formed when this ratio was >or= 0.4.
authors.affiliation: Department of Creative Science and Engineering, Faculty of Science and Engineering, Waseda University, Tokyo 169-8555, Japan. tokoro@waseda.jp
authors.forename: Chiharu
authors.initials: C
authors.lastname: Tokoro
authors.forename: Yohei
authors.initials: Y
authors.lastname: Yatsugi
authors.forename: Hajime
authors.initials: H
authors.lastname: Koga
authors.forename: Shuji
authors.initials: S
authors.lastname: Owada
mesh_terms: D000327:Adsorption; D001149:Arsenates / Q000737:chemistry*; D011232:Chemical Precipitation; D005290:Ferric Compounds / Q000737:chemistry*; D012996:Solutions; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical; D014961:X-Ray Diffraction
chemical_list: D001149:Arsenates; D005290:Ferric Compounds; D012996:Solutions; D014874:Water Pollutants, Chemical; D014867:Water; C092844:ferric oxyhydroxide; C025657:arsenic acid