Sorption mechanisms of arsenate during coprecipitation with ferrihydrite in aqueous solution.
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.
Tokoro
Chiharu
C
Department of Creative Science and Engineering, Faculty of Science and Engineering, Waseda University, Tokyo 169-8555, Japan. tokoro@waseda.jp
Yatsugi
Yohei
Y
Koga
Hajime
H
Owada
Shuji
S
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
D001149:Arsenates; D005290:Ferric Compounds; D012996:Solutions; D014874:Water Pollutants, Chemical; D014867:Water; C092844:ferric oxyhydroxide; C025657:arsenic acid