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.

Removal of arsenate by ferrihydrite via surface complexation and surface precipitation

“…Tokoro et al [23] found that arsenate was primarily adsorbed on ferrihydrite as a surface complex when the initial molar ratio of As/Fe was less than 0.4. Otherwise, a ferric arsenate would be formed instead.…”

Arsenic Removal and Transformation by Pseudomonas sp. Strain GE-1-Induced Ferrihydrite: Co-precipitation Versus Adsorption

“…Ferrihydrite, a poorly ordered hydrous Fe oxide with a high specific surface area (241-272 m 2 ·g −1 ) and commonly present in low-temperature geochemical environments, is one of the most important minerals in the sequestration of As (Jang et al 2006;Michel et al 2007). Previous studies showed that abiotically synthesized ferrihydrite has a high capacity for As removal via both co-precipitation and adsorption (Bhandari et al 2011;Jia and Demopoulos 2005;Raven et al 1998;Tokoro et al 2010;Zhao et al 2011). Jia and Demopoulos (2005) suggested that almost all As (300 mg/L) was removed by either adsorption or coprecipitation at molar ratio of Fe/As=8 and pH=8.…”

Evaluation of arsenic immobilization in red mud by CO2 or waste acid acidification combined ferrous (Fe2+) treatment

“…Meanwhile, it was also reported that green rusts and hydrous ferric oxides were effective in arsenic adsorption [25]. The mechanisms of iron-arsenic combination should be surface complexation and surface precipitation [26].…”