Rapid abiotic As removal from As-rich acid mine drainage: Effect of pH, Fe/As molar ratio, oxygen, temperature, initial As concentration and neutralization reagent

Oxygen-induced abio-oxidation of Fe(II) and As(III) for Fe-As co-precipitation is proposed in this work as a cost-saving and time-saving method to remove As from As-rich acid mine drainage (AMD). The effect of pH, Fe/As molar ratio, oxygen flow rate, temperature, initial As concentration and neutralization reagent on As removal was investigated. The results showed that As removal efficiency was strongly controlled by pH, which increased from 33.0% to 96.2% as increasing pH from 2 to 7 after 12 h-reactions. pH was also very important to As(III) oxidation. The oxidation degree of As(III) (12.4-35.4%) generally increased with the increase of pH, but the optimal As(III) oxidation (45%) occurred at pH 5. Arsenic removal is much less affected by other five factors than pH. Insufficient and excessive Fe(II) supply caused the decrease of oxidation degree of As(III). Fenton-like reaction between Fe(II) and O-2 with reactive oxygen species (ROS) as oxidizers was the probable mechanism for Fe (II) and As(III) oxidation. Tooeleite/ferric arsenite hydroxysulfate, ferric arsenate and As(III+V)-bearing ferrihydrite were major responsible for As immobilization.