Effect of co-existent Al(III) in As-rich Acid Mine Drainage (AMD) on As removal during Fe(II) and As(III) abiotic oxidation process

The effect of co-existent Al(III) in As-rich AMD on As removal via oxygen-induced abiotic oxidation caused concern due to weak affinity between Al(III) hydroxide and As(III). The removal of As from As-rich AMD with and without Al(III) at various pH and Fe/(Al)/As molar ratios was investigated. The results showed that 92.3–99.8% of As in Al(III)-containing systems was removed by 70–100% of Fe(II) and 40.2–67.8% of As(III) oxidation in 1–4 h at pH 3–9 and Fe/Al/As molar ratios of 2–8:1:1. Arsenic removal efficiencies generally increased with increasing the pH and Fe/Al/As molar ratio. Arsenic oxidation efficiencies first increased from pH 3 to 5 and then decreased from pH 5 to 9, while an opposite trend occurred with increasing the Fe/Al/As molar ratio. As(III) oxidation was controlled by ROS contents involving the Fenton-like reaction between Fe(II) and O2. Ferric arsenite hydroxysulfate, ferric arsenate and As-bearing ferrihydrite+schwertannite were the main As sinks. Co-existent Al(III) promoted As(III) oxidation. The proposed method for aqueous As removal with the total As (As(T)) leaching solid product at pH 5 and Fe/Al/As molar ratio of 8:1:1 can bring the As level to the required limit as emphasized in regulatory frameworks.