Highly Efficient Utilization of Soluble Fe in the Removal of Arsenic during Oxidative Flocculation of Fe(II)

Flocculation using Fe(II) instead of Fe(III) has been considered more efficient in the removal of As. However, excess Fe(II) used in the process always leaves substantial TFe [Fe(II)+Fe(III)] unutilized. We therefore developed three methods [the one-staged process (OS), the one-staged process with H2O2 (OSH) and the two-staged process (TS)] to remove As(III)/As(V) by Fe(II) (Fe:As = 2.0). Our results indicate that pH is an important factor that determines the utilization efficiency of TFe and the removal efficiency of As. In OS, the initial pH was adjusted before the reaction. At the optimal pHs of 10.0 and 11.0, the removal efficiencies of As(V) and TAs [As(III)+As(V)] could reach 84.0% and 66.7%, with only 61.9% and 80.2% TFe being utilized, respectively. In OSH, H2O2 was added after pH adjustment. After OS, pH was re-adjusted to the optimal values before the next 30 min reaction (TS). Compared with OS, the removal efficiencies of As could increase by more than 9% in OSH and TS at the optimal pHs. Besides, there is more than 10% improvement in the utilization efficiencies of TFe except at 12.0. Accelerating oxidation of Fe(II) or re-adjusting pH is therefore highly efficient for a more efficient removal of As from Fe(II)-rich groundwater.