UV-induced highly efficient removal of As(III) through synergistic photo-oxidation in the presence of Fe(II).

In polluted waters, arsenic (As) poses substantial risks to the environment and human health. Inorganic As mainly exists as As(V) and As(III), and As(III) usually shows higher mobility and toxicity and is more difficult to be removed by coagulation. The oxidation of coexisting Fe(II) can accelerate As(III) oxidation and removal by promoting the generation of reactive intermediates and Fe(III) coagulant in the presence of dissolved oxygen. However, the removal efficiency of As from acidic wastewaters is far from satisfactory due to the low Fe(II) oxidation rate by dissolved oxygen. Herein, UV irradiation was applied to stimulate the synergistic oxidation of Fe(II)/As(III), and the effects of coexisting Fe(II) concentration and pH were also evaluated. The synergistic oxidation of Fe(II)/As(III) significantly enhanced the removal of As from acidic waters. Under UV irradiation, Fe(II) significantly promoted the generation of reactive oxygen species (ROS), thereby facilitating As(III) oxidation. In addition, the formation of ferric arsenate and amorphous ferric (hydr)oxides contributed much to As removal. In the As(III)-containing solution with 200 μmol L Fe(II) at initial pH 4.0, the total arsenic (As(T)) concentration decreased from 67.0 to 1.3 and 0.5 μmol L, respectively, at 25 and 120 min under UV irradiation. The As(T) removal rate increased with increasing Fe(II) concentration, and first increased and then decreased with increasing initial pH from 2.0 to 6.0. This study clarifies the mechanism for the synergistic photo-oxidation of Fe(II)/As(III) under UV irradiation, and proposes a new strategy for highly efficient As(III) removal from acidic industrial and mining wastewaters.