Solar oxidation and removal of arsenic at circumneutral pH in iron containing waters

An estimated 30−50 million people in Bangladesh consume groundwater with arsenic contents far above accepted limits. A better understanding of arsenic redox kinetics and simple water treatment procedures are urgently needed. We have studied thermal and photochemical As(III) oxidation in the laboratory, on a time scale of hours, in water containing 500 μg/L As(III), 0.06−5 mg/L Fe(II,III), and 4−6 mM bicarbonate at pH 6.5−8.0. As(V) was measured colorimetrically, and As(III) and As(tot) were measured by As(III)/As(tot)-specific hydride-generation AAS. Dissolved oxygen and micromolar hydrogenperoxide did not oxidize As(III) on a time scale of hours. As(III) was partly oxidized in the dark by addition of Fe(II) to aerated water, presumably by reactive intermediates formed in the reduction of oxygen by Fe(II). In solutions containing 0.06−5 mg/L Fe(II,III), over 90% of As(III) could be oxidized photochemically within 2−3 h by illumination with 90 W/m2 UV-A light. Citrate, by forming Fe(III)citrate complexes t...