Photoreduction of chromium (VI) in aqueous solutions containing ferric and carboxylate ions

In this paper, the photochemical reduction process of Cr(VI) in aqueous solutions containing ferric oxalate (Ox) and alginate (Alg) complexes was studied. Under the radiation of high-pressure mercury lamp ( lambda greater than or equal to 365 nm, 125W), Fe(III)-oxalate and Fe(III)-alginate complexes undergo photolysis to produce ferrous ions and other organic reductive species, which reduce Cr(VI) subsequently. The photo-chemical reduction efficiency is comparatively higher in the solution at pH 3.0 than that over the range of 3.0-7.0. The reduction efficiency decreases with increasing initial Cr(VI) concentrations from 0.5 to 2.0 mg/L in the solutions containing 10.0 mu mol/L ferric ions and 48.0 mu mol/L oxalate ions. For 10.0 mg/L Cr(VI), the reduction efficiency could reach 92.3% by increasing the concentrations of both ferric and oxalate ions from 10.0 and 48.0 mu mol/L to 100 and 480 mu mol/L, respectively, in the solutions after radiation for 80 min. Under the conditions of [Cr(VI)] sub(0) = 1.0 mg/L, [Fe(III)] sub(0) = 20.0 mu mol/L, [Na-Alg] sub(0) = 0.5 g/L and pH = 3.0, the reduction efficiency of Cr(VI) could achieve 97% after 80 min of radiation. The increase of the ferric, oxalate and alginate concentrations studied in this work result from the increase of reduction efficiency of Cr(VI).