Electroreduction of Cr(VI) to Cr(III) on reticulated vitreous carbon electrodes in a parallel-plate reactor with recirculation.

The reduction of Cr(VI) to Cr(III) is achieved in a flow-by, parallel-plate reactor equipped with reticulated vitreous carbon (RVC) electrodes;this reduction can be accomplished by the application of relatively small potentials. Treatment of synthetic samples and field samples (from an electrodeposition plant) results in final Cr(VI) concentrations of 0.1 mg/L (i.e., the detection limit of the UV-vis characterization technique used here) in 25 and 43 min, respectively. Such concentrations comply with typical environmental legislation for wastewaters that regulate industrial effluents (at presenttime = 0.5 mg/L for discharges). The results show the influence of the applied potential, pH, electrode porosity, volumetric flow, and solution concentration on the Cr(VI) reduction percentage and on the required electrolysis time. Values for the mass transfer coefficient and current efficiencies are also obtained. Although current efficiencies are not high, the fast kinetics observed make this proposed treatment an appealing alternative. The lower current efficiency obtained in the case of a field sample is attributed to electrochemical activation of impurities. The required times for the reduction of Cr(VI) are significantly lower than those reported elsewhere.