Direct electrochemical reduction of hexavalent chromium in a filter-press reactor

The direct electrochemical reduction of toxic Cr(VI) species was studied by cyclic voltammetry, rotating disk electrode and in a flow-by filter press reactor. The key voltammetric reduction peak was found at -340 mV (vs. Ag/AgCl), whereas the limiting current under hydrodynamic conditions was observed at ca. - 850 mV. A continuous flow filter-press reactor with a reticulated vitreous. carbon (RVC) cathode was used to achieve Cr(VI) reduction. It was found that the RVC itself reduces part of the Cr(VI) in the absence of an applied potential and becomes oxidized to CO2. The application of a relatively small potential (-1 V) to 200 mL of a 100 ppm Cr(VI) solution circulating at a flow rate of 40 mL min(-1) achieves the reduction of c.a. 99% of the Cr(VI) initially present in only 8 min.