A comparative study of global hexavalent chromium removal by chemical and electrochemical processes

Direct electroreduction of Cr(VI) to Cr(III) has been widely proposed as an alternative for the treatment of effluents polluted with hexavalent chromium, however, no analysis is available on the cost of a global process, that considers both, the energy required to carry out the reduction reaction, and that associated with the operation of the process, to remove Cr(VI) via precipitation of Cr(OH)3. This paper presents a study of the operation cost, considering raw material and electric power required by the electrochemical process, to remove Cr(VI) from real samples. A comparison between chemical reduction is presented, where both processes are followed by a step of alkaline chemical precipitation. The differences in pH required for each step are determinant in the overall cost of the process. Operating under optimal conditions the cost is almost 7 times higher for direct electroreduction process compared with the chemical method, and power consumption being secondary. The ratio decreases to 1.3 times when the electrochemical method is carried out at pH 2, but operating time is increased threefold, thereby increasing the cost of pumping the solution to be treated.