Chemical and electrochemical considerations on the removal process of hexavalent chromium from aqueous media

This study investigates two methods for the removal of hexavalent chromium (Cr(VI)) from industrial wastewater, focusing on their chemical and electrochemical aspects. The objective was to compare the efficiency and sludge generation of these processes. The chemical method employs the addition of Fe(II)(aq) through the dissolution of FeSO4, while the electrochemical approach generates Fe(II)(aq) ions via the anodic dissolution of a steel electrode. Both methods follow the same reaction where Fe(II) reduces Cr(VI) to Cr(III), subsequently precipitating Cr(III) and Fe(III) ions as insoluble hydroxides through pH modification. Our results indicate that the electrochemical method not only offers enhanced control over the reduction process but also produces significantly less sludge compared to the chemical method. Moreover, the aging of the produced sludge leads to the formation of soluble polynuclear Cr(III) species, highlighting the importance of separating the chromium and iron phases post-formation. We present optimized hydraulic conditions for the continuous reduction of Cr(VI) in a plug-flow reactor system, thereby contributing to more sustainable environmental practices in wastewater treatment.