Hexavalent chromium reduction from real electroplating wastewater by chemical precipitation

Abstract

The immense use of chromium in the electroplating process leads to the discharge of hexavalent chromium in its effluent. Since Cr(VI) is highly toxic, its exposure poses an acute risk of health. On the contrary, Cr(III) which is naturally occurring, is much less toxic than Cr(VI). Therefore the easiest way to deal with Cr(VI) is to reduce it into its trivalent form. Exhaustive chemical analysis was done to reduce Cr(VI) to Cr(III) by using sodium metabisulfite (Na2S2O5) and ferrous sulfate (FeSO4). And after the reduction process, precipitating agents such as (Ca(OH)2), (NaOH) and a combination of the two were used to precipitate Cr(III) as hydroxides. Various parameters were varied and optimized. It was observed that the % Cr(VI) reduction increased from 88% to 99.97% when the dosage of sodium metabisulfite increased from 40 mg/L to 100 mg/L at a pH of 2. The maximum removal of 98.2% was achieved by using the combination of Ca(OH)2 + NaOH at a pH of 9.