Removal of hexavalent chromium by electrochemical reduction–precipitation: Investigation of process performance and reaction stoichiometry

[Display omitted] ▶ Lower pH favors Cr(VI) reduction to Cr(III). ▶ Maximum 10% Cr(VI) absorption on Cr(OH)3(s)/Fe(OH)3(s) sludge. ▶ PO43− has higher inhibiting effect to Cr(VI) reduction in comparison to Cl−, NO3− and SO42−. ▶ Cr(VI) reduction stoichiometry varies from 2.49 to 2.92. This work experimentally investigates aqueous Cr(VI) reduction/removal by electrotreatment with mild steel electrode in a batch stirred reactor. Cr(VI) removal is due to simultaneous reduction to Cr(III) followed by precipitation and adsorption of Cr(VI) on Fe(OH)3(s)/Cr(OH)3(s) sludge formed. Cr(VI) adsorbed on sludge increases to maximum 10% and decreases to negligible level with diminishing concentration of Cr(VI) in solution. Concentration of Cr(VI) can be decreased to its discharge limit (0.5mg/l) in a single process step without addition of any precipitating agent. The highest reduction rate of Cr(VI) was found to be 3.8mgl−1min−1 at lowest initial pH 2 at the beginning (treatment time