Optimization of Hexavalent Chromium Removal from Wastewater by Ferrite Precipitation

Abstract

Removal of hexavalent chromium ions (Cr6+) from wastewater produced by surface treatment of aluminum was performed by ferrite precipitation. By varying the reactant concentrations and reaction conditions the optimal conditions were established for chromium removal. The following variables were tested: concentration of ferric salt (FeSO4·7H2O), the pH during oxidation-reduction, the pH during co-precipitation, the reaction temperature and the incubation time. The results indicate that chromium removal is optimal when ferric salt is added in excess to chromium at a ratio of 14 to 1 (above the theoretical optimum), the redox reaction is performed at pH 4, precipitation is performed at pH 9, the reaction temperature is set at 75°C and the reaction duration is 20 min. Under these conditions, a removal rate of 99.97% could be obtained, resulting in a residual concentration of 0.29 mg/L hexavalent chromium from with initial concentrations of 1539 mg/L. Wastewater thus treated fulfilled the maximum allowed standard of 0.5 mg/L.