Treatment of hexavalent chromium by using a combined Fenton and chemical precipitation process

This work aimed to remove hexavalent chromium and three treatment schemes were examined based on a laboratory scale design: (a) Fenton process, (b) precipitation process, and (c) Fenton process followed by precipitation process. Variations of this study including pH, Fenton and precipitation reagents (molar ratio of Fe2+/H2O2 and FeCl3), contact time, and initial concentration of chromium were investigated. The results showed that about 98% of Cr+6 is removed by the coagulation property of the Fenton process, and the ideal conditions for its removal included Cr+6 = 10 mg/L, pH = 4, molar ratio Fe2+/H2O2 = 2.4 with a time duration of 30 min. Maximal removal efficiency of Cr+6 in the precipitation process was equivalent to 97% in the following optimum conditions: Cr+6 = 5 mg/L, pH = 7, FeCl3 = 0.7 g/L and deposition time of 20 min. Combination of these two methods can remove greater concentrations of chromium (15 mg/L) to about 99.99%. Therefore, removal of Cr+6 by the combined Fenton and precipitation process was better than any of the methods alone (Kruskal-Wallis, P value ≤0.05). Consequently, the Fenton process followed by precipitation process can be considered as a suitable process for Cr+6 removal to achieve environmental standards.