Treatment of combined acid mine drainage (AMD)-Flotation circuit effluents from copper mine via Fenton's process

The treatability of a copper mine wastewater, including heavy metals, AMD, as well as flotation chemicals, with Fenton process was investigated. Fenton process seems advantageous for this treatment, because of Fe2+ content and low pH of AMD. First, optimum Fe2+ condition under constant H2O2 was determined, and initial Fe2+ content of AMD was found sufficient (120 mg/L for removal of chemical oxygen demand (COD) of 6125 mg/L). In the second step, without any additional Fe2+, optimum H2O2 dosage was determined as 40 mg/L. Fe2+/H2O2 molar ratio of 1.8 was enough to achieve the best treatment performance. In all trials, initial pH of AMD was 4.8 and pH adjustment was not performed. Utilization of existing pH and Fe2+, low H2O2 requirements, and up to 98% treatment performances in COD, turbidity, color, Cu2+, Zn2+ made the proposed treatment system promising. Since the reaction occurs stepwise, a two-step kinetic model was applied and calculated theoretical maximum removal rate was consistent to experimental one, which validates the applied model. For the optimum molar ratio (1.8), 140 mL/L sludge of high density (1.094 g/mL), high settling velocity (0.16 cm/s) with low specific resistance (3.15 × 108 m/kg) was obtained. High reaction rates and easily dewaterable sludge characteristics also made the proposed method advantageous.