An investigation of the effect of NaCl concentration on the electrocoagulation of coal preparation plant tailings

Coal preparation is the process of separating the coal from mineral impurities to produce high-grade coal, and the wastewater of the coal separation process is mainly consisted of fine coal and clay particles. Electrocoagulation (EC) is one of the effective methods for wastewater treatment. In this context, this study was aimed to investigate the evaluation of EC process for coal preparation plant wastewaters. Several key parameters affecting the efficiency of EC were investigated with laboratory scale experiments in search of optimal parameter values. Most importantly, the effect of NaCl concentration on the precipitation of coal preparation plant tailings by EC was investigated. Current density, electrolysis time, mixing speed, mixing time, pH, and salt concentration were studied using an aluminum electrode. Based on the results obtained from this study, the optimum conditions were found to be as pH 7.88 (natural pH), current density 40 (A/m2), mixing speed 360 rpm, premixing time 120 sec, and electrolysis time 300 sec. Under the optimum operating conditions, the results indicated that EC can be successfully applied for the coal preparation wastewaters, and the turbidity was reduced from 1260 NTU to 63 NTU (95% efficiency) with an operating cost of $5.67/Mg of tailings. By the increasing the salt content, a small increase in the turbidity was observed with a decrease in the voltage. With only a 1% decrease in the removal efficiency, the cost was reduced to $3.19/Mg with a 44% operating cost reduction.