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/m(2)), 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.
This study compares the results of the dewatering of coal preparation plants tailings by conventional coagulation processes using different types of coagulants and by electrocoagulation methods carried out by two different electrodes. When the results of electrocoagulation and conventional coagulation experiments were compared
(aluminium electrode vs. ferric chloride), it was found that the coagulation efficiencies for both methods were similar, in the case that the aluminium electrode was used, there was a 22.2% decrease in the process cost compared to the use of ferric chloride.