Applicability of weathered coal waste as a reactive material to prevent the spread of inorganic contaminants in groundwater

It is necessary to determine an environmentally friendly method of reusing the vast amount of coal waste that is generated during coal preparation. This study evaluates the applicability of using weathered coal waste in a permeable reactive barrier to prevent groundwater contamination. Coal waste, with different weathering degrees, was obtained from two coal mining sites in South Jeolla Province, Korea. The reactivities of the coal waste with inorganic contaminants, such as copper, cadmium, and arsenic, were examined in batch and column experiments. The batch experiment results indicate that the coal waste removal efficiencies of copper (99.8%) and cadmium (95.4%) were higher than those of arsenic (71.0%). The maximum adsorption capacities of coal waste for copper, cadmium, and arsenic calculated from the Langmuir isotherm model were 4.440 mg/g, 3.660 mg/g, and 0.718 mg/g, respectively. The equilibrium of adsorption was attained within 8 h. The column experiment results reveal that the coal waste effectively removed inorganic contaminants under flow-through conditions. Faster breakthrough times were observed in single solute system (As(V) = 19.3 PV, Cu(II) = 47.6 PV) compared with binary solute system (As(V) = 27.8 PV, Cu(II) = 65.4 PV). To confirm the applicability of using coal waste in a groundwater environment, its decontamination ability was analyzed at low concentrations and under various pH conditions. To examine the potential ecological risks in the subsurface environment, a test to determine acute toxicity to Daphnia magna and a toxic characteristic leaching procedure (TCLP) test were conducted. The coal waste was found to satisfy appropriate standards. The acute toxicity test also confirmed the ecological safety of using coal waste in a groundwater environment. The acceptably high capacity and fast kinetics of inorganic contaminant sorption by the coal waste indicate it could potentially be employed as a reactive material. The recycling and application of this abundant waste material will contribute to solving both coal waste disposal and water pollution problems.