Leaching Behavior of Trace Elements in Coal Spoils from Yangquan Coal Mine, Northern China

The long-term dumping of coal waste piles has caused serious environmental problems. Release of trace elements (including rare earth elements, REEs) from coal spoils gobs was investigated at Yangquan coal mine, Shanxi Province, China. X-ray diffraction (XRD) was used to analyze the mineral composition of the coal spoils. The minerals of the coal-spoil samples are mainly kaolinite and quartz, with a minor proportion of pyrite. The batch and column tests were employed to simulate the leaching behavior of trace elements from coal spoils. Elements V, Cr, Zn, As, Pb, and Cd are highly enriched in all coal spoils. The coal spoils also have elevated levels of Ga, Ge, Se, Sn, Hf, and Th. The leachate of coal spoils, fried coal spoils and CSFGM (coal spoils fire gas mineral) samples are acidic, with the pH values ranging between 3.0 and 6.6. The released elements with high concentrations (over 100 mu g/L) include Fe, Mn, Co, Ni and Zn, while moderately-released elements are Cu, Se, Mo and As. A high content of heavy metals in batch-test leachate with CSFGM indicates an increased mobility of heavy metals in coal spoil combustion byproduct. Within the first hour washing with the electrolyte solution, a rapid rise of common cations, trace elements, and REEs content, as well as a drop of pH value, in effluent was observed. An increased leaching velocity favors the release of trace elements from coal spoils. In addition, the pulse input of precipitation led to more elements to be released than continuous leaching.