Evaluating the distribution and potential ecological risks of heavy metal in coal gangue.

The heavy metals, which derived from accumulated coal gangue, are important source of environmental pollution. In this study, coal gangue dumps, collected in Shaanxi Province, China, were used to evaluate the potential ecological risks and release characteristics of heavy metals, including the chemical forms, release characteristics, and potential ecological risks by using the methods of Tessier's sequential extractions, leaching experiments, gray GM (1, 1) forecasting mode, and potential ecological risk index. The results indicated that gangue samples contained high levels of metals, especially of Pb, which was the 20-31 times of the background value, whereas the sum of exchangeable and carbonate fractions in Co and Cu was a large proportion (4-11%) of the total. Potential ecological risks were at strong level regardless of the type of the coal gangue because of Mo and Pb and the comprehensive ecological risk index of 351.51-412.27. Weathering promotes the release of heavy metals in the gangue. Furthermore, the contents of Cu and Pb in leaching solution and their release times in weathered gangue were significantly higher than those of the fresh one. This research provides a scientific basis for the prevention and control of heavy metal pollution in coal-containing areas.