In Situ Leaching of Trace Elements in a Coal Ash Dump and Time Dependence Laboratory Evaluation

摘要

This paper investigates the leaching behavior of trace elements in a typical ash dump in the Guizhou province of western China. The ash samples obtained from a power plant were sieved into three sizes: < 45, 45-71, and > 71μm. Column leaching tests were performed for the size-classified fly ash samples. The HCl solution of pH 4.5 was used to simulate local precipitation. The flow rate was chosen as 1 mL/min. Leaching time intervals were selected in a range from 15 min to 40 days. The results show that the surrounding soil is strongly affected by the ash dump, and the concentrations of some harmful elements in soil are much higher than the background values. The maximal single element pollution index of the soil sample is 134.81 for Cd. In comparison to the concentrations of trace elements in the upstream water, Cr, Cd, Pb, Zn, and Co are greatly enriched in the downstream water. The pollution of the underground water is mitigated by the use of leakproof film. The column leaching test results show that the concentrations of Pb and Cd fluctuate in short-time column leaching. The concentrations of Cd are kept stable after 16 days in three size-classified fly ash samples. However, the concentrations of Pb increase from 1 day to 40 days in the fly ash with a small particle size but are kept stable after 16 days for large particle size fly ash. In comparison to Cd and Pb, the concentrations of Zn in short-time column leaching increase significantly with relatively small fluctuations.