Transport patterns and numerical simulation of heavy metal pollutants in soils of lead-zinc ore mines

Exploring transport patterns of soil contaminants is essential for solving the problem of heavy metal contamination in mine soils. In this study, contamination of Pb, Zn, and Cd in the mountain soils of the lead-zinc ore mines in Ganxi Township, Hengdong County, Hunan Province, China was investigated, and their transport patterns were further explored using a soil-column model and numerical simulation techniques. In total, 111 mine soil samples were collected and placed into six experimental soil columns. By controlling the water flow, a control soil column group (CK), two mixed soil columns X-1 with daily water flows of 1 and 5 L, and three mixed soil columns X-3 with daily water flows of 2, 3, and 4 L were evaluated. The results showed that the residual fraction of Pb accounted for 71.93 % of the content on average, whereas the exchangeable fractions of Zn, Cd, and Fe-Mn oxide-bound fractions of Zn and Cd accounted for 28.60%, 31.07%, and 43.2% and 53.54% of the content, respectively. Pb, Zn, and Cd in the soils of the CK, X-1, and X-3 groups mainly were accumulated at a depth from approximately 0 to 20 cm, and the content at this depth accounted for 60.09% of that at a 0 similar to 40 cm depth. The soil at a depth range of 0 similar to 10 cm was most seriously contaminated, and the proportion of content was 32.39% of that at a 0 similar to 40 cm depth. Numerical simulation showed that on the 5(th) day, the pollutant transport range was 0 similar to 24 cm, and on the 9(th) day, the pollutant transport range exceeded 40 cm. On the 15(th) day, the transport capacity of pollutants at depths of 0 similar to 40 cm was close to the stable state, but the soil at a depth of 0 similar to 10 cm was still heavily polluted. These results reflect the transport pattern of heavy metal pollutants in the soil of lead-zinc ore mines and may provide a reliable scientific support for the prevention of heavy metal contamination in mine environments.