Distribution of heavy metals and pollution evaluation in soil surrounding the metal mining area

摘要

Aiming at the problem of heavy metal pollution in soil surrounding the metal mining area, the heavy metal pollution is evaluated and studied from 4 aspects, including the surface soil around the metal mining area, the soil profile, the different directions of the mining area and the morphological characteristics of heavy metals in the surface soil. The results show that the pollution level of Cd and Pb elements is the highest in the soil, which are classified as severe pollution and moderate pollution respectively. The pollution level of Cu, Zn, As and Ni belongs to light pollution, and the pollution level of Cr and Hg is the lowest. The calculation results of the cumulative index weighted values in the soil shows that the soil pollution around the metal mining area is more serious, with the pollution in most areas seriously exceeding the standard. Heavy metals are mostly concentrated within a range of 10cm of surface soil. With the increase of depth, the content of heavy metals decreases rapidly. When the depth exceeds lm, the soil is basically clear of heavy metal pollution. The content of heavy metals in the west and south of the metal mines is higher than that in the east and the north. Cu, Ni, Pb, Zn and Cr are mainly in the residual form, accounting for 65.4% of the overall form, followed by the oxidation form with an average value of 19.6%, then followed by reducible form, with an average value of 9.2%, and the proportion of exchangeable form is the lowest, accounting for 6.4%. The average sum values of the residual and exchangeable forms of these 5 elements can reach to more than 70%, thus they are easy to adsorb onto plants or humus and other objects on the surface soil, causing serious damage to the surrounding environment.