The potential environmental risk implications of two typical non-ferrous metal smelting slags: contrasting toxic metal(loid)s leaching behavior and geochemical characteristics

PurposeAs one of the most critical sources of pollution from detrimental elements, smelting slags pose a huge threat to the surrounding environment. A comprehensive environmental risk evaluation of slag is beneficial to propose more rational suggestions on their management and treatment. Therefore, the aim of this study was to assess the potential environmental hazard of toxic elements in non-ferrous metal slags from Guangxi (GX) and Yunnan (YN) by comparing the leaching behavior and geochemical characteristics.MethodsThe pH(stat) and semi-dynamic leaching tests were used to study the leaching behavior of metal(loid)s at different pH and simulate local rainfall, respectively. The potential mobility, bioavailability, and bioaccessibility of metal(loid)s were determined through a series of extraction experiments. In addition, a combination of leachability, mobility, bioavailability, and bioaccessibility is used to explore the potential environmental risk implications of slags.ResultsThe release of metal(loid)s showed a strong dependence on pH. Most metal(loid)s release decreased with increasing pH, while some metal(loid)s release increased under alkaline conditions. Variation in metal(loid)s concentrations induced by pH changes is due to the dissolution/precipitation and the adsorption/desorption processes of minerals. The results of the simulated rainfall indicate different trends in metal(loid)s release due to the differences in slag composition, rainfall, and pH between the two regions. The leaching of metal(loid)s decreases with increasing rainfall, which is due to the depletion of the slag surface. The mobility, bioavailability, and bioaccessibility of Cd, Cu, and Zn in GX were higher than in YN, while As and Pb were lower than in YN. These metal(loid)s are more likely to enter the environment and pose a greater threat to plants and humans. The correlation analysis showed that the exchange and carbonate-bound fractions of metal(loid)s have a positive effect on their bioavailability and bioaccessibility.ConclusionThe results show that among the elements studied, the potential environmental risks of Cd, Cu, and Zn in GX are greater than those of YN, while As and Pb are less than those of YN. The toxic elements in the slags may pose a potential risk to the surrounding environment.