Effects of Simulated Reclaimed Water on Soil Particle Sizes and Cd Adsorption and Migration in Soils at Smelting Sites.

This work studied the vertical migration characteristics of Cd in soil profiles from a zinc smelting site under the influence of simulated reclaimed water containing NaCl and Na2SO4. The isothermal adsorption curves of Cd in the soils of miscellaneous fill and weathered slate well fitted the Freundlich and Langmuir models, with R2 ranging from 0.991 to 0.998. The maximum adsorption capacity of Cd in the soils decreased significantly under the salt ion treatments with NaCl and Na2SO4. After leaching, the Cd concentrations in the leachates and Cd contents in the subsoil layers of 10-60 cm followed the order NaCl treatment > Na2SO4 treatment > CK (p < 0.05), suggesting that the salt ions promoted the vertical migration of exogenous Cd. The proportion of coarse particles (> 0.02 mm) decreased, while that of fine particles (< 0.02 mm) increased under salt ion treatments (p < 0.05). The morphological characterization indicated that salt ions accelerated the erosion and fragmentation of coarse particles to form fine particles. The use of reclaimed water to flush smelting sites may increase the risk of Cd migration with small-sized soil particles from the soil to groundwater.

Source identification and migration fate of metal(loid)s in soil and groundwater from an abandoned Pb/Zn mine.

Understanding the spatial distribution, source identification, and migration fate of toxic metals is crucial for managing the potential risks associated with metal(loid)s in abandoned Pb/Zn mines. This study provides a comprehensive analysis of the heterogeneous characteristics, contamination sources, and migration fate of metal(loid)s in both mine soil and groundwater. The results reveal that the abandoned mine soil is primarily contaminated with As and Pb, whereas groundwater in the mining and smelting area is mainly contaminated with Pb. The concentrations of As and Pb in the soil reached a maximum of 37.5 mg/kg and 289 mg/kg, respectively, significantly exceeding the local background values of 13.6 mg/kg for As and 29 mg/kg for Pb. The sources of soil contamination were attributed to historical smelting activities (31.4 %) for As, Cd, Hg, and Sb, while Pb and Mn were primarily derived from the ore-deposited belt (21.5 %). Machine learning predictions indicate that the migration of As in the soil can extend up to six meters or more, predominantly influenced by the presence of grit and silt. As a significant source of groundwater contamination, both soil As and Cd can infiltrate the groundwater through convection or diffusion processes. In conclusion, it is imperative to address the long-term release of heterogeneous metal ores in the soil of abandoned mine sites, as this can severely deteriorate the quality of both soil and groundwater.