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.