[Vertical Migration Characteristics and Fate of Heavy Metals from Zinc Smelting Slag in Soil Profile]

To investigate the influence of heavy metals in smelting waste residue on the quality of soil and groundwater, a simulation column experiment was conducted to study the migration characteristics of heavy metals from the leaching solution of zinc volatilizing kiln residue in the site soil profile under continuous or intermittent leaching for 90 days. The concentrations of Cd, Cu, Pb, and Zn in leachate and their accumulation, chemical fractions, and particle size distribution characteristics in the soil profile were analyzed, and the retention mechanism of heavy metals was also discussed. The results showed that the concentration of heavy metals in the soil column leachate decreased rapidly after reaching the peak at the earlier leaching stage, and the Cd concentration far exceeded the threshold limit of 0.1 mg·L^-1(class Ⅳ) of the Quality Standard for Groundwater(GB/T 14848-2017), indicating that there was Cd pollution risk of groundwater. The soil profile had a great adsorption capacity for heavy metals in the waste residue. Cd, Cu, Pb, and Zn were predominately accumulated in the shallow soil depth(0-10 cm), which was 237-429, 1.25-16.2, 1.38-2.31, and 1.79-3.17 times of the content of corresponding heavy metals in the soil profile before leaching, respectively. The migration distance of heavy metals in the slag under continuous leaching was longer than that under intermittent leaching, and Cd was significantly accumulated in the deep layer of the soil column. The contribution of soil coarse particles(0.5-2.0 mm) to the total cumulative amount of Cd, Cu, and Zn was larger, whereas Pb was more prone to accumulate in the particle size of<0.25 mm. The results of BCR sequential extraction fraction showed that the accumulated Cd, Cu, and Zn in shallow soil depth were mainly present in the weak acid extraction, accounting for 62.4%-76.7%, 72.0%-95.8%, and 67.6%-85.8% of total content, respectively. The X-ray diffraction(XRD) and Fourier transform infrared spectroscopy(FTIR) analysis showed that exogenous heavy metals in slag entering the soil would not form a stable mineral phase within 90 days, and the soil hydroxyl(-OH) and carbonyl(C=O) functional groups and iron aluminum silicate oxides were the main retention factors.