Leaching Behavior and Leaching Mechanism Analysis of Pb in Soil Under the Action of Sulfate Leaching Agent: A Case Study of Ion-Adsorption Rare Earth Mining Area

This study took Pb as the research object and investigated the leaching behavior of Pb under different sulfate leaching agents and soil conditions, respectively. The results showed that the Pb content in the soil of the mining area was as high as 182.07 mg<middle dot>kg-1, mainly in exchangeable form, Fe/Mn oxide-bound form, and residual form. Mg2+ had a more substantial promoting effect on H+ release than NH4+, and was not affected by soil pH. When the external input pH was higher than the soil pH, the release of Pb was mainly influenced by the soil pH. In addition, the effect of (NH4)2SO4 on Pb leaching was significantly higher than that of MgSO4 and MgSO4-ac. The Elovich, Double logarithmic, and Intraparticle diffusion models could fit Pb leaching in soil well, indicating that multiple factors controlled Pb leaching. Leaching agents mainly led to the leaching of Pb in the exchangeable form, but leaching agents could also activate Pb in the residual form, increasing the potential risk of Pb. The leaching mechanism of Pb under the action of the sulfate leaching agent mainly includes chemical form, soil pH, and ion exchange.