Unveiling the release mechanism of potentially toxic elements from Pb/Zn smelter contaminated soils under the coupled effects of freeze-thaw and acidification: Insights from mineralogical analysis

Most Pb/Zn smelter contaminated sites in China are often encountered natural phenomenon known as freeze-thaw (F-T) cycles and acid rain. However, the coupled effects of F-T cycles and acidification on the release behavior of potentially toxic elements (PTEs) from soils remains unclear. A mechanistic study on PTEs release from soils was conducted by revealing the physicochemical weathering characteristics of minerals under F-T cycles combined with acidification. The results from F-T test indicated that among F-T parameters, F-T frequency were the more important factors influencing PTEs release, with the corresponding contribution ranges of 21.20-94.40 %. As pH decreased, the leaching concentrations of As, Cd, Cu, Mn, Pb and Zn did not increase under the same F-T frequency. As F-T frequency increased, the leaching concentrations of these studied PTEs also did not increase under the same pH condition. Microstructure characteristics revealed that the soils were a complex system with multi-mineral aggregates, which had experienced complex physicochemical weathering after F-T combined with acidification treatment. Combined with geochemical modeling results, PTEs release was found to be mainly influenced by the microstructure damage and proton corrosion of minerals, while little affected by their precipitation and dissolution. The mutual coupling relationships of mineral weathering and PTEs release were conducive to the better understanding of the migration behavior of PTEs in contaminated sites under complex environment scenarios. The present study results would provide theoretical instruction and technical support for the longevity evaluation of multi-metal stabilization remediation.