The release of antimony from soils surrounding the smelters in Karst Areas and its Environmental Implications

Antimony(Sb) in soil can be reintroduced into the environment through leaching processes driven by rainfall and surface runoff, raising concerns about secondary pollution. This study examined the release dynamics of Sb in carbonate-rich soils from an Sb smelting area in the karst region of southern China, aiming to elucidate the roles of pH, organic matter (OM), and geological conditions in Sb mobilization. The experiment was conducted under three different pH conditions (4.5, 6.0, and 7.5) and explores the influence of OM on the release behavior of Sb in the soil. Results indicated a characteristic release pattern for Sb in the soil solution, with an initial rapid increase, followed by a sharp decline, and a subsequent rise.The leaching rate of Sb was higher in neutral to weakly alkaline soil compared to acidic soils.The removal of soil OM enhanced Sb release by 3.21-4.09 times, with a significant inhibition rate reaching 50.01-76.86 %. The findings suggested Sb release kinetics followed a triphasic pattern consisting of rapid initial release, mid-term adsorption inhibition, and late-stage secondary release, which elucidated the underlying mechanisms of long-term leaching risks and provided a theoretical foundation for predicting contaminant dispersion. Soil OM effectively reduced Sb mobility through functional group complexation and soil aggregate formation, offering direct evidence for OM-based remediation strategies such as organic amendment applications. Neutral to weakly alkaline conditions (pH 6.0-7.5) significantly enhanced Sb release rates by promoting mineral desorption, indicating elevated contamination risks of Sb in karst region soils. This study emphasizes that priority should be given to increasing OM concentration and regulating pH buffering capacity to suppress Sb activity in karst areas, providing actionable scientific solutions for the remediation and management of Sb-contaminated sites.