Unveiling vegetation restoration effect on the heavy metal immobilization and aggregate-associated organic carbon in lead-zinc tailings.

Tailings contaminated with multiple metals represents a significant environmental concern owing to their toxicity, persistence, and capacity to bioaccumulate within the food chain. Heavy metal distribution in tailings is closely linked to aggregate-related characteristics. To elucidate the effect of vegetation restoration on heavy metals and organic carbon in lead-zinc tailings, this study investigated tailing aggregates across four different vegetation coverage types: dense area (DA), sparse area (SA), bare area (BA), and control group (CK). The results showed that the heavy metals in lead-zinc tailings were mainly Pb, Cd, Cu, and Zn. Heavy metals in tailings accumulate more readily in microaggregates, while macroaggregates have lower heavy metal concentrations. With the improvement of vegetation restoration, the form transformation of heavy metals occurred, and the residual-state Pb, Cd, Cu, and Zn in tailings increased. In addition, vegetation restoration promoted macroaggregate formation and enhanced aggregate stability in tailings. Macroaggregates in tailings contained higher organic carbon contents relative to microaggregates, and vegetation restoration enhanced the sequestration and accumulation of organic carbon in tailing aggregates. Correlation analysis indicated that the tailing pH was negative correlated with acid-soluble Cd, acid-soluble Cu, and acid-soluble Zn in tailings. A positive correlation was found between aggregate stability and macroaggregate-associated organic carbon, along with a strong negative correlation between organic carbon in <0.05 mm and acid-soluble Cd, Cu, and Zn. These findings suggest that vegetation restoration regulates heavy metal concentrations, enhances aggregate stability, and promotes organic carbon sequestration in lead-zinc tailings.