Study on the treatment of heavy metals in typical acidic mine drainage by Solanum nigrum L.

Acid mine drainage (AMD) poses a significant environmental threat to mining areas due to its elevated heavy metal content and low pH. It is imperative to conduct research on efficient, sustainable, cost-effective, and environmentally friendly AMD treatment technologies. This study focused on two types of strong acidic AMD, namely the pyrite deposit type (PR) and Ag-Pb deposit type (SL), as experimental subjects. An absorption simulation experiment was devised with Solanum nigrum L. for the treatment of AMD. The pH of AMD was adjusted to 5 or 7 (PR-pH5, PR-pH7, SL-pH5, SL-pH7) using sodium hydroxide, followed by hydroponic experiments to assess heavy metal removal. The results revealed that PR-AMD had high concentrations of Fe and sulfate but the degree of heavy metals contamination was low, while SL-AMD exhibited combined contamination of Cd, Zn, and Cu. Adjusting the pH to 5 favored Solanum nigrum L. growth, yet the AMD composition significantly influenced its ability to absorb heavy metals. Solanum nigrum L. demonstrated a remarkable capacity to accumulate and transfer Cd in SL-AMD, whereas Cd in PR-AMD was predominantly concentrated in the roots. Except for Cd in SL-pH5 treatment, heavy metal concentrations in all treatments were significantly below the limits specified in the Integrated Wastewater Discharge Standard (GB 8978-1996). Cd reduction in PR-AMD was primarily attributed to Solanum nigrum L. uptake, while neutralization and precipitation processes were the main mechanisms for removing Pb, Zn, Cu, and As from water in SL-AMD. In summary, the study suggested that the combination of alkaline neutralization and Solanum nigrum L. phytoremediation hold promise for AMD treatment, showcasing potential applications in addressing this environmental challenge.