Passivation effect of modified biochar on cadmium in mining contaminated soil

Cadmium contamination in agricultural soils poses significant risks to crop safety and ecosystem health. This study investigated the efficacy of modified biochar for Cadmium immobilization in mining-impacted soils through a pot experiment with Chinese cabbage (Brassica pekinensis (Lour.) Rupr.). Four treatments were evaluated: Control (CK), Biochar (6 g/kg, T1), KMnO₄-modified biochar (6 g/kg, T2), and H₃PO₄-modified biochar (6 g/kg, T3). The results showed that both T1 and T2 treatments significantly enhanced the pH and organic matter content of the contaminated soil in the mining area. Specifically, the T2 treatment improved the soil pH from 6.3 to 6.7 and the organic matter content from 29.3 g/kg to 34.3 g/kg. Furthermore, the T2 treatment significantly reduced the available cadmium content in the contaminated soil by 43.4%, the cadmium content in the edible parts of Chinese cabbage by 66.4%, the cadmium accumulation coefficient in the edible parts by 45.5%, the cadmium accumulation coefficient in the roots by 40%, and the transport coefficient by 33.9% compared to the control (CK). In conclusion, the treatment with KMnO₄-modified biochar outperformed both regular biochar and H₃PO₄-modified biochar treatments. The results of the study provide a theoretical basis for the production of vegetables grown in heavy-metal-contaminated soils and promote the recycling of resources and the environment.