Role of biochar–mineral composite amendment on the immobilization of heavy metals for Brassica chinensis from naturally contaminated soil

Heavy metals are prevalent in the environment and can cause disease in humans via the soil–plant–food chain. However, singular soil remediation techniques, such as pristine biochar, are susceptible to instabilities and low efficiency. Here, biochar–mineral (kaolin/vermiculite/attapulgite) composites were fabricated and characterized. A pot culture was carried out to certify the efficacy of the biochar–mineral composites to immobilize naturally heavy metals contaminated soils and reduce the bioavailability of heavy metals to plants. The results confirmed that biochar–mineral composites significantly impact the available K, available P, total N, and organic matter content of soil, which improved Brassica chinensis growth. Furthermore, the heavy metals’ phytoavailability in naturally polluted soil and the accumulation in B. chinensis were reduced significantly. Biochar–attapulgite composite addition, especially at the 2% application rate, significantly enhanced heavy metal immobilization and had the highest efficacy. These findings demonstrated that biochar–mineral composites could be applied in naturally contaminated soil as effective and eco-friendly heavy metals passivators.