Pyrite-functionalized biochar via the mechanochemical ball-milling method enhanced soil lead/cadmium passivation and...

In the study, based on mechanical ball milling technology, pyrite (FeS₂) functionalized biochar (BC) (FeS₂@BC_BM) was synthesized to investigate the passivation performance of lead (Pb) and cadmium (Cd) in soil and the mitigation effect on plant growth under Pb and Cd stress by measuring change of soil Pb/Cd speciation, plant growth parameters and physiological and biochemical indexes. Results showed that FeS₂@BC_BM achieved highly efficient sorption of Pb(II)/Cd(II) through a combination of complexation, chemical precipitation, electrostatic attraction, and pore filling, with maximum sorption capacities of 159.43/66.81 mg/g. Furthermore, FeS₂@BC_BM reduced bioavailable content of Pb/Cd by 68.70/0.75 mg/kg and achieved directional transformation of more stable Pb/Cd forms (such as residual fractions) with Pb and Cd passivation efficiencies of 51.19% and 61.14%, respectively. In addition, FeS₂@BC_BM increased the content of available nutrients, enhanced enzyme activity, and promoted the richness of core microorganisms (Terrabacter, Noviherbaspirillum, Dyella, and Alicyclobacillus), which could promote nutrient cycling and synergistically immobilize heavy metals, thereby restoring the microenvironment of Pb/Cd-polluted soil as well as facilitating cucumber seedlings' growth. In conclusion, FeS₂@BC_BM achieved the synergy of Pb/Cd remediation and agricultural production, providing a new strategy for remediating Pb-Cd pollution.