Synthesis of biochar-loaded green synthetic iron nanocomposite and passivation mechanism of cadmium in pig manure aerobic composting

Heavy metal contamination, especially cadmium (Cd), in pig manure poses significant environmental challenges to agriculture. This study utilized pig manure as a raw material for biochar production and employed tea tree waste leaf extract to reduce iron ions, synthesizing biochar-loaded green synthetic iron nanoparticles (PBC@G-nFe). The PBC@G-nFe was then applied in the composting of pig manure to investigate its effects on the morphological changes of cadmium during the composting process, providing a sustainable solution. The results demonstrated that PBC@G-nFe significantly enhanced composting efficiency. At the optimal 5 % addition rate, the residual cadmium content increased by 31.91 %, and its bioavailability decreased by 57.65 %. This method promoted heavy metal passivation through the formation of metal phosphate precipitates, offering a feasible solution for the safe use of agricultural waste. Future research should focus on optimizing the cost-effectiveness and scalability of this method, while evaluating its long-term impact on soil health and crop growth. • PBC@G-nFe made from pig manure and tea tree waste leaves was reused in pig manure composting. • PBC@G-nFe accelerated the conversion of Cd to the residue state in the thermostatic aerobic composting of pig manure. • The addition of 5 % of PBC@G-nFe reduced the BF of Cd in the thermostatic aerobic composting of pig manure by 57.65 %. • PBC@G-nFe passivated Cd by accelerating the formation of metal phosphates.