Innovative application of recyclable magnetic LDO beads for enhancing the remediation of Cd and Pb contamination and the humification during composting

This study developed recyclable magnetic layered double oxide beads (Mag-LDO) for composting with heavy metal-contaminated soil and agricultural waste, aiming to reduce heavy metals (HMs) concentration and bioavailable forms, enhance humification, and elucidate the underlying mechanisms. Results showed that a 5 % addition of Mag-LDO increased humic acid (HA) formation by 16.02 % and significantly reduced total Cd and Pb by 18.38 % and 21.93 %, respectively, compared to the control group. Moreover, it effectively reduced BF-Cd and BF-Pb by 16.31 % and 10.37 %, respectively. These results demonstrated its potential for enhancing humification and remediating HM-contaminated soil. The analysis of microbial community and Mantel-test showed that Mag-LDO facilitated the formation of HA mainly by modulating the microbial community. Meantime, Mag-LDO not only adsorbed Pb and Cd via ion exchange and precipitation processes to reduce the mobile forms of these metals, but also enhanced the stabilized state of HMs through increasing HA in compost and proliferating Bacillus and Pseudomonas . Furthermore, recovering the Mag-LDO adsorbed HMs could decrease the total HM content in the compost. These findings contribute to advancing new perspectives for the HMs removal and the promotion of humification during composting.