Phosphate tailings-based slow-release heavy metal passivation materials: Mechanism, environmental risk, and microbial community evolution

Phosphorus-containing materials are effective in remediating heavy metal-contaminated soil. However, the excessive release of phosphorus could become a new environmental risk. On the basis of the concept of developing slow-release soil passivators from phosphorus-containing solid wastes, three materials-phosphoric acid -phosphate tailings (PPT), heat-treated PPT (H-PPT), and chitosan-coated PPT (C-PPT)-were successfully pre-pared from phosphate tailings (PT). The phosphorus in both H-PPT and C-PPT showed slow-release properties in aqueous solutions, and their release behaviors could be well fitted by the Korsmeyer-Peppas model. The stabi-lization efficiency of the slow-release materials for lead increased with the gradual release of phosphorus, with a maximum increase from 56.09% to 91.41%. In experiments simulating phosphorus loss, the slow-release ma-terials H-PPT and C-PPT showed decreased phosphorus leaching concentrations (from 72.33 to 12.70 and 0.73 mg/L) and rates (from 10.01% to 1.69% and 0.43%) compared with those of PPT, significantly reducing the environmental risk. Meanwhile, the remediation process has to some extent improved the structure and function of the soil microbial community, which in turn has contributed to the stabilization of lead. Overall results suggest that PT-based slow-release materials may be an excellent strategy and technology for solving phosphorus loss because it achieves resource utilization of PT and solves the secondary pollution caused by the application of phosphorus-containing materials, thereby avoiding phosphorus pollution and improving the utilization of phosphorus resources.