Co-application of organic phosphate fertilizer, manure, and biochar synergistically improves chemical and biological properties of Pb-Zn mine tailings: Insights from a pot trial

The incorporation of amendments is a commonly employed strategy to enhance the effectiveness of phytostabilization in remediating mine tailings. Although the remediation effectiveness of organic phosphate fertilizer (P), manure (M), and biochar (B) as individual amendments for heavy metal pollution has been extensively investigated, yet, the effectiveness of combined amendments for mine tailings remains unknown. The objective of this study is to assess the potential effectiveness of the co-application of P, M, and B in remediating Pb-Zn mine tailings by examining the alterations of chemical and biological properties. In this study, the mine tailings were amended with single and combined P, M, and B at a dosage of 5 % (w/w) followed by a two-month pot trial involving the seeding of ryegrass (Lolium perenne L.). In comparison to the control, all amendments effectively elevated the levels of organic matter, total nitrogen, and total phosphorus in the mine tailings while reducing diethylenetriamine-pentaacetic acid (DTPA)-extractable Pb, Cd, and As; Zn did not show significant changes except in combined treatment with P + M + B (i.e. PMB combination). The combined amendment treatments, particularly PMB, resulted in a substantial enhancement in both microbial biomass and the activities of alkaline phosphatase, urease, invertase, and dehydrogenase. Moreover, the combined amendments facilitated ryegrass growth while concurrently mitigating heavy metal uptake. Pearson's correlation analysis demonstrated a positive association between biological properties of the mine tailings (microbial biomass, enzyme activities, and ryegrass biomass) and nutritional levels while showing a negative correlation with DTPA-extractable heavy metals. Principal component analysis revealed that the addition of PMB exhibited superior efficacy in remediating mine tailings. Overall, our findings suggest that the application of PMB shows promise for in-situ remediation of Pb-Zn mine tailings; however, further research is required to validate these findings under field conditions.