Novel thermal modification of phosphate tailings for enhanced heavy metals immobilization in soil

Recent interest in amendments derived from industrial by-products has highlighted their potential for both resource recycling and heavy metal remediation. Phosphate tailings (PT), primarily dolomite-based solid waste with low utilization rates, offer a promising yet underexplored solution. This study pioneers the thermal modification of PT into a novel amendment, thermally modified phosphate tailings (TPT), to assess its adsorption performance, underlying mechanisms, and effectiveness in immobilizing heavy metals in soils. The thermal modification process transformed dolomite in PT into calcite and periclase, dramatically enhancing the maximum adsorption capacities by 28-fold for both Cd²⁺ and Cu²⁺, and 7-fold for Pb²⁺, with the capacities reaching 248, 531, and 433 mg g^-1 for Cd²⁺, Pb²⁺, and Cu²⁺, respectively. The dominant removal mechanism for TPT was surface precipitation, complemented by electrostatic adsorption, surface complexation, and ion exchange. Practical applications of TPT in contaminated soil reduced TCLP-extracted Cd, Pb, and Cu by up to 44 %, 60 %, and 61 %, respectively, effectively transforming heavy metals into relatively stable form. This study demonstrates the potential of TPT as a novel amendment for heavy metal immobilization, providing both effective contamination control and enhanced resource utilization, thus addressing a critical gap in the remediation of contaminated soils. Given its low-cost nature derived from industrial waste, TPT holds significant promise for large-scale application, making it a practical and sustainable solution for soil remediation.