Impurity removal from phosphogypsum: Mechanisms, treatment technologies, and challenges for sustainable utilization

The rapid expansion of the phosphate chemical industry has led to the massive generation and long-term accumulation of phosphogypsum (PG), creating serious environmental concerns related to land occupation, acidic leachate, and the release of phosphorus, fluorine, organic matter, heavy metals, and naturally occurring radionuclides. These impurity-related risks greatly hinder the safe disposal and high-value utilization of PG. This review systematically summarizes the physicochemical characteristics of PG, the occurrence forms of major impurities, and recent advances in purification technologies for impurity removal. The main treatment routes are classified into physical methods (e.g., water washing, flotation, ball milling, and screening), chemical methods (e.g., neutralization, precipitation, complexation, and solidification/stabilization), thermal treatment, and emerging bio-mineralization strategies such as microbially induced calcium carbonate precipitation (MICP) and enzyme-induced calcium carbonate precipitation (EICP). Their corresponding removal and control mechanisms, including dissolution–leaching, adsorption, ion exchange, chemical precipitation, co-precipitation, phase transformation, encapsulation, and mineral fixation, are critically discussed. Particular emphasis is placed on the current challenges in balancing impurity removal efficiency, process cost, secondary pollution control, and long-term environmental safety. Future research should focus on impurity-speciation-guided process design, multi-unit process integration, closed-loop wastewater recycling, by-product valorization, and reliable long-term assessment of leaching and radiological risks. This review provides a mechanistic and engineering-oriented framework for advancing the sustainable utilization of PG. Roadmap for Comprehensive Utilization Technology of Phosphogypsum Solid Waste • Impurity occurrence and environmental constraints of phosphogypsum are systematically summarized. • Mechanisms of impurity removal, fixation, and stabilization are critically discussed. • Physical, chemical, thermal, and MICP/EICP-based treatments are comparatively evaluated. • Multi-unit integrated routes are identified as the most feasible pathway for PG valorization. • Future development should prioritize closed-loop processing and verifiable environmental safety