Efficient recovery of phosphorus from phosphogypsum leachate based on struvite precipitation

Phosphogypsum leachate is a liquid produced during phosphogypsum stacking. It has the characteristics of high phosphorus content, low pH, high corrosivity, and high concentrations of heavy metals. If it seeps into the ground over time, it will seriously pollute the groundwater and surface water and pose a significant threat to the surrounding basin environment and human health. In this study, a struvite precipitation method was proposed to recover phosphorus sources from phosphogypsum and its leachate to prepare valuable percolate-based struvite crystal (PSL-S). The core idea is to improve the recovery rate of valuable components by converting the raw mineral phase of phosphorus in the leachate, which enables the production of struvite using industrial solid waste instead of pure reagents, thereby solving two issues: the high price of struvite prepared by pure reagents and the substantial waste of valuable components in phosphogypsum leachate. The study involved three variables: Mg/P molar ratio, N/P molar ratio, and pH. Two indicators, namely, the phosphorus recovery rate in leachate and the purity of struvite from PSL-S, were selected. Through a combination of single-factor influence experiments and optimization orthogonal experiments, combined with phase analysis, the optimal conditions for the preparation of PSL-S were obtained, specifically, when the N/P molar ratio was 5∶1, the Mg/P molar ratio was 1.6∶1, and the pH value was 9.5, with a phosphate recovery rate of 87.73% and a PSL-S preparation purity of 78.24%. The successful preparation of PSL-S enables the efficient resource utilization of phosphogypsum leachate, greatly reduces the production cost of struvite, and provides technical support for the resource utilization of phosphorus chemical waste.