Research on the leaching behavior and morphological transformation of pollutants in the phosphogypsum filling body.

To investigate the environmental risks associated with phosphogypsum (PG) applied for mine backfilling, this paper analyzed the migration characteristics of pollutants (total P, F-, Cr(VI), As, Mn, Se) within PG filling body under different pH and solid-liquid ratio conditions. The research integrated filling body matching experiments, toxic leaching experiments and long-term static immersion experiments. The key findings are summarized as follows: (1) The uniaxial compressive strength of PG filling body at 90d curing age reached 1.27 MPa when the sand-cement ratio was 1:8 and the mass concentration was 60%; (2) The leaching concentration of pollutant elements increased with decreasing pH, and the highest amount was released at pH 2. Additionally, the leaching concentration of Cr(VI) at a solid-liquid ratio of 1:20 was 6.6 times higher than that at 1:5; (3) The migration of pollutant elements was controlled by their observed speciation, and the weak acid extraction state and reducible state ions showed higher mobility; (4) In the PG-cement system, the main immobilization mechanisms of the pollutant elements are physical adsorption and chemical binding. Using the optimized mixing proportion achieved an immobilization efficiency exceeding 99.9% for total phosphorus and 96.5% for fluoride ions.