Study on the leaching of harmful elements and pore characteristics of phosphogypsum-based cemented paste backfill under multi-field coupling interaction

The phosphogypsum-based cemented paste backfill (PCPB) in the mining goaf has been in the mine water environment for a long time, and its rich toxic and harmful elements have the risk of migrating and diffusing to the surrounding rock, polluting groundwater. The occurrence environment of underground space in mines is complex, and the filling body is often subject to multiple coupled effects such as seepage, stress, and chemistry. Consolidation instrument and three chemical solutions of HCl solution, NaOH solution, and pure water were used to simulate pressure and water physical and chemical actions. The changes in P and F element leaching and porosity with soaking time in the filling were analyzed, and an expression for the damage variable of the filling based on secondary porosity was established. Considering the combined effect of pressure and chemical solution, the influence coefficient of element diffusion pressure and element binding ability were introduced, and a relationship model between the porosity and the amount of element leaching of the filling body was constructed. The results show that the effect of pressure and chemical solution will increase the porosity of the filling body. The total secondary porosity of the filling material at a certain moment under the action of pressure and chemical solution is composed of three parts: secondary porosity generated by water physical action, water chemical action, and pressure action. The theoretical and experimental values of the porosity of the filling body are in good agreement with the concentrations of P and F elements leached, which verifies the correctness of the relationship model between the porosity and the leaching amount of elements of the filling body.