Immobilization of phosphogypsum for cemented paste backfill and its environmental effect

The gradual accumulation of phosphogypsum (PG) has attracted worldwide attention because of its occupation of considerable surface land and serious environmental consequences. This work demonstrates the feasibility of PG-based cemented paste backfill (CPB) by considering its physical properties and environmental effects, thus providing an approach for significant disposal of PG in an economical way. Firstly, the mechanical properties of the PG-based CPB specimens were tested. The specimens were prepared with original PG, and the maximum compressive strength reached around 1.5 MPa with the phosphogypsum/cementitious agents ratio of 4:1 and the slurry concentration of 66% at 120 d of curing age. Then, the pollution potential of the PG before and after its inclusion into cementitious agents was investigated. The results showed that when PG was included into backfill samples, the release of P, F and metals dramatically decreased. Additionally, the results of five rounds of leaching tests with backfill samples having different curing ages suggested that the risk of diffusion of pollutants was much less than that from the leachates of PG. Synthetic precipitation leaching procedure (SPLP) results suggested that the metal contents in leachates were within the limits defined in the Chinese standard (DZ/T 0290-2015). Therefore, the PG-based CPB technology could provide an economical alternative for the consumption and reutilization of a significant amount of PG while alleviating its pollution potential.