Preparation of phosphogypsum-based cemented paste backfill and its environmental impact based on multi-source industrial solid waste

Cemented Paste Backfill (CPB) technology is considered as an effective method to solve the serious problems caused by the solid wastes' accumulation, and to mitigate the risk of mined-out areas. However, the serious influence on the environment and higher pro-treating costs of solid wastes limits their application in CPB. Meanwhile, due to the high carbon emissions and high costs of Portland cement, its use as a binder in CPB is also limited. This paper used raw phosphogypsum (PG) as filler. Yellow phosphorus slag (YPS), fly ash (FA), steel slag (SS), and Portland cement were mixed to make a composite binder. Solid wastes addition was ranged from 80% to 98%. The feasibility of CPB co-preparation with a high percentage of multi-source industrial solid waste was verified by analyzing the performance and environmental impact of CPB produced with different percentages of solid wastes. The results showed that a higher PG addition was harmful to the property of CPB, leading to a lower fluidity, longer setting time, and weaken strength. However, the development and use of composite binder offset those negative aspects effectively. Composite binder is a CaO-rich binder that provides an alkaline environment for hydration reactions which enhanced CPB strength. Because its unconfined compressive strength reached to 3.1 MPa similar to 19.5 MPa after 60 d's curing. This will provide a highly strengthen support to the mine to be filled with CPB, thus hindering its re-collapse. The gradually increased hydration products observed from the microstructural characterization further corroborated the strength development path of the CPB. Moreover, the adsorption and precipitation process in the alkaline system contributed to the stabilization of the contaminants from those solid wastes. Therefore, the CPB technology based on the multi-source industrial solid waste is considered as a green, promising, and cost-saving choice on supporting safe mining and mitigating environmental pollution.