Solid waste binder cemented dihydrate phosphogypsum aggregate to prepare backfill material

Abstract

The accumulation of large quantities of dihydrate phosphogypsum (DPG) presents notable environmental challenges and obstacles to the sustainable growth of the phosphogypsum industry. Utilizing DPG as a backfill aggregate represents an effective approach to enhance its utilization rate. This study aims to prepare backfill materials by consolidating DPG with industrial waste granulated blast furnace slag (GBFS) and calcium carbide residue (CCR) as binders. The fluidity, bleeding rate, setting time, strength, and water resistance of the backfill materials were tested. Additionally, their phase composition, microstructure, hydration mechanisms, and environmental behavior were analyzed. The results showed that: the optimized backfill material exhibited high fluidity, a lower bleeding rate, and a significantly reduced setting time. GBFS and CCR greatly improved the strength and water resistance, with a 28-day compressive strength of 40.86 MPa, a water absorption rate of 4.89 %, and a softening coefficient of 0.81. CCR accelerated the formation of ettringite crystals, enhancing early strength. As the curing period extended and the GBFS content increased, a stable three-dimensional network structure formed, optimizing pore structure and improving performance. Furthermore, the combination of GBFS and CCR effectively neutralized residual acids in DPG, reducing phosphorus and heavy metal elements leaching, and enhancing environmental safety. Using industrial waste binders reduced carbon emission and cost, with 40 % GBFS and 6 % CCR content performing optimally. This study could offer important support for sustainable mine development and efficient resource utilization.