Life Cycle Assessment of Portland Cement Alternatives in Mine Paste Backfill

Mining activities generate huge volumes of mine tailings (MTs), which pose huge environmental management challenges. Reuse as cemented paste backfill (CPB), a mixture of tailings with water and a binder—often cementitious or alkaline—is amongst the best methods to reduce surface disposal, and it is used to backfill underground mine voids. Although the most widely used binder in CPB production remains Ordinary Portland Cement (OPC), it is associated with a high carbon footprint and a high economic cost. In this study, both the economic feasibility and the environmental performance of three alkaline activators—sodium hydroxide (NaOH), sodium silicate (Na2SiO3), and a high MgCO3 and MgO content calcined magnesite residue—are evaluated as OPC replacements in CPB products. A gate-to-grave life cycle assessment (LCA) was performed at a CPB plant located in southwestern Spain with the use of tailings from a massive sulfide deposit. The results from the uniaxial compressive strength test and LCA demonstrate that paste formulations using the magnesite residue achieve comparable mechanical performance while significantly reducing both the environmental footprint and total cost relative to OPC-based mixtures. These results support the use of alkaline binders as viable substitutes that enable more sustainable and cost-effective tailings management practices in the mining sector.