Eco-efficient valorization of gold tailings: A low-carbon binder with high early strength and reduced carbon footprint

To address the demand for low-carbon binders with high early-age strength for gold tailings cementation, a sulfur-aluminum-ferric gold tailings cementitious material (SGCM) was developed using low-carbon sulfur-aluminum-ferric cementitious material (LSCM), gypsum, lime, and ordinary Portland cement (OPC). The binder composition was optimized through ternary and quaternary system experiments, and the corresponding hydration mechanism was investigated by isothermal calorimetry, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The optimal proportion was identified as an LSCM:(gypsum + lime):OPC mass ratio of 1:1.2:0.4. At a cement-to-sand ratio of 1:4 and a filling concentration of 71%, the optimized SGCM achieved compressive strengths of 3.40 MPa at 3 d and 8.26 MPa at 28 d, showing superior early-age strength and competitive long-term strength compared with representative cementitious systems reported in previous studies. In addition, when applied at a reduced cement-to-sand ratio of 1:6, SGCM maintained compressive strength comparable to that of the OPC system at 1:4, while reducing the carbon emission factor by 70.2%; under the self-produced LSCM scenario, the material cost was further reduced by 15.0%. Mechanistic analyses revealed that increasing gypsum and lime contents promoted AFt formation but also transformed AFt into shorter and thicker crystals, whereas OPC incorporation enhanced early hydration, increased C-S-H generation, and densified the microstructure. AFt provided skeletal support, while C-S-H provided filling and bonding, and their synergy governed the strength development of SGCM.