Carbonate-activated binder modified by supplementary materials for mine backfill and the associated heavy metal immobilization effects

Cemented paste backfill (CPB) is one of the effective methods for resource utilization of tailings, but the high cost of ordinary Portland cement (OPC) limits its utilization. Considering the poor performance of Na₂CO₃-activated binders, in this work, supplementary materials, including CaO, MgO, and calcined layered double hydroxide (CLDH), were used to modify their properties with the aim of finding an alternative binder to OPC. Isothermal calorimetry, X-ray diffraction, and thermogravimetric analyses were conducted to explore the reaction kinetics and phase assembles of the binder. The properties of the CPB samples, such as flowability, strength development, and heavy metal immobilization effects, were then investigated. The results show that the coupling utilization of MgO and CLDH showed good performance. The strength of the Mg₂-CLDH₃ sample was approximately 2.94 MPa after curing for 56 d, which was higher than that of the OPC-based sample. Moreover, the cost of the modified Na₂CO₃-activated binder was lower than that of the OPC-based binder. Modified sample showed satisfactory heavy metal immobilization effects. These findings demonstrate that carbonate-activated binder modified by supplementary materials can be suitable in CPB.