Physical–chemical properties and economic–environmental evaluation of paste backfill prepared with solid waste from alumina production

To achieve comprehensive utilization of solid wastes from alumina production, a novel cemented paste backfill material mainly prepared with red mud (RM) and bauxite solid waste was proposed. The cement and solid wastes accounted for 9.1 % and 90.9 % of the solid mass, respectively. The mechanical properties, internal morphology, and hydration reactions of tailing cemented paste backfill (TCPB) samples with various RM proportions and 54.5 % bauxite tailings (BT) were systematically studied. Physical–chemical properties of TCPB were systematically described, and the TCPB hydration reaction mechanism was discussed. The economic cost and environmental assessment of TCPB were evaluated. The findings indicated that TCPB sample R4 (cement:RM:fly ash:BT = 1:3:1:6) exhibited optimal mechanical performance. The sample exhibited a uniaxial compressive strength of 6.53 MPa and an elastic modulus of 0.55 GPa after being cured for 28 d, thus meeting the filling engineering requirements. The properties of the backfill materials are influenced by volcanic ash activity and micro-aggregates present in RM. Herein, leaching of OH− ions by RM boosted hydration reactivity and led to more hydration substances. With the increase in the RM content up to R4, internal ettringite crystals gradually decomposed. Calcium aluminate hydrate (C–A–H) and calcium–silicate–hydrate (C–S–H) gelling systems became denser. Al3+ replaced by Si4+ resulted in geopolymer reaction. However, further increase in the RM content to R5 (cement:RM:fly ash:BT = 1:4:0:6), excessive RM content results in the formation of excessive rod-like AFt within the sample, led to more pores and weakened strength. The BT plays the role of aggregate support in the backfill materials. The BT surface is associated with the hydration products, forming a three-dimensional structure system. Through economic cost comparison and environmental impact assessment, it was found that TCPB has lower filling costs and better environmental benefits. The research outcomes can contribute to obtain an in-depth understanding about the disposal of solid wastes from alumina production.