A novel alkali-slag cemented tailings backfill: Recycling of soda residue and calcium carbide slag

In order to address the safety and environmental concerns associated with high disposal cost and low disposal rate associated with mine tailings, low-cost cemented paste backfills (CPBs) were prepared from solid wastes such as calcium carbide slag (CS), soda residue (SR), ground granulated blast-furnace slag (GGBS) and iron tailings (TA) in this study. The effects of mass concentration of filling slurry, GGBS content, activator dosage, and SR proportion on the mechanical properties of CPBs were studied. The results showed that a flow of 235.8 mm and 28-d compressive strength of 2.3 MPa for the freshly mixed slurry could be attained with 75 % mass concentration, 14 % GGBS content, an activator-to-binder ratio of 0.4, and a CS-to-SR ratio of 3:7. The strength of CPBs first increased and then decreased with the increasing of activator dosage or SR proportion contents, and reached the optimal value for the activator-to-binder ratio of 0.4 and SR of 70 % – 75 %. Microstructural analyses by TG-DTG, FTIR, SEM-EDS, and XRD revealed that mainly C-(A)-S-H gel, hydrotalcite (HT), and Friedel's salt (FS) were formed as the hydration products in CS-SR synergistically-activated GGBS paste. The Ca2+ dissolved from CS facilitated GGBS hydration to generate the C-(A)-S-H gels and further reacted with Cl− in SR and [Al(OH)6]3− dissolved from GGBS to generate FS. The combined effect of C-(A)-S-H gel and FS enhances the strength of CPBs. When the percentage of SR is in the range of 70–75 %, the synergistic excitation of slag by alkali slag and calcium carbide slag is superior, and the matrix structure is denser. [Display omitted] •A novel alkali-slag cemented tailings backfill was prepared by low-cost multi-source solid wastes.•The SP has a major effect on UCS of CPB matrix, which accounted for 70∼75 % was optimal.•Ca2+ dissolved from CS can not only promote slag hydration to form C-(A)-S-H gel but also further react with Cl− and [Al(OH)6]3− to generate FS.•The interaction of C-(A)-S-H and FS increased the UCS of the cementitious materials.