The influence of industrial solid waste in conjunction with lepidolite tailings on the mechanical properties and microstructure of cemented backfill materials

The global demand for lithium resources continues to increase, resulting in significant solid waste generation, including tailings, during the process of lithium mining. To maintain a consistent 80% solid content and a cement-to-solid waste ratio of 1:12 in cementitious backfill (CB), an orthogonal experimental design was employed. The curing periods were set at 7 and 14 days respectively. Uniaxial compressive strength tests were conducted on specimens of CB containing varying proportions of desulfurization gypsum (DG), fly ash (FA), steel slag (SS), and lepidolite tailings (LT). Mechanical properties and microstructure were studied and analyzed using scanning electron microscopy (SEM), gray value analysis, as well as other equipment and methods. The results indicate that:(1)The compressive strength of CB specimens cured for 7 days ranged between 1.28 and 3.05 MPa, while those cured for 14 days exhibited compressive strengths ranging from 2.14 to 3.17 MPa, with the optimal solid waste mix ratio being 2:4:4:3. (2) The predominant macroscopic failure modes of the CB specimens are tensile failure and a combination of tensile and shear failure. The entire failure process encompasses four stages: initial pore compaction, linear elastic deformation, micro-crack propagation, and post-peak failure development. (3) Appropriately increasing the content of DG, FA, and LT and appropriately reducing the content of SS can effectively improve the mechanical properties of CB samples and contribute to the formation of hydration products by hydration reaction. The internal hydration products within the CB specimens encompass ettringite AFt (3CaO·Al₂O₃·3CaSO₄·32 H₂O) and C-(A)-S-H gel, with the latter demonstrating superior binding properties compared to AFt. As the curing age increases, the quantity of hydration products correspondingly grows. Furthermore, CB samples prepared with an optimal solid waste ratio exhibit a more compact internal microstructure. This work provides theoretical support for seeking the best proportions of multiple industrial solid wastes, such as lithium mica mine tailings, as backfill materials, while significantly reducing the cement costs associated with conventional filling and the handling burden of tailings generated from lithium mine extraction.