Calcium lignosulfonate-modified soil-rock mixture: Research on mechanical properties and microscale mechanisms

The remodeling of soil-rock mixtures (S-RM) in open-pit mining slopes is critical for ensuring dump slope stability and promoting efficient resource recovery. This study investigates the modification of S-RM using calcium lignosulphonate (CLS) to enhance its engineering properties. Unconfined compressive strength (UCS), shear strength, and permeability tests were performed to quantitatively evaluate the effects of modification. The underlying mechanisms were analyzed using SEM, FT-IR, XRD, and ESP. The results indicate that the addition of 4 % CLS significantly improves the mechanical performance of S-RM while reducing its permeability. Compared to unmodified S-RM, the addition of 4 % CLS increased UCS by 48 %, reaching 0.49 MPa. Cohesion increased from 22.33 kPa to 51.15 kPa, and the internal friction angle rose from 35.5° to 39.8°. The permeability coefficient also decreased from 1.23 × 10^-5 cm/s to 6.95 × 10^-6 cm/s. CLS enhanced interparticle bonding through cementation and filling effects, resulting in interwoven and stacked structures that increased density and stability. Additionally, ion exchange between CLS-provided Ca²⁺ ions and S-RM particle surfaces altered the cation distribution, compressed the electrical double layer, and reduced particle spacing, thereby enhancing structural integrity. These findings provide valuable insights into spoil dump slope stabilization and sustainable resource recovery in open-pit mining operations.