An investigation of the engineering properties and environmental impact of low-temperature modified electrolytic manganese residue for karst grouting materials.

Electrolytic manganese residue (EMR) has large stockpiles, low reactivity, and high environmental risk. The presence of pollutants such as NH-N and Mn complicates the direct reuse of disposal sites. A composite activator (CA) is prepared by calcining EMR at a low temperature and mixing it with cement clinker (CC) and calcium carbide slag (CCS) in an optimal ratio. This CA replaces GGBS to create an efficient grouting material. This study analyzes the effect of CA content on the setting time, fluidity, mechanical strength, and impermeability of the grouting material under different water-to-cement ratios. The results show that the EMR-based composite activator, consisting of EMR calcined at 300 °C for 2 h, CCS, and CC, is highly effective. The optimal ratio of EMR to CCS to CC is 25:3:4. The setting time decreases with the increase of water-cement ratio, but gradually decreases with the increase of CA content. Fluidity increases with a higher water-to-cement ratio but decreases with more CA. Both compressive and flexural strengths decrease as the water-to-cement ratio rises. The unconfined compressive strength and flexural strength of EGC could exceeded 24.0 MPa and 5 MPa in 28 days, and the hydraulic conductivity remained below than 10 cm/s, which favored the landfill leakage remediation and pollution control. The main hydration products are calcium silicate hydrate (C-S-H), calcium alumino-silicate hydrate (C-A-S-H) and ettringite (AFt), contributing to the formation of network compact structure. The leaching concentrations of Mn and NH-N in EGC are lower than the threshold values specified in the national standard GB 8978-1996. This innovative grouting material exhibits excellent performance and environmental adaptability, making it a high-quality sealing material for karst disposal sites.