Acid reduction and corrosion resistance of alkaline full solid waste backfill based on oil shale residue

Acid mine drainage (AMD) in the goaf of a medium-high sulphur mining area is a solution with low pH and high SO₄^2-, which poses a serious threat to the environment and ecosystem. To simultaneously realize filling mining and in situ acid reduction of AMD, a low-carbon alkaline full waste oil shale residue-based gangue backfill (FWOGB) without cement was prepared. A wetting‒drying cycle corrosion experiment with FWOGB coupled with AMD at various pH values was conducted. These findings indicate that FWOGB demonstrates effective acid reduction and corrosion resistance properties. The lower the pH is, the greater the loss of FWOGB mass and uniaxial compressive strength (UCS), and the more severe the deterioration. After 24 wetting‒drying cycles, the FWOGB mass and UCS loss rates of the pH 3 group were 6.00% and 35.57%, respectively. Digital image correlation (DIC) revealed that the strain concentration zone in different directions of the FWOGB migrated from the top to the bottom, which was related to the top enrichment of corrosive ions during the wetting‒drying cycles. Microscopic analysis revealed that the deterioration of FWOGB was due to the formation of the expansive corrosion products ettringite (AFt) and gypsum. After FWOGB interacts with AMD, the pH of AMD increases from 3.00 to approximately 8.50. The leaching concentrations of Fe²⁺ and Mn²⁺ were less than 0.27 mg/L and 0.07 mg/L, respectively, which met the Chinese groundwater quality standard (III). The research results provide new ideas for paste filling mining in medium-high sulphur mining areas.