Novel polymer and slag amended soil–cement–bentonite backfill in cutoff walls for acid mine drainage containment
摘要
The lateral migration of Acid mine drainage (AMD) leachate contaminated groundwater raises significant concerns about environmental protection. To address this issue, a novel soil–cement–bentonite (SCB) backfill amended with carboxymethyl cellulose (CMC) and slag was developed. Initially, the optimal slag-to-cement ratio for amended backfills was determined. The microstructure and hydration products of amended backfill were then analyzed. Subsequently, the chemical compatibility of the amended backfill under the permeant of real AMD leachate and its heavy meatal (Zn(II)) adsorption capacity were investigated as compared to unamended backfill. Finally, the mechanisms affecting the k of both amended and unamended backfills using tap water and AMD leachate as permeants was discussed. The test results showed that the optimal GGBS-to-cement ratio for amended backfill was 8:2, referred as G8SCB backfill. The scanning electron microscopy image of G8SCB backfill revealed a denser and more homogenous microstructure, with abundant ettringite and C-(A)-S-H formation. The hydraulic conductivity of G8SCB to AMD leachate was one order of magnitude lower than that of SCB (4.2 × 10−10 versus 5.9 × 10−9 m/s), the k of SCB was higher than the commonly used limit of 10−9 m/s. The findings suggest that G8SCB backfill is a promising candidate for constructing cutoff walls in AMD-contaminated sites, offering superior chemical compatibility, mechanical reliability and reduced carbon footprint.