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Hydraulic conductivity of bentonite polymer composite geosynthetic clay liners permeated with bauxite liquor from China

The high ionic strength of the porewater in red mud (i.e., bauxite liquor) can suppress swelling of montmorillonite, resulting in geosynthetic clay liners (GCLs) that are too permeable to be effective as liners in red mud disposal facilities. Bentonite-polymer composite GCLs (BPC-GCLs) have been developed as more resilient lining materials, and some BPC-GCLs have been shown to have very low hydraulic conductivity to bauxite liquors that have extreme ionic strength and pH. In this study, a nationwide investigation was conducted in China to evaluate the characteristics of bauxite liquor in Chinese impoundments, and to evaluate the suitability of GCLs containing granular sodium bentonite or BPCs for containment. Hydraulic conductivity tests were conducted on three BPC-GCLs with two characteristic Chinese bauxite liquors that are hyperalkaline (pH > 12) and have ionic strengths of 76.9 mM and 620.3 mM. The BPC GCLs had hydraulic conductivities ranging from 10-9-10-12 m/s, which is higher than the hydraulic conductivity of BPC GCLs to deionized water (10-11-10-12 m/s), but lower than the hydraulic conductivity of conventional GCLs with granular sodium bentonite GCLs to the same liquors (10-8-10-7 m/s). The hydraulic conductivity of the BPC-GCLs depends on the chemical properties of the leachate, the polymer loading, and the type of polymer. Microstructural analysis by scanning electron microscopy (SEM) suggests that the hydraulic conductivity of BPC GCLs is controlled by the polymer hydrogel filling pores, which can be affected by the bauxite liquor.