Approximately 250 Tg (275 million tons) of bauxite ore is mined each year globally for aluminum production, with Australia (33%), China (20%), and Brazil (16%) the leading global producers. Approximately 55 Tg of red mud, a highly alkaline residue from refining bauxite ore to alumina, is generated annually, with 6 Tg produced in China. The porewater in red mud is “bauxite liquor” that can have pH 14 or higher and ionic strength over 1 M.

Geosynthetic clay liners (GCLs) containing sodium bentonite are used as liners for red mud impoundments. The clay mineral montmorillonite is the primary constituent in bentonite. The high ionic strength of bauxite liquor can suppress swelling of the montmorillonite, resulting in GCLs with high hydraulic conductivity. Consequently, 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 pH and/or ionic strength.

A nationwide investigation was conducted to evaluate the characteristics of bauxite liquor in Chinese impoundments, and to evaluate the suitability of GCLs for containment. Major, minor, and trace elements in the liquors were measured. Hydraulic conductivity tests were conducted on six BPC-GCLs and one sodium bentonite GCL using two characteristic bauxite liquors. Hydration behavior of the BPCs with bauxite liquor was investigated using swell index tests and micro-scale image analysis to understand the mechanisms controlling the hydraulic conductivity of BPC GCLs. Attenuation of Cd, Cr, Pb, Ni, and Zn, by the BPCs was also evaluated.

The bauxite liquors are hyperalkaline (pH > 12) with concentrations of Al, Na, Cl⁻, F⁻, NO₃²⁻, and SO₄²⁻ exceeding Chinese groundwater quality standards by up to 6637 times. Minor elements in bauxite liquor include As, B, Ba, Cr, Cu, Fe, Ni, Mn, Mo, Ti, V, and Zn and the trace elements include Ag, Be, Cd, Co, Hg, Li, Pb, Sb, Se, Sr, and Tl. Some of these elements are present in concentrations up to 272 times above Chinese groundwater quality standards.

The BPC GCLs had hydraulic conductivities to the liquors ranging from 10^-8-10^-12 m/s, which is higher the hydraulic conductivity of BPC GCLs permeated with deionized water (10^-12-10^-13 m/s), but lower than the hydraulic conductivity of conventional sodium bentonite GCLs to the same liquors (10^-8-10^-7 m/s). The hydraulic conductivity of BPC-GCLs depends on the chemical properties of the liquor, the polymer loading, and the type of polymer. For two cases, the hydraulic conductivity to synthetic bauxite liquor was approximately 1 order of magnitude higher than to actual bauxite liquor. Attenuation experiments indicate that the BPC-GCLs retain Cr and Pb from bauxite liquor.