Influence of bauxite liquors on multi-scale pore structure and impermeability of GCLs
The object of this study is to reveal the mechanism controlling the hydraulic conductivity of geosynthetic clay liners to bauxite liquors based on multi-scale pore structures.Flexible wall permeation tests were conducted on two GCLs(GCL1 with artificial sodium bentonite and GCL2 with natural sodium bentonite)with DI water and bauxite liquors as permeant liquids.The mineralogy changes were determined by X-ray diffraction tests to analyze the solid-liquid interactions between GCLs and bauxite liquors.Noteworthy,this study combined the mercury intrusion porosimetry and nitrogen gas adsorption tests to characterize the multi-scale pore structure of bentonite in GCLs after permeation.The results indicate that the intensity of the characteristic reflection and interlayer distance of montmorillonite decreases after permeation because of solid-liquid interactions.Moreover,the hyper-alkaline bauxite liquors reduce the montmorillonite content in GCLs owing to the dissolution.These solid-liquid interactions control the hydraulic conductivity of GCLs to bauxite liquors by changing the multi-scale pore structures of bentonite.Bauxite liquor with higher ionic strength can suppress the thickness of the double diffusing layer in bentonite and inhibit the osmotic swelling process of bentonite,leading to the increase of flow path volume(inter-aggregate and intra-aggregate pores)and hydraulic conductivity.The hyper-alkalinity of bauxite liquors also causes the montmorillonite dissolution and the generation of non-expansive secondary minerals.The dissolution weakens the swelling performance of bentonite,resulting in more flow path volume and higher hydraulic conductivity.However,the secondary minerals might clog the flow paths,leading to lower hydraulic conductivity.GCL2 has better chemical compatibility with bauxite liquors than GCL1 due to more montmorillonite content,considering that the better swelling performance made GCL2 less flow path volume.When GCL is permeated with bauxite liquor with higher ionic strength and alkalinity,GCL has less interlayer pore volume and more flow path volume,resulting in higher hydraulic conductivity.
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