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Geosynthetic clay liners (GCLs) have become a suitable substitute for compacted clay liners used for prevention of leachate percolation from landfills and tailings dams into the groundwater system. The characteristics of most bentonites is improved through a process of activation by mixing with soda ash (Na2CO3). This paper presents the investigation results of the suitability of bentonites from the Imerys Mine in South Africa for use in GCLs. Both activated and non-activated bentonites were investigated through X-ray diffraction (XRD) analysis and swell index, fluid loss, plate water absorption and Atterberg limits tests. The XRD analysis results indicate that the activated and non-activated bentonite have a smectite content of 58% and 67%, respectively. The swell index of non-activated bentonite was significantly lower than that of activated bentonite. The activated bentonite samples tested at different times subsequent to activation revealed that a minimum of 4 weeks of activation time is required to fully activate it to the ideal soda ash to bentonite ratio of 1:16. The fluid loss tests displayed results slightly above the required minimum of 18 mL because of the low swell index of the bentonites tested. The activated and non-activated bentonites have absorption capacities of 133% and 121%, respectively. The plasticity index of the activated bentonite is 101%, 15% higher than the non-activated bentonite. The overall results concluded that the Imerys bentonite is a medium-quality bentonite with borderline index properties that requires at least 4 weeks of beneficiation to achieve complete activation to suitably be used as GCLs. Significance: • The significance of this paper is the beneficiation process of bentonite in the geotextile industry. • This study is relevant to geotechnical engineers, environmental geologists, engineering geologists and other related professionals working with geosynthetic clay liners whereby bentonite is the key ingredient. • The study provides an optimum ratio of bentonite to sodium carbonate and the required time for beneficiation. • We further recommend that quality control measures should be implemented to ensure complete activation of bentonite, including the blending process of different qualities of bentonite. [ABSTRACT FROM AUTHOR]