Investigation of the suitability of activated and non-activated bentonites from the Imerys Mine (South Africa) for geosynthetic clay liners

Abstract

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.