Hydraulic Performance Evaluation of Clay, Laterite, and Bentonite-Modified Laterite Soils for Use as Liner Materials

Abstract

Artisanal and small-scale gold mining (ASGM) generates large volumes of tailings that pose serious risks to soil and groundwater due to inadequate containment systems. Developing cost-effective, locally available liner materials is therefore critical to improving environmental protection in resource-constrained settings. This study evaluates the hydraulic conductivity of clays, laterite soils, and bentonite-modified laterites as potential liner materials for tailings storage facilities. Three clay soils (CL1–CL3), three lateritic soils (LS1–LS3), and calcium bentonite were characterised through particle size distribution, Atterberg limits, compaction, free swell index, X-ray diffraction (XRD), chemical analysis, and hydraulic conductivity testing. Untreated clays exhibited moderate to high plasticity (LL = 41–71%; PI = 25–44%) and low hydraulic conductivity (10⁻¹⁰ – 10⁻¹¹ m/s), satisfying international liner hydraulic conductivity criteria. In contrast, untreated laterites showed low plasticity (PI = 9–17%) and higher hydraulic conductivity (10⁻⁸–10⁻⁹ m/s), making them unsuitable as standalone liners. Mineralogical analysis revealed kaolinite and vermiculite dominance in clays; laterites contained quartz, hematite, and kaolinite, while bentonite is montmorillonite-rich. Incremental bentonite contents (1–10%) increased linear shrinkage, liquid limit, plasticity index, and free swell index, while decreasing maximum dry density and increasing optimum moisture content. Hydraulic conductivity decreased by 1–2 orders of magnitude with increased bentonite addition, meeting the adopted hydraulic conductivity criterion of 1 x 10⁻⁹ m/s. Depending on the initial gradation, baseline hydraulic conductivity of the laterite soil, and the hydraulic gradients under which the samples were tested, 2–4% bentonite addition resulted in a hydraulic conductivity of <1 × 10⁻⁹ m/s. The results indicate that bentonite-modified laterite is promising for liner applications under the tested laboratory conditions.