Acid induced degradation of the bentonite component used in geosynthetic clay liners
Introduction
Bentonites are naturally occurring soft rocks with a high content of the clay mineral montmorillonite. Montmorillonite is capable of swelling during uptake of water. In addition, montmorillonite has a large specific surface area, excellent plasticity, and low hydraulic conductivity. Because of these properties, hydrated bentonites are of great significance for industrial, environmental, and civil engineering activities requiring sealants, absorbents, and hydraulic barriers. Bentonite is the key component in geosynthetic clay liners (GCLs) which are low permeable materials increasingly used in barriers, or components of barriers, for a wide variety of hydraulic and gas containment applications in mining waste containment facilities. (Kashir and Yanful, 2001; Bouazza, 2002; Vangpaisal and Bouazza, 2004; Bouazza et al., 2006; Bouazza and Rahman, 2007; Gates et al., 2009; Lange et al., 2007, 2009; Benson et al., 2010; Hornsey et al., 2010; Gates and Bouazza, 2010; Shackelford et al., 2010).
Bentonites can be used as originally mined or after some physico-chemical treatments. A common chemical modification of bentonite is acid activation, usually with HCl or H2SO4 (e.g. see Komadel and Madejová, 2006) to enhance catalytic and absorptive properties (e.g. see Wallis et al., 2007). The treatment results in an increase in specific surface area, porosity and surface acidity (Komadel, 2003). The increase in specific surface area can improve the performance of bentonites in applications, for example, as catalyst (Mokaya and Jones, 1994; Bovey and Jones, 1995), bleaching earth (Siddiqui, 1968; Wu et al., 2006), and as a component in carbonless copying papers (Fahn and Fenderl, 1983). However, the increase in porosity caused by acid is expected to produce a negative effect on the hydraulic performance of bentonite, as has been shown for GCLs (Petrov et al., 1997; Shackelford et al., 2000, 2010). Interaction with acidic solutions can result in increased porosity of bentonite and decreased swelling thus causing increased hydraulic conductivity of the GCL (Kolstad et al., 2004a; Fall et al., 2009; Shackelford et al., 2010). Kolstad et al. (2004b) reported a drop in swell index of a granular bentonite GCL from 35.5 mL/2 g (water) to 18 mL/2 g (acidic solution, pH = 1.2) and an increase in hydraulic conductivity from 1.2 × 10−11 m/s (to water) to 1.5 × 10−7 m/s when permeated with the acidic solution. Similarly, Shackelford et al. (2010) noted an increase from 1.7 × 10−11 m/s (to water) to 2.7–3.9 × 10−8 m/s when a GCL was permeated with an acidic solution of pH = 2.5.
The scarcity of suitable and economical clayey soil resources for traditional liners (i.e. compacted clay liners) throughout mining localities has resulted in recent increased interest in alternative hydraulic barrier materials, such as GCLs (Fourie et al., 2010; Bouazza, 2010). As a result, the bentonite component has a high probability to coming into contact with acids in mining projects, e.g., in heap leach containment systems (Hornsey et al., 2010) or the acidic leachate caused by the oxidation of impounded tailings (Shackelford et al., 2010).
A wide variety of research has been conducted to analyze the degree of decomposition of clays by acids, changes of surface acidity, cation exchange capacity, and catalytic power, most focused on the physico-chemical properties of the resulting acid-activated material (Breen et al., 1995a; Gates et al., 2002; Önal, 2007; Önal and SarIkaya, 2007; Wallis et al., 2007). However, few studies have focused directly on how some of the engineering index properties (Atterberg limits, swelling index, and fluid loss etc.) of bentonites may degrade when subjected to acid solutions. These parameters have close relationships with hydraulic conductivity and could be used as indicators of potential changes to the hydraulic conductivity (Jo et al., 2001; Lee et al., 2005; Mishra et al., 2011).
Thus, the purpose of this study is to clarify the degradation in Atterberg limits, free swelling and fluid loss properties of bentonites when subjected to different concentrations of sulphuric acid solutions to evaluate the potential deterioration in hydraulic performance of geosynthetic clay liners in light of studies by Kolstad et al. (2004a) and Singh and Prasad (2007).
Section snippets
Materials
Three bentonites were used in this study. Bentonite 1 (B1) was a powdered sodium-magnesium bentonite from Australia having low swell index (SI), generally ∼11 mL/2 g, and which had received no beneficiation other than drying and grinding at the plant. Bentonite 2 (B2) was an activated powdered sodium bentonite (undisclosed beneficiation besides drying and grinding) from Australia with a SI of ∼23 mL/2 g. Bentonite 3 (B3) was a powdered natural sodium bentonite from South Africa with a SI
Mineralogy analysis
The X-ray diffraction (XRD) results are given in Fig. 1 for the three bentonites. The XRD results illustrate that the predominant mineralogy of the three bentonites is smectite, while the position of the d-(060) reflection at ∼62°/2θ (d ≈ 1.5 Å) indicates it is dioctahedral. For untreated B1, the intense peak of d-(001) registers at 5.82°, which corresponds to an interlamellar distance of 15.2 Å, while the main corresponding reflection in B2 and B3 registers at interlamellar distances of 15.4 Å
Conclusions
Results of laboratory tests show changes of Atterberg limits, free swell values, and fluid loss of three different bentonites with various concentrations of sulphuric acid solution. Liquid limit values generally decreased with increasing acid concentration, while only slight changes occurred in plastic liquid values, the resulting plasticity index mirrored the changes in the liquid limit. B1 had the lowest liquid limit values but was relatively stable to the influence of low pH solutions. The
Acknowledgment
The technical support provided by the Department of Civil Engineering, Monash University is gratefully acknowledged. The first author is grateful for the funding provided by the China Scholarship Council to support his PhD studies. We also thank the bentonite producers and the GCL manufacturers for providing bentonites and GCL samples for this project. The anonymous reviewers made many constructive comments and valuable suggestions and their efforts associated are greatly appreciated by the
References (49)
- et al.
Hydraulic conductivity of two geosynthetic clay liners permeated with a hyperalkaline solution
Geotextiles and Geomembranes
(2010) Geosynthetic clay liners
Geotextiles and Geomembranes
(2002)- et al.
Correlation of catalytic activity with infra-red, 29Si MAS NMR and acidity data for HCl-treated fine fractions of montmorillonites
Applied Clay Science
(1995) - et al.
A surface complex reaction model for the pH-dependence of corundum and kaolinite dissolution rates
Geochimica et Cosmochimica Acta
(1988) - et al.
Geotechnical properties indicated environmental uses for an unusual Australian bentonites
Applied Clay Science
(2002) - et al.
Suitability of bentonite-paste tailings mixtures as engineering barrier material for mine waste containment facilities
Minerals Engineering
(2009) Crystalline swelling of organo-modified clays in ethanol-water solutions
Applied Clay Science
(2004)- et al.
Bentonite transformations in strongly alkaline solutions
Geotextiles and Geomembranes
(2010) - et al.
Mineralogy of a bentonite from Miles, Queensland, Australia and characterisation of its acid activation products
Applied Clay Science
(2002) - et al.
The impact of mining solutions/liquors on geosynthetics
Geotextiles and Geomembranes
(2010)
Hydraulic conductivity of nonprehydrated geosynthetic clay liners permeated with inorganic solutions and waste leachates
Soils and Foundations
Alteration of smectites by treatments with hydrochloric acid and sodium carbonate solutions
Applied Clay Science
Comparative leaching of minerals by sulphuric acid in a Chinese ferruginous nickel laterite ore
Hydrometallurgy
Comparative FT-IR study of structural modifications during acid treatment of dioctahedral smectites and hectorite
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Controlling factors of the swelling of various bentonites and their correlations with the hydraulic conductivity of soil-bentonite mixtures
Applied Clay Science
An X-ray diffraction (XRD) and Fourier transform infrared spectroscopic (FT-IR) investigation of the long-term effect on the solidification/stabilization (S/S) of Arsenic(V) in Portland cement type-V
Science of The Total Environment
Swelling and cation exchange capacity relationship for the samples obtained from a bentonite by acid activations and heat treatments
Applied Clay Science
Preparation and characterization of acid-activated bentonite powders
Powder Technology
Evaluating the hydraulic conductivity of GCLs permeated with non-standard liquids
Geotextiles and Geomembranes
Hydraulic conductivity of geosynthetic clay liners to tailings impoundment solutions
Geotextiles and Geomembranes
Characterization, acid activation and bleaching performance of bentonite from Xinjiang
Chinese Journal of Chemical Engineering
Geosynthetics in mining applications
Oxygen diffusion through partially hydrated geosynthetic clay liners
Géotechnique
Effect of wet–dry cycles and cation exchange on gas permeability of geosynthetic clay liners
Journal of Geotechnical and Geoenvironmental Engineering
Cited by (53)
Hydraulic conductivity of novel geosynthetic clay liner to bauxite liquor from China: Modified fluid loss test evaluation
2022, Journal of Environmental ManagementCitation Excerpt :Geosynthetic clay liners (GCLs) are manufactured clay barriers composed of bentonite sandwiched between two layers of geotextile (Bouazza, 2002; Chai and Prongmanee, 2020), and are commonly used in migration control of contaminants (Rowe et al., 2004; Sharma and Reddy, 2004). Conventional sodium bentonite (NaB) GCLs exhibit incompatibility (higher hydraulic conductivity, k, usually >10−10 m/s) to the leachate with high salt concentration and extreme pH (pH > 13 or pH < 2) (Ruhl and Daniel, 1997; Jo et al., 2001; Katsumi et al., 2008; Liu et al., 2013). To improve the compatibility of the bentonite to the leachate, GCLs with modified bentonite (usually by polymer) have been developed and investigated with various types of leachate.
Swelling characteristics of soils subjected to acid contamination
2018, Soils and FoundationsHeat mitigation in geosynthetic composite liners exposed to elevated temperatures
2017, Geotextiles and GeomembranesWater retention curve of GCLs using a modified sample holder in a chilled-mirror dew-point device
2017, Geotextiles and Geomembranes