Polymer-treated bentonite clay for chemical-resistant geosynthetic clay liners

Abstract

The purpose of hydraulic barriers, such as geosynthetic clay liners (GCLs), is to isolate waste liquids from the environment. Bentonite clay is widely used in GCLs because of its elevated sealing capacity in the presence of water and its ability to restrict the migration of solutes (chemico-osmotic efficiency or semi-permeable membrane behaviour). However, exposure to high concentrations of inorganic solutions can change the clay fabric increasing its hydraulic conductivity and degrading its membrane behaviour, with a consequent harm to the environment. The aim of this research was to study the hydraulic and chemico-osmotic performance of amended clays. For this purpose, an engineered clay (HYPER clay) was developed through treatment of a natural bentonite with an anionic polymer and the results were compared with two amended clay materials [multi-swellable bentonite (MSB) and a dense prehydrated GCL (DPH GCL)]. To demonstrate the potential benefits of polymer treatment, material characterisation through x-ray diffraction analysis, density of solid particles, Atterberg limits, and swelling tests was performed on treated and untreated samples. Subsequently, hydraulic conductivity and chemico-osmotic tests were performed with CaCl2 solutions on treated and untreated clays, to evaluate the modified clays resistance to chemical attack. The results of this research showed that the present amendment technology has a great potential for future GCL applications. x-ray diffraction analysis demonstrated the intercalation of the polymer in the interlayer region of the clay inducing a dispersed clay structure. The swell index and the liquid limit of the clay increased with increasing polymer dosage suggesting a potential benefit of the polymer on preserving the hydraulic performance of the clay. Unlike the untreated clay, HYPER clay treatment maintained low hydraulic conductivity of the clay to CaCl2 even in the long term and protected the clay against the destructive role of diffusion, maintaining the initial osmotic efficiency in the long term. Test results were also compared with other amended clays MSB and DPH GCL. These two amended clay materials displayed a chemico-osmotic behaviour at the steady state similar to that observed on untreated clay. On the other hand, the preservation of the chemico-osmotic efficiency of the HYPER clay with time suggests that the carboxymethyl cellulose was not flushed out during the long period of permeation with deionised water

Membrane behavior of compacted sand–bentonite mixture

“…Except for the 5 mmol/L KCl stage for specimen RW-2, the difference between ave and o , ⌬, was generally ≤0.033, and tended to decrease with increasing C ot . The closeness in values between o and ave for both tests for all values of C ot likely is due, in part, to the circulation of TW across the bottom boundary of the specimens in this study relative to previous studies, where DIW generally has been circulated across the bottom boundary of the specimen (e.g., Malusis and Shackelford 2002;Shackelford and Lee 2003;Yeo et al 2005;Kang and Shackelford 2010;Mazzieri et al 2010;Bohnhoff 2012;Dominijanni et al 2013;Meier et al 2014;Tang et al 2014aTang et al , 2014bTang et al , 2015Di Emidio et al 2015). The use of TW as the bottom circulation liquid resulted in values of −⌬C o and −⌬C ave that were closer in magnitude relative to the differences in these values based on the use of DIW as the bottom circulation liquid.…”

“…Values of o reported in the literature for compacted bentonite specimens (Kemper and Rollins 1966;Kemper and Quirk 1972;Dominijanni et al 2013;Di Emidio et al 2015) are compared to the o measured in this study for compacted SB specimens in Fig. 12c.…”

“…Therefore, the relatively low values of for low values of C ot and CaCl 2 (e.g., ≤5 mmol/L CaCl 2 ) reported by Di Emidio et al (2015) are likely due to diffusion of Ca 2+ ions and the concomitant increase in pore sizes due to compression of DDLs (e.g., see Shackelford and Lee 2003).…”

Review of the fundamental geochemical and physical behaviors of organoclays in barrier applications

“…QAC-modified clays, when mixing with unmodified bentonite, offer some chemical compatibility. Meanwhile, recent advances in polymer-clay hybrid barrier materials, including multi-swellable bentonite (MSB), dense prehydrated geosynthetic clay liner (DPH-GCL), HYPER clay and bentonite polymer nanocomposite (BPN) Di Emidio et al, 2015;Bohnhoff and Shackelford, 2014;Kolstad et al, 2004;Katsumi et al, 2008), were developed to improve chemical compatibility of a barrier. Their hydraulic conductivity and swelling index are tabulated in Table 5.…”

“…However, the long term performance of DPH-GCL declined to that of a unmodified GCL (Di , which is also postulated to be due to the transient nature of the amendment. HYPER clay, a barrier material with excellent chemical compatibility to aggressive permeants, was developed based on the observation that dehydration at elevated temperature (N 60°C) enhanced irreversible adsorption of CMC adsorption on the clay surface (cited by Di Emidio et al, 2015;Di Emidio, 2010). HYPER clay was synthesized by mixing bentonite slurry with varied amount of Na-CMC (0-16% by weight), oven-dried at 105°C, and then ground to powder (Di Emidio, 2010).…”