Geosynthetic clay liners: Perceptions and misconceptions

Hydraulic performance of geosynthetic clay liners to sulfuric acid solutions

In this study, natural clay minerals with green appearance were treated with sulfuric acid. Mass percentage of acid (wt%), temperature (T), contact time (t) and liquid-to-solid mass ratio (R) are used as the prevailing factors that determine the extent of acid-activation. The values of these factors range from 15–50%, 60–90 °C, 1.5–6 h and 4–7, respectively. The study has focused on the structural changes as well as textural characteristics of the clay. Three activated clay samples were prepared under different treatment conditions. The samples were characterized using X-ray powder diffraction (XRD), fourier transform infrared (FTIR), scanning electron microscope (SEM), chemical analysis and N2 adsorption techniques. Characterization of the treated clay minerals exhibited significant structural changes to a greater extent of acid-activation, from being partially crystalline to being amorphous silica. The surface area and total pore volume of clay increased proportionally with the level of acid treatment. The average pore diameter behaved differently. During the strong acid treatment, a large increase in pore volume and the enlargement of the pore size distribution were observed. This suggests that considerable structural changes and partial destruction may have occurred in this condition. The removal of methylene blue, used as cationic dye, from aqueous solution by the batch adsorption technique on three prepared acid-activated clay samples was studied. The Langmuir model was found to agree well with the experimental data.

Effect of Structure and Chemical Activation on the Adsorption Properties of Green Clay Minerals for the Removal of Cationic Dye

Geosynthetic clay liners (GCLs) are frequently used in lieu of, or as an augmentation to, compacted clay liners as secondary hydraulic barriers in municipal solid waste containment facilities. GCLs are lately being assessed for use in industrial and mining applications, not only for the temporary storage of process waters and permanent disposal of tailings, but also beneath heap leach pads, where their performance will be subjected to loads, hydraulic heads and leachate chemistries outside the normal conditions found in conventional municipal solid waste landfills for which they were designed. This paper considers recent limited research assessing the compatibility of GCLs to leachates having extreme chemistry. Extreme chemistry is here defined as strongly alkaline (pH > 12), strongly acidic (pH 1 M). Based on the limited research available, GCLs cannot be expected to perform for the long-term when in contact with strongly acidic leachates; however there exists some indic...

Overview of performance compatibility issues of GCLs with respect to leachates of extreme chemistry

Breakthrough time-based design of landfill composite liners

This study reports supportive evidence, from scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM) of bentonite cakes, of the textural effects caused by reac...

Impact of acid leachates on microtexture of bentonites used in geosynthetic clay liners

Introduction Geosynthetic clay liners (GCLs) are now a common feature of environmental lining systems in landfills, leach-heap pads, impoundments, irrigation canals and aesthetic ponds. The ASTM standard method (ASTM D5891-02) for fluid loss (FL) is an adaptation from the older American Petroleum Institute methods (API Specification 13A; API Specification 13B) for determining gel strength of bentonite and drilling mud suspensions. While the method provides an index to assist with evaluating water retention characteristics of a bentonite filter cake when deposited at elevated pressure from suspension, in its current form it is a qualitative test only (Rosin-Paumier et al., 2010). Such guidance is required to adapt the test for testing compatibility of the bentonite component of GCLs to leachates from landfills, mineral processing, or subsurface waters more typically encountered in field conditions (Chung and Daniel, 2008). Likewise, the ASTM standard method (ASTM D5890-06) for swell index (SI) provides an operator-dependent qualitative result suitable only for bentonite swelling in good quality water. We report here modified FL and SI values, along with flux and permeability of the filtrate and gel strength and effective porosity of the filter cake obtained on up to 5 M aqueous NaCl. We show that both modified methods can be semi-quantitative and are well-suited to compatibility testing of bentonite in saline leachates, can be used to differentiate between high quality bentonites and are potentially useful as tests for ‘fit-for-purpose’ products.

/pdf/improving-the-swell-index-and-fluid-loss-methods-for-26aqju4vww.pdf

Improving the swell index and fluid loss methods for compatibility testing of bentonites

The fluid loss test has been used by geotechnical engineers for rapid evaluation of the hydraulic barrier properties of bentonites. In this study, a modified fluid loss test, along with viscometric...

Colloidal aspects of incompatibility reactions of bentonite with saline leachates as indicated from a modified fluid loss test

Acid induced degradation of the bentonite component used in geosynthetic clay liners

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