Factors influencing hydraulic conductivity and metal retention capacity of geosynthetic clay liners exposed to acid rock drainage (original) (raw)
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Jioshinsetikkusu Rombunshu (Geosynthetics Engineering Journal), 2010
The capacity of geosynthetic clay liners (GCLs) to attenuate metals and metalloids such as Al, Fe, Cu, Zn, As, and Pb was evaluated in this study. For this purpose, free swell, sorption, and hydraulic conductivity tests on a needlepunched geosynthetic clay liner against a pH 3 artificial acid rock drainage (ARD) were conducted. Free swelling tests showed that at high metal concentration, the swell index decreased dramatically. Sorption test results showed that Na-bentonite had high capacity to sorb metals and metalloids. Hydraulic conductivity tests showed that k was 10 times lower when GCL was prehydrated with water, before permeating with ARD. Effluents were also evaluated in each case and results showed that the GCL tested has strong attenuation capacity toward metals and metalloids present in ARD, although desorption was observed in some cases.
Long-Term Performance of Geosynthetic Clay Liners Used in Acid Rock Drainage Mitigation
Geosynthetics engineering journal, 2011
Longterm barrier performance of geosynthetic clay liners (GCLs) when exposed to acid rock drainage (ARD), which is one of the most severe and expensive environmental problems facing the mining and some construction operations, was evaluated. Free swelling, sorption, and a ninemonth hydraulic conductivity tests on a needle punched GCL against an artificial ARD (pH = 3) that contained Al, Fe, Cu, Zn, As, and Pb, were conducted. Free swelling tests showed that a high metal concentration and/or a low pH negatively impacted on osmotic swelling. Sorption test results provided information about the competition among metals, and the Nabentonite capacity to sorb single metals and metalloids. Ninemonth hydraulic conductivity tests demonstrated that pH, EC and permeability changes over time, due to metal sorption/release and precipitation (physical clogging). The hydraulic conductivity remained low during the test duration and was approximately five times lower when GCL was prehydrated with water before ARD permeation (1.1x10 10 m/s) compared to the case in which prehydration and permeation were done using ARD (5.0x10 10 m/s). In each case, effluents were evaluated and breakthrough curves were constructed to get information about the GCL attenuation capacity toward metals present in ARD. Considering that bentonite (or GCLs) has the potential to retain heavy metals present in solution, showed relatively low hydraulic conductivity under even extreme conditions, and is available in many parts of the world, GCLs seem to be one possible solution for ARD mitigation.
Soils and Foundations, 2019
The hydraulic and chemical compatibility of a geosynthetic clay liner (GCL), containing powdered Na-bentonite, was evaluated against artificial acid rock drainage (ARD) in terms of the swell index, hydraulic conductivity and heavy metal retention. Six artificial ARDs with an approximate pH of 3 and different metal concentrations (electrical conductivity, EC, ranging between 75 and 1000 mS/m; ionic strength ranging between 8 and 400 mM) were used in the experiments. The results of free swelling tests showed that high metal concentrations (EC higher than 70 mS/m) negatively impact the swell volume by lowering it. The hydraulic conductivity of the GCL permeated with distilled water was 1.2 Â 10 À11 m/s, falling in the range of 7.9 Â 10 À12 to 1.1 Â 10 À10 m/s when prehydrated with distilled water and permeated with ARDs. The ion exchange and metal precipitation appeared to be the main mechanisms controlling the metal attenuation on the bentonite. The ion exchange mechanism starts with the release of Na from the bentonite and the sorption of the biand tri-metals present in the ARDs onto the bentonite. After the depletion of Na, the ion exchange reaction proceeds with the desorption of Ca and Mg from the bentonite and the sorption of cations present in the ARDs onto the bentonite layers. The depletion of Na from the bentonite and the subsequent release of Ca and Mg correlate to the sudden drop in pH and a gradual increase or equilibration of the hydraulic conductivity. It is possible to say that, after this point, hydraulic and chemical equilibrium is reached. From the overall results, the tested GCL showed acceptably low hydraulic conductivity and the potential to attenuate heavy metals present in ARDs.
Influence of Mass Per Unit Area on the Hydraulic Conductivity of Geosynthetic Clay Liners (GCLs)
2021
In the content of this study, barrier performance of geosynthetic clay liners (GCLs) in terms of mass per unit area of bentonite (MPUA) was investigated. For this purpose, a Na-GCL with MPUAs of 3.0 and 5.0 kg/m were tested. Hydraulic conductivity tests were conducted with deionized water (DIW) and calcium chloride solutions prepared with various concentrations (i.e., 15 mM and 30 mM CaCl2). The free swell characteristic of bentonite in GCL was also determined. The swell index results showed that increase in the CaCl2 concentration results to a decrease in the swell index values. That is, swell indices were 23, 13, and 10 mL/2g with DIW, 15 mM, and 30 mM CaCl2, respectively. The influence of MPUA on the hydraulic performance of Na-GCL was not observed with DIW. The hydraulic conductivity of GCL with MPUA of 3.0 and 5.0 kg/m was 4.6×10 and 2.1×10 m/s, respectively. However, MPUA had a significant effect on the hydraulic conductivity when CaCl2 solutions were used as the permeant. Inc...
Hydraulic conductivity of two geosynthetic clay liners permeated with a hyperalkaline solution
Geotextiles and Geomembranes, 2010
GCLs containing powdered Na-bentonite treated with different dosages of a proprietary additive intended to reduce the impacts of chemical interactions were permeated with three solutions: a hyperalkaline solution (1 M NaOH and 1.3 mM CsCl) having similar pH to aluminum refining leachate, a 1.3 mM CsCl solution (no NaOH), and DI water. For a given permeant solution, the hydraulic conductivity of both GCLs was similar. Thus, the higher additive dosage had no measureable impact on hydraulic conductivity. Hydraulic conductivity of both GCLs decreased by a factor of approximately 1.5-1.8 during permeation with CsCl in response to osmotic swelling induced by the low ionic strength of the CsCl solution entering the pore space. In contrast, permeation with the NaOH-CsCl solution caused the hydraulic conductivity of both GCLs to increase modestly (<50 times the hydraulic conductivity to DI water), and then level out (or decrease slightly) as a result of reduced osmotic swelling in the interlayer combined with dissolution of the mineral. For the tests conducted with CsCl solution, nearly all of the Cs was adsorbed by the bentonite. In contrast, Cs broke through readily when the NaOH-CsCl solution was used as the permeant solution. Permeation with the NaOH-CsCl solution also increased the sodicity of the bentonite by replacing bound K, Ca, and Mg on the mineral surface.
Effect of ammonium on the hydraulic conductivity of geosynthetic clay liners
Geotextiles and Geomembranes, 2017
Hydraulic conductivity and swell index tests were conducted on a conventional geosynthetic clay liner (GCL) containing sodium-bentonite (Na-B) using 5, 50, 100, 500, and 1000 mM ammonium acetate (NH 4 OAc) solutions to investigate how NH 4 þ accumulation in leachates in bioreactor and recirculation landfills may affect GCLs. Control tests were conducted with deionized (DI) water. Swell index of the NaB was 27.7 mL/2 g in 5 mM NH 4 þ solution and decreased to 5.0 mL/2 g in 1000 mM NH 4 þ solution, whereas the swell index of NaB in DI water was 28.0 mL/2 g. Hydraulic conductivity of the NaB GCL to 5, 50, and 100 mM NH 4 þ was low, ranging from 1.6e5.9 Â 10 À11 m/s, which is comparable to the hydraulic conductivity to DI water (2.1 Â 10 À11 m/s). Hydraulic conductivities of the NaB GCL permeated with 500 and 1000 mM NH 4 þ solutions were much higher (e.g., 1.6e5.2 Â 10 À6 m/s) due to suppression of osmotic swelling. NH 4 þ replaced native Na þ , K þ , Ca 2þ , and Mg 2þ in the exchange complex of the NaB during permeation with all NH 4 þ solutions, with the NH 4 þ fraction in the exchange complex increasing from 0.24 to 0.83 as the NH 4 þ concentration increased from 5 to 1000 mM. A NaB GCL specimen permeated with 1000 mM NH 4 þ solution to chemical equilibrium was subsequently permeated with DI water. Permeation with the NH 4 þ converted the NaB to "NH 4-bentonite" with more than 80% of the exchange complex occupied by NH 4 þ. Hydraulic conductivity of this GCL specimen decreased from 5.9 Â 10 À6 m/s to 2.9 Â 10 À11 m/s during permeation with DI water, indicating that "NH 4-bentonite" can swell and have low hydraulic conductivity, and that the impact of more concentrated NH 4 þ solutions on swelling and hydraulic conductivity is reversible.
2021
A tremendous increase in the waste is observed specially in metropolitan cities with the increase in population and industrialization. Corresponding to this increase in the produced waste the number of landfill dumping sites are also on an increasing spree in most of the cities. A solution for the development of these dumping sites is provided by geosynthetic clay liners (GCLs) having low hydraulic conductivity and greater structural stability. GCLs are used as a part of liner system to contain the leachate percolation from solid waste management sites. GCLs are made by encapsulating bentonite between geotextiles (either woven or nonwoven), bonded together by needle-punching. Hydraulic conductivity of GCLs is dependent upon the chemical composition of bentonite as well as the chemical composition of leachate. In this study various commercially available GCLs are tested for their hydraulic conductivity for distilled water as well as for synthetically prepared leachates. A flexi wall ...
Application of a geochemical transport model to predict heavy metal retention (Pb) by clay liners
Applied Clay Science, 2002
PHREEQC, a geochemical transport model, is used to simulate diffusive transport of Pb through a 10-cm-thick clay liner. The results are compared to those of Roehl and Czurda [Applied Clay Science 12 (1998) 387] who studied Pb migration by diffusion in a carefully monitored laboratory experiment. The computer simulation accounts for effects due to adsorption by ion exchange, changes in CEC, variable ion selectivity, and porosity or compacted density. It facilitates evaluation of changes in the diffusion coefficient and solution input parameters. The effective Pb diffusion coefficient determined for the simulation is 3 Â 10 À 10 m 2 s À 1 and for the 520-day experiment of Roehl and Czurda it is 2.3 Â 10 À 10 m 2 s À 1. Differences in the retardation factors (23.6 and 503, respectively) indicate that the model does not account for all of the adsorption mechanisms suggested by the experimental investigation. Thus, less Pb is retained and the liner is predicted to fail more rapidly than the actual results indicate. Models have great flexibility, but need to be verified by field data before they can be applied to specific waste site conditions.
Impact of Bentonite Quality on Hydraulic Conductivity of Geosynthetic Clay Liners
Journal of Geotechnical and Geoenvironmental Engineering, 2005
The differences in hydraulic conductivity for two geosynthetic clay liners (GCLs) containing different qualities of bentonite are evaluated based on permeation with water and chemical solutions containing 5, 10, 20, 50, 100, and 500 mM CaCl 2. The GCL with the higher quality bentonite (GCL-HQB) is characterized by a greater content of sodium montmorillonite (86 versus 77%), a higher plasticity index (548 versus 393%), and a higher cation exchange capacity (93 versus 64 meq/ 100 g) relative to the GCL with the lower quality bentonite (GCL-LQB). The tests using CaCl 2 solutions as permeant liquids were continued until chemical equilibrium between the influent and effluent was established, resulting in test durations that ranged from less than 1 to more than 900 days. The hydraulic conductivity for GCL-HQB, k HQB , is ϳ3ϫ lower than the hydraulic conductivity for GCL-LQB, k LQB , when specimens of both GCLs are permeated with water. However, the hydraulic conductivity for GCL-HQB is always higher than that for GCL-LQB when the specimens are permeated with the CaCl 2 solutions. For example, k HQB / k LQB ranges from 2.0 to 2.6 for the tests performed using 5, 10, and 20 mM CaCl 2 solutions as the permeant liquids, whereas the k HQB / k LQB values are ϳ230, ϳ100, and ϳ40 for the tests performed using 50, 100, and 500 mM CaCl 2 solutions as the permeant liquids, respectively. Thus, the GCL with the higher quality bentonite is more susceptible to chemical attack than the GCL with the lower quality bentonite.
The results of confined swell, consolidation, and hydraulic conductivity tests on a needle-punched geosynthetic clay liner (GCL) are reported. The effects of permeant (distilled water, aqueous single salt solutions with concentrations between 0.01 and 2.0 M NaCl, and a synthetic municipal solid waste (MSW) leachate), static confining stress, hydrating medium, and degree of bentonite hydration at the time of the application of the confining stress are examined. Increases in the permeant salt concentration and decreases in the magnitude of the confining stress caused increases in the hydraulic conductivity. It is shown that high salt concentrations in the hydrating fluid increased the hydraulic conductivity. The GCLs permeated with 0.6 and 2.0 M NaCl solutions were more permeable than GCLs initially hydrated with water. The hydrating fluid was not as critical for permeation of 0.1 M NaCl. The effect of the degree of bentonite hydration at the time of the application of the confining stress was also found to be significant, highlighting the hydraulic benefits of maximizing overburden stress prior to GCL hydration. Tests performed using a synthetic MSW leachate gave results comparable to those obtained for aqueous salt solutions between 0.2 and 0.8 M NaCl. Practical implications are discussed. Résumé : On rapporte ici les résultats d'essais de gonflement sous confinement, d'essais de consolidation et de conductivité hydraulique effectués sur une membrane argile-géosynthétique (MAG) aiguilletée. On a examiné les effets du liquide de percolation (eau distillée, solutions aqueuses salines avec des concentrations en NaCl de 0,01 et 2,0 M, lixiviat synthétique de type déchets municipaux), ainsi que les effets de la contrainte statique, du liquide hydratant et du degré d'hydratation de la bentonite à l'instant de l'application de la pression de confinement. L'augmentation de la concentration en sel de la solution et la diminution de la pression de confinement ont entrainé une augmentation de la conductivité hydraulique. On a aussi montré que des concentrations en sel élevées dans le liquide hydratant augmentent la conductivité hydraulique. Les MAG soumises à des solutions de NaCl à des concentrations de 0,6 et 2,0 M étaient plus perméables que les MAG initialement hydratées à l'eau. Le liquide hydratant n'était pas un facteur aussi critique pour des circulations de fluide à 0,1 M NaCl. On a également constaté l'importance du degré d'hydratation de la bentonite lors de l'application de la pression de confinement, ce qui souligne les avantages hydrauliques qu'il y a à maximiser la contrainte verticale avant l'hydratation de la membrane. Les essais effectués avec le lixiviat synthétique ont donné des résultats comparables à ceux obtenus avec les solutions salines entre 0,2 et 0,8 M NaCl. On discute finalement les conséquences pratiques de ces essais.