DIFFUSION THROUGH SODIUM AND POLYMER ENHANCED BENTONITES EXPOSED TO DILUTE AND AGGRESSIVE SOLUTIONS

Canadian Geotechnical Journal ◽

10.1139/cgj-2019-0809 ◽

2020 ◽

Author(s):

Shan Tong ◽

Kristin Sample-Lord ◽

Gretchen Bohnhoff

Keyword(s):

Diffusion Coefficients ◽

Transport Mechanism ◽

Sodium Bentonite ◽

Apparent Diffusion Coefficients ◽

Steady State Flux ◽

Expected Performance ◽

Apparent Diffusion ◽

Order Of Magnitude ◽

Cacl2 Concentration ◽

Diffusion Properties

Chemical incompatibility between sodium bentonite (NaB) and aggressive waste solutions has led to the development of enhanced bentonites for geoenvironmental applications. Enhanced bentonites, such as bentonite-polyacrylic-acid composite (BPC), have been shown to maintain low enough values of hydraulic conductivity (e.g. < 10-10 m/s) for diffusion to be the dominant transport mechanism, even upon exposure to aggressive solutions. However, quantification of diffusion properties of enhanced bentonites has been limited. In this study, apparent diffusion coefficients (Da) for chloride were measured for NaB and polymer enhanced NaBs. Diffusion tests were performed using dilute (5 mM) to aggressive (100 mM) calcium chloride (CaCl2) solutions. In addition, scanning electron microscopy was performed to support interpretation of diffusion results. For CaCl2 solutions < 100 mM, Da values for BPC were lower (by approximately half an order of magnitude) than Da values for NaB. However, differences in Da due to polymer enhancement diminished as CaCl2 concentration increased. Predicted steady-state flux through a BPC geosynthetic clay liner (GCL) was dominated by diffusion and up to two orders of magnitude lower than flux through an NaB GCL. These results provide insight regarding diffusion in polymer enhanced bentonites and expected performance of containment barriers with enhanced-bentonite GCLs.

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Development of a Gas Method for Migration Studies in Fractured and Porous Media.

MRS Proceedings ◽

10.1557/proc-294-851 ◽

1992 ◽

Vol 294 ◽

Cited By ~ 1

Author(s):

Kusti VÄÄtÄinen ◽

Jussi Timonen ◽

Aimo HautojÄrvi

Keyword(s):

Porous Media ◽

Liquid Phase ◽

Gas Phase ◽

Diffusion Coefficients ◽

Tracer Gas ◽

Phase Measurements ◽

Apparent Diffusion Coefficients ◽

Apparent Diffusion ◽

Standard Techniques ◽

Diffusion Properties

ABSTRACTA gas method for fast measurements of diffusion properties of porous materials has been developed. Diffusion coefficients in the gas phase are typically four orders of magnitude larger than those in the liquid phase. For samples whose structures do not change much upon drying it is possible to estimate the diffpision properties of the liquid phase when the properties of the gas phase are known. Advantages of the gas method are quick and easy measurements and therefore they can be used to optimize the liquid-phase measurements which may last months or years. For materials with good correlation between the gas and liquid-phase diffusion, the number of liquid phase measurements can be greatly reduced.Nitrogen was used as the carrier gas and helium as the tracer gas. Helium concentrations were measured by using standard techniques. The equipment was tested for two sample geometries, a column made of a polished granite slab and an acrylic slab with a flow channel in between, and a hollow bore core where diffusion occurs through the sample. Both types of measurement were modelled and apparent diffusion coefficients in the gas phase were determined.

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Apparent salt diffusion coefficients for soil–bentonite backfills

Canadian Geotechnical Journal ◽

10.1139/cgj-2019-0058 ◽

2020 ◽

Vol 57 (5) ◽

pp. 623-634 ◽

Cited By ~ 1

Author(s):

Kristin M. Sample-Lord ◽

Wenjie Zhang ◽

Shan Tong ◽

Charles D. Shackelford

Keyword(s):

Diffusion Coefficients ◽

Test Method ◽

Solute Diffusion ◽

Leaching Test ◽

Contaminant Migration ◽

Apparent Diffusion Coefficients ◽

Cutoff Walls ◽

Apparent Diffusion ◽

Salt Diffusion ◽

Diffusion Properties

Apparent diffusion coefficients, Da, were measured for two soil–bentonite (SB) backfills characteristic of those used in SB vertical cutoff walls for subsurface control of contaminant migration. The base soils for the backfills comprised either a natural lean clay or sand–bentonite mixtures. The base soils were mixed with 5% bentonite–water slurry to obtain a slump of 125 mm, resulting in total bentonite contents ranging from 4.76% to 7.31%. Values of Da for sodium chloride were measured using a recently developed dialysis-leaching test method. The Da values for the clay–bentonite and sand–bentonite backfills ranged from 2.5 × 10−10 to 5.3 × 10−10 m2/s and from 1.4 × 10−10 to 8.1 × 10−10 m2/s, respectively. Values of Da for both backfills increased with increasing average salt concentration in the specimen (Cave). Values of Da decreased by ≤50% with increasing backfill bentonite content. For all Cave values, the clay backfills exhibited lower Da than the sand–bentonite backfills, likely due to additional fines from the lean clay. Results of this study enhance understanding of solute diffusion through SB cutoff walls, as well as support future use of the dialysis-leaching test method to measure diffusion properties of SB backfills.

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Diffusion Behavior for Se and Zr in Sodium-Bentonite

MRS Proceedings ◽

10.1557/proc-353-269 ◽

1994 ◽

Vol 353 ◽

Cited By ~ 23

Author(s):

Haruo Sato ◽

Mikazu Yui ◽

Hideki Yoshikawa

Keyword(s):

Diffusion Coefficients ◽

Dominant Species ◽

Atmospheric Condition ◽

Aerobic Condition ◽

Diffusion Method ◽

Dry Density ◽

Sodium Bentonite ◽

Apparent Diffusion Coefficients ◽

Anion Exclusion ◽

Apparent Diffusion

AbstractApparent diffusion coefficients for Se and Zr in bentonite were measured by in-diffusion method at room temperature using water-saturated sodium-bentonite. KunigelVl® * containing 50wt% Na-smectite as a major mineral was used as the bentonite material. The experiments were carried out in the dry density range of 400–1800kg/m3. Bentonite samples were immersed with distilled water and saturated before the experiments. The experiments for Se were carried out under N2 atmospheric condition (O2: 2.5ppm). Those for Zr were carried out under aerobic condition. The apparent diffusion coefficients decrease with increasing density of the bentonite. Since dominant species of Se in the pore water is predicted SeO32-, Se may be retarded by anion-exclusion because of negative charge on the surface of the bentonite and little sorption. The dominant species of Zr in the porewater is predicted Zr(OH)5- or HZrO3-. Distribution coefficient measured for Zr on the bentonite was about 1.0m3/kg from batch experiment. Therefore, the retardation may be caused by combination of the sorption and the anion-exclusion. A modelling for the diffusion mechanisms in the bentonite were discussed based on an electric double layer theory. Comparison between the apparent diffusion coefficients predicted by the model and the measured ones shows a good agreement.

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