Soil Bentonite Research Articles

Long-Term Column Testing of Zeolite-Amended Backfills. II: Solute Transport Properties

AbstractEight, long-term column tests (1.05–3.75 year) involving soil-bentonite (SB) backfills with 5 or 10% (by dry weight) of one of three types of zeolite amendment (clinoptilolite, chabazite-UB...

An investigation into effect of sawdust treatment on permeability and compressibility of soil-bentonite slurry cut-off wall

Landfills containing municipal solid waste (MSW) are increasing with growing population and consumption rate in Australia. However, construction of conventional containment systems such as slurry walls are a cost-effective and timesaving approach to control the leachate diffusion, they are weak barriers when exposed to volatile organic compounds (VOCs) or heavy metals, which are abundant in municipal solid wastes. This study investigates effect of sawdust addition on hydraulic conductivity and compressibility of the Soil-Bentonite (SB) slurry cut-off wall. A series of hydraulic conductivity and consolidation tests performed on SB backfill amended with 2%, 5% and 10% sawdust contents. The results showed that application of sawdust reduced the final hydraulic conductivity (kf) in the range of 2.13 × 10−10 ≤ kf ≤ 3.5 × 10−10 m/s. The computed hydraulic conductivity values using consolidation theory (ktheory) also showed an identical decreasing trend in the range of 5.10 × 10−11 ≤ ktheory ≤ 3.50 × 10−10 m/s under 24 ≤ σ′n ≤ 1280 kPa effective overburden pressure (σ′n). The coefficient of consolidation (cv) was computed using Casagrande and Taylor methods showed a good agreement range value. Additionally, the computed compression index (Ci) and swelling index (Cs) were calculated using void ratio and effective overburden pressure graphs (e - logσ′n) showed that application of sawdust had no significant impact on settlement of the SB backfill.

Effect of plastic fines on initial shear modulus of sand-clay mixtures

This paper presents the dynamic properties of sand-fines mixtures based on the results of undrained cyclic triaxial tests. The sand was obtained from Sabarmati River, and three types of fines F1, F2, and F3 were obtained from locally available fine grained soils i.e. Black cotton soil, Suddha soil, and Bentonite soil. Sand-fines mixtures of wide range of plasticity from non-plastic to highly plastic mixture with PI = 86 were prepared using the fines passing 75 μ size. The initial shear moduli of all sand-fines mixtures are evaluated in terms of fines content, Plasticity Index (IP) and equivalent plasticity index (IP*) determined for soil passing 2 mm size IS Sieve. There is good correlation between the initial shear modulus of sand-fines mixtures and equivalent plasticity index (IP*) compared to Plasticity Index (IP). An empirical equation for obtaining initial shear modulus is formulated based on equivalent plasticity index and mean-effective stress.

A SIMPLE METHOD FOR TESTING THE FRACTAL DIMENSION OF COMPACTED BENTONITE IMMERSED IN SALT SOLUTION

This study employs swelling deformation test for estimating the fractal dimension of salt-modified bentonite soil by measuring the void ratio of montmorillonite ([Formula: see text]) and the effective stress ([Formula: see text]). For the compacted Tsukinuno bentonite, a typical Na-montmorillonite, the fractal dimension is tested by the swelling deformation test conducted in sodium chloride solutions with different concentrations. According to the results, the fractal dimension of the specimens is essentially constant irrespective of the concentration of inundating NaCl solution. The strong correlation of the results from the swelling deformation test with those from the nitrogen adsorption test indicates that the swelling deformation test is an effective laboratory method for testing the fractal dimension of compacted bentonite in salt solution.

Numerical Evaluation of Vertical Cutoff Walls Comprising Zeolite-Amended Backfills for Enhanced Metals Containment

AbstractThe potential for enhanced containment of two metals, potassium (K) and zinc (Zn), by soil-bentonite (SB) vertical cutoff walls comprising zeolite-amended backfills was evaluated on the bas...

Groundwater Remediation Using a Pyrolysis Oily Sludge Composite

The absorption capacity of oily sludge pyrolysis residue was utilized to prepare oxygen-releasing composites for groundwater remediation. The physical properties of the oily sludge pyrolysis residue were specific surface area of 13.936 m2/g and main pore size on the order of nanometers. The pyrolysis residue was nontoxic and would not cause secondary contamination of groundwater. The rate of mass loss of calcium peroxide and the oxygen release rate in water were analyzed. An oxygen-releasing composite containing 35% calcium peroxide, 15% oily sludge pyrolysis residue, 30% fluviatile sand, 10% calcium-based bentonite soil, and 10% deionized water was proposed. Addition of oily sludge to the composite plugged some of the oxygen-releasing surface and slowed the rate of oxygen release. Continuous precipitation of CaCO3 on the surface and in the pores of the composite also reduced the initial oxygen release rate and slowed the overall oxygen release rate.

Transport parameters of lead (Pb) Ions migrating through saturated lateritic soil–bentonite column

This paper describes experiments and analyses conducted to determine the transport parameters of lead (Pb) ions diffusing through compacted lateritic soil–bentonite column. Experimental programme included the batch sorption tests and diffusion tests conducted in cells containing water-saturated lateritic soil treated with up to 10% bentonite by dry weight of soil. Specimens for diffusion tests were compacted at approximately 2% wet of optimum moisture content with British standard heavy (BSH) effort and exposed to municipal waste leachate placed on top of the specimens. Migration of Pb ions was monitored by measurement of pore water concentrations at various depths along the soil mixture columns together with the soil transport parameters (i.e. distribution coefficient, Kd, retardation factor, Rd and diffusion coefficient, D*). Based on sorption data, linear sorption isotherms were derived. Kd values of 2.0, 2.2, 2.5, 2.7, 3.9 as well as Rd values of 11.0, 11.1, 12.5, 12.5, 16.7 were recorded for 0, 2.5, 5, 7.5, 10% bentonite contents, respectively. The distribution of Pb was limited to upper sections (1.6–3.2 cm) of the soil column in mixtures. Diffusion testing established D* values of 4.50, 3.15, 2.78, 2.42 and 2.06 × 10−10 m2/s for the same sequence of bentonite treatment which is consistent with very strong sorption on mixtures particularly with higher bentonite contents.

Prediction of hydraulic conductivity for soil–bentonite mixture

Owing to its low hydraulic conductivity, soil and bentonite mixture is applied as a liner material. However, the experimental determination of hydraulic conductivity, which is controlled by various physical, chemical and mineralogical factors, requires an expensive and time-consuming setup. In the present work, multigene symbolic, genetic programming was used to model functional relationships for hydraulic conductivity. The developed model was able to generalize highly nonlinear variations in data as well as predict system behavior from experimental observations. It was found that the predictions obtained from developed model agree well with experimental observations.

Investigating the performance of Ogata-banks' one-dimensional dispersion equation in oil contamination dispersion in Bentonite soil

In recent years, the soil and its surrounding environment have undergone and faced irrecoverable changes and contaminations due to human activities. From among contaminating sources, hydrocarbon compounds are very important because they easily permeate into soil and aquifers due to storage or leakage (when transferred). Investigating contamination transfer peculiarities is, in fact, a vital and basic issue in the environmental studies because of their high potential of permeation into soil and aquifers. In the present research, effort has been made to introduce the mechanism of contaminations' dispersion and the basic equation in the related theory while applying boundary conditions, and extending the equation to study one-dimensional dispersion. Next, the results of one-dimensional dispersion in Bentonite with and without surface absorption in time intervals of 15, 30, and 90 days from the beginning of dispersion have been compared using the C-Tran Software. The results of this research study have revealed that the oil contamination density (concentration) variations along the soil column experience a decreasing trend; under the conditions of one-dimensional dispersion, the reduction rate is nearly constant 90 days after the commencement of the dispersion process.

Investigating the performance of Ogata-banks' one-dimensional dispersion equation in oil contamination dispersion in Bentonite soil

In recent years, the soil and its surrounding environment have undergone and faced irrecoverable changes and contaminations due to human activities. From among contaminating sources, hydrocarbon compounds are very important because they easily permeate into soil and aquifers due to storage or leakage (when transferred). Investigating contamination transfer peculiarities is, in fact, a vital and basic issue in the environmental studies because of their high potential of permeation into soil and aquifers. In the present research, effort has been made to introduce the mechanism of contaminations' dispersion and the basic equation in the related theory while applying boundary conditions, and extending the equation to study one-dimensional dispersion. Next, the results of one-dimensional dispersion in Bentonite with and without surface absorption in time intervals of 15, 30, and 90 days from the beginning of dispersion have been compared using the C-Tran Software. The results of this research study have revealed that the oil contamination density (concentration) variations along the soil column experience a decreasing trend; under the conditions of one-dimensional dispersion, the reduction rate is nearly constant 90 days after the commencement of the dispersion process.

Triaxial shear behaviour of oil contaminated clays

This study is focused on investigating the geotechnical behaviour of oil-contaminated clays through a series of laboratory experiments including standard compaction, uniaxial and triaxial compression tests. The contaminated samples were prepared with addition of gasoil and kerosene in the amount of 3, 6 and 9% in two different series. The first series includes kerosene contaminated kaolinite which is compacted at optimum moisture content of the clean soil, whereas the second series contains kaolinite and bentonite soils with optimum moisture content of already contaminated batches. The results show an improvement in compaction characteristics of kaolinite and bentonite specimens upon the addition of contamination. Furthermore, the triaxial shear strength of the first set of samples undergoes a decrease in parallel with the addition of kerosene which is more significant at higher confinement levels. On the other hand, the uniaxial and shear strength values of second series increases when mixed with contamination which is more notable in presence of gasoil compared to kerosene. Finally, the 9% contaminated kaolinite specimens do not follow the same pattern of changes in strength similar to 3 and 6% contamination due to the different structure of 9% contaminated clay observed in scanning electron micrograph photos.

Lead adsorption and transport in loess-amended soil-bentonite cut-off wall

Soil-bentonite slurry-trench cutoff walls using backfill consisting on-site sandy or silty soil and bentonite are extensively used as engineered barriers for the containment of groundwater and soil pollution. Chinese loess has been shown to have large adsorption capacity regarding heavy metals. There is a great potential to use Chinese loess as amendments to improve the adsorption capacity of the wall. Batch and column tests were carried out to investigate the adsorption and transport of Pb(II) in loess modified soil-bentonite (LSB). Batch tests were conducted to study the effects of contact time, initial Pb(II) concentration, loess proportion in LSB, and pH on Pb(II) adsorption. The rate constant of pseudo-second-order kinetic adsorption model of LSB is two times greater than that of soil-bentonite (SB), which indicates that the adsorption rate of LSB is much faster than that of SB. The mean free energy of adsorption evaluated by D-R model is 15.56kJ/mol and 18.89kJ/mol for SB and LSB, respectively. This indicates the adsorption mechanisms of SB and LSB are mainly ion exchange and chemical reaction. The adsorption capacity of LSB increases linearly with the increase of the loess amount in LSB. The maximum adsorption amount of LSB containing 20% loess can be 2 times greater than that of SB. Results also indicate that Pb(II) is first adsorbed onto loess until the adsorption amount Pb(II) onto loess reaches its adsorption maximum. An equation considering this effect was proposed for prediction of the adsorption capacity of LSB. A set of column tests were carried out to evaluate the tortuosity, mechanical dispersion and retardation factor regarding lead transport in SB and LSB vertical engineered barrier. The retardation factor of LSB and SB are determined to be 38 and 15, respectively, by the column tests. The Kd values obtained from batch tests are significantly larger than those obtained from column tests due to the difference of soil-water ratio used for these two types of tests. Using the obtained parameter values, the breakthrough time of Pb(II) through LSB wall is evaluated to be about 2 times greater than that of the SB wall when the hydraulic head difference is <3m. This may be due to the increase of adsorption capacity of the soil-bentonite wall amended with the loess.

Phosphate-amended sand/Ca-bentonite mixtures as slurry trench wall backfills: Assessment of workability, compressibility and hydraulic conductivity

In regions and countries where sodium bentonite is scarce, the resourceful calcium bentonite can be considered as an alternative material for soil-bentonite slurry trench walls. However, the lower swelling capacity of calcium bentonite as compared to Na-bentonite may result in the unacceptable high hydraulic conductivity of the sand/calcium bentonite backfills, and, therefore, amendment of calcium bentonite is necessary. However, studies on the feasibility of using amended calcium bentonite for soil bentonite backfills are limited. This study investigates the feasibility of using sodium hexametaphosphate amended calcium bentonite for the backfill material through a comprehensive laboratory investigation. First, a series of viscosity, density and filtrate loss tests are conducted using bentonite-tap water slurries with different amounts of phosphate to determine the optimal amendment dosage. Subsequently, the Atterberg limits and free swell index are evaluated for the amended/un-amended calcium bentonite and backfills, which consist of sand and amended/un-amended calcium bentonite. Finally, slump, oedometer tests and flexible-wall hydraulic conductivity tests are conducted on the backfills. The results indicate that the slurry with 20% calcium bentonite amended by 2% phosphate results in the target slurry, and the optimum phosphate dosage for amended calcium bentonite is found to be 2%. The phosphate amendment causes an increase of 1.21 times in the liquid limit, and an increase of 1.40 times in the free swell index of the amended bentonite relative to those of the un-amended bentonite. The sand/calcium bentonite backfill changes from non-plasticity to plasticity after the amendment. The amended backfill displays two times higher swell index value and one order of magnitude lower consolidation coefficient value than the un-amended backfill. The hydraulic conductivity of un-amended backfills containing 15% to 25% un-amended bentonite is greater than the commonly targeted value of 10−9m/s for slurry trench walls. In contrast, the hydraulic conductivity of the amended backfill with 15% to 25% amended bentonite varies from 8.3×10−10m/s to 2.7×10−10m/s, which is lower than 10−9m/s. In addition, the amended backfills containing 20% and 25% amended calcium bentonite have nearly the same magnitude of hydraulic conductivity as the conventional sand/sodium bentonite backfill. This study demonstrates that phosphate is a promising amendment for achieving low hydraulic conductivity of sand/calcium bentonite backfills for soil-bentonite slurry trench walls.

Mitigation of reverse faulting deformation using a soil bentonite wall: Dimensional analysis, parametric study, design implications

Recent major seismic events, such as the Chi-Chi (1999) and the Wenchuan (2008) earthquakes occurred in Taiwan and China, have offered a variety of case histories on the performance of structures subjected to reverse faulting–induced deformation. A novel faulting mitigation method has recently been proposed, introducing a soft deformable wall barrier in order to divert the fault rupture away from the structure. This can be materialized by constructing a thick diaphragm-type soil bentonite wall (SBW) between the structure and the fault rupture path. The paper investigates the key parameters in designing such a SBW, aiming to mitigate the fault rupture hazard on shallow foundations. The paper employs a thoroughly validated finite element analysis methodology to explore the efficiency of a weak SBW barrier in protecting slab foundations from large tectonic deformation due to reverse faulting. A dimensional analysis is conducted in order to generalize the validity of the derived conclusions. The dimensionless formulation is then used to conduct a detailed parametric study, exploring the effect of SBW thickness w/H, depth HSBWl/H, and shear strength τsoil/τSBW, as well as the bedrock fault offset h/H, foundation surcharge load q/ρgB, and fault outcrop location s/B. It is shown that the wall thickness, depth, and shear strength should be designed on the basis of the magnitude of the bedrock fault offset, the location of the fault relative to the structure, and the shear strength of the soil. The efficiency of the weak barrier is improved using lower strength and stiffness material compared to the alluvium. A simplified preliminary design methodology is proposed, and presented in the form of a flowchart.

Pulsed Electrokinetic Removal of Chromium, Mercury and Cadmium from Contaminated Mixed Clay Soils

ABSTRACTElectrokinetic remediation (EKR) processes are energy intense systems as they are mainly run under continuous constant current supply mode. In this study, pulsed electrokinetic remediation (PEKR) technique was employed for the removal of Cd, Hg and Cr from mixed contaminated natural clay and bentonite soils. The effects of voltage gradient, pulse duty cycle and bentonite/clay ratio on the simultaneous removal efficiencies of the heavy metals and specific energy consumption were investigated. Fifteen (15) PEKR experiments were conducted according to Box–Behnken design (BBD) with each experiment allowed to continuously run for 21 days. Increase in the proportion of the bentonite significantly decreased the removal efficiency of the heavy metals while having insignificant effect on the energy consumption. Conversely, increase in both voltage gradient and pulse duty cycle increased the heavy metals removal efficiencies, though at the expense of increase in energy consumption due to combine effects of increase in the soil electrical conductivity, amount of current needed to sustain the applied voltage gradient as well as the raise in the soil pH. The maximum achievable removal efficiencies for Cd, Hg and Cr were 21.87, 78.06 and 89.64% respectively. The specific energy consumption significantly increased from the range of 91.67–154.17 kwh/m3 to 1700–2441.67 kwh/m3 as a result of combined effect of increasing voltage gradient and pulse duty cycle. This demonstrated that effective PEKR could be achieved with significance reduction in the energy consumption via appropriate selection of pulse duty and voltage gradient for clay soils of different proportion of montmorillonite.

Performance enhancement of sand–bentonite mixture due to addition of fiber and geosynthetic clay liner

In the absence of impermeable natural soils, compacted sand–bentonite mixture along with a layer of geosynthetic clay liner (GCL) is used as a liner material at the waste disposal site. However, due to desiccation, the bentonite present in the liner shrinks resulting in an increase in the hydraulic conductivity of the liner. To prevent the desiccation cracking of bentonite, glass fibre is added to the mixture as a reinforcing material. However, the addition of the fibre can influence the geotechnical properties of liner material. To study the effect of the fibre on the geotechnical properties of the sand–bentonite mixtures with one layer of GCL, glass fibre of 10 mm length was added in the proportion of 0.5 and 1.0% to different sand–bentonite mixtures. Result shows that the swelling pressure and swelling potential of the soil–bentonite mixture with a layer of GCL decreased significantly with the increase in the glass fibre content in the mixture. The hydraulic conductivity of the mixtures was decreased with the inclusion of the GCL to mixtures; however, it increased considerably when glass fibre was added to the mixture. The compression index of the mixtures with GCL decreased marginally due to the inclusion of fibre.

Influence of freeze–thaw cycles on the performance of covers with capillary barrier effects made of crushed rock–bentonite mixtures to control oxygen migration

In temperate climates, covers with capillary barrier effects (CCBEs) are being used successfully to prevent oxygen fluxes from reaching covered potentially acid mine drainage (AMD) generating mine tailings. In northern climates, the more attractive option for mine site reclamation is insulation covers, which are designed to keep reactive materials frozen. This article suggests that CCBEs can simultaneously control oxygen migration and mine waste temperature to inhibit AMD generation. However, in northern conditions, where natural fine-grained materials needed for the CCBE moisture-retaining layer are not always available, soil–bentonite mixtures could be used instead. This laboratory study assessed — using instrumented columns — the effects of freeze–thaw cycles on the performance of three CCBEs made with crushed rock–bentonite mixtures. An oxygen diffusion test was developed to determine the effective diffusion coefficient of oxygen (De) and its sensitivity to freeze–thaw cycles. The results show good initial performance for the saturated CCBEs. However, the tested CCBEs are significantly affected by freeze–thaw cycles and have limited oxygen-limiting ability.

Graphene quantum dot soil moisture sensor

A soil sensor to measure moisture content in soil is fabricated and described. The sensor is based on graphene quantum dots (GQDs) and is highly sensitive. The simplicity of the process and use of an inexpensive material GQDs make it an affordable low cost sensing unit in comparison to existing soil moisture sensing units. It is a resistive micro-sensor with interdigitated electrodes (IDE) where MEMS fabrication process is used and GQDs serve as the channel material between IDEs. The sensor is tested in two different soil environments viz. white clay (passive soil) and bentonite clay (an active soil). The conductance of IDE structure with GQDs changes from 0.06×10−61/Ω to 0.68×10−61/Ω in white clay as the gravimetric moisture content changes from 4 to 45%. For bentonite soil, the conductance of the sensor changes from 0.06×10−61/Ω to 0.48×10−61/Ω across the gravimetric moisture range of 11 to 90%. The sensor shows higher sensitivity at higher moisture content which can be attributed to Grotthuss chain reaction and ionic conductivity. Response time of the fabricated micro-sensor is found to be 2–3min which is the lowest response time reported for a resistive based soil moisture sensor. The sensitivity of sensor towards gravimetric moisture contents is 0.014×10−61/Ω per percent increase in moisture content (1/Ω/1%) for the white clay and 0.005×10−61/Ω/1% for the bentonite soil.

Evaluating the hydraulic barrier performance of soil-bentonite cutoff walls using the piezocone penetration test

When using cutoff walls to prevent the migration of mobile contaminants in aquifers, we should ensure that these cutoff walls maintain both low hydraulic conductivity and high homogeneity before the start of their operation. However, the on-site assessment of the properties of their main component, soil-bentonite (SB), is challenging because of the difficulty in the obtention of high-quality solid core samples after installation. This paper discusses an experimental approach for on-site quality control/quality assurance (QC/QA) immediately after installation to enhance the reliability of SB cutoff walls as containment barriers. In particular, the piezocone penetration test (CPTU) was conducted using a large-scale soil tank in which SB – prepared with different contents of bentonite powder – was filled to simulate vertically homogeneous or heterogeneous SB cutoff walls. The response to the penetration test varied according to the bentonite content, suggesting that the piezocone penetration test can be used for QC/QA of constructed soil-bentonite cutoff walls. Corrected cone resistance values were larger in layers prepared with lean SB mixture than in those prepared with rich SB mixture, with a difference similar to that of undrained shear strength as evaluated by triaxial compression tests. It was also found that the hydraulic barrier performance of SB cutoff walls could be assessed via a pore pressure dissipation test during CPTU, within one order of magnitude accuracy in a short period. A basic process for QC/QA using the piezocone penetration test in the field is proposed for the practical interpretation of experimental results.

Adsorptive Behavior of Zeolite-Amended Backfills for Enhanced Metals Containment

AbstractThe containment function of soil-bentonite (SB) cutoff walls can be enhanced when the adsorption capacity of the SB backfill for targeted contaminants is increased. In this regard, the potential use of three commercially available zeolites, i.e., two chabazites and a clinoptilolite, as SB backfill amendments to enhance the adsorption capacity for two metal sorbates, potassium (K) and zinc (Zn), was evaluated via batch equilibrium adsorption testing. The adsorptive behaviors of K and Zn to both the unamended and zeolite-amended backfill sorbents were nonlinear over the concentration ranges of interest. Depending on the specific zeolite, the addition of only 5% zeolite increased the adsorption capacity relative to that for the unamended backfill sorbent by a factor ranging from 6.2 to 7.3 for K and from 2.8 to 3.4 for Zn, whereas 10% zeolite amendment increased the adsorption capacity by a factor ranging from 7.5 to 13.5 for K and 3.1 to 3.7 for Zn. The lower increase in adsorption capacity for Zn r...