Bentonite Water Research Articles

Development of a multiparametric system based on solid-state microsensors for monitoring a nuclear waste repository

Nuclear waste repositories are being installed in deep excavated rock formations in some places in Europe to isolate and store radioactive waste. Containers with radioactive waste are also protected with barriers made from porous materials such as bentonite. The objective of this work is to study the transport of radioactive compounds thorough bentonite models to obtain a database of the bentonite–water interaction processes. Among the chemical parameters tested in these barriers, the most significant are pH, conductivity and redox potential. For that purpose, solid-state microsensors fabricated with silicon semiconductor technology such as ion sensitive field effect transistors (ISFETs) for measuring pH and interdigitated structures (IDS) for measuring conductivity and redox potential were used. Response characteristics of these sensors were tested in aqueous samples with compositions similar to those present inside a bentonite barrier and results were compared with those obtained with commercial electrodes obtaining a good agreement between commercial and our sensors.

Influences of nonionic poly(ethylene glycol) polymer PEG on electrokinetic and rheological properties of bentonite suspensions

AbstractThe determination of the electrokinetic properties of colloidal systems is very important for the chracterization of these systems. Colloidal systems have high adsorption performance due to the carrying of negative charges and the colloid structure. The control of the electrokinetic properties of the bentonite–water system are important not only from a technological point view; they are also important from a scientific point of view. Knowing the electrokinetic and rheological properties of bentonite minerals is important for the estimation of the behavior of clays under various environmental conditions. The purpose of this study was to interpret the effect of the nonionic poly(ethylene glycol) (PEG) polymer on electrokinetic and rheological properties. Zeta potential and viscosity measurements were done as a function of PEG molecular weights (400, 3000, and 8000) and their concentrations (2.5 × 10−5 to 1.25 × 10−2 mol/L). We interpreted the experimental data, taking into account these two parameters. X‐ray diffaction studies were done together with the electrokinetic and rheological measurements. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 341–346, 2002

By particle interactions and rheological properties of bentonites+ALS suspensions

The influence of an anionic surfactant, ammonium lauryl sulfate (ALS), on the flow behaviour and colloidal properties of bentonite suspensions (2% w/w) was studied with two objectives. The first one was to determine the rheological properties of three types of bentonite–water systems: two of which were prepared using natural Ca- and Na-bentonites, and the other one from soda-activated bentonite. The second objective was to describe the particle interactions of the three types of bentonite with ALS in the concentration range of 10 −4–10 −2 mol/l.

The effect of SDS surfactant on the flow and zeta potential of bentonite suspensions

The influence of the surfactant on the flow behaviour of bentonite suspensions (2% w/w) was studied for an anionic surfactant, sodium dodecyl sulphate (SDS). In the range of 10 −4–10 −2 mol/l, SDS was added to the bentonite water system in eight different concentrations and the observed result was the different effects on the viscosity, which is related to the interactions among particles and surfactant, particles and particles, and particles and water molecules. IR studies have been carried out in parallel to the viscosity and zeta potential studies. Based on the structural changes due to the SDS additions, the rheological and colloidal properties of the altered bentonite–water systems have been interpreted.

Effect of Mud Compositions on the Rheological Behavior

The aim of this work is to study the effect of mud compositions on it’s rheological behavior under high temperature conditions. Seventeen samples of five types of water base mud in which (fresh water bentonite mud. Lignosulphonate mud, gypsum mud, polymer mud, and salt saturated mud) were tested with different temperatures using the fann viscometer model 50-c. All the tested samples, except the fresh water bentonite mud, have the same trend reduction in both plastic viscosity and yield point with increasing temperature. Six rheological models has been adapted: Bingham plastic, power law, Casson model represent the laboratory data accurately

Membrane filtration of surface water in the presence of ozone

The preliminary study investigated the effect of pre-ozonation of synthetic raw water (bentonite and humic acid) on membrane fouling. The results showed that humic acid, not bentonite, was the dominant factor in membrane fouling. When the synthetic raw water was pre-treated using ozone and activated carbon, stable operation was possible at twice the flux of membrane filtration without pre-treatment. Thus, ozone and activated carbon reduced the concentration of organic matter (humic acid), leading to an increase in flux. Secondly, an MF membrane filtration device with ozone tolerance was attached downstream of the ozone reactor so that residual ozone could reach the membrane surface. When water was treated with MF membrane filtration in the presence of ozone, the flux was stable at 4 m/d. The membrane filtration resistance increased when ozone was not injected, and decreased when it was injected. This phenomenon was repeatable. In the presence of ozone, organic matter that could accelerate fouling as decomposed and converted to less fouled materials, resulting in a suppression of fouling as well as facilitating removal of the fouling layer during back washing.

Microfiltration through an inorganic tubular membrane with high frequency retrofiltration

High frequency backpulsing is a promising technique of flux enhancement that could contribute to the development of cross-flow micro-/ultrafiltration in water and wastewater treatment. A systematic study of the influence of the operational parameters was carried out with three suspensions, bentonite in tap water, biologically treated wastewater and activated sludge. The alumina membranes were tubular (0.02, 0.05 or 0.2 μm), with internal or external skin, the latter being not suitable. The technique was particularly efficient for bentonite; a minimal cross-flow velocity was required to reach a net flux independent of the cross-flow. The results are less good for the biological suspensions since the same fluxes could be reached by an increase of cross-flow velocity. However, the energy required by high frequency backpulsing is lower. The average reverse fluxes, measured by a tracer method, are surprisingly high and could hamper the development of the technique. At low Reynolds number ( Re=3500), the net flux increased with the reverse flux, then reached a plateau corresponding to the total penetration of the laminar layer against the membrane wall by the backwash water.

Prediction of cross-flow microfiltration through an inorganic tubular membrane with high-frequency retrofiltration

High-frequency retrofiltration is a promising technique of flux enhancement, which should contribute to the development of cross-flow microfiltration. Most published models have assumed cake deposit in the forward filtration phase, incomplete cleaning by backwash, and delays in cake formation and erosion. However, they were fitted to the overall net flux since the transient signals could not be monitored. The experimental set-up of this work allowed obtaining the forward flux response to periodical backpulsing and measuring the average reverse flux. The tested suspensions were bentonite in tap water and biologically treated wastewater. Average reverse flux was accurately measured by two different methods leading to the same results. Moreover most parameters, introduced in the published models, were experimentally measured and not fitted to the results as previously, e.g. the cleaning efficiency, which has been an adjusted parameter, was measured by two methods leading to the same value. The forward flux responses are not in agreement with the models. Moreover, the models do not accurately predict the average reverse flux when the suspension interacted with the membrane. The average reverse flux could even be higher than the forward flux, which could hamper the economical achievement of the technique. However, the optimal frequency was fairly well predicted by all the models for both the suspensions. A method of determination of the net flux and the optimal conditions was proposed. This method is based on the forward flux response to one pulse obtained when the system is well stabilised; it accurately predicted the net flux.

Interactions of polyacrylamide polymer with bentonite in aqueous systems

The flow properties of natural Ca bentonite and Na bentonite–water systems were studied after adding an anionic polyacrylamide (PAM) polymer. The effect of the PAM has also been investigated at different quantities. The experimental results are discussed in terms of bentonite forms and concentration of PAM. Besides, measurement of rheological properties of Ca bentonite+PAM and Na bentonite+PAM systems have been examined in detail through XRD, FT-IR and DTA analyses.

Solidification/stabilization of a tannery waste with blended cement and wyoming bentonite

The solidification/stabilization of a tannery waste, which has a high chromium content, was studied by thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA). Pastes prepared with water, cement, tannery waste and Wyoming bentonite were analyzed after different setting times during the first 28 days of solidification. In the present work it is clear that Wyoming bentonite combined with waste affects cement hydration, while bentonite alone does not affect it significantly. The presence of the waste results in a small acceleration of the cement hydration reactions, probably due to the presence of extra Ca and alkalinity in the waste. When waste is present in the sample during TG and DTG analysis, it is burned to carbon dioxide, which partially reacts with the calcium hydroxide formed during cement hydration. This results in an underestimate of the calcium hydroxide content of the solidified sample. The greater the degree of hydration of the waste‐containing cement sample, the greater the amount of carbon dioxide absorbed.

The influence of cationic surfactants on rheological properties of bentonite–water systems

The influence of surfactants on the flow behaviour of bentonite–water systems (2% w/w) was studied for two cationic surfactants, cetyltrimethylammonium bromide (CTAB) and distearlydimethylammonium chloride (DDAC), in the range of 10 −5–10 −2 mol/l. These surfactants were added to Ca- and Na-bentonite–water systems in seven different concentrations and the observed result was the different effects on the viscosity, which is related to the interactions between particles and surfactant, particles and particles, and particles and water molecules. The adsorption of cationic surfactant on a charged surface leads to significant modification of the charge distribution in the electrical double layer, and, thus, in the interaction of particles with each other.

Coupled Thermo-Hydro-Geochemical Models of Engineered Barrier Systems: The Febex Project

ABSTRACTFEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository (HLWR). It includes two main experiments: an situ full-scale test performed at Grimsel (GTS) and a mock-up test operating since February 1997 at CIEMAT facilities in Madrid (Spain) [1,2,3]. One of the objectives of FEBEX is the development and testing of conceptual and numerical models for the thermal, hydrodynamic, and geochemical (THG) processes expected to take place in engineered clay barriers. A significant improvement in coupled THG modeling of the clay barrier has been achieved both in terms of a better understanding of THG processes and more sophisticated THG computer codes. The ability of these models to reproduce the observed THG patterns in a wide range of THG conditions enhances the confidence in their prediction capabilities. Numerical THG models of heating and hydration experiments performed on small-scale lab cells provide excellent results for temperatures, water inflow and final water content in the cells [3]. Calculated concentrations at the end of the experiments reproduce most of the patterns of measured data. In general, the fit of concentrations of dissolved species is better than that of exchanged cations. These models were later used to simulate the evolution of the large-scale experiments (in situ and mock-up). Some thermo-hydrodynamic hypotheses and bentonite parameters were slightly revised during TH calibration of the mock-up test. The results of the reference model reproduce simultaneously the observed water inflows and bentonite temperatures and relative humidities. Although the model is highly sensitive to one-at-a-time variations in model parameters, the possibility of parameter combinations leading to similar fits cannot be precluded. The TH model of the “in situ” test is based on the same bentonite TH parameters and assumptions as for the “mock-up” test. Granite parameters were slightly modified during the calibration process in order to reproduce the observed thermal and hydrodynamic evolution. The reference model captures properly relative humidities and temperatures in the bentonite [3]. It also reproduces the observed spatial distribution of water pressures and temperatures in the granite. Once calibrated the TH aspects of the model, predictions of the THG evolution of both tests were performed. Data from the dismantling of the in situ test, which is planned for the summer of 2001, will provide a unique opportunity to test and validate current THG models of the EBS.

Simfuel Leaching Experiments in Presence of Gamma External Source (60CO)

One of the factors considered within the studies of performance assessment on spent fuel under final repository conditions is the effect of the radiation on its leaching behavior. Radiation from spent fuel can modify some properties of both solid phase and leachant and therefore it would alter the chemical behavior of the near field. Particularizing in the effect of the radiation on the leachant, it will cause generation of radiolytic species that could change the redox potential of the environment and therefore may bring on variations in the leaching process. In this work, the chemical analogue utilized was SIMFUEL (natural UO 2 doped with non-radioactive elements simulating fission products) and the leachants selected were saline and granite bentonite waters both under initial anoxic conditions. To emulate γ radiation field of a spent fuel, leaching experiments with external 60 Co sources in a irradiation facility (Nayade) were performed. Initial dose rate used was 0.014 Gy/s. Preliminary results indicate that radiation produces an increase of the uranium dissolution rate, being the concentrations measured close to those obtained in oxic atmosphere without radiation field. In addition the solubility solid phases from experimental conditions were calculated, for both granite bentonite water and 5 m NaCl media. On the other hand, a tentative approach to model the role of γ radiolysis in these SIMFUEL tests has been carried out as well.

Influences of Electrolytes, Polymers and a Surfactant on Rheological Properties of Bentonite–Water Systems

Characteristic rheological properties, such as viscosity, shear stress, yield point, gel strength and thixotropy, of natural Ca- bentonite and Na-peptized bentonite were studied after adding LiCl, KCl, CaCl2, MgCl2·6H2O electrolytes; (NaPO3)n, polyvinyl pyrolidone (PVP) polymers and an anionic surfactant (linear alkyl benzene sulphonate, LABS). Changes in flow properties under the influence of various additives at different quantities were investigated in these slurries. The experimental results are discussed in terms of bentonite forms, types and concentrations of additives and influence of exchangeable cations. Bivalent and monovalent cations display entirely different rheological properties in two groups of muds. Furthermore, the difference in the degree of activity of PVP polymer on the viscosity of two mud systems depend on the clay mineral structure. The slurry prepared with Na-bentonite contains a minimum number of tactoids and a maximum number of sheet-bearing clay particles, which reduces the surface area of the clay minerals and increases viscosity by adding PVP polymer.

Effect of Shear Displacement Rate on Internal Shear Strength of a Reinforced Geosynthetic Clay Liner

Torsional ring shear tests were performed to evaluate the effect of shear displacement rate on the internal shear strength of a needle-punched geosynthetic clay liner (GCL) under different normal stresses. The test results suggest that the internal shear strength of the needle-punched GCL depends on the following three factors: (i) resistance against reinforcement fibers pulling out and/or tearing; (ii) amount of positive pore-water pressure induced during shear; and (iii) bentonite water content at the time of shearing. The laboratory tests indicate that the net effect of these three factors result in the peak internal shear strength being less sensitive to shear displacement rate at normal stresses between 200 and 400 kPa than at normal stresses less than 200 kPa. Shear displacement rate appears to have little influence on the residual internal shear strength regardless of normal stress. The amount of shear displacement required to reach the peak and residual internal shear strengths is dependent on the shearing normal stress, shear displacement rate, and quantity of needle-punched fibers.

An Evaluation of Hydrogen Evolution from Corrosion of Carbon Steel in Low/Intermediate Level Waste Repositories

AbstractAs a sequence of studies to evaluate the quantity of gas evolution from low/intermediate level waste repositories,hydrogen gas evoluted from corrosion of carbon steel in simulated repository environment was evaluated by laboratory experiments. The experimental results on the hydrogen gas evolution both in air purging condition simulated oxidizing environment and nitrogen purging condition simulated reducing environment, are summarized as follows.(1)Hydrogen gas evolution enough to analyze quantitavely by gas chromatography (>5ppm) has been recognized under almost all test conditions except reducing equilibrium cement water.(2)Effects of purging gas (air,nitrogen) on the hydrogen gas evolution and the corrosion rate calculated from weight loss were air purge > nitrogen purge. On the other hand, the contribution ratio of hydrogen evolution reaction in corrosion rate was nitrogen purge > air purge.(3)Effects of test solution on the hydrogen evolution rate were as fo11ows. • Air Purge :Equilibrium Bentonite Water ≈ Equilibrium Cement Water > Synthetic Sea Watert• N2 Purge:Synthetic Sea Water > Equilibrium Bentonite Water >> Equilibrium Cement Water(4)No distinct effect of crevice geometry of test specimen on hydrogen evolution rate was recognized. Only under the reducing equilibrium cement water, however, the increase of hydrogen evolution was confirmed after the immersion of several hundred hours.(5)Hydrogen evolution rates tended to decrease with testing time except in the reducing equilibrium cement water.(6)No distinct difference of hydrogen evolution rate between steels (SPHC, SPCC) was observed.

Coupled Chemical and Diffusion Model for Compacted Bentonite

AbstractA chemical equilibrium model has been developed for ion-exchange and to a limited extent for other reactions, such as precipitation or dissolution of calcite or gypsum, in compacted bentonite water systems. The model was successfully applied to some bentonite experiments, especially as far as monovalent ions were concerned. The fitted log-binding constants for the exchange of sodium for potassium, magnesium, and calcium were 0.27, 1.50, and 2.10, respectively. In addition, a coupled chemical and diffusion model has been developed to take account of diffusion in pore water, surface diffusion and ion-exchange. The model was applied to the same experiments as the chemical equilibrium model, and its validation was found pardy successful. The above values for binding constants were used also in the coupled model. The apparent (both for anions and cations) and surface diffusion (only for cations) constants yielding the best agreement between calculated and experimental data were 3.0×10-11 m2/s and 6.0×10-12m2/s, respectively. These values are questionable, however, as experimental results good enough for fitting are currently not available.

New Bentonite Extension Test Provides A Better Gel Quality Evaluation

Abstract A bentonite extension (BEXT) lest has been developed as a bentonite quality control procedure. Unlike the API bentonite quality control test, the HEXT test will differentiate between poorer and better grades of bentonitic ores. The BEXT lest generates an ultimate yield point for a bentonite based upon that bentonite's maximum extendability in fresh water. Beneficiating polymers commercially added to bentonite samples do not affect ultimate yield point values. Bentonite samples with ultimate yield paints greater than 30 pascals are shown to produce fresh water bentonite muds with acceptable rheological properties. Poorer quality bentonites having ultimate yield points of less than 16 pascals do not give adequate yield points or gel values. Data presented from the BEXT test correlates closely to western Canadian drilling performance. Field data demonstrate that faster drilling rates and fewer hole problems have been realized when good quality bentonites, as specified by the BEXT test, have been used. A review of case histories for foothills wells indicates better hole cleaning and improved suspension properties have been observed when poorer quality bentonites were replaced by better quality gels. Drilling costs have been significantly reduced when better quality bentonites are used for fresh water drilling operations. Introduction Improved hole cleaning and suspension characteristics or drilling fluids have commonly been associated with reduced drilling problems. This is especially true when fresh water systems normally associated with significant hole washouts are used. Most of Shell Canada's rheological problems in recent years have been associated with poor quality bentonite. Therefore, a quality control program was initiated ror bentonitic clays to reduce drilling problems and mud costs in the field. This paper discusses testing procedures as well as field results for fresh water drilling fluids. Gel/XC polymer costs have been reduced by at least 37% in areas where the program has been implemented. Bentonite Quality Most bentonitic days used in the drilling industry have beneficiating agents added during milling operations. .Although the agents have qualified interior clays to API specifications, problems meeting our rheological specifications in the field have been observed where poor quality bentonite has been used(1). With additions of poor quality bentonite minimal increases in yield point and initial gels have been observed, while methylene blue test values, plastic viscosity, gel progression and % sounds increase significantly making the drilling fluid more susceptible to contamination as well as more costly. In contrast, with higher quality bentonite additions both yield point and initial gel values improve significantly. The current approved use of extending polymers to upgrade bentonite has led to concern about true bentonite quality(2). A new method to ensure bentonite quality is required to replace the current API procedure. Alternate quality procedures for bentonite have been proposed, however, none of these methods quantitatively measure raw bentonite quality(3,4). Bentonite Extension Text (BEXT Test) The BEXT test was developed to quantitatively measure bentonite quality. This procedure measures the maximum yield potential of bentonite samples for a standard bentonite extender Alcomer 1773.

Methods to measure apparent diffusion coefficients in compacted bentonite clays and data interpretation

The methods used to determine apparent diffusion coefficients and the appropriate parameters for modelling diffusion through compacted bentonite–water systems are assessed and discussed. The measured apparent diffusion coefficient can vary between methods. The discrepancies are shown to be due to heterogeneous diffusivities arising from the proximity of the surface of clay particles. Two different diffusivity pathways are identified and the diffusive flux is shown to be dictated by the charge of diffusing species, diffusion time, and soil fabric. Key words: apparent diffusion coefficient, methods, compacted bentonite, heterogeneous diffusion, parameters, pathways.

Ozone‐Induced Particle Destabilization

The purpose of this study was to gain insight into the mechanisms that are operative in ozone‐induced particle destabilization. Both the nature of background dissolved organic matter and the nature of the particles themselves were investigated. It appears that commercial humic acid preparations and natural dissolved organic matter respond differently to ozonation. The analyses performed suggest that polymerization of metastable organics is the primary mechanism responsible for ozone‐induced particle destabilization in a natural water–bentonite system.