Search Results (10)

Natural polymer materials are increasingly utilized in drilling fluid additives. Starch has come to be applied extensively due to its low cost and favorable fluid loss reduction properties. However, its poor temperature resistance and high viscosity limit its application in high-temperature wells. This study innovatively introduces for the first time diatomite as an inorganic material in the modification process of starch-based fluid loss additives. Through synergistic modification with acrylamide and acrylic acid, we successfully resolved the longstanding challenge of balancing temperature resistance with viscosity control in existing modification methods. The newly developed fluid loss additive demonstrates remarkable performance: It remains effective at 160 °C when used independently. When added to a 4% sodium bentonite base mud, it achieves an 80% fluid loss reduction rate—significantly higher than the 18.95% observed in conventional starch-based products. The resultant filter cake exhibits thin and compact characteristics. Moreover, this additive shows superior contamination resistance, tolerating 30% NaCl and 0.6% calcium contamination, outperforming other starch-based treatments. With starch content exceeding 75%, the product not only demonstrates enhanced performance but also achieves significant cost reduction compared to conventional starch products (typically containing < 50% starch content). Full article

Buffer material (compacted bentonite), one of the engineered barrier elements in the geological disposal of a high-level radioactive waste, develops swelling stress due to groundwater penetration from the surrounding rock mass. Montmorillonite is the major clay mineral component of bentonite. Even previous studies provide few mechanical and thermodynamic data on Ca-montmorillonite. In this study, thermodynamic data on Ca-montmorillonite were obtained as a function of water content by measuring relative humidity (RH) and temperature. The activities of water and the relative partial molar Gibbs free energies of water were determined from the experimental results, and the swelling stress of Ca-bentonite was calculated using the thermodynamic model and compared with measured data. The activities of water and the relative partial molar Gibbs free energies obtained in the experiments decreased with decreasing water content in water contents lower than about 25%. This trend was similar to that of Na-montmorillonite. The swelling stress calculated based on the thermodynamic model was approximately 200 MPa at a montmorillonite partial density of 2.0 Mg/m³ and approximately 10 MPa at a montmorillonite partial density of 1.4 Mg/m³. The swelling stresses in the high-density region (around 2.0 Mg/m³) were higher than that of Na-montmorillonite and were similar levels in the low-density region (around 1.5 Mg/m³). Comparison with measured data showed the practicality of the thermodynamic model. Full article

This study investigates the performance of two bentonite materials, specifically MX-80 (Na-bentonite) and FEBEX (Ca-Mg-Na-bentonite), employed as engineered barriers in deep geological disposal facilities for the isolation of high-level radioactive waste, contained in metallic canisters. Experiments conducted at the laboratory scale focused on the interaction of these bentonites with FeCl₂ powder, used as a soluble iron source, to observe enhanced alteration of the bentonite. The experiments were carried out under a hydrothermal gradient. A dominant Na-Cl-SO₄ saline solution was put in contact with the compacted bentonites from the top, while a constant temperature of 100 °C was maintained at the bottom using a heater in contact with the layer of FeCl₂. The experimental cells were examined after six months of interaction. Various changes in the physical and chemical properties of the bentonites were observed. An increase in the water content, a reduction in the specific surface area and cation exchange capacity, changes in the distribution of aqueous species, and the formation of secondary minerals were observed. Reaction products formed at the bentonite interface with FeCl₂, primarily comprising akaganeite, goethite, and hematite. The smectites showed evident structural modifications, with an enrichment in iron content, and a shift in the exchangeable ion distribution in the case of MX-80 bentonite. This work provides valuable insights into the complex interactions between bentonite barriers and materials that dissolve iron, serving as proxies for deep geological disposal environments and indicating the potential long-term behavior, taking into account higher concentrations of dissolved iron than those expected in a real repository. Full article

Aluminosilicates are adsorbents able to bind mycotoxins, and their chemical modification increases their affinity to adsorb low-polarity mycotoxins. To further investigate if the inclusion of salts in bentonite modifies its adsorptive capacity, we studied T-2 toxin adsorption in natural bentonite (NB) and when modified with quaternary ammonium salts differing in polarity and chain length: myristyl trimethyl ammonium bromide (B14), cetyl trimethyl ammonium bromide (B16) and benzyl dimethyl stearyl ammonium chloride (B18). The results showed that quaternary salts made bentonite: displace monovalent (Na⁺¹, K⁺¹) and divalent (Mg⁺², Ca⁺²) ions; reduce its porosity; change its compaction and structure, becoming more crystalline and ordered; and modify the charge balance of sheets. T-2 adsorption was higher in all modified materials compared to NB (p ≤ 0.0001), and B16 (42.96%) better adsorbed T-2 compared to B18 (35.80%; p = 0.0066). B14 (38.40%) showed no differences compared to B16 and B18 (p > 0.05). We described the T-2 adsorption mechanism in B16, in which hydrogen bond interactions, Van der Waals forces and the replacement of the salt by T-2 were found. Our results showed that interaction types due to the inclusion in B16 might be more important than the hydrocarbon chain length to improve the adsorptive capacity of bentonite. Full article

In a deep geological disposal system, bentonite buffer material is an important barrier used to protect the disposal canister from the inflow of groundwater and prevent the outflow of radionuclides. This study aimed to characterize the mineralogical and chemical reactions of bentonite caused by copper corrosion of the canister in a radioactive waste repository. We investigated the d-spacings of montmorillonite in Gyeongju bentonite (Ca-type, KJ-I) under groundwater-saturated conditions over 10 years and compared their characteristics with those of Wyoming bentonite (Na-type, MX-80) in the Korea Atomic Energy Research Institute Underground Research Tunnel. Mineralogical investigations using X-ray diffraction and focused ion beam energy-dispersive spectroscopy indicated that no transformation of smectite or neo-formed clay phases occurred. In the Ca-type bentonite (KJ-I), the swelling was observed when it was in contact with rolled plate (RP) and cold-spray-coated (CSC) copper, with d-spacing expansions of 2.9% and 3.8%, respectively. In contrast, the Na-type bentonite (MX-80) showed d-spacing expansions of 17.6% and 19.6% when it was in contact with the RP and CSC Cu, respectively. The Cu concentration and distribution indicated that the corrosion products dissolved and then diffused into the surrounding bentonite, with maximum penetration depths of 2.0 and 0.5 mm over 10 years, respectively. Full article

It is crucial to address the performance deterioration of water-based drilling fluids (WDFs) in situations of excessive salinity and high temperature while extracting deep oil and gas deposits. The focus of research in the area of drilling fluid has always been on filter reducers that are temperature and salt resistant. In this study, a copolymer gel (PAND) was synthesized using acrylamide, N-isopropyl acrylamide, and 3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate through free-radical polymerization. The copolymer gel was then studied using FTIR, NMR, TGA, and element analysis. The PAND solution demonstrated temperature and salt stimulus response characteristics on rheology because of the hydrophobic association effect of temperature-sensitive monomers and the anti-polyelectrolyte action of zwitterionic monomers. Even in conditions with high temperatures (180 °C) and high salinities (30 wt% NaCl solution), the water-based drilling fluid with 1 wt% PAND displayed exceptional rheological and filtration properties. Zeta potential and scanning electron microscopy (SEM) were used to investigate the mechanism of filtration reduction. The results indicated that PAND could enhance bentonite particle colloidal stability, prevent bentonite particle aggregation, and form a compact mud cake, all of which are crucial for reducing the filtration volume of water-based drilling fluid. The PAND exhibit excellent potential for application in deep and ultra-deep drilling engineering, and this research may offer new thoughts on the use of zwitterionic polymer gel in the development of smart water-based drilling fluid. Full article

Compacted bentonite–sand mixture (CBM) is a kind of candidate buffer material of high-level radioactive waste (HLW) disposal in many countries. It is believed that the permeability of CBM is greatly related to its microstructure. The aim of this study was to search the effect of various aqueous mediums on the microstructure and pore characteristics of this buffer material. Permeation experiments and X-ray computerized tomography (X-ray CT) were used to explain the correlation between microstructure and permeability. Representative samples of CBM at a dry density of 1.7 g/cm³ were used. X-ray CT was used to study the CBM under the de-ionized water (DI) and three other aqueous medium conditions. After reconstruction with Dragonfly software, the pore characteristics and permeability of different solution-saturated samples were analyzed using AVIZO software, including pore size distribution (PSD), porosity, and connectivity. The results showed that the permeability coefficient of samples was NaOH > NaCl-Na₂SO₄ > Simulated Beishan groundwater > DI water, and the maximum swelling pressure of samples was NaOH < NaCl-Na₂SO₄ < Simulated Beishan groundwater < DI water. The permeability coefficient decreased with the increasing of maximum swelling pressure. Quantitative analysis indicated that the volume of interconnected pores increased owing to the infiltration of NaCl-Na₂SO₄ and NaOH. Full article

Compacted bentonite is envisaged as engineering buffer/backfill material in geological disposal for high-level radioactive waste. In particular, Na-bentonite is characterised by lower hydraulic conductivity and higher swelling competence and cation exchange capacity, compared with other clays. A solid understanding of the hydraulic behaviour of compacted bentonite remains challenging because of the microstructure expansion of the pore system over the confined wetting path. This work proposed a novel theoretical method of pore system evolution of compacted bentonite based on its stacked microstructure, including the dynamic transfer from micro to macro porosity. Furthermore, the Kozeny–Carman equation was revised to evaluate the saturated hydraulic conductivity of compacted bentonite, taking into account microstructure effects on key hydraulic parameters such as porosity, specific surface area and tortuosity. The results show that the prediction of the revised Kozeny–Carman model falls within the acceptable range of experimental saturated hydraulic conductivity. A new constitutive relationship of relative hydraulic conductivity was also developed by considering both the pore network evolution and suction. The proposed constitutive relationship well reveals that unsaturated hydraulic conductivity undergoes a decrease controlled by microstructure evolution before an increase dominated by dropping gradient of suction during the wetting path, leading to a U-shaped relationship. The predictive outcomes of the new constitutive relationship show an excellent match with laboratory observation of unsaturated hydraulic conductivity for GMZ and MX80 bentonite over the entire wetting path, while the traditional approach overestimates the hydraulic conductivity without consideration of the microstructure effect. Full article

Shaft seals are geotechnical barriers in nuclear waste deposits and underground mines. The Sandwich sealing system consists of alternating sealing segments (DS) of bentonite and equipotential segments (ES). MiniSandwich experiments were performed with blended Ca-bentonite (90 mm diameter and 125 mm height) to study hydration, swelling, solute transport and cation exchange during hydration with A3 Pearson water, which resembles pore water of Opalinus Clay Formation at sandy facies. Two experiments were run in parallel with DS installed either in one-layer hydrate state (1W) or in air-dry two-layer hydrate (2W) state. Breakthrough at 0.3 MPa injection pressure occurred after 20 days and the fluid inlet was closed after 543 days, where 4289 mL and 2984 mL, respectively, passed both cells. Final hydraulic permeability was 2.0–2.7 × 10⁻¹⁷ m². Cells were kept for another 142 days before dismantling. Swelling of DS resulted in slight compaction of ES. No changes in the mineralogy of the DS and ES material despite precipitated halite and sulfates occurred. Overall cation exchange capacity of the DS does not change, maintaining an overall value of 72 ± 2 cmol(+)/kg. Exchangeable Na⁺ strongly increased while exchangeable Ca²⁺ decreased. Exchangeable Mg²⁺ and K⁺ remained nearly constant. Sodium concentration in the outflow indicated two different exchange processes while the concentration of calcium and magnesium decreased potentially. Concentration of sulfate increased in the outflow, until it reached a constant value and chloride concentration decreased to a minimum before it slightly increased to a constant value. The available data set will be used to adapt numerical models for a mechanism-based description of the observed physical and geochemical processes. Full article

With the aim to determine the influence of dominant interlayer cation on the sorption and diffusion properties of bentonite, diffusion experiments with Sr on the compacted homoionous Ca- and Na-forms of Czech natural Mg/Ca bentonite using the planar source method were performed. The bentonite was compacted to 1400 kg·m⁻³, and diffusion experiments lasted 1, 3 or 5 days. Two methods of apparent diffusion coefficient D_a determination based on the analytical solution of diffusion equation for ideal boundary conditions in a linear form were compared and applied. The determined D_a value for Ca-bentonite was 1.36 times higher than that for Na-bentonite sample. Values of K_d were determined in independent batch sorption experiments and were extrapolated for the conditions of compacted bentonite. In spite of this treatment, the use of K_d values determined by batch sorption experiments on a loose material for the determination of effective diffusion coefficient D_e values from planar source diffusion experiments proved to be inconsistent with the standard Fickian description of diffusion taking into account only the pore diffusion in compacted bentonite. Discrepancies between K_d and D_e values were measured in independent experiments, and those that resulted from the evaluation of planar source diffusion experiments could be well explained by the phenomenon of surface diffusion. The obtained values of surface diffusion coefficients D_s were similar for both studied systems, and the predicted value of total effective diffusion coefficient D_e(tot) describing Sr transport in the Na-bentonite was four times higher than in the Ca-bentonite. Full article