In the present work, a novel heterogeneous photo-Fenton catalyst was prepared by iron and cerium pillared bentonite. The catalyst Fe-Ce/bentonite was characterized by X-ray diffraction （XRD）, X-ray fluorescence （XR...In the present work, a novel heterogeneous photo-Fenton catalyst was prepared by iron and cerium pillared bentonite. The catalyst Fe-Ce/bentonite was characterized by X-ray diffraction （XRD）, X-ray fluorescence （XRF）, Brunauer-Emmett-Teller （BET） and scanning electron microscopy （SEM） methods. It is found that Fe and Ce intercalate into the silicate layers of bentonite successfully. Tetracycline was removed by heterogeneous photo-Fenton reaction using the catalyst in this work. The effects of different reaction systems, hydrogen peroxide concentration, initial pH, catalyst dosage, UV power and introduction of different anions on degradation were investigated in details. The stability of catalyst was investigated through recycling experiment. The results show that removal rate of tetracycline is 98.13% under the conditions of 15 mmol/L H202, 0.50 g/L catalyst dosage, initial pH 3.0, 11 W UV lamp power and 60 min reaction time. However, the removal rate decreases after adding some anions. The hydroxyl radical plays an important role in heterogeneous photo-assisted Fenton degradation of tetracycline. The catalyst is very stable and can be recycled many times.展开更多
Polymer-modified bentonite(PMB)is much more effective at containing chemically aggressive liquids than conventional bentonite.The PMB manufacturing process typically utilizes natural,high-quality sodium bentonite(NaB)...Polymer-modified bentonite(PMB)is much more effective at containing chemically aggressive liquids than conventional bentonite.The PMB manufacturing process typically utilizes natural,high-quality sodium bentonite(NaB)owing to its excellent hydrophilicity and swelling capacity.However,calcium bentonite(CaB),which is much more abundant worldwide,is rarely used for containment applications owing to its poor hydrophilicity.This study proposed a polymerization method that transforms sodium-activated calcium bentonite(NCB)into PMB to achieve low hydraulic conductivity(k)to aggressive liquids.The mechanism for its low k was revealed through characterization techniques and analyses(e.g.X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),and Brunauer-Emmett-Teller(BET)).The results showed that the PMB had a small amount of polymer elution(indicating better interface stability)and thus exhibited excellent barrier properties under chemically aggressive conditions,with the k of<10^(-11) m/s for 0.6 mol/L NaCl solution,which is four orders of magnitude lower than that of the NCB(k=3×10^(-7) m/s).Various microscopic analyses indicated that the selected monomers were successfully polymerized,and intercalated into and grafted onto the montmorillonite layers of bentonite.The formed polymer network increased the swelling capability of PMB granules,decreased the pore size,and created narrow and tortuous flow pathways leading to a very low k to aggressive liquids.展开更多
Bentonite is a necessary binder in producing pellets.Its excessive use reduces the iron grade of pellets and increases production costs.Minimizing bentonite dosage is essential for producing high-quality iron ore pell...Bentonite is a necessary binder in producing pellets.Its excessive use reduces the iron grade of pellets and increases production costs.Minimizing bentonite dosage is essential for producing high-quality iron ore pellets.Addressing the gap in the application of organically-intercalated modified bentonite in the pelletizing field,this study introduces an innovative modification process for bentonite that employs the synergistic effect of mechanical force and dimethyl sulfoxide to enhance the intercalation of organic compounds within bentonite,thus significantly enhancing its binding performance.The colloid value and swell capacity of modified bentonite(98.5 m L/3g and 55.0 m L/g)were much higher than the original bentonite(90.5 m L/3g and 17.5 m L/g).With the decrease of bentonite dosage from1.5wt%to 1.0wt%,the drop number of green pellets from a height of 0.5 m and the compressive strengths of roasted pellets using the modified bentonite(6.0 times and 2916 N per pellet)were significantly higher than those of the original bentonite(4.0 times and 2739 N per pellet).This study provides a comprehensive analysis of the intercalation modification mechanism of bentonite,offering crucial technical insights for the development of high-performance modified bentonite as iron ore pellet binders.展开更多
Acid mine drainage(AMD)leachate is a global pollutant issue that impacts groundwater environment quality.This study investigated the feasibility of a composite biopolymer-amended bentonite as a geosynthetic clay liner...Acid mine drainage(AMD)leachate is a global pollutant issue that impacts groundwater environment quality.This study investigated the feasibility of a composite biopolymer-amended bentonite as a geosynthetic clay liner core material to contain AMD leachate.The real AMD leachate with a pH of 3.1,sourced from an acidic pyrite tailings site,was employed as a specific test leachate used in this study.The composite biopolymer was composed of welan gum(WG)and xanthan gum(XG)at different dry weight-based ratios.Modified fluid loss(MFL)tests were conducted to evaluate hydraulic conductivity(k)of bentonites to optimize WG:XG ratio.Rheological properties of biopolymer solutions were measured,serving as indicative parameters of biopolymer elution.The results indicated biopolymer-amended bentonites with the WG:XG ratio of 8:2 possessed lowest k(1.5×10^(−11)m/s to 7.2×10^(−11)m/s),lower than unamended bentonite(1.2×10^(−10)m/s to 8.6×10^(−10)m/s)in the AMD leachate condition.In addition,biopolymer solutions with WG:XG ratio of 8:2 exhibited highest viscosity.Thermogravimetric analysis,ultraviolet–visible spectroscopy,and Fourier transform infrared spectroscopy were conducted on the composite biopolymer,revealing that WG and XG interacted via physical cross-linking.Additionally,scanning electron microscopy and atomic force microscopy images indicated that a physical cross-linking and dense network structure conformation was developed in the composite biopolymer hydrogel at the WG:XG ratio of 8:2.The results demonstrate that the composite biopolymer is a promising low-carbon amendment material for enhancing containment performance of bentonite used in geosynthetic clay liners to contain AMD leachate.展开更多
Bentonite is a very useful material for improving soil properties,which enhances the ability of plants to grow and produce in different conditions.The experiment was carried out in an agricultural nursery in one of th...Bentonite is a very useful material for improving soil properties,which enhances the ability of plants to grow and produce in different conditions.The experiment was carried out in an agricultural nursery in one of the areas of the City of Diwaniyah,in a house covered with green netting,with a shade rate of 25%,to study the effect of bentonite and humic acid on the growth and flowering of a Catharanthus roseus L.plant in sandy soil.The experiment included two factors:the first factor was bentonite clay,and the second factor was humic acid.Using a randomized complete block design(R.C.B.D)with three replications,data were analyzed using the analysis of variance(ANOVA)method,and comparison was made according to the least significant difference(L.S.D)test at a probability level of 0.05.The experiment consisted of adding bentonite clay at 0,2,6,and 8 g L-1,humic acid at 0,0.5,1,and 10 g L-1.The results showed that adding bentonite clay and humic acid to sandy soil can have a significant positive effect on the growth and flowering of the Catharanthus roseus plant grown in poor sandy soil conditions.Bentonite,clay and humic acid were added at concentrations of 8 and 10 g L-1,which led to an increase in plant height and number of leaves and leaf area.They reached 30.07,23.84 cm2,76.62,63.42 cm2 for leaf-1 and 24.73,20.22 cm2 for leaf-1,respectively.The results also showed an increase in the content of nitrogen(N),phosphorus(P),and potassium(K)in leaves by 2.27,1.92,1.99%and 1.51,1.22,1.77%.This also led to an increase in chlorophyll pigment and anthocyanin at the highest concentration and gave the highest value.Therefore,adding bentonite and humic acid together gave the highest values in vegetative and chemical characteristics,compared to treatments without addition.展开更多
The corrosion of waste canisters in the deep geological disposal facilities(GDFs)for high-level radioactive waste(HLRW)can generate gas,which escapes from the engineered barrier system through the interfaces between t...The corrosion of waste canisters in the deep geological disposal facilities(GDFs)for high-level radioactive waste(HLRW)can generate gas,which escapes from the engineered barrier system through the interfaces between the bentonite buffer blocks and the host rock and those between the bentonite blocks.In this study,a series of water infiltration and gas breakthrough experiments were conducted on granite and on granite-bentonite specimens with smooth and grooved interfaces.On this basis,this study presents new insights and a quantitative assessment of the impact of the interface between clay and host rock on gas transport.As the results show,the water permeability values from water infiltration tests on granite and granite-bentonite samples(10−19-10−20m^(2))are found to be slightly higher than that of bentonite.The gas permeability of the mock-up samples with smooth interfaces is one order of magnitude larger than that of the mock-up with grooved interfaces.The gas results of breakthrough pressures for the granite and the granite-bentonite mock-up samples are significantly lower than that of bentonite.The results highlight the potential existence of preferential gas migration channels between the rock and bentonite buffer that require further considerations in safety assessment.展开更多
In the deep geological disposal repository of high-level radioactive waste,buffer/backfill materials typically consist of compacted bentonite block and granular bentonite.As these materials undergo a long-term hydrati...In the deep geological disposal repository of high-level radioactive waste,buffer/backfill materials typically consist of compacted bentonite block and granular bentonite.As these materials undergo a long-term hydration,it is anticipated that the two forms of bentonite materials(i.e.compacted bentonite powder(CBP)and granular bentonite(GB))are expected to exhibit differing hydro-mechanical behaviors due to the differences in their structures.This work aims to investigate the differences in swelling pressure and compressibility through a series of swelling pressure tests,compression tests and mercury intrusion porosimetry(MIP)tests.The experimental results demonstrated that swelling pressure curves of the CBP specimens showed higher first peak values and more pronounced collapse than those of the GB specimens at a given dry density,regardless of vapor-water hydration or liquid-water hydration.The final swelling pressures of the two materials were similar at the same dry density,suggesting an independent correlation between swelling pressure and dry density.At the high suction range,the compression curves exhibited an obvious bi-linear pattern for the CBP specimens and a significant nonlinearity for the GB specimens.Meanwhile,the CBP specimens presented higher pre-consolidation pressures and larger compression indices than the GB specimens at a given suction.As suction decreased,the compression curves of the two materials gradually approached each other and their differences were reduced accordingly.After reaching saturation,a good consistency between them was observed whether for final swelling pressure or compressibility.Pore structure analysis revealed that the two materials both presented an initially double structure,and their differences were primarily manifested at the macrostructural level.Eventually,the differences in swelling pressure or compression curves of the two materials were well interpreted by combining microstructural evolutions.展开更多
Understanding the mechanisms of gas transport and the resulting preferential pathways formation through bentonite-based barriers is essential for their performance evaluation.In this experimental study,gas migration w...Understanding the mechanisms of gas transport and the resulting preferential pathways formation through bentonite-based barriers is essential for their performance evaluation.In this experimental study,gas migration within a heterogenous mixture of MX80 bentonite pellets and powder with a ratio of 80/20 in dry mass was investigated.A novel X-ray transparent constant volume cell has been developed to assess the effect of gas pressure,material heterogeneities,and water vapor gas saturation on breakthrough pressure and gas pathways.The new cell allows to perform high-resolution X-ray computed micro-tomography(X-ray μCT)scans to track microstructural changes during different phases of saturation and gas injection.Experimental results showed that the gas breakthrough occurred when the pressure was raised to 3 MPa.This is slightly higher than the expected swelling pressure(2.9 MPa)of the bentonite sample.Each gas injection was followed by a long resaturation phase restoring material homogeneity at μCT resolution scale(16 mm).However,the elapsed time needed for gas to breakthrough at 3 MPa diminished at each subsequent injection test.X-ray μCT results also revealed the opening of the specimen/cell wall interface during gas passage.This opening expanded as the injection pressure increased.The gas flow along the interface was associated with the development of dilatant pathways inside the sample,although they did not reach the outlet surface.It was observed that the water vapor gas saturation had no effect on the breakthrough pressure.These findings enhance the understanding of the complex mechanisms underlying microstructural evolution and gas pathway development within the highly heterogeneous mixture.The experimental outcomes highlight the effectiveness of X-ray μCT to improve quality protocols for engineering design and safety assessments of engineered barriers.展开更多
Flexible wearable electronic devices based on hydrogels have immense potential in a wide range of applications.However,many existing strain sensors suffer from significant limitations including poor mechanical propert...Flexible wearable electronic devices based on hydrogels have immense potential in a wide range of applications.However,many existing strain sensors suffer from significant limitations including poor mechanical properties,low adhesion,and insufficient conductivity.To address these challenges,this study successfully developed an organic-inorganic double-network conductive hydrogel using acrylic-modified bentonite (AABT) as a key component.The incorporation of AABT significantly enhanced the mechanical properties of the ATHG@LiCl hydrogel,achieving an impressive stretchability of 4000% and tensile strength of 250 kPa.Moreover,it improved the electrical conductivity of the hydrogel to a maximum of 1.53 mS/cm.The catechol structure of tannic acid (TA) further augmented the adhesive properties of the ATHG@LiCl hydrogel toward various substrates such as copper,iron,glass,plastic,wood,and pigskin.The addition of lithium chloride (LiCl) and dimethyl sulfoxide(DMSO) endowed the hydrogel with exceptional freezing resistance and flexibility,even at low temperatures of-20℃.Remarkably,the hydrogel maintained a conductivity of 0.53 mS/cm under these conditions,surpassing the performance of many other reported hydrogels.Furthermore,the ATHG@LiCl hydrogel demonstrated outstanding characteristics,such as high sensitivity (gauge factor GF=4.50),excellent transparency (90%),and reliable strain-sensing capabilities,indicating that the ATHG@LiCl hydrogel is a highly promising candidate for flexible wearable soft materials,offering significant advancements in both functionality and performance.展开更多
Predicting the gas diffusion coefficient of water-saturated Na-bentonite is crucial for the overall performance of the geological repository for isolating high-level radioactive waste(HLW).In this study,a conceptual m...Predicting the gas diffusion coefficient of water-saturated Na-bentonite is crucial for the overall performance of the geological repository for isolating high-level radioactive waste(HLW).In this study,a conceptual model that incorporates a multi-porosity system was proposed,dividing the pore space into free water pores,interlayer water pores,and diffuse double layer(DDL)water pores,to describe the molecular diffusion behaviour of the dissolved gas in saturated bentonite.In this model,gas diffusion in these three porosities is considered as independent and parallel processes.The apparent gas diffusion coefficient is quantified by applying weighted approximations that consider the specific porosity,tortuosity factor,and constrictivity factor within each porosity domain.For verification,experimental data from gas diffusion tests on saturated MX-80 and Kunipia-F bentonite specimens across a wide range of dry densities were utilized.The proposed model could successfully capture the overall trend of the apparent gas diffusion coefficient for bentonite materials across the partial dry density of montmorillonite ranging from 900 kg/m^(3)to 1820 kg/m^(3),by employing only one fitting parameter of the scaling factor.When the partial dry density of montmorillonite decreased to 800 kg/m^(3),the proposed model shows an underestimation of the apparent gas diffusion coefficient due to possible changes of the tortuosity factor.Model predictions indicate that gas diffusion in saturated bentonite is primarily controlled by the free pore domain,with minimal contributions from DDL pores.Despite being the dominant pore type,interlayer pores contribute limitedly to total Da/Dw values due to significant constrictivity effects.展开更多
Understanding the effects of temperature on the hydro-mechanical behavior of compacted bentonite is important for performance assessments of bentonitebased buffer,backfill,and sealing systems in deep geological dispos...Understanding the effects of temperature on the hydro-mechanical behavior of compacted bentonite is important for performance assessments of bentonitebased buffer,backfill,and sealing systems in deep geological disposal of high-level radioactive wastes.Motivated by such applications,most past experimental studies were focused on highly compacted and high-quality bentonite.Such degrees of dry densities may not be economically or technically feasible for other emerging applications,including as an alternative material to cement in plugging and abandonment of wells.A bespoke high-pressure high-temperature constant rate of strain(CRS)apparatus was developed for the work reported here to conduct a series of tests for evaluating the hydro-mechanical response of compacted bentonite to elevated temperatures.Experiments were performed with bentonite specimens with high impurity contents at a range of dry densities(1.1,1.4,and 1.7 Mg/m^(3))and temperatures between 20 and 80℃.The results show that temperature increase leads to the decrease of swelling pressure for all studied densities.Larger reductions of swelling pressure were observed with increasing dry densities,suggesting the possibility of a larger exchange of pore water in the microstructure system of the clay.The transfer of water from micropores to macropores at elevated temperatures is shown to be a key controlling process at high-density compacted bentonite by which temperature affects the swelling pressure and hydraulic conductivity.展开更多
Colloids are prevalent in nuclear waste repositories,with bentonite colloids posing an uncontrollable risk factor for nuclide migration processes.In this study,static adsorption experiments were coupled with dynamic s...Colloids are prevalent in nuclear waste repositories,with bentonite colloids posing an uncontrollable risk factor for nuclide migration processes.In this study,static adsorption experiments were coupled with dynamic shower experiments to comprehensively investigate the influence of bentonite colloids on Sr^(2+)migration in granite,considering adsorption capacity.Bentonite colloids have a considerably greater adsorption capacity than both bentonite and granite,with a maximum adsorption of 30.303 mg/g.The adsorption behavior of bentonite colloids on Sr^(2+)is well described by the Langmuir isotherm and pseudo-second-order kinetic models,indicating that a single-layer chemical adsorption process is controlled by the site activation energy.The adsorbed Sr^(2+)is unevenly distributed on the colloids,and the adsorption mechanism may involve ion exchange with Ca.Bentonite colloids exhibit superior adsorption in neutral environments.The cations in groundwater inhibit Sr^(2+)adsorption,and the inhibition efficacy decreases in the order Fe^(3+)>Ca^(2+)>Mg^(2+)>K^(+).The presence of bentonite colloids in a granite column slightly influences the retention of Sr^(2+)in the column while markedly reducing the Sr^(2+)penetration time from 70 h to 18 h.However,the coexistence of Co^(2+),Ni^(2+),and Cs^(+)in a multinuclide system weakens the ability of the colloids to promote Sr^(2+)migration.In comigration of colloid and multinuclide systems,the adsorption of nuclides by bentonite colloids causes the nuclide migration speed to decrease in the order Sr^(2+)>Cs^(+)>Ni^(2+)>Co^(2+).This study provides insights into Sr^(2+)migration in cave repositories for low-and medium-level radioactive waste.展开更多
Wet flue gas desulfurization(WFGD)could effectively reduce sulfur dioxide emission.However,magnesium sulfite(MgSO_(3)),a by-product of desulfurization,was easy to result in secondary pollution.In this study,the solid ...Wet flue gas desulfurization(WFGD)could effectively reduce sulfur dioxide emission.However,magnesium sulfite(MgSO_(3)),a by-product of desulfurization,was easy to result in secondary pollution.In this study,the solid catalyst Co-Bent(bentonite supported cobalt)was prepared by blending method for MgSO_(3) oxidation with bentonite as the carrier and cobalt as the active component.At the calcination temperature of 550℃ and the Co loading level of 3 wt.%,the catalyst showed excellent catalytic performance for the oxidation of high concentration MgSO_(3) slurry,and the oxidation rate of MgSO_(3) was 0.13 mol/(L·h).The research indicated that the active component was uniformly distributed within porous structure of the catalyst as Co_(3)O_(4),which facilitated the oxidation of SO_(3)^(2-) catalyzed by Co_(3)O_(4).Kinetic researches indicated the oxidation rate of MgSO_(3) was influenced by the catalyst dosage,the reaction temperature,the solution pH,the airflow rate,and the SO_(3)^(2-) concentration.Additionally,after recycling experiments,the regenerated catalyst retained its high catalytic performance for the MgSO_(3) oxidation.The reaction mechanism for the catalytic oxidation of MgSO_(3) by Co-Bent catalyst was also proposed.The generation of active free radicals(OH·,SO_(4)^(-)·,SO_(3)^(-)·,SO_(5)^(-)·)accelerated the MgSO_(3) oxidation.These results provide theoretical support for the treatment of MgSO_(3) and the development of durable catalyst.展开更多
Deep geological repository is typically situated at depths ranging from several hundred to 1000 m below ground,making bentonite engineered barrier potentially vulnerable to high water pressure and even inducing hydrau...Deep geological repository is typically situated at depths ranging from several hundred to 1000 m below ground,making bentonite engineered barrier potentially vulnerable to high water pressure and even inducing hydraulic fracturing.This study conducted injection tests on compacted GMZ(Gaomiaozi)bentonite with a self-developed visualization set-up.The objective was to unveil the roles of dry density,water content,and pressurization rate in hydraulic fracturing from the perspective of fracturing macromorphological dynamics and breakthrough characteristics.Moreover,the relationships between breakthrough characteristics and microstructure were examined by MIP(mercury intrusion porosimetry)analysis.Results showed that the fracturing dynamics were characterized by three stages:hydration,cracking,and fracturing stages.Compared to water content and pressurization rate,dry density exerted more pronounced effects on these stages.Increasing dry density can lead to an expansion of circular hydration zone,a more complex cracking network,and a change in fracturing patterns from long and clear to short and fuzzy.In terms of breakthrough characteristics,the breakthrough pressure was positively correlated with dry density and negatively correlated with water content.Interestingly,there is a good and unique logarithmic correlation between the breakthrough pressure and the ratio eM/em of inter-aggregate void ratio and intra-aggregate void ratio,regardless of dry density and water content.Within a certain range(i.e.200-50 kPa/min),breakthrough pressure showed slight dependency on pressurization rate.Nevertheless,an extremely low pressurization rate of 20 kPa/min caused a transition for the specimen from quasi-brittle to plastic state owning to more water infiltration,thereby hindering fracture initiation and propagation.展开更多
Buffer material and metal disposal containers are the key engineering barriers in the geological disposal of high-level radioactive waste.The durability of disposal containers largely depends on the water con-tent in ...Buffer material and metal disposal containers are the key engineering barriers in the geological disposal of high-level radioactive waste.The durability of disposal containers largely depends on the water con-tent in buffer material.This work focused on investigating the corrosion evolution of NiCu low alloy steel in compacted GMZ bentonite with different water contents for 270 d by using weight loss,electrochemi-cal measurements,and various methods for analyzing corrosion products.As the water content increased from 13%to 20%,the water in the bentonite transformed from an unsaturated to a critical saturated state,and the corrosion rate of NiCu steel clearly increased.In these two systems,the oxygen could mi-grate to the thin liquid film on the steel surface through the air pores in the bentonite in the gas phase and undergo cathodic reduction.Meanwhile,it oxidized the ferrous hydrolysis products into ferric corro-sion products and formed a rust layer,which could block the diffusion of oxygen.At that moment,the cathodic process of NiCu steel corrosion changed to rust reduction.When the water content continually increased to 30%and 40%,the compacted bentonite was in a saturation state,and the corrosion rate of NiCu steel was significantly decreased.This was because most pores among the bentonite particles were occupied by a large amount of free water,which hindered the diffusion of oxygen and inhibited its cathodic reduction.Furthermore,it restrained the oxidation of ferrous corrosion products,which greatly weakened the cathodic depolarization of rust,leading to the cathodic process being dominated by the hydrogen evolution reaction.展开更多
Globally bentoite clay has been proposed as an engineered barrier material for safe underground disposal of high-level nuclear waste.Clay has many favorable properties such as high liquid limit,and plastic limit along...Globally bentoite clay has been proposed as an engineered barrier material for safe underground disposal of high-level nuclear waste.Clay has many favorable properties such as high liquid limit,and plastic limit along with other properties which make it the most suitable for this application.In the present study,an attempt has been made to study the behavior of Barmer bentonite under the influence of high temperatures up to 120℃.Properties of barmer bentonite namely,liquid limit,plastic limit,and maximum dry density have been determined after thermal treatment at 25℃,60℃,80℃,100℃ and 120℃.The extensive experimental results indicate that liquid limit and plastic limit show a decreasing trend while maximum dry density increases with an increase in temperature.Liquid limit and plastic limit decrease up to 12%and 11%respectively when the temperature reaches up to 120℃.Maximum dry density increases by 10%due to thermal treatment and optimum water content decreases by up to 4%.Statistical analysis has been carried out to obtain the correlation between temperature and physical properties of Barmer bentonite such as liquid limit,plastic limit,maximum dry density,and optimum water content.The XRD analysis of Barmer bentonite at room temperature and 120℃ shows very small variation in mineralogical composition.Whereas,interlayer distance has been measured and found to be decreasing with an increase in temperature.Further,a comparative analysis shows that the measured properties of studied Barmer bentonite lie in the range of previously measured values of other types of bentonite across the globe.展开更多
Investigation of thermal effects on the strain rate-dependent properties of compacted bentonite is crucial for the long-term safety assessment of deep geological repository for disposal of high-level radioactive waste...Investigation of thermal effects on the strain rate-dependent properties of compacted bentonite is crucial for the long-term safety assessment of deep geological repository for disposal of high-level radioactive waste.In the present work,cylindrical GMZ01 bentonite specimens were compacted with suction-controlled by the vapor equilibrium technique.Then,a series of temperature-and suction-controlled stepwise constant rate of strain(CRS)tests was performed and the rate-dependent compressibility behavior of the highly compacted GMZ01 bentonite was investigated.The plastic compressibility parameterλ,the elastic compressibility parameterκ,the yield stress p0,as well as the viscous parameterαwere determined.Results indicate thatλ,κandαdecrease and p0 increases as suction increases.Upon heating,parametersλ,αand p0 decrease.It is also found that p0 increases linearly with increasing CRS in a double-logarithm coordinate.Based on the experimental results,a viscosity parameterα(s,T)was fitted to capture the effects of suction s and temperature T on the relationship between yield stress and strain rate.Then,an elastic-thermo-viscoplastic model for unsaturated soils was developed to describe the thermal effects on the rate-dependent behavior of highly compacted GMZ01 bentonite.Validation showed that the calculated results agreed well to the measured ones.展开更多
Predicting the gas breakthrough pressure of saturated compacted bentonite is crucial for ensuring the long-term safe operation of deep geological repositories for the disposal of high-level radioactive nuclear wastes....Predicting the gas breakthrough pressure of saturated compacted bentonite is crucial for ensuring the long-term safe operation of deep geological repositories for the disposal of high-level radioactive nuclear wastes.In this work,the swelling pressure,water injection,gas injection and mercury intrusion porosimetry(MIP)tests on saturated compacted Gaomiaozi(GMZ)bentonite specimens with a dry density of 1.3 Mg/m^(3),1.4 Mg/m^(3),1.5 Mg/m^(3),1.6 Mg/m^(3) and 1.7 Mg/m^(3) were conducted.Subsequently,the relationships between the swelling pressure and average inter-particle distance,as well as between the gas entry pressure and the maximum effective pore size were analyzed and established.Considering that gas migration and breakthrough are all closely related to the pore structures of the tested geomaterials,a novel gas breakthrough pressure prediction model based on the pore size distribution(PSD)curve was constructed using an existing prediction model based on gas entry pressure and swelling pressure.Finally,based on the test results of the specimens 1.5 Mg/m^(3),1.6 Mg/m^(3) and 1.7 Mg/m^(3),gas breakthrough pressures of the specimens with dry densities of 1.3 Mg/m^(3) and 1.4 Mg/m^(3) were predicted.The results show that the calculated gas breakthrough pressures of 0.76 MPa and 1.28 MPa are very close to the measured values of 0.80 MPa and 1.30 MPa,validating the accuracy of the proposed model.展开更多
基金Project(51004053)supported by National Natural Science Foundation of ChinaProject(2009J01033)supported by Natural Science Foundation of Fujian Province,China+2 种基金Project(3502Z20116008)supported by the Science and Technology Research Project of Xiamen City,ChinaProject(JA11146)supported by Program for Fostering Distinguished Young Scholars in University of Fujian Province,ChinaProject(2011B003)supported by the Foundation for Young Professors of Jimei University,China
文摘In the present work, a novel heterogeneous photo-Fenton catalyst was prepared by iron and cerium pillared bentonite. The catalyst Fe-Ce/bentonite was characterized by X-ray diffraction （XRD）, X-ray fluorescence （XRF）, Brunauer-Emmett-Teller （BET） and scanning electron microscopy （SEM） methods. It is found that Fe and Ce intercalate into the silicate layers of bentonite successfully. Tetracycline was removed by heterogeneous photo-Fenton reaction using the catalyst in this work. The effects of different reaction systems, hydrogen peroxide concentration, initial pH, catalyst dosage, UV power and introduction of different anions on degradation were investigated in details. The stability of catalyst was investigated through recycling experiment. The results show that removal rate of tetracycline is 98.13% under the conditions of 15 mmol/L H202, 0.50 g/L catalyst dosage, initial pH 3.0, 11 W UV lamp power and 60 min reaction time. However, the removal rate decreases after adding some anions. The hydroxyl radical plays an important role in heterogeneous photo-assisted Fenton degradation of tetracycline. The catalyst is very stable and can be recycled many times.
基金supported by the National Natural Science Foundation of China(Grant Nos.52478351,52208329)the Shenzhen Science and Technology Innovation Commission(Grant No.JCYJ20240813143306009)support is gratefully acknowledged.
文摘Polymer-modified bentonite(PMB)is much more effective at containing chemically aggressive liquids than conventional bentonite.The PMB manufacturing process typically utilizes natural,high-quality sodium bentonite(NaB)owing to its excellent hydrophilicity and swelling capacity.However,calcium bentonite(CaB),which is much more abundant worldwide,is rarely used for containment applications owing to its poor hydrophilicity.This study proposed a polymerization method that transforms sodium-activated calcium bentonite(NCB)into PMB to achieve low hydraulic conductivity(k)to aggressive liquids.The mechanism for its low k was revealed through characterization techniques and analyses(e.g.X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),and Brunauer-Emmett-Teller(BET)).The results showed that the PMB had a small amount of polymer elution(indicating better interface stability)and thus exhibited excellent barrier properties under chemically aggressive conditions,with the k of<10^(-11) m/s for 0.6 mol/L NaCl solution,which is four orders of magnitude lower than that of the NCB(k=3×10^(-7) m/s).Various microscopic analyses indicated that the selected monomers were successfully polymerized,and intercalated into and grafted onto the montmorillonite layers of bentonite.The formed polymer network increased the swelling capability of PMB granules,decreased the pore size,and created narrow and tortuous flow pathways leading to a very low k to aggressive liquids.
基金financial support by the National Key Research and Development Program of China(No.2023YFC2907801)the Hunan Provincial Natural Science Foundation of China(No.2023JJ40760)the Scientific and Technological Project of Yunnan Precious Metals Laboratory,China(No.YPML-2023050276)。
文摘Bentonite is a necessary binder in producing pellets.Its excessive use reduces the iron grade of pellets and increases production costs.Minimizing bentonite dosage is essential for producing high-quality iron ore pellets.Addressing the gap in the application of organically-intercalated modified bentonite in the pelletizing field,this study introduces an innovative modification process for bentonite that employs the synergistic effect of mechanical force and dimethyl sulfoxide to enhance the intercalation of organic compounds within bentonite,thus significantly enhancing its binding performance.The colloid value and swell capacity of modified bentonite(98.5 m L/3g and 55.0 m L/g)were much higher than the original bentonite(90.5 m L/3g and 17.5 m L/g).With the decrease of bentonite dosage from1.5wt%to 1.0wt%,the drop number of green pellets from a height of 0.5 m and the compressive strengths of roasted pellets using the modified bentonite(6.0 times and 2916 N per pellet)were significantly higher than those of the original bentonite(4.0 times and 2739 N per pellet).This study provides a comprehensive analysis of the intercalation modification mechanism of bentonite,offering crucial technical insights for the development of high-performance modified bentonite as iron ore pellet binders.
基金funding support from the National Natural Science Foundation of China(Grant No.42477178)the National Key Research and Development Program of China(Grant No.2023YFC3709600)the Primary Research and Development Plan of Anhui Province(Grant No.2023t07020018).
文摘Acid mine drainage(AMD)leachate is a global pollutant issue that impacts groundwater environment quality.This study investigated the feasibility of a composite biopolymer-amended bentonite as a geosynthetic clay liner core material to contain AMD leachate.The real AMD leachate with a pH of 3.1,sourced from an acidic pyrite tailings site,was employed as a specific test leachate used in this study.The composite biopolymer was composed of welan gum(WG)and xanthan gum(XG)at different dry weight-based ratios.Modified fluid loss(MFL)tests were conducted to evaluate hydraulic conductivity(k)of bentonites to optimize WG:XG ratio.Rheological properties of biopolymer solutions were measured,serving as indicative parameters of biopolymer elution.The results indicated biopolymer-amended bentonites with the WG:XG ratio of 8:2 possessed lowest k(1.5×10^(−11)m/s to 7.2×10^(−11)m/s),lower than unamended bentonite(1.2×10^(−10)m/s to 8.6×10^(−10)m/s)in the AMD leachate condition.In addition,biopolymer solutions with WG:XG ratio of 8:2 exhibited highest viscosity.Thermogravimetric analysis,ultraviolet–visible spectroscopy,and Fourier transform infrared spectroscopy were conducted on the composite biopolymer,revealing that WG and XG interacted via physical cross-linking.Additionally,scanning electron microscopy and atomic force microscopy images indicated that a physical cross-linking and dense network structure conformation was developed in the composite biopolymer hydrogel at the WG:XG ratio of 8:2.The results demonstrate that the composite biopolymer is a promising low-carbon amendment material for enhancing containment performance of bentonite used in geosynthetic clay liners to contain AMD leachate.
文摘Bentonite is a very useful material for improving soil properties,which enhances the ability of plants to grow and produce in different conditions.The experiment was carried out in an agricultural nursery in one of the areas of the City of Diwaniyah,in a house covered with green netting,with a shade rate of 25%,to study the effect of bentonite and humic acid on the growth and flowering of a Catharanthus roseus L.plant in sandy soil.The experiment included two factors:the first factor was bentonite clay,and the second factor was humic acid.Using a randomized complete block design(R.C.B.D)with three replications,data were analyzed using the analysis of variance(ANOVA)method,and comparison was made according to the least significant difference(L.S.D)test at a probability level of 0.05.The experiment consisted of adding bentonite clay at 0,2,6,and 8 g L-1,humic acid at 0,0.5,1,and 10 g L-1.The results showed that adding bentonite clay and humic acid to sandy soil can have a significant positive effect on the growth and flowering of the Catharanthus roseus plant grown in poor sandy soil conditions.Bentonite,clay and humic acid were added at concentrations of 8 and 10 g L-1,which led to an increase in plant height and number of leaves and leaf area.They reached 30.07,23.84 cm2,76.62,63.42 cm2 for leaf-1 and 24.73,20.22 cm2 for leaf-1,respectively.The results also showed an increase in the content of nitrogen(N),phosphorus(P),and potassium(K)in leaves by 2.27,1.92,1.99%and 1.51,1.22,1.77%.This also led to an increase in chlorophyll pigment and anthocyanin at the highest concentration and gave the highest value.Therefore,adding bentonite and humic acid together gave the highest values in vegetative and chemical characteristics,compared to treatments without addition.
基金The Royal Society,UK,Grant/Award Number:IEC\NSFC\211366Fundamental Research Funds for the Central Universities(China University of Mining and Technology),Grant/Award Number:2023ZDPY11National Natural Science Foundation of China,Grant/Award Numbers:51809263,52174133。
文摘The corrosion of waste canisters in the deep geological disposal facilities(GDFs)for high-level radioactive waste(HLRW)can generate gas,which escapes from the engineered barrier system through the interfaces between the bentonite buffer blocks and the host rock and those between the bentonite blocks.In this study,a series of water infiltration and gas breakthrough experiments were conducted on granite and on granite-bentonite specimens with smooth and grooved interfaces.On this basis,this study presents new insights and a quantitative assessment of the impact of the interface between clay and host rock on gas transport.As the results show,the water permeability values from water infiltration tests on granite and granite-bentonite samples(10−19-10−20m^(2))are found to be slightly higher than that of bentonite.The gas permeability of the mock-up samples with smooth interfaces is one order of magnitude larger than that of the mock-up with grooved interfaces.The gas results of breakthrough pressures for the granite and the granite-bentonite mock-up samples are significantly lower than that of bentonite.The results highlight the potential existence of preferential gas migration channels between the rock and bentonite buffer that require further considerations in safety assessment.
基金funded by the National Natural Science Foundation of China(Grant Nos.42207227)the Natural Science Foundation of Hunan Province,China(Grant No.2022JJ40586)The authors also thank the China Postdoctoral Science Foundation(Grant Nos.2022M722428).
文摘In the deep geological disposal repository of high-level radioactive waste,buffer/backfill materials typically consist of compacted bentonite block and granular bentonite.As these materials undergo a long-term hydration,it is anticipated that the two forms of bentonite materials(i.e.compacted bentonite powder(CBP)and granular bentonite(GB))are expected to exhibit differing hydro-mechanical behaviors due to the differences in their structures.This work aims to investigate the differences in swelling pressure and compressibility through a series of swelling pressure tests,compression tests and mercury intrusion porosimetry(MIP)tests.The experimental results demonstrated that swelling pressure curves of the CBP specimens showed higher first peak values and more pronounced collapse than those of the GB specimens at a given dry density,regardless of vapor-water hydration or liquid-water hydration.The final swelling pressures of the two materials were similar at the same dry density,suggesting an independent correlation between swelling pressure and dry density.At the high suction range,the compression curves exhibited an obvious bi-linear pattern for the CBP specimens and a significant nonlinearity for the GB specimens.Meanwhile,the CBP specimens presented higher pre-consolidation pressures and larger compression indices than the GB specimens at a given suction.As suction decreased,the compression curves of the two materials gradually approached each other and their differences were reduced accordingly.After reaching saturation,a good consistency between them was observed whether for final swelling pressure or compressibility.Pore structure analysis revealed that the two materials both presented an initially double structure,and their differences were primarily manifested at the macrostructural level.Eventually,the differences in swelling pressure or compression curves of the two materials were well interpreted by combining microstructural evolutions.
基金funding from the European Union's Horizon 2020 research and innovation program European Joint Program on RadioactiveWaste Management(EURAD)(2019e2024)WP-Gas‘Mechanistic understanding of gas transport in clay materials’under Grant agreement No.847593.
文摘Understanding the mechanisms of gas transport and the resulting preferential pathways formation through bentonite-based barriers is essential for their performance evaluation.In this experimental study,gas migration within a heterogenous mixture of MX80 bentonite pellets and powder with a ratio of 80/20 in dry mass was investigated.A novel X-ray transparent constant volume cell has been developed to assess the effect of gas pressure,material heterogeneities,and water vapor gas saturation on breakthrough pressure and gas pathways.The new cell allows to perform high-resolution X-ray computed micro-tomography(X-ray μCT)scans to track microstructural changes during different phases of saturation and gas injection.Experimental results showed that the gas breakthrough occurred when the pressure was raised to 3 MPa.This is slightly higher than the expected swelling pressure(2.9 MPa)of the bentonite sample.Each gas injection was followed by a long resaturation phase restoring material homogeneity at μCT resolution scale(16 mm).However,the elapsed time needed for gas to breakthrough at 3 MPa diminished at each subsequent injection test.X-ray μCT results also revealed the opening of the specimen/cell wall interface during gas passage.This opening expanded as the injection pressure increased.The gas flow along the interface was associated with the development of dilatant pathways inside the sample,although they did not reach the outlet surface.It was observed that the water vapor gas saturation had no effect on the breakthrough pressure.These findings enhance the understanding of the complex mechanisms underlying microstructural evolution and gas pathway development within the highly heterogeneous mixture.The experimental outcomes highlight the effectiveness of X-ray μCT to improve quality protocols for engineering design and safety assessments of engineered barriers.
基金supported by the National Natural Science Foundation of China(No,22271074)Natural Science Foundation of Hebei Province(Nos.B2023208042,B2022208032,B2021208066,E2024208084 , E2024208088)+2 种基金Science Research Project of Hebei Education Department(No.JZX2024013)Special Fund for Local Scientific and Technological Development under the Guidance of the Central Government(No.236Z3704G)Hebei Province High Level Talent Funding(No.A202001010).
文摘Flexible wearable electronic devices based on hydrogels have immense potential in a wide range of applications.However,many existing strain sensors suffer from significant limitations including poor mechanical properties,low adhesion,and insufficient conductivity.To address these challenges,this study successfully developed an organic-inorganic double-network conductive hydrogel using acrylic-modified bentonite (AABT) as a key component.The incorporation of AABT significantly enhanced the mechanical properties of the ATHG@LiCl hydrogel,achieving an impressive stretchability of 4000% and tensile strength of 250 kPa.Moreover,it improved the electrical conductivity of the hydrogel to a maximum of 1.53 mS/cm.The catechol structure of tannic acid (TA) further augmented the adhesive properties of the ATHG@LiCl hydrogel toward various substrates such as copper,iron,glass,plastic,wood,and pigskin.The addition of lithium chloride (LiCl) and dimethyl sulfoxide(DMSO) endowed the hydrogel with exceptional freezing resistance and flexibility,even at low temperatures of-20℃.Remarkably,the hydrogel maintained a conductivity of 0.53 mS/cm under these conditions,surpassing the performance of many other reported hydrogels.Furthermore,the ATHG@LiCl hydrogel demonstrated outstanding characteristics,such as high sensitivity (gauge factor GF=4.50),excellent transparency (90%),and reliable strain-sensing capabilities,indicating that the ATHG@LiCl hydrogel is a highly promising candidate for flexible wearable soft materials,offering significant advancements in both functionality and performance.
基金financial support from the National Natural Science Foundation of China(Grant No.42202304)is greatly acknowledged.
文摘Predicting the gas diffusion coefficient of water-saturated Na-bentonite is crucial for the overall performance of the geological repository for isolating high-level radioactive waste(HLW).In this study,a conceptual model that incorporates a multi-porosity system was proposed,dividing the pore space into free water pores,interlayer water pores,and diffuse double layer(DDL)water pores,to describe the molecular diffusion behaviour of the dissolved gas in saturated bentonite.In this model,gas diffusion in these three porosities is considered as independent and parallel processes.The apparent gas diffusion coefficient is quantified by applying weighted approximations that consider the specific porosity,tortuosity factor,and constrictivity factor within each porosity domain.For verification,experimental data from gas diffusion tests on saturated MX-80 and Kunipia-F bentonite specimens across a wide range of dry densities were utilized.The proposed model could successfully capture the overall trend of the apparent gas diffusion coefficient for bentonite materials across the partial dry density of montmorillonite ranging from 900 kg/m^(3)to 1820 kg/m^(3),by employing only one fitting parameter of the scaling factor.When the partial dry density of montmorillonite decreased to 800 kg/m^(3),the proposed model shows an underestimation of the apparent gas diffusion coefficient due to possible changes of the tortuosity factor.Model predictions indicate that gas diffusion in saturated bentonite is primarily controlled by the free pore domain,with minimal contributions from DDL pores.Despite being the dominant pore type,interlayer pores contribute limitedly to total Da/Dw values due to significant constrictivity effects.
基金University of Manchester and the China Scholarship Council,Royal Society,UK,Grant/Award Number:IECNSFC211366National Natural Science Foundation of China,Grant/Award Numbers:5247415,52174133Natural Science Foundation of Jiangsu Province of China,Grant/Award Number:BK20240107。
文摘Understanding the effects of temperature on the hydro-mechanical behavior of compacted bentonite is important for performance assessments of bentonitebased buffer,backfill,and sealing systems in deep geological disposal of high-level radioactive wastes.Motivated by such applications,most past experimental studies were focused on highly compacted and high-quality bentonite.Such degrees of dry densities may not be economically or technically feasible for other emerging applications,including as an alternative material to cement in plugging and abandonment of wells.A bespoke high-pressure high-temperature constant rate of strain(CRS)apparatus was developed for the work reported here to conduct a series of tests for evaluating the hydro-mechanical response of compacted bentonite to elevated temperatures.Experiments were performed with bentonite specimens with high impurity contents at a range of dry densities(1.1,1.4,and 1.7 Mg/m^(3))and temperatures between 20 and 80℃.The results show that temperature increase leads to the decrease of swelling pressure for all studied densities.Larger reductions of swelling pressure were observed with increasing dry densities,suggesting the possibility of a larger exchange of pore water in the microstructure system of the clay.The transfer of water from micropores to macropores at elevated temperatures is shown to be a key controlling process at high-density compacted bentonite by which temperature affects the swelling pressure and hydraulic conductivity.
基金supported by the General Project of the National Natural Science Foundation of China(No.42377413).
文摘Colloids are prevalent in nuclear waste repositories,with bentonite colloids posing an uncontrollable risk factor for nuclide migration processes.In this study,static adsorption experiments were coupled with dynamic shower experiments to comprehensively investigate the influence of bentonite colloids on Sr^(2+)migration in granite,considering adsorption capacity.Bentonite colloids have a considerably greater adsorption capacity than both bentonite and granite,with a maximum adsorption of 30.303 mg/g.The adsorption behavior of bentonite colloids on Sr^(2+)is well described by the Langmuir isotherm and pseudo-second-order kinetic models,indicating that a single-layer chemical adsorption process is controlled by the site activation energy.The adsorbed Sr^(2+)is unevenly distributed on the colloids,and the adsorption mechanism may involve ion exchange with Ca.Bentonite colloids exhibit superior adsorption in neutral environments.The cations in groundwater inhibit Sr^(2+)adsorption,and the inhibition efficacy decreases in the order Fe^(3+)>Ca^(2+)>Mg^(2+)>K^(+).The presence of bentonite colloids in a granite column slightly influences the retention of Sr^(2+)in the column while markedly reducing the Sr^(2+)penetration time from 70 h to 18 h.However,the coexistence of Co^(2+),Ni^(2+),and Cs^(+)in a multinuclide system weakens the ability of the colloids to promote Sr^(2+)migration.In comigration of colloid and multinuclide systems,the adsorption of nuclides by bentonite colloids causes the nuclide migration speed to decrease in the order Sr^(2+)>Cs^(+)>Ni^(2+)>Co^(2+).This study provides insights into Sr^(2+)migration in cave repositories for low-and medium-level radioactive waste.
基金supported by the State Key Laboratory of Urban Water Resource and Environment,Harbin Institute of Technology (No. 2022TS10)the Taishan Industrial Experts Programthe Natural Science Foundation of Shandong Province of China (No. ZR2023ME212).
文摘Wet flue gas desulfurization(WFGD)could effectively reduce sulfur dioxide emission.However,magnesium sulfite(MgSO_(3)),a by-product of desulfurization,was easy to result in secondary pollution.In this study,the solid catalyst Co-Bent(bentonite supported cobalt)was prepared by blending method for MgSO_(3) oxidation with bentonite as the carrier and cobalt as the active component.At the calcination temperature of 550℃ and the Co loading level of 3 wt.%,the catalyst showed excellent catalytic performance for the oxidation of high concentration MgSO_(3) slurry,and the oxidation rate of MgSO_(3) was 0.13 mol/(L·h).The research indicated that the active component was uniformly distributed within porous structure of the catalyst as Co_(3)O_(4),which facilitated the oxidation of SO_(3)^(2-) catalyzed by Co_(3)O_(4).Kinetic researches indicated the oxidation rate of MgSO_(3) was influenced by the catalyst dosage,the reaction temperature,the solution pH,the airflow rate,and the SO_(3)^(2-) concentration.Additionally,after recycling experiments,the regenerated catalyst retained its high catalytic performance for the MgSO_(3) oxidation.The reaction mechanism for the catalytic oxidation of MgSO_(3) by Co-Bent catalyst was also proposed.The generation of active free radicals(OH·,SO_(4)^(-)·,SO_(3)^(-)·,SO_(5)^(-)·)accelerated the MgSO_(3) oxidation.These results provide theoretical support for the treatment of MgSO_(3) and the development of durable catalyst.
基金supported by the National Natural Science Foundation of China(Grant Nos.42430713 and 42125701)Innovation Program of Shanghai Municipal Education Commission(Grant No.2023ZKZD26)。
文摘Deep geological repository is typically situated at depths ranging from several hundred to 1000 m below ground,making bentonite engineered barrier potentially vulnerable to high water pressure and even inducing hydraulic fracturing.This study conducted injection tests on compacted GMZ(Gaomiaozi)bentonite with a self-developed visualization set-up.The objective was to unveil the roles of dry density,water content,and pressurization rate in hydraulic fracturing from the perspective of fracturing macromorphological dynamics and breakthrough characteristics.Moreover,the relationships between breakthrough characteristics and microstructure were examined by MIP(mercury intrusion porosimetry)analysis.Results showed that the fracturing dynamics were characterized by three stages:hydration,cracking,and fracturing stages.Compared to water content and pressurization rate,dry density exerted more pronounced effects on these stages.Increasing dry density can lead to an expansion of circular hydration zone,a more complex cracking network,and a change in fracturing patterns from long and clear to short and fuzzy.In terms of breakthrough characteristics,the breakthrough pressure was positively correlated with dry density and negatively correlated with water content.Interestingly,there is a good and unique logarithmic correlation between the breakthrough pressure and the ratio eM/em of inter-aggregate void ratio and intra-aggregate void ratio,regardless of dry density and water content.Within a certain range(i.e.200-50 kPa/min),breakthrough pressure showed slight dependency on pressurization rate.Nevertheless,an extremely low pressurization rate of 20 kPa/min caused a transition for the specimen from quasi-brittle to plastic state owning to more water infiltration,thereby hindering fracture initiation and propagation.
基金supported by the National Natural Science Foundation of China(Nos.52173304 and U1867216)the National Key R&D Program of China(No.2022YFB3207600)China Scholarship Council(No.2018SLJ014508).
文摘Buffer material and metal disposal containers are the key engineering barriers in the geological disposal of high-level radioactive waste.The durability of disposal containers largely depends on the water con-tent in buffer material.This work focused on investigating the corrosion evolution of NiCu low alloy steel in compacted GMZ bentonite with different water contents for 270 d by using weight loss,electrochemi-cal measurements,and various methods for analyzing corrosion products.As the water content increased from 13%to 20%,the water in the bentonite transformed from an unsaturated to a critical saturated state,and the corrosion rate of NiCu steel clearly increased.In these two systems,the oxygen could mi-grate to the thin liquid film on the steel surface through the air pores in the bentonite in the gas phase and undergo cathodic reduction.Meanwhile,it oxidized the ferrous hydrolysis products into ferric corro-sion products and formed a rust layer,which could block the diffusion of oxygen.At that moment,the cathodic process of NiCu steel corrosion changed to rust reduction.When the water content continually increased to 30%and 40%,the compacted bentonite was in a saturation state,and the corrosion rate of NiCu steel was significantly decreased.This was because most pores among the bentonite particles were occupied by a large amount of free water,which hindered the diffusion of oxygen and inhibited its cathodic reduction.Furthermore,it restrained the oxidation of ferrous corrosion products,which greatly weakened the cathodic depolarization of rust,leading to the cathodic process being dominated by the hydrogen evolution reaction.
文摘Globally bentoite clay has been proposed as an engineered barrier material for safe underground disposal of high-level nuclear waste.Clay has many favorable properties such as high liquid limit,and plastic limit along with other properties which make it the most suitable for this application.In the present study,an attempt has been made to study the behavior of Barmer bentonite under the influence of high temperatures up to 120℃.Properties of barmer bentonite namely,liquid limit,plastic limit,and maximum dry density have been determined after thermal treatment at 25℃,60℃,80℃,100℃ and 120℃.The extensive experimental results indicate that liquid limit and plastic limit show a decreasing trend while maximum dry density increases with an increase in temperature.Liquid limit and plastic limit decrease up to 12%and 11%respectively when the temperature reaches up to 120℃.Maximum dry density increases by 10%due to thermal treatment and optimum water content decreases by up to 4%.Statistical analysis has been carried out to obtain the correlation between temperature and physical properties of Barmer bentonite such as liquid limit,plastic limit,maximum dry density,and optimum water content.The XRD analysis of Barmer bentonite at room temperature and 120℃ shows very small variation in mineralogical composition.Whereas,interlayer distance has been measured and found to be decreasing with an increase in temperature.Further,a comparative analysis shows that the measured properties of studied Barmer bentonite lie in the range of previously measured values of other types of bentonite across the globe.
基金the support of the National Natural Science Foundation of China(Grant Nos.42030714,42177138 and 41907239).
文摘Investigation of thermal effects on the strain rate-dependent properties of compacted bentonite is crucial for the long-term safety assessment of deep geological repository for disposal of high-level radioactive waste.In the present work,cylindrical GMZ01 bentonite specimens were compacted with suction-controlled by the vapor equilibrium technique.Then,a series of temperature-and suction-controlled stepwise constant rate of strain(CRS)tests was performed and the rate-dependent compressibility behavior of the highly compacted GMZ01 bentonite was investigated.The plastic compressibility parameterλ,the elastic compressibility parameterκ,the yield stress p0,as well as the viscous parameterαwere determined.Results indicate thatλ,κandαdecrease and p0 increases as suction increases.Upon heating,parametersλ,αand p0 decrease.It is also found that p0 increases linearly with increasing CRS in a double-logarithm coordinate.Based on the experimental results,a viscosity parameterα(s,T)was fitted to capture the effects of suction s and temperature T on the relationship between yield stress and strain rate.Then,an elastic-thermo-viscoplastic model for unsaturated soils was developed to describe the thermal effects on the rate-dependent behavior of highly compacted GMZ01 bentonite.Validation showed that the calculated results agreed well to the measured ones.
基金the National Natural Science Foundationof China (Grant No. 42030714).
文摘Predicting the gas breakthrough pressure of saturated compacted bentonite is crucial for ensuring the long-term safe operation of deep geological repositories for the disposal of high-level radioactive nuclear wastes.In this work,the swelling pressure,water injection,gas injection and mercury intrusion porosimetry(MIP)tests on saturated compacted Gaomiaozi(GMZ)bentonite specimens with a dry density of 1.3 Mg/m^(3),1.4 Mg/m^(3),1.5 Mg/m^(3),1.6 Mg/m^(3) and 1.7 Mg/m^(3) were conducted.Subsequently,the relationships between the swelling pressure and average inter-particle distance,as well as between the gas entry pressure and the maximum effective pore size were analyzed and established.Considering that gas migration and breakthrough are all closely related to the pore structures of the tested geomaterials,a novel gas breakthrough pressure prediction model based on the pore size distribution(PSD)curve was constructed using an existing prediction model based on gas entry pressure and swelling pressure.Finally,based on the test results of the specimens 1.5 Mg/m^(3),1.6 Mg/m^(3) and 1.7 Mg/m^(3),gas breakthrough pressures of the specimens with dry densities of 1.3 Mg/m^(3) and 1.4 Mg/m^(3) were predicted.The results show that the calculated gas breakthrough pressures of 0.76 MPa and 1.28 MPa are very close to the measured values of 0.80 MPa and 1.30 MPa,validating the accuracy of the proposed model.
