To understand the self-healing property of an engineered barrier for radioactive waste disposal,the hydraulic conductivity of compacted bentoniteesand mixtures saturated with artificial seawater(SW)before and after ga...To understand the self-healing property of an engineered barrier for radioactive waste disposal,the hydraulic conductivity of compacted bentoniteesand mixtures saturated with artificial seawater(SW)before and after gas migration was examined.Na-and Ca-bentonites were mixed with fine sand at a ratio of 70%bentonite in dry weight.Two aspects were considered during the experiment:the hydraulic conductivity of the specimen that was resaturated after gas migration and the distribution of water content immediately after gas migration to study gas migration pathways.The gas migrated through the entire cross-section of the specimen,and gas breakthrough occurred in the equilibrium swelling pressure range approximately.Subsequently,the gas flow rate reached a sufficient large value when the gas pressure was approximately twice the equilibrium axial pressure(the sum of swelling and confining pressures),which excluded the back pressure.Although the gas migration pathway was not visible when the specimen was observed immediately after gas migration,the water content distribution showed that several parts of the specimen with lower water content were connected in the direction of gas migration.After resaturation,the change in permeability was within a limited rangedtwo to three times larger than that before gas migration for each type of bentonite in SW.This slight change suggests that gas migration creates a pore structure that cannot be sealed via crystalline swelling of montmorillonite in SW,even if highly compacted bentonite is used under a constant-volume condition.展开更多
Recently,the Institute for Radiological protection and Nuclear Safety(IRSN)has launched VSEAL(Vertical SEALing)project to investigate the impact of gas migration on the long-term performance of bentonite based vertica...Recently,the Institute for Radiological protection and Nuclear Safety(IRSN)has launched VSEAL(Vertical SEALing)project to investigate the impact of gas migration on the long-term performance of bentonite based vertical sealing systems(VSS).The first VSEAL in situ test was emplaced in IRSN’s Underground Research Laboratory(URL)in Tournemire(France)in 2019 and was equipped with 76 wired and wireless sensors.The test is still in progress,but the collected set of data provides already valuable information of the hydro-mechanical behavior of VSS during hydration.The swelling core consists of a mixture of highdensity pellets and powder of MX80 bentonite in a ratio of 80/20(in dry mass).An innovative method was adopted to drill a 1-m diameter and w10-m deep shaft in order to minimize the rock perturbation at the sidewalls.Because a specific protocol was adopted to install the bentonite mixture together with a careful characterization of the core during construction,VSEAL 1 constitutes the unique in situ sealing test with a well-known initial structural distribution of the pellets and the powder.Some heterogeneities occurred within the experiment during the installation process:a damaged zone developed around the shaft walls due to the interruption of the installation operations caused by COVID19 lockdown in France;a technological gap with a variable thickness between the last pellets layer and the top confining lid and a heterogeneous distribution of the bentonite powder at some layers inducing large inter pellets voids close to the bentonite-rock interface.Artificially injected water volume,relative humidity,water content and swelling pressure in both radial and axial directions were monitored.Comparison of the results showed that the presence of installation-induced heterogeneities led to the generation of preferential flow paths that influenced the swelling pressure evolution at radial and axial directions.展开更多
The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling,intrusion into rock fractures,and erosion.Inevitably,erosion and subsequent bentonite mass loss due to gr...The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling,intrusion into rock fractures,and erosion.Inevitably,erosion and subsequent bentonite mass loss due to groundwater inflow can aggravate the overall integrity of the engineered barrier system.Therefore,the coupled hydro-mechanical interaction between the buffer and rock during groundwater inflow and bentonite intrusion should be evaluated to guarantee the long-term safety of deep geological disposal.This study investigated the effect of bentonite erosion and intrusion on the elastic wave propagation characteristics in jointed rocks using a quasi-static resonant column test.Jointed rock specimens with different joint conditions(i.e.joint surface saturation and bentonite filling)were prepared using granite rock discs sampled from the Korea Underground Research Tunnel(KURT)and Gyeongju bentonite.The long-wavelength longitudinal and shear wave velocities were measured under different normal stress levels.A Hertzian-type power model was used to fit the wave velocities,and the relationship between the two fitted parameters provided the trend of joint conditions.Numerical simulations using three-dimensional distinct element code(3DEC)were conducted to better understand how the long-wavelength wave propagates through wet bentonite-filled rock joints.展开更多
Bentonite,consisting of clay minerals of the montmorillonite group,has been widely used as an adsorbent and backfill material in nuclear waste disposal and groundwater remediation.It is challenging to use bentonite as...Bentonite,consisting of clay minerals of the montmorillonite group,has been widely used as an adsorbent and backfill material in nuclear waste disposal and groundwater remediation.It is challenging to use bentonite as a filling material in cold regions since bentonite is highly sensitive to thermal environmental changes,during which its bulk volume and microstructure change significantly.In this study,a series of one-dimensional and three-dimensional freeze-thaw tests were carried out within a closed system to investigate the influencing factors of the deformation of bentonite under freeze-thaw cycles.Results show that the initial soil water content greatly impacts bentonite's deformation during freeze-thaw cycles.For an initial higher degree of saturation(Sr),the expansion caused by the formation of ice lenses has a greater impact than the shrinkage induced by dehydration,ice-cementation,and so on.Conversely,bentonite tends to shrink at a lower degree of saturation during freezing.And the critical degree of saturation that determines bentonite's behavior of frost heave or frost shrinkage seems to be roughly 0.8.As the number of freeze-thaw cycles rises,initially uncompacted bentonite clay becomes more compacted,and initially compacted bentonite clay remains unchanged.展开更多
Iron-pillared bentonite(FB)was prepared by Fe(III)modified bentonite,and then the composites(FB-OS)were prepared by iron-pillared bentonite and oyster shell powder.The composites were characterized by FTIR,SEM,TGA,and...Iron-pillared bentonite(FB)was prepared by Fe(III)modified bentonite,and then the composites(FB-OS)were prepared by iron-pillared bentonite and oyster shell powder.The composites were characterized by FTIR,SEM,TGA,and EDS,and the phosphorus removal test was carried out.The results showed that FB-OS contained a large amount of CaO.Its structure was compact,but there were gaps in it.The maximum bending stress and compressive strength were 43.7 N and 0.927 MPa,respectively.The phosphorus removal test showed that the phosphorus removal rate of FB-OS was more than 90%,and measured the maximum adsorption capacity was 48.31 mg/g.A large amount of spherical products were produced on the surface and inside of FB-OS after phos-phorus removal,it was speculated that spherical products were amorphous calcium phosphate in the paper.Ana-lysis indicated that there was chemical adsorption during phosphorus removal.The kinetic equation of phosphorus adsorption by FB-OS was qt=10:193t/1+2:574t (R^(2)=0.995).The adsorption rate was mainly controlled by outerfilm diffusion and intraparticle diffusion.展开更多
In the French deep geological disposal for radioactive wastes,compacted bentonite/claystone mixtures have been considered as possible sealing materials.After emplacement in place,such mixtures are hydrated by the site...In the French deep geological disposal for radioactive wastes,compacted bentonite/claystone mixtures have been considered as possible sealing materials.After emplacement in place,such mixtures are hydrated by the site solution as well as the cement solution produced by the degradation of concrete.In this study,the effects of synthetic site solution and cement solution on the hydro-mechanical behaviour of compacted mixtures of claystone and two types of bentonites(MX80 Na-bentonite and Sardinia Cabentonite)were investigated by carrying out a series of swelling pressure,hydraulic conductivity and mercury intrusion porosimetry(MIP)tests.It was found that for the MX80 bentonite/claystone mixture hydrated with synthetic site solution,the swelling capacity was reduced compared to the case with deionised water owing to the transformation of Na-montmorillonite to multi-cation dominant montmorillonite by cation exchanges.For the Sardinia bentonite/claystone mixture,the similar increasing rate of swelling pressure was observed during the crystalline swelling process for different solutions,suggesting insignificant cation exchanges.Additionally,the cations in the synthetic site solution could reduce the thickness of diffuse double layer and the osmotic swelling for both MX80 bentonite/claystone and Sardinia bentonite/claystone mixtures.The large-pore volume increased consequently and enhanced water flow.In the cement solution,the hydroxide could also dissolve the montmorillonite,reducing the swelling pressure,and increase the large-pore volume,facilitating the water flow.Furthermore,the decrease of swelling pressure and the increase of hydraulic conductivity were more significant in the case of low dry density because of more intensive interaction between montmorillonite and hydroxide due to the high permeability.展开更多
The adsorption of the bentonite toward Ni(II) from aqueous solution was studied to obtain optimum conditions,equilibrium model,thermodynamic and kinetic parameters.Statistical method was used to evaluate maximum amoun...The adsorption of the bentonite toward Ni(II) from aqueous solution was studied to obtain optimum conditions,equilibrium model,thermodynamic and kinetic parameters.Statistical method was used to evaluate maximum amount of adsorbed Ni(II).In this work,p H of solution during stirring,contact time,initial Ni(II) concentration,particle size of bentonite and amount of bentonite were considered as effective parameters which should be examined.The increase of temperature has negative effect on the Ni(II) adsorption.The equilibrium data were correlated well with Freundlich and Dubinin–Radushkevich isotherm models the correlation coefficients of which are(R^2) 0.994 and 0.971,respectively.This model indicates heterogeneous and chemical absorption or ion exchange process.The values of thermodynamic parameters such as ΔH°,ΔS° and ΔG° of nickel adsorption reveal that it is a spontaneous,exothermic and associative process.The experimental data fit the pseudo-second-order kinetic very well with correlation coefficient(R^2) more than 0.995.展开更多
Gaomiaozi(GMZ)bentonite is a potential buffer/backfill material for a deep geological disposal of highlevel radioactive waste.It has a wide pore size distribution(PSD)with sizes ranging from several nanometers to more...Gaomiaozi(GMZ)bentonite is a potential buffer/backfill material for a deep geological disposal of highlevel radioactive waste.It has a wide pore size distribution(PSD)with sizes ranging from several nanometers to more than one hundred microns.Thus,properly characterizing the pore structures of GMZ bentonite is a challenging issue.In this study,pressure-controlled porosimetry(PCP),ratecontrolled porosimetry(RCP),and scanning electron microscopy(SEM)were used to investigate the PSD of GMZ bentonite,The results indicate that each method has its limitation,and a combined use of PCP and RCP is suitable to obtain the full-scale PSD of GMZ bentonite.Moreover,we also compared the full-scale PSD with nuclear magnetic resonance(NMR)result.It is found that there is no significant difference in the range of PSD characterization between NMR and mercury intrusion method(PCP and RCP).However,in a ce rtain range,the detection accuracy of NMR is higher than that of mercury injection method.Finally,permeability prediction based on PCP and SEM data was conducted,and both of the two methods were found to be able to predict the permeability.The combined method is effective to obtain the full-scale PSD of GMZ bentonite,which is the key to estimation of the sealing ability of bentonite buffer.展开更多
Ni supported on bentonite was prepared by the impregnation method with different nickel contents, applied to the hydrogenation of nitrobenzene to aniline in a fixed-bed reactor, and it was characterized by X-ray diffr...Ni supported on bentonite was prepared by the impregnation method with different nickel contents, applied to the hydrogenation of nitrobenzene to aniline in a fixed-bed reactor, and it was characterized by X-ray diffraction(XRD), H_2-temperature programmed reduction(H_2-TPR), and X-ray photoelectron spectrometry(XPS). The results showed that Ni/bentonite catalyst with 20 wt% nickel content provided a higher conversion of nitrobenzene and selectivity of aniline compared to other catalysts. Ni O was the precursor of the active component of the catalyst, and the small crystallite size as well as the highly dispersed Ni O on the Ni/bentonite-20 catalyst, contributed to the catalytic performance. The hydrogenation of nitrobenzene was carried out at 300 °C with a H_2 gaseous hourly space velocity of 4800 ml·(g cat)^(-1)·h^(-1)and a nitrobenzene liquid hourly space velocity of4.8 ml·(g cat)^(-1)·h^(-1)over Ni/bentonite-20. A 95.7% nitrobenzene conversion and 98.8% aniline selectivity were obtained. While the nitrobenzene liquid hourly space velocity was 4.8 ml·(g cat)^(-1)·h^(-1), the yield of aniline was more than 95.0% during a 10-hour reaction.展开更多
A 20 wt% Ni/bentonite catalyst was prepared by a solution combustion synthesis (SCS), which exhibited higher activity for the CO_2methanation than that of an impregnation method (IPM), and the catalyst prepared by SCS...A 20 wt% Ni/bentonite catalyst was prepared by a solution combustion synthesis (SCS), which exhibited higher activity for the CO_2methanation than that of an impregnation method (IPM), and the catalyst prepared by SCS showed a CO_2 conversion of 85% and a CH4selectivity of 100% at 300 °C, atmospheric pressure, and 3600 ml·(g cat)-1·h-1, and the catalyst exhibited stable within a 110-h reaction. The results showed higher me- tallic Ni dispersion, smaller Ni particle size, larger specific surface area and lower reduction temperature in the Ni/ bentonite prepared by SCS than that of IPM. And the Ni/bentonite prepared by the SCS moderated the interaction between NiO and bentonite.展开更多
Kozeny-Carman(KC) equation is a well-known relation between hydraulic conductivity and pore properties in porous material. The applications of KC equation to predicting saturated hydraulic conductivities of sands and ...Kozeny-Carman(KC) equation is a well-known relation between hydraulic conductivity and pore properties in porous material. The applications of KC equation to predicting saturated hydraulic conductivities of sands and non-expansive soils are well documented. However, KC equation is incapable of predicting saturated hydraulic conductivity of expansive soil(e.g. bentonite) well. Based on a new dualpore system, this study modified KC equation for improving the prediction of saturated hydraulic conductivities of bentonites. In this study, an assumption that inter-layer space(micropore) has limited effect on fluid flow performance of compacted bentonite was adopted. The critical parameters including total porosity and total tortuosity in conventional KC equation were replaced by macroporosity and tortuosity of macropore, respectively. Macroporosity and microporosity were calculated by basal spacing of compacted bentonite, which was estimated by assuming that specific surface area is changeable during saturation process. A comprehensive comparison of bentonite’s saturated hydraulic conductivity predictions, including modified KC equation proposed in this study, conventional KC equation, and prediction method based on diffuse double layer(DDL) theory, was carried out. It was found that the predicted saturated hydraulic conductivity of bentonites calculated using modified KC equation fitted the experimental data better than others to a certain extent.展开更多
The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion ...The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion techniques to investigate the diffusion behavior of HTO and ^(99)TcO_4^- on GMZ bentonite of various densities. Diffusion rates were calculated by measuring the diffusion coefficients(De, Da), plotting breakthrough curves and interpreting experiment data. The apparent and effective diffusion coefficients of HTO ranged from(1.68 ± 0.40) 9 × 10^(-11) to(2.80 ± 0.62) 9 × 10^(-11) m^2/s and from(4.61 ±1.28) 9 × 10^(-12) to (16.2 ± 2.50) 9 × 10^(-12) m^2/s, respectively.The apparent and effective diffusion coefficients of^(99)TcO_4^-ranged from(5.26 ± 0.16) 9 × 10^-12to(7.78 ± 0.43) 9× 10^-12m^2/s and from(1.49 ± 0.002) 9 × 10^(-12) to(4.16 ±0.07) 9 × 10^(-12) m^2/s, respectively. The distribution coefficients of HTO and^(99)TcO_4^-ranged from(0.70 ± 0.12) 9× 10^(-2) to(1.36 ± 0.53) 9 × 10^(-2) mL/g and from(1.12 ±0.06) 9 × 10^(-2) to(5.79 ± 2.22) 9 × 10^(-2) mL/g, respectively.The Deand Kdvalues were shown to decrease with an increase in the bulk dry density of compacted bentonite. Our results show that HTO and ^(99)Tc could be considered nonsorbent radionuclides. The data obtained in this studyprovide a valuable reference for the safety assessment of waste repositories.展开更多
The objective of this work is to determine changes of surface properties of a bentonite after acid activation, using hydrochloric acid solutions (HCl) at room temperature. XRD, FX, FTIR, MEB, and BET analyses of the s...The objective of this work is to determine changes of surface properties of a bentonite after acid activation, using hydrochloric acid solutions (HCl) at room temperature. XRD, FX, FTIR, MEB, and BET analyses of the samples have been carried out to examine the structure of bentonite before and after acid activation. It is found that the raw bentonite is composed of dioctahedral montmorillonite with predominant quantity and certain amounts of quartz, albite and illite, etc. It has an cation exchange capacity (CEC) of 74.32 meq/g which allows it to be characterized as typical sodium bentonite. The changes, at low acid concentrations, are the result from from cation exchange (exchangeable cations with H+ ions). Differences of surface area at high acid concentrations (0.25 - 0.4 M) were caused by structural changes and partial decomposition of the samples. Data of surface area measurements have showed that with increase of concentration of hydrochloric acid, the surface area increased. The maximum value (837.11 m2/g) was reached by the sample activated with 0.4 M HCl. By against, activation with higher concentration (0.6 M) caused a decrease in the surface area.展开更多
The aim of this study is to report batch adsorption results of Cd (II) and Cr (VI) onto Algerian bentonite. The equilibrium adsorption process was achieved at about 120 min contact time. The kinetic and isotherms aspe...The aim of this study is to report batch adsorption results of Cd (II) and Cr (VI) onto Algerian bentonite. The equilibrium adsorption process was achieved at about 120 min contact time. The kinetic and isotherms aspects of Cr (VI) and Cd (II) adsorption were investigated by varying operation parameters such as pH (0.5 - 6), initial Cd (II) and Cr (VI) concentrations (50 - 200 mg/l) and temperature (293.15 K - 343.15 K). The optimum conditions obtained were: pH = 6.0 and 4.0 for Cd (II) and Cr (VI) respectively, initial concentrations of Cd (II) and Cr (VI) = 50 mg/L and T = 293.15 K. The kinetic of the adsorption process was studied by application of the most important kinetic models namely the pseudo-first order, the pseudo-second order and Elovich equations. The results showed that the pseudo-second order model fitted well the adsorption data of Cr (VI) whereas, and the Cd (II) adsorption data fitted best the Elovich equation. The equilibrium data fitted best the Langmuir isotherm, and the maximum adsorption capacity was determined through this model and was found to be 13.17 and 12.61 mg/g for Cd (II) and Cr (VI) respectively. The temperature had a reverse effect on the Cd (II) and Cr (VI) adsorption;our results showed that the removal efficiency increased to82.4% and 55.70% for Cd (II) and Cr (VI)when the temperature decreasedto 293.15 K.The negative figures of the Gibbs free energy ΔG°ads values range from -15.23 kJ/mol to -14.37 kJ/mol for Cd (II) and from -9.70 kJ/mol to -9.64 kJ/mol for Cr(VI) at 293.15 K to 343.15 K showed that the adsorption process is spontaneous and favourable. These results confirmed the ability of the low-cost Algerian natural bentonite to efficiently and competitively adsorb the two toxic elements investigated: cadmium (II) and chromium (VI).展开更多
The problem of colority control of printing and dyeing wastewater has become a technical problem that plagues related companies.Bentonite is an adsorbent with excellent properties.Modification of bentonite with enviro...The problem of colority control of printing and dyeing wastewater has become a technical problem that plagues related companies.Bentonite is an adsorbent with excellent properties.Modification of bentonite with environmentally friendly substances can improve its decolorization performance.In this experiment,the simulated printing and dyeing wastewater was taken as the control object,and the bentonite was modified with environmentally friendly materials such as sodium carboxymethyl cellulose(CMC)and lignin to prepare a new modified bentonite;then the modified bentonite was used to adsorb the simulated wastewater to reduce the water colority and COD;finally the relevant design of the adsorption process was made.Results indicate that M lignin∶M CMC∶M original bentonite=1∶2∶97 had the optimum treatment effect,the optimum modification temperature was 30℃ and the modification time was 4 h;the optimum conditions for the adsorption process were:pH=5,temperature=30℃,reaction time=60 min,dosage=0.05 g of modified bentonite/mL simulated dye solution.The final removal rate of colority and COD reached 95.0% and 98.2%,respectively.Compared with the original bentonite,this new modified bentonite has greater adsorption capacity and thus has greater application value.展开更多
The sorption of Pb(II), Cd(II), and Ni(II) toxic metal ions from aqueous solution by composite alginate-bentonite and alginate was investigated. The affinity and sorption capacity of the toxic metal ions for both type...The sorption of Pb(II), Cd(II), and Ni(II) toxic metal ions from aqueous solution by composite alginate-bentonite and alginate was investigated. The affinity and sorption capacity of the toxic metal ions for both type of samples were evaluated. The Langmuir maximum sorption capacity for each toxic metal ion increased for alginate-bentonite as compared to alginate. However, affinity for toxic metal ion remained unchanged for both alginate-bentonite and alginate in the order of Pb(II) > Cd(II) > Ni(II). Alginate-bentonite also shortens the duration required for complete sorption. Elementary mapping analysis depicts the gradient diffusion of toxic metal ions into the centre of alginate-bentonite beads indicated that sorption was contributed by surface adsorption and diffusion.展开更多
A new adsorbent namely bentonite/chitosan beads has been synthesized and studied for its defluoridation efficiency. Bentonite was activated and the beads were prepared using the inverse suspension polymerization metho...A new adsorbent namely bentonite/chitosan beads has been synthesized and studied for its defluoridation efficiency. Bentonite was activated and the beads were prepared using the inverse suspension polymerization method. The bentonite/chitosan beads (bentonite dosage of 3.0 g) showed an adsorption capacity of 0.895 mg/g whereas chitosan beads had only 0.359 mg/g. The optimal pH value was observed at pH 5 where the adsorbent reached the maximum defluoridation capacity of 1.164 mg/g. The effect of temperature, contact time and initial fluoride concentration on the adsorption capacity of the adsorbent has also been investigated. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and Fourier-transform infrared spectrometry (FTIR) were used to characterize the adsorbent. The adsorption of fluoride onto the adsorbent followed Freundlich isotherm model and pseudo-second order kinetic model. The fluoride loaded adsorbent could be regenerated using sodium hydroxide.展开更多
This research presents the evaluation of activated Bentonite material for treatment of used transformer oil. Different properties such as;electrical, physical, chemical and thermal of used transformer oil were meas-ur...This research presents the evaluation of activated Bentonite material for treatment of used transformer oil. Different properties such as;electrical, physical, chemical and thermal of used transformer oil were meas-ured before and after purification and treatment. Two power transformers were used in this research (6.4: 4.6 MVA, 3 phases, 50 Hz). One of them was filled with purified oil and the other was filled with activated Bentonite treated oil after purification, and then the two power transformers were tested for one year under practical conditions of the operating field. Initial tests have indicated that the use of Activated BENTONITE in the treatment process for the aged transformer oil improved breakdown voltage, water content, total acidi-ty and flash point. Thus activated Bentonite gives an ideal treatment of aged transformer oil with its environmental and economic advantages. Moreover, activated Bentonite is available at many places in Egypt with low costs.展开更多
Acetals and ketals are among the important materials of organic synthesis and as protecting agent of carbonyl functionality. A milder, efficient and green synthesis of acetals and ketals has been developed using Silic...Acetals and ketals are among the important materials of organic synthesis and as protecting agent of carbonyl functionality. A milder, efficient and green synthesis of acetals and ketals has been developed using Silicotungstic acid modified Bentonite (STA-Ben) as a catalyst. STA-Ben has been synthesized and characterized by various analytical techniques. It has been found to be an efficient and reusable catalyst for the synthesis of acetyl derivatives in excellent yields. In order to elucidate the efficiency of the STA-Ben as catalyst, reaction has also been performed using various catalysts. The reaction conditions (time and amount of catalyst) have been optimized using various catalysts. The products of the various reactions have been characterized by FT-IR, NMR.展开更多
The removing zinc cation from aqueous solution by Ca-bentonite and Na-exchanged bentonite was studied. The factors such as the initial concentration of Zn2+, the liquid-to-solid ratio, pH, adsorption time, stirring sp...The removing zinc cation from aqueous solution by Ca-bentonite and Na-exchanged bentonite was studied. The factors such as the initial concentration of Zn2+, the liquid-to-solid ratio, pH, adsorption time, stirring speed, coexisting ions, temperature and bentonite particle size were investigated. The results show that the adsorption process of bentonite accorded with the Freundlich isotherm model, the removal of Zn2+ by Ca-bentonite and Na-exchanged bentonite reached equilibrium in 2 h, and adsorption of Na- bentonite was superior to Ca-bentonite. The adsorption rate of zinc increased with increasing pH, temperature, stirring speed, time span and with decreasing bentonite particle, the initial concentration of Zn2+ and the liquid-to-solid ratio. In mixed solution which contains Pb2+and Cr6+, Pb2+ has no influ- ence on the removal of Zn2+ by both the bentonites while Cr6+can decease it.展开更多
文摘To understand the self-healing property of an engineered barrier for radioactive waste disposal,the hydraulic conductivity of compacted bentoniteesand mixtures saturated with artificial seawater(SW)before and after gas migration was examined.Na-and Ca-bentonites were mixed with fine sand at a ratio of 70%bentonite in dry weight.Two aspects were considered during the experiment:the hydraulic conductivity of the specimen that was resaturated after gas migration and the distribution of water content immediately after gas migration to study gas migration pathways.The gas migrated through the entire cross-section of the specimen,and gas breakthrough occurred in the equilibrium swelling pressure range approximately.Subsequently,the gas flow rate reached a sufficient large value when the gas pressure was approximately twice the equilibrium axial pressure(the sum of swelling and confining pressures),which excluded the back pressure.Although the gas migration pathway was not visible when the specimen was observed immediately after gas migration,the water content distribution showed that several parts of the specimen with lower water content were connected in the direction of gas migration.After resaturation,the change in permeability was within a limited rangedtwo to three times larger than that before gas migration for each type of bentonite in SW.This slight change suggests that gas migration creates a pore structure that cannot be sealed via crystalline swelling of montmorillonite in SW,even if highly compacted bentonite is used under a constant-volume condition.
文摘Recently,the Institute for Radiological protection and Nuclear Safety(IRSN)has launched VSEAL(Vertical SEALing)project to investigate the impact of gas migration on the long-term performance of bentonite based vertical sealing systems(VSS).The first VSEAL in situ test was emplaced in IRSN’s Underground Research Laboratory(URL)in Tournemire(France)in 2019 and was equipped with 76 wired and wireless sensors.The test is still in progress,but the collected set of data provides already valuable information of the hydro-mechanical behavior of VSS during hydration.The swelling core consists of a mixture of highdensity pellets and powder of MX80 bentonite in a ratio of 80/20(in dry mass).An innovative method was adopted to drill a 1-m diameter and w10-m deep shaft in order to minimize the rock perturbation at the sidewalls.Because a specific protocol was adopted to install the bentonite mixture together with a careful characterization of the core during construction,VSEAL 1 constitutes the unique in situ sealing test with a well-known initial structural distribution of the pellets and the powder.Some heterogeneities occurred within the experiment during the installation process:a damaged zone developed around the shaft walls due to the interruption of the installation operations caused by COVID19 lockdown in France;a technological gap with a variable thickness between the last pellets layer and the top confining lid and a heterogeneous distribution of the bentonite powder at some layers inducing large inter pellets voids close to the bentonite-rock interface.Artificially injected water volume,relative humidity,water content and swelling pressure in both radial and axial directions were monitored.Comparison of the results showed that the presence of installation-induced heterogeneities led to the generation of preferential flow paths that influenced the swelling pressure evolution at radial and axial directions.
基金funding support from the Nuclear Research and Development Program of the National Research Foundation of Korea(Grant Nos.2021M2E1A1085193 and 2020M2C9A1062949).
文摘The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling,intrusion into rock fractures,and erosion.Inevitably,erosion and subsequent bentonite mass loss due to groundwater inflow can aggravate the overall integrity of the engineered barrier system.Therefore,the coupled hydro-mechanical interaction between the buffer and rock during groundwater inflow and bentonite intrusion should be evaluated to guarantee the long-term safety of deep geological disposal.This study investigated the effect of bentonite erosion and intrusion on the elastic wave propagation characteristics in jointed rocks using a quasi-static resonant column test.Jointed rock specimens with different joint conditions(i.e.joint surface saturation and bentonite filling)were prepared using granite rock discs sampled from the Korea Underground Research Tunnel(KURT)and Gyeongju bentonite.The long-wavelength longitudinal and shear wave velocities were measured under different normal stress levels.A Hertzian-type power model was used to fit the wave velocities,and the relationship between the two fitted parameters provided the trend of joint conditions.Numerical simulations using three-dimensional distinct element code(3DEC)were conducted to better understand how the long-wavelength wave propagates through wet bentonite-filled rock joints.
基金supported by the National Natural Science Foundation of China(Nos.42072316,51979002).
文摘Bentonite,consisting of clay minerals of the montmorillonite group,has been widely used as an adsorbent and backfill material in nuclear waste disposal and groundwater remediation.It is challenging to use bentonite as a filling material in cold regions since bentonite is highly sensitive to thermal environmental changes,during which its bulk volume and microstructure change significantly.In this study,a series of one-dimensional and three-dimensional freeze-thaw tests were carried out within a closed system to investigate the influencing factors of the deformation of bentonite under freeze-thaw cycles.Results show that the initial soil water content greatly impacts bentonite's deformation during freeze-thaw cycles.For an initial higher degree of saturation(Sr),the expansion caused by the formation of ice lenses has a greater impact than the shrinkage induced by dehydration,ice-cementation,and so on.Conversely,bentonite tends to shrink at a lower degree of saturation during freezing.And the critical degree of saturation that determines bentonite's behavior of frost heave or frost shrinkage seems to be roughly 0.8.As the number of freeze-thaw cycles rises,initially uncompacted bentonite clay becomes more compacted,and initially compacted bentonite clay remains unchanged.
基金supported by the Project of Guangdong Academy of Building Research Group Co.,Ltd.,China(No.0100RDY2022D0000036).
文摘Iron-pillared bentonite(FB)was prepared by Fe(III)modified bentonite,and then the composites(FB-OS)were prepared by iron-pillared bentonite and oyster shell powder.The composites were characterized by FTIR,SEM,TGA,and EDS,and the phosphorus removal test was carried out.The results showed that FB-OS contained a large amount of CaO.Its structure was compact,but there were gaps in it.The maximum bending stress and compressive strength were 43.7 N and 0.927 MPa,respectively.The phosphorus removal test showed that the phosphorus removal rate of FB-OS was more than 90%,and measured the maximum adsorption capacity was 48.31 mg/g.A large amount of spherical products were produced on the surface and inside of FB-OS after phos-phorus removal,it was speculated that spherical products were amorphous calcium phosphate in the paper.Ana-lysis indicated that there was chemical adsorption during phosphorus removal.The kinetic equation of phosphorus adsorption by FB-OS was qt=10:193t/1+2:574t (R^(2)=0.995).The adsorption rate was mainly controlled by outerfilm diffusion and intraparticle diffusion.
基金supported by Ecole des Ponts Paris Tech and the French National Radioactive Waste Management Agency(Andra)China Scholarship Council for the grant scholarship。
文摘In the French deep geological disposal for radioactive wastes,compacted bentonite/claystone mixtures have been considered as possible sealing materials.After emplacement in place,such mixtures are hydrated by the site solution as well as the cement solution produced by the degradation of concrete.In this study,the effects of synthetic site solution and cement solution on the hydro-mechanical behaviour of compacted mixtures of claystone and two types of bentonites(MX80 Na-bentonite and Sardinia Cabentonite)were investigated by carrying out a series of swelling pressure,hydraulic conductivity and mercury intrusion porosimetry(MIP)tests.It was found that for the MX80 bentonite/claystone mixture hydrated with synthetic site solution,the swelling capacity was reduced compared to the case with deionised water owing to the transformation of Na-montmorillonite to multi-cation dominant montmorillonite by cation exchanges.For the Sardinia bentonite/claystone mixture,the similar increasing rate of swelling pressure was observed during the crystalline swelling process for different solutions,suggesting insignificant cation exchanges.Additionally,the cations in the synthetic site solution could reduce the thickness of diffuse double layer and the osmotic swelling for both MX80 bentonite/claystone and Sardinia bentonite/claystone mixtures.The large-pore volume increased consequently and enhanced water flow.In the cement solution,the hydroxide could also dissolve the montmorillonite,reducing the swelling pressure,and increase the large-pore volume,facilitating the water flow.Furthermore,the decrease of swelling pressure and the increase of hydraulic conductivity were more significant in the case of low dry density because of more intensive interaction between montmorillonite and hydroxide due to the high permeability.
文摘The adsorption of the bentonite toward Ni(II) from aqueous solution was studied to obtain optimum conditions,equilibrium model,thermodynamic and kinetic parameters.Statistical method was used to evaluate maximum amount of adsorbed Ni(II).In this work,p H of solution during stirring,contact time,initial Ni(II) concentration,particle size of bentonite and amount of bentonite were considered as effective parameters which should be examined.The increase of temperature has negative effect on the Ni(II) adsorption.The equilibrium data were correlated well with Freundlich and Dubinin–Radushkevich isotherm models the correlation coefficients of which are(R^2) 0.994 and 0.971,respectively.This model indicates heterogeneous and chemical absorption or ion exchange process.The values of thermodynamic parameters such as ΔH°,ΔS° and ΔG° of nickel adsorption reveal that it is a spontaneous,exothermic and associative process.The experimental data fit the pseudo-second-order kinetic very well with correlation coefficient(R^2) more than 0.995.
基金support of the National Natural Science Foundation of China(Grant Nos.51809263)the Open Fund of Key Laboratory of Deep Earth Science and Engineering(Sichuan University)(Grant Nos.DESE201906 and DESE201907)。
文摘Gaomiaozi(GMZ)bentonite is a potential buffer/backfill material for a deep geological disposal of highlevel radioactive waste.It has a wide pore size distribution(PSD)with sizes ranging from several nanometers to more than one hundred microns.Thus,properly characterizing the pore structures of GMZ bentonite is a challenging issue.In this study,pressure-controlled porosimetry(PCP),ratecontrolled porosimetry(RCP),and scanning electron microscopy(SEM)were used to investigate the PSD of GMZ bentonite,The results indicate that each method has its limitation,and a combined use of PCP and RCP is suitable to obtain the full-scale PSD of GMZ bentonite.Moreover,we also compared the full-scale PSD with nuclear magnetic resonance(NMR)result.It is found that there is no significant difference in the range of PSD characterization between NMR and mercury intrusion method(PCP and RCP).However,in a ce rtain range,the detection accuracy of NMR is higher than that of mercury injection method.Finally,permeability prediction based on PCP and SEM data was conducted,and both of the two methods were found to be able to predict the permeability.The combined method is effective to obtain the full-scale PSD of GMZ bentonite,which is the key to estimation of the sealing ability of bentonite buffer.
基金Supported by the National Natural Science Foundation of China(21566005,21425627)Natural Science Foundation of Guangxi province(2014GXNSFAA118049)+1 种基金the Open Project of Guangxi Key Laboratory of Petrochemical Resource Processing and Process Intensification Technology(2013K011)the Patent Project of Colleges and Universities of Guangxi Zhuang Autonomous Region(KY2015ZL001)
文摘Ni supported on bentonite was prepared by the impregnation method with different nickel contents, applied to the hydrogenation of nitrobenzene to aniline in a fixed-bed reactor, and it was characterized by X-ray diffraction(XRD), H_2-temperature programmed reduction(H_2-TPR), and X-ray photoelectron spectrometry(XPS). The results showed that Ni/bentonite catalyst with 20 wt% nickel content provided a higher conversion of nitrobenzene and selectivity of aniline compared to other catalysts. Ni O was the precursor of the active component of the catalyst, and the small crystallite size as well as the highly dispersed Ni O on the Ni/bentonite-20 catalyst, contributed to the catalytic performance. The hydrogenation of nitrobenzene was carried out at 300 °C with a H_2 gaseous hourly space velocity of 4800 ml·(g cat)^(-1)·h^(-1)and a nitrobenzene liquid hourly space velocity of4.8 ml·(g cat)^(-1)·h^(-1)over Ni/bentonite-20. A 95.7% nitrobenzene conversion and 98.8% aniline selectivity were obtained. While the nitrobenzene liquid hourly space velocity was 4.8 ml·(g cat)^(-1)·h^(-1), the yield of aniline was more than 95.0% during a 10-hour reaction.
基金Supported by the National Natural Science Foundation of China(21566005)the Natural Science Foundation of Guangxi Province(2016GXNSFFA380015)
文摘A 20 wt% Ni/bentonite catalyst was prepared by a solution combustion synthesis (SCS), which exhibited higher activity for the CO_2methanation than that of an impregnation method (IPM), and the catalyst prepared by SCS showed a CO_2 conversion of 85% and a CH4selectivity of 100% at 300 °C, atmospheric pressure, and 3600 ml·(g cat)-1·h-1, and the catalyst exhibited stable within a 110-h reaction. The results showed higher me- tallic Ni dispersion, smaller Ni particle size, larger specific surface area and lower reduction temperature in the Ni/ bentonite prepared by SCS than that of IPM. And the Ni/bentonite prepared by the SCS moderated the interaction between NiO and bentonite.
基金support from the Ministry of Economy, Trade, and Industry (METI) of Japanfunding support from Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (Grant No. KYCX21_0122)
文摘Kozeny-Carman(KC) equation is a well-known relation between hydraulic conductivity and pore properties in porous material. The applications of KC equation to predicting saturated hydraulic conductivities of sands and non-expansive soils are well documented. However, KC equation is incapable of predicting saturated hydraulic conductivity of expansive soil(e.g. bentonite) well. Based on a new dualpore system, this study modified KC equation for improving the prediction of saturated hydraulic conductivities of bentonites. In this study, an assumption that inter-layer space(micropore) has limited effect on fluid flow performance of compacted bentonite was adopted. The critical parameters including total porosity and total tortuosity in conventional KC equation were replaced by macroporosity and tortuosity of macropore, respectively. Macroporosity and microporosity were calculated by basal spacing of compacted bentonite, which was estimated by assuming that specific surface area is changeable during saturation process. A comprehensive comparison of bentonite’s saturated hydraulic conductivity predictions, including modified KC equation proposed in this study, conventional KC equation, and prediction method based on diffuse double layer(DDL) theory, was carried out. It was found that the predicted saturated hydraulic conductivity of bentonites calculated using modified KC equation fitted the experimental data better than others to a certain extent.
基金the Nuclear Backend Management Department at Taiwan Power Company for financially supporting this research
文摘The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion techniques to investigate the diffusion behavior of HTO and ^(99)TcO_4^- on GMZ bentonite of various densities. Diffusion rates were calculated by measuring the diffusion coefficients(De, Da), plotting breakthrough curves and interpreting experiment data. The apparent and effective diffusion coefficients of HTO ranged from(1.68 ± 0.40) 9 × 10^(-11) to(2.80 ± 0.62) 9 × 10^(-11) m^2/s and from(4.61 ±1.28) 9 × 10^(-12) to (16.2 ± 2.50) 9 × 10^(-12) m^2/s, respectively.The apparent and effective diffusion coefficients of^(99)TcO_4^-ranged from(5.26 ± 0.16) 9 × 10^-12to(7.78 ± 0.43) 9× 10^-12m^2/s and from(1.49 ± 0.002) 9 × 10^(-12) to(4.16 ±0.07) 9 × 10^(-12) m^2/s, respectively. The distribution coefficients of HTO and^(99)TcO_4^-ranged from(0.70 ± 0.12) 9× 10^(-2) to(1.36 ± 0.53) 9 × 10^(-2) mL/g and from(1.12 ±0.06) 9 × 10^(-2) to(5.79 ± 2.22) 9 × 10^(-2) mL/g, respectively.The Deand Kdvalues were shown to decrease with an increase in the bulk dry density of compacted bentonite. Our results show that HTO and ^(99)Tc could be considered nonsorbent radionuclides. The data obtained in this studyprovide a valuable reference for the safety assessment of waste repositories.
文摘The objective of this work is to determine changes of surface properties of a bentonite after acid activation, using hydrochloric acid solutions (HCl) at room temperature. XRD, FX, FTIR, MEB, and BET analyses of the samples have been carried out to examine the structure of bentonite before and after acid activation. It is found that the raw bentonite is composed of dioctahedral montmorillonite with predominant quantity and certain amounts of quartz, albite and illite, etc. It has an cation exchange capacity (CEC) of 74.32 meq/g which allows it to be characterized as typical sodium bentonite. The changes, at low acid concentrations, are the result from from cation exchange (exchangeable cations with H+ ions). Differences of surface area at high acid concentrations (0.25 - 0.4 M) were caused by structural changes and partial decomposition of the samples. Data of surface area measurements have showed that with increase of concentration of hydrochloric acid, the surface area increased. The maximum value (837.11 m2/g) was reached by the sample activated with 0.4 M HCl. By against, activation with higher concentration (0.6 M) caused a decrease in the surface area.
文摘The aim of this study is to report batch adsorption results of Cd (II) and Cr (VI) onto Algerian bentonite. The equilibrium adsorption process was achieved at about 120 min contact time. The kinetic and isotherms aspects of Cr (VI) and Cd (II) adsorption were investigated by varying operation parameters such as pH (0.5 - 6), initial Cd (II) and Cr (VI) concentrations (50 - 200 mg/l) and temperature (293.15 K - 343.15 K). The optimum conditions obtained were: pH = 6.0 and 4.0 for Cd (II) and Cr (VI) respectively, initial concentrations of Cd (II) and Cr (VI) = 50 mg/L and T = 293.15 K. The kinetic of the adsorption process was studied by application of the most important kinetic models namely the pseudo-first order, the pseudo-second order and Elovich equations. The results showed that the pseudo-second order model fitted well the adsorption data of Cr (VI) whereas, and the Cd (II) adsorption data fitted best the Elovich equation. The equilibrium data fitted best the Langmuir isotherm, and the maximum adsorption capacity was determined through this model and was found to be 13.17 and 12.61 mg/g for Cd (II) and Cr (VI) respectively. The temperature had a reverse effect on the Cd (II) and Cr (VI) adsorption;our results showed that the removal efficiency increased to82.4% and 55.70% for Cd (II) and Cr (VI)when the temperature decreasedto 293.15 K.The negative figures of the Gibbs free energy ΔG°ads values range from -15.23 kJ/mol to -14.37 kJ/mol for Cd (II) and from -9.70 kJ/mol to -9.64 kJ/mol for Cr(VI) at 293.15 K to 343.15 K showed that the adsorption process is spontaneous and favourable. These results confirmed the ability of the low-cost Algerian natural bentonite to efficiently and competitively adsorb the two toxic elements investigated: cadmium (II) and chromium (VI).
基金Supported by Project of Shandong Province Natural Science Foundation of China(ZR2015PC022&BS2014HZ011)
文摘The problem of colority control of printing and dyeing wastewater has become a technical problem that plagues related companies.Bentonite is an adsorbent with excellent properties.Modification of bentonite with environmentally friendly substances can improve its decolorization performance.In this experiment,the simulated printing and dyeing wastewater was taken as the control object,and the bentonite was modified with environmentally friendly materials such as sodium carboxymethyl cellulose(CMC)and lignin to prepare a new modified bentonite;then the modified bentonite was used to adsorb the simulated wastewater to reduce the water colority and COD;finally the relevant design of the adsorption process was made.Results indicate that M lignin∶M CMC∶M original bentonite=1∶2∶97 had the optimum treatment effect,the optimum modification temperature was 30℃ and the modification time was 4 h;the optimum conditions for the adsorption process were:pH=5,temperature=30℃,reaction time=60 min,dosage=0.05 g of modified bentonite/mL simulated dye solution.The final removal rate of colority and COD reached 95.0% and 98.2%,respectively.Compared with the original bentonite,this new modified bentonite has greater adsorption capacity and thus has greater application value.
文摘The sorption of Pb(II), Cd(II), and Ni(II) toxic metal ions from aqueous solution by composite alginate-bentonite and alginate was investigated. The affinity and sorption capacity of the toxic metal ions for both type of samples were evaluated. The Langmuir maximum sorption capacity for each toxic metal ion increased for alginate-bentonite as compared to alginate. However, affinity for toxic metal ion remained unchanged for both alginate-bentonite and alginate in the order of Pb(II) > Cd(II) > Ni(II). Alginate-bentonite also shortens the duration required for complete sorption. Elementary mapping analysis depicts the gradient diffusion of toxic metal ions into the centre of alginate-bentonite beads indicated that sorption was contributed by surface adsorption and diffusion.
文摘A new adsorbent namely bentonite/chitosan beads has been synthesized and studied for its defluoridation efficiency. Bentonite was activated and the beads were prepared using the inverse suspension polymerization method. The bentonite/chitosan beads (bentonite dosage of 3.0 g) showed an adsorption capacity of 0.895 mg/g whereas chitosan beads had only 0.359 mg/g. The optimal pH value was observed at pH 5 where the adsorbent reached the maximum defluoridation capacity of 1.164 mg/g. The effect of temperature, contact time and initial fluoride concentration on the adsorption capacity of the adsorbent has also been investigated. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and Fourier-transform infrared spectrometry (FTIR) were used to characterize the adsorbent. The adsorption of fluoride onto the adsorbent followed Freundlich isotherm model and pseudo-second order kinetic model. The fluoride loaded adsorbent could be regenerated using sodium hydroxide.
文摘This research presents the evaluation of activated Bentonite material for treatment of used transformer oil. Different properties such as;electrical, physical, chemical and thermal of used transformer oil were meas-ured before and after purification and treatment. Two power transformers were used in this research (6.4: 4.6 MVA, 3 phases, 50 Hz). One of them was filled with purified oil and the other was filled with activated Bentonite treated oil after purification, and then the two power transformers were tested for one year under practical conditions of the operating field. Initial tests have indicated that the use of Activated BENTONITE in the treatment process for the aged transformer oil improved breakdown voltage, water content, total acidi-ty and flash point. Thus activated Bentonite gives an ideal treatment of aged transformer oil with its environmental and economic advantages. Moreover, activated Bentonite is available at many places in Egypt with low costs.
文摘Acetals and ketals are among the important materials of organic synthesis and as protecting agent of carbonyl functionality. A milder, efficient and green synthesis of acetals and ketals has been developed using Silicotungstic acid modified Bentonite (STA-Ben) as a catalyst. STA-Ben has been synthesized and characterized by various analytical techniques. It has been found to be an efficient and reusable catalyst for the synthesis of acetyl derivatives in excellent yields. In order to elucidate the efficiency of the STA-Ben as catalyst, reaction has also been performed using various catalysts. The reaction conditions (time and amount of catalyst) have been optimized using various catalysts. The products of the various reactions have been characterized by FT-IR, NMR.
文摘The removing zinc cation from aqueous solution by Ca-bentonite and Na-exchanged bentonite was studied. The factors such as the initial concentration of Zn2+, the liquid-to-solid ratio, pH, adsorption time, stirring speed, coexisting ions, temperature and bentonite particle size were investigated. The results show that the adsorption process of bentonite accorded with the Freundlich isotherm model, the removal of Zn2+ by Ca-bentonite and Na-exchanged bentonite reached equilibrium in 2 h, and adsorption of Na- bentonite was superior to Ca-bentonite. The adsorption rate of zinc increased with increasing pH, temperature, stirring speed, time span and with decreasing bentonite particle, the initial concentration of Zn2+ and the liquid-to-solid ratio. In mixed solution which contains Pb2+and Cr6+, Pb2+ has no influ- ence on the removal of Zn2+ by both the bentonites while Cr6+can decease it.
