Fluorographene with Narrow Lateral Size and Thickness Distributions Prepared for Enhancing Lubrication Performance of Bentonite Grease

Fluorographene(FG)with narrow lateral size and thickness distributions was prepared by a liquid-phase exfoliation method,based on liquid cascade centrifugation.The Rtec MFT-5000 tribo-meter was used to investigate the lubricating performance of bentonite grease enhanced by the as-prepared FG.The results showed that the coefficient of friction and the wear volume of bentonite grease with 0.3 wt%FG were decreased by 20.4%and 44.9%,respectively,as compared to those of the base grease.The main reason is that FG can promote the formation of the tribo-chemical reaction film consisting of complex carbon oxide,Fe_(2)O_(3)and FeF_(3)on the friction surface,which can remarkably improve the performance of friction reduction and prevent the appearance of severe wear.

Effect of drying cracks on swelling and self-healing of bentonite-sand blocks used as engineered barriers for radioactive waste disposal

Experiments were conducted to evaluate the healing of drying cracks in air-dried bentonite-sand blocks after hydration and swelling in groundwater,providing justifications to simplify the protection of blocks prior to installation in a high-level radioactive waste repository.Synthetic groundwater was prepared to represent the geochemistry of Beishan groundwater,and was used to hydrate the blocks during the swelling pressure and swelling strain measurements,as Beishan is the most promising site for China's repository.Healing of the surface cracks was recorded by photography,and healing of the internal cracks was visualized by CT images and hydraulic conductivity of air-dried blocks.The results indicate that the maximum swelling pressure and swelling strain are primarily affected by the geochemistry of Beishan groundwater,but not affected by the drying cracks.The maximum swelling pressure and swelling strain of air-dried blocks are comparable to or even higher than the pressure and strain of fresh blocks.The maximum swelling pressure measured in strong(i.e.high ion strength)Beishan groundwater was 44%of the pressure measured in deionized(DI)water,and the maximum swelling strain was reduced to 23%of the strain measured in DI water.Nevertheless,the remained swelling of the blocks hydrated in strong Beishan groundwater was sufficient to heal the surface and internal drying cracks,as demonstrated by the pictures of surface cracks and CT images.The hydraulic conductivity of the air-dried block permeated with strong groundwater was comparable(3.7×higher)to the hydraulic conductivity of the fresh block,indicating the self-healing of drying cracks after hydration and swelling in groundwater.A simplified method of protecting the block with plastic wraps before installation is recommended,since the remained swelling of the block hydrated in Beishan groundwater is sufficient to heal the drying cracks.

Saturated hydraulic conductivity of compacted bentonite-sand mixtures before and after gas migration in artificial seawater

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.

On the installation of an in situ large-scale vertical SEALing (VSEAL) experiment on bentonite pellet-powder mixture

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.

Influence of relative compaction and degree of saturation on the deformation characteristics of bentonite under freeze-thaw cycles

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.

Preparation of Iron-Pillared Bentonite/Oyster Shell Composite and Phosphate Adsorption in Water

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.

Investigation of long-wavelength elastic wave propagation through wet bentonite-filled rock joints

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.

Effect of shaking time, ionic strength, temperature and pH value on desorption of Cr(III) adsorbed onto GMZ bentonite

The Cr（III） desorption experiments of Gaomiaozi （GMZ） bentonite in aqueous solutions were performed. The variables affecting the desorption behaviors, such as contact time, concentration of the desorbent, pH value of the solution, temperature and desorption isotherms, were investigated by the batch experiments. The results show that the adsorbed Cr（III） on GMZ bentonite can be easily extracted by the desorbent. Kinetics examination shows that desorption is slower than adsorption, and the desorption rate increases with time and reaches the equilibrium after 3 h. The final desorption ratios of Cr（III） are 89.4%, 56.5%and 77.2%in the desorption solution with 0.1 mol/L HCl, 1 mol/L NaCl, and 1 mol/L CaCl2, respectively, and the concentration can promote the desorption progress. Furthermore, the results of successive regeneration cycles indicate that the bentonite has a good regeneration ability and reusability. The pH value is an important factor in the Cr（III） desorption from the GMZ bentonite. The results of adsorption and desorption isotherms show that both adsorption and desorption isotherms are consistent with the Freundlich equation. The comparison of adsorption and desorption isotherms implies that the adsorption/desorption hysteresis is negligible and the transport of Cr（III） in bentonite can be described by a reversible adsorption process.

Synthesis of nano-MoS_2/bentonite composite and its application for removal of organic dye

A nano-MoS2/bentonite composite was synthesized by calcinating MoS3 deposited on bentonite in H2. The obtained composite was characterized using thermogravimetric analysis, X-ray diffractometer, scanning electron microscope and transmission electron microscope. The results show that nano-MoS2 particles are distributed on the surface of bentonite and form layered structures with layer distance of about 0.64 nm. The composite presents an excellent performance for the removal of methyl orange. Some operation conditions affect the removal efficiency of methyl orange, such as dosage of composite, initial concentration of methyl orange, temperature and pH value. However, light source does not influence the removal efficiency. The removal mechanism is attributed to the adsorption of methyl orange on the nano-MoS2/bentonite composite. The adsorption of methyl orange on the composite is in accordance with the pseudo-second-order kinetic model.

Fe离子在Soil-Bentonite Slurry wall中的渗透行为研究

采用实验室研究方法,研究了SB(Soil Bentonite)材料对Fe离子的吸附,以及Fe离子在SB Slurry wall中的穿透行为,实验结果显示,SB对Fe离子的吸附符合langmuir等温线,Fe离子在SB中迁移时,导致SB材料的渗透系数比纯水的渗透系数大一个数量级,Fe离子流出浓度随着时间的增加在不断增加。

纳米级团簇结构Bentonite-DMDAAC-AM乳胶粒的合成与表征

：在 Ｗ／Ｏ乳液的分散相内，使分散于Ｂｅｎｏｎｉｔｅ层间的ＡＭ与预先插层其中的阳离子单体ＤＭＤＡＡ就地共聚合，利用聚合热使 Ｂｅｎｔｏｎｉｔｅ崩解，并进一步层间剥离，从而制备纳米级团簇结构一Ｂｅｎｔｏｎｉｔｅ-ＤＭＤＡＡ-ＡＭ乳胶粒。用动力学方法研究各种因素对聚合热的影响以及聚合热与Ｂｅｎｔｏｎｉｔｅ层片剥离程度的关系；用 ＸＲＤ、ＤＳＣ等手段研究了 Ｂｅｎｔｏｎｉｔｅ的插层与剥离程度，并用乳胶粒的电泳行为及ＩＲ对产物进行了表征。

苯酚在Soil-Bentonite Slurry walls中的传输研究

实验室研究了SB(Soil Bentonite)材料对苯酚的阻截性能,以及无机离子对苯酚在SB Slurry wall中传输的影响。实验结果显示,苯酚在SB Slurry wall材料中的渗透速度与水在材料中的渗透的速度相同。无机离子的加入,改变了墙体材料的渗透系数,使得苯酚在墙体材料中的迁移速度加快。迁移速度变化与无机离子的加入量有关,加入量越大,苯酚在墙体中的迁移速度越快。

Experimental investigation into temperature effect on hydro-mechanical behaviours of bentonite

The bentonite barrier of underground repositories for high-level radioactive waste will be hydrated by the groundwater while it is subjected to high temperatures due to the radioactive decay of the wastes. These changes of temperature affect the hydraulic and mechanical responses of bentonite, which has important effects on design and performance of repositories. The temperature influence on the hydro-mechanical behaviour of bentonite was studied in this paper by experiments, which were carried out with the Spanish FEBEX bentonite compacted at dry densities expected in the＇ repository （from 1.5 to 1.8 Mg/m^3）. The dependence of the swelling strains of bentonite on the temperature has been measured from 30℃ to 90 ℃. At high temperatures the swelling capacity of clay slightly decreases. Also, a clear decrease of swelling pressure as a function of temperature was observed for the same dry densities. Nevertheless, the deformation of bentonite is more dependent on the stress than the temperature. An increase in the permeability of water saturated bentonite with temperature has also been detected. The water retention curves of bentonite compacted at different dry densities were determined under isochoric conditions and in the range of temperatures from 20 ℃ to 120℃. For a given density and water content, the suction decreases as the temperature increases at a rate, which is larger than the one predicted on the basis of water surface tension changing with temperature. Mechanisms related to the physico-chemical interactions that take place at microscopic level, in particular the transfer of interlayer water to the macropores triggered by temperature, seem to explain qualitatively the experimental observations.

Statistical design and kinetic and thermodynamic studies of Ni(Ⅱ) adsorption on bentonite

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.

Effect of background electrolytes on the adsorption of nitroaromatic compounds onto bentonite

To further elucidate interaction of nitroaromatic compounds with mineral surface, the sorption of m-dinitrobenzene （m-DNB） and nitrobenzene to original bentonite in aqueous solution containing different electrolytes （i.e., KCl, NH4Cl, CaCl2 and Tetramethylammonium bromide （TMAB）） was studied. The sorption of m-DNB was greatly enhanced with the presence of KCl and NH4Cl, while little influence was observed with CaCl2 and TMAB, following the order of KCl 〉 NH4Cl 〉〉 TMAB, CaCl2, or DI water. For nitrobenzene, sorption enhancement only occurred at high nitrobenzene concentrations in the presence of KCl, and the solute equilibrium concentration at inflexion point was lowered with increasing KCl concentration. These sorption enhancements were significantly promoted with the increase of electrolyte concentration. The salting-out effect is insufficient to account for the sorption enhancement by original bentonite with increasing KCI or NH4Cl concentration. X-ray diffraction patterns of bentonite suspensions indicated that the sorption enhancement of m-DNB was attributed to the intercalation of K^＋ or NH4^＋ into bentonite interlayer and then dehydration with m-DNB to form inner-sphere complexes, which caused previously expanded bentonite interlayers to collapse in aqueous suspension, thus further enhanced the interaction of phenyl with siloxane surface. In comparison, the sorption enhancement of NB is attributed to the formation of outer-sphere complexes with K^＋ at high solute-loadings （〉 20（0-400 mg/kg）. The sorption of m-DNB to initially modified TMA^＋-bentonite and K^＋-bentonite was almost the same as respective sorption to original bentonite in solution containing TMA^＋ and K^＋.

Characterization, Acid Activation and Bleaching Performance of Bentonite from Xinjiang

Bentonite produced in Xiazijie, Xinjiang (China) was characterized by X-ray diffraction (XRD), dif- ferential thermal analysis (DTA), thermogravimetric analysis (TG) and cation exchange capacity (CEC). The ben- tonite is composed of dioctahedral montmorillonite with predominant quantity, certain amounts of quartz, feldspar and illite and minor amounts of kaolinite, gypsum, etc. The raw bentonite has a CEC of 0.6497 meq·g-1 and allows to be characterized as typical sodium bentonite. In order to bleach cottonseed oil, optimum conditions for sulfuric acid activation of the raw bentonites were investigated, which were obtained by selecting various acid strength, at 96—98℃ and activating for 4h with 1︰2 solid-liquid ratio. The acid activation bentonites were suitable for decol- orization of cottonseed oil through removing carotene and chlorophyll. The bleaching capabilities of different pig- ments with activated bentonite with treatment of 25% sulfuric acid were 70.3%, 73.1%, 83.2%, 81.8% and 88.9%, respectively. Bleaching with acid activated bentonite gave oils lower peroxide values and acid values.

NBR/ORGANOMODIFIED BENTONITE INTERCALATED HYBRIDS AND THEIR EFFECTS ON THE TOUGHNESS OF PVC

Hybrids of intercalative nitrile-butadiene rubber/organomodified bentonite (NBR/OMB) were prepared by thelatex intercalation technique. Investigation of their mechanical properties and the microstructore of NBR/OMB showed thatthe organomodified bentonite is an effective toughener for NBR. Transmission electronic microscopy (TEM) and X-rnydiffraction (XRD) tests showed that the NBR macromolecule could be intercalated into the galleries of bentonite.Incorporation of NBR/OMB hybrids as tougheners into poly(vinyl chloride) (PVC) results in a substantial increase in theimpact strength of PVC, but little decrease in its tensile strength and flexural strength, compared to the unmodified PVC.

Synthesis and Photocatalytic Activity of Ti-pillared Bentonite

Ti-pillared bentonite has been successfully prepared using a modified method that can induce the transformation of TiO2 pillar from amorphous to anatase phase at a low temperature （150℃）. The value of d0.01 =1.94 nm obtained by Ti-pillared bentonite is larger than that of corresponding raw clay （1.56 nm）. Due to large numbers of Ti-pillars formed, the Ti-pillared bentonite shows an excellent ability in adsorbing Rhodamine B （RB）. The photocatalytic activity and kinetic equation are investigated by decomposing RB solution under the UV irradiation. It is found that the Ti- pillared bentonite shows super photocatalytic activity for the degradation of RB solution compared with the untreated bentonite and pure TiO2, and the kinetic equation of the degradation of RB solution is a 1.5-oder equation.

Preparation of Bentonite Supported Nano Titanium Dioxide Photocatalysts by Electrostatic Self-assembly Method

Electrostatic self-assembly method （ESAM） was used to prepare bentonite supported-nano titanium dioxide photocatalysts. The materials were characterized by X-ray diffraction （XRD）, fourier transform infrared spectroscopy （FT-IR） and scanning electron microscopy （SEM）. Methyl orange was used to estimate the photocatalytic activity of the materials. The effects of the calcination temperature and silane dosage on the photocatalytic activity of the samples were investigated. The experimental results show that the bentonite facilitates the formation of anatase and restrains the transformation of anatase to rutile. Part of nano-size TiO2 particles insert into the galleries of bentonite. The photocatalysts exhibit a synergistic effect of adsorption and photocatalysis on methyl orange. Photocatalysts prepared by ESAM method exhibit higher photocatalytic activity and better recycle ability than those of the traditional method.

Ni/bentonite catalysts prepared by solution combustion method for CO_2 methanation

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.