Article

Water Adsorption on Clay Minerals As a Function of Relative Humidity: Application of BET and Freundlich Adsorption Models

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Abstract

Water adsorption on kaolinite, illite, and montmorillonite clays was studied as a function of relative humidity (RH) at room temperature (298 K) using horizontal attenuated total reflectance (HATR) Fourier transform infrared (FTIR) spectroscopy equipped with a flow cell. The water content as a function of RH was modeled using the Brunauer, Emmett, and Teller (BET) and Freundlich adsorption isotherm models to provide complementary multilayer adsorption analysis of water uptake on the clays. A detailed analysis of model fit integrity is reported. From the BET fit to the experimental data, the water content on each of the three clays at monolayer (ML) water coverage was determined and found to agree with previously reported gravimetric data. However, BET analysis failed to adequately describe adsorption phenomena at RH values greater than 80%, 50%, and 70% RH for kaolinite, illite, and montmorillonite clays, respectively. The Freundlich adsorption model was found to fit the data well over the entire range of RH values studied and revealed two distinct water adsorption regimes. Data obtained from the Freundlich model showed that montmorillonite has the highest water adsorption strength and highest adsorption capacity at RH values greater than 19% (i.e., above ML water adsorption) relative to the kaolinite and illite clays. The difference in the observed water adsorption behavior between the three clays was attributed to different water uptake mechanisms based on a distribution of available adsorption sites. It is suggested that different properties drive water adsorption under different adsorption regimes resulting in the broad variability of water uptake mechanisms.

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... Two commercially available clay samples, kaolinite (CAS: 1318-74-7, Lot# BCBS7473V) and montmorillonite K-10 (CAS: 1318-93-0, Lot# 14772-106) natural clays, were purchased from Sigma-Aldrich, St. Louis, MO, U.S. The third clay sample, mainly composed of illite (85-90% purity) (CAS# 12173-60-3), was obtained from Clay Mineral Society, Aurora, CO, USA and contains 10-15% of quartz. All three minerals are phyllosilicates whose structure is characterized by varying arrangements of alumina and silica sheets stacked in repeating layers [48]. Kaolinite (Al 2 Si 2 O 5 (OH) 4 ) is a 1:1 type clay mineral in which each layer contains one silica and one alumina sheet held together by shared oxygen atoms, while montmorillonite ((Na,Ca) 0.33 (Al,Mg) 2 Si 4 O 10 (OH) 2 ·nH 2 O) and illite (K,H 3 O)(Al,Mg,Fe) 2 (Si,Al) 4 O 10 [(OH) 2 ,(H 2 O)] are 2:1 clays, where the alumina sheet is sandwiched between two silica sheets. ...
... Kaolinite (Al 2 Si 2 O 5 (OH) 4 ) is a 1:1 type clay mineral in which each layer contains one silica and one alumina sheet held together by shared oxygen atoms, while montmorillonite ((Na,Ca) 0.33 (Al,Mg) 2 Si 4 O 10 (OH) 2 ·nH 2 O) and illite (K,H 3 O)(Al,Mg,Fe) 2 (Si,Al) 4 O 10 [(OH) 2 ,(H 2 O)] are 2:1 clays, where the alumina sheet is sandwiched between two silica sheets. Kaolinite is unique relative to illite and montmorionite because the external surface of its alumina sheet contains structural hydroxyl groups [48]. Kaolinite and illite have a very low ability to adsorb water, while montmorillonite has a high adsorption capacity [48]. ...
... Kaolinite is unique relative to illite and montmorionite because the external surface of its alumina sheet contains structural hydroxyl groups [48]. Kaolinite and illite have a very low ability to adsorb water, while montmorillonite has a high adsorption capacity [48]. ...
Article
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The experimental investigation of heterogeneous atmospheric processes involving mineral aerosols is extensively performed in the literature using proxy materials. In this work we questioned the validity of using proxies such as Fe2O3, FeOOH, Al2O3, MgO, CaO, TiO2, MnO2, SiO2, and CaCO3 to represent the behavior of complex mixtures of minerals, such as natural desert and volcanic dusts. Five volcanic dusts and three desert dusts were compared to a number of metal oxides, commonly used in the literature to mimic the behavior of desert dusts in the ability to form sulfites and sulfates on the surface exposed to SO2 gas. First, all samples were aged at room temperature, atmospheric pressure, under controlled experimental conditions of 175 ppm SO2 for 1 h under 30% of relative humidity. Second, they were extracted with 1% formalin and analyzed by High-Performance Liquid Chromatography (HPLC) to quantify and compare the amount of sulfites and sulfates formed on their surfaces. It was evidenced that under the experimental conditions of this study neither one selected pure oxide nor a mixture of oxides can adequately typify the behavior of complex mixtures of natural minerals. Therefore, to evaluate the real-life impact of natural dust on atmospheric processes it is of vital importance to work directly with the natural samples, both to observe the real effects of desert and volcanic dusts and to evaluate the relevancy of proposed proxies.
... Numerous standards adopt methylene blue (MB) adsorption for the determination of the clay content in MS [6,7]. The influence of clay containment on cementitious materials is largely revealed: i) to adsorb water [4][5][6]8,9] and improve the cohesiveness, and ii) to adsorb superplasticizer and decrease workability of mixtures [4,6,8,10], iii) to contract upon drying [11][12][13][14][15][16][17]. Clay minerals, such as kaolinite, illite, and montmorillonite, are primarily composed of aluminosilicate. ...
... Clay minerals, such as kaolinite, illite, and montmorillonite, are primarily composed of aluminosilicate. The lamellar structure and high cation exchange capacity of the free metallic ions in the crystal lattice endow clay minerals with a high water absorption capacity, which would induce substantial swelling [9,[18][19][20]. According to Hatch [9] and Norvell [4], montmorillonite normally has the highest water absorption capacity as well as swelling potential, followed by kaolinite and illite. ...
... The lamellar structure and high cation exchange capacity of the free metallic ions in the crystal lattice endow clay minerals with a high water absorption capacity, which would induce substantial swelling [9,[18][19][20]. According to Hatch [9] and Norvell [4], montmorillonite normally has the highest water absorption capacity as well as swelling potential, followed by kaolinite and illite. Generally, clay containing a higher proportion of minerals with high water absorption capacity and expansion potential would impose a greater effect on the plastic shrinkage cracking of cementitious materials. ...
... While the original model was created simply to project the experimental data, later, it was derived theoretically as well [37,38]. Hatch et al. [40] expressed that the Freundlich model can successfully describe the sorption process from an aqueous media as well as gas adsorption on porous surfaces. Moreover, Hatch et al. [40] pointed out the key feature of this model that it accounts for the intermolecular interactions between adsorbates and can imply heterogeneity of adsorption sites. ...
... Hatch et al. [40] expressed that the Freundlich model can successfully describe the sorption process from an aqueous media as well as gas adsorption on porous surfaces. Moreover, Hatch et al. [40] pointed out the key feature of this model that it accounts for the intermolecular interactions between adsorbates and can imply heterogeneity of adsorption sites. However, the simplicity of the model cannot correctly comprehend more intricate adsorption systems and, therefore, typically shows significantly lower accuracy than the Toth model or the D-A model. ...
... The D-R (Dubinin-Radushkevich) model is typically applied to express the adsorption mechanism with a Gaussian energy distribution onto a heterogeneous surface [40,41]. In contrast with the Langmuir surface adsorption, the D-R model also accounts for the porous structure for the adsorbent and includes the microporous filling. ...
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In this study, we evaluated the performance of low Global Warming Potential (GWP) refrigerant R1234yf on the activated carbon (MSC-30) for adsorption heating applications. The adsorption isotherms of MSC-30/R1234yf were measured using a constant-volume–variable-pressure (CVVP) method from very low relative pressure to the practical operating ranges. The data were fitted with several isotherm models using non-linear curve fitting. An improved equilibrium model was employed to investigate the influence of dead thermal masses, i.e., the heat exchanger assembly and the non-adsorbing part of the adsorbent. The model employed the model for the isosteric heat of adsorption where the adsorbed phase volume was accounted for. The performance of the heat pump was compared with MSC-30/R134a pair using the data from the literature. The analysis covered the desorption temperature ranging from 60 °C to 90 °C, with the evaporation temperature at 5 °C and the adsorption temperature and condensation temperature set to 30 °C. It was observed that the adsorption isotherms of R1234yf on MSC-30 were relatively lower than those of R134a by approximately 12%. The coefficient of performance (COP) of the selected pair was found to vary from 0.03 to 0.35 depending on the heat source temperature. We demonstrated that due to lower latent heat, MSC-30/R1234yf pair exhibits slightly lower cycle performance compared to the MSC-30/R134a pair. However, the widespread adaptation of environmentally friendly R1234yf in automobile heat pump systems may call for the implementation of adsorption systems such as the direct hybridization using a single refrigerant. The isotherm and performance data presented in this work will be essential for such applications.
... Numerous standards adopt methylene blue (MB) adsorption for the determination of the clay content in MS [6,7]. The influence of clay containment on cementitious materials is largely revealed: i) to adsorb water [4][5][6]8,9] and improve the cohesiveness, and ii) to adsorb superplasticizer and decrease workability of mixtures [4,6,8,10], iii) to contract upon drying [11][12][13][14][15][16][17]. Clay minerals, such as kaolinite, illite, and montmorillonite, are primarily composed of aluminosilicate. ...
... Clay minerals, such as kaolinite, illite, and montmorillonite, are primarily composed of aluminosilicate. The lamellar structure and high cation exchange capacity of the free metallic ions in the crystal lattice endow clay minerals with a high water absorption capacity, which would induce substantial swelling [9,[18][19][20]. According to Hatch [9] and Norvell [4], montmorillonite normally has the highest water absorption capacity as well as swelling potential, followed by kaolinite and illite. ...
... The lamellar structure and high cation exchange capacity of the free metallic ions in the crystal lattice endow clay minerals with a high water absorption capacity, which would induce substantial swelling [9,[18][19][20]. According to Hatch [9] and Norvell [4], montmorillonite normally has the highest water absorption capacity as well as swelling potential, followed by kaolinite and illite. Generally, clay containing a higher proportion of minerals with high water absorption capacity and expansion potential would impose a greater effect on the plastic shrinkage cracking of cementitious materials. ...
Article
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Clay minerals in manufactured sand exacerbate plastic shrinkage cracking of cementitious materials. The impact of clay content on plastic shrinkage cracking and the underlying mechanism were comprehensively investigated. The results indicate that clay considerably mitigates the plastic settlement while significantly aggravates the plastic shrinkage, triggering more severe cracking. Water absorption of clay substantially lowers the permeability of mortars, which accounts for the reduction in bleeding, evaporation and plastic settlement. The intensified plastic shrinkage can be attributed to the accelerated build-up of capillary pressure and the self-contraction of clay. Furthermore, the critical cause of the more severe cracking with higher clay content is the rapid increase of plastic shrinkage and the reduction in plastic tensile strength.
... Numerous standards adopt methylene blue (MB) adsorption for the determination of the clay content in MS [6,7]. The influence of clay containment on cementitious materials is largely revealed: i) to adsorb water [4][5][6]8,9] and improve the cohesiveness, and ii) to adsorb superplasticizer and decrease workability of mixtures [4,6,8,10], iii) to contract upon drying [11][12][13][14][15][16][17]. Clay minerals, such as kaolinite, illite, and montmorillonite, are primarily composed of aluminosilicate. ...
... Clay minerals, such as kaolinite, illite, and montmorillonite, are primarily composed of aluminosilicate. The lamellar structure and high cation exchange capacity of the free metallic ions in the crystal lattice endow clay minerals with a high water absorption capacity, which would induce substantial swelling [9,[18][19][20]. According to Hatch [9] and Norvell [4], montmorillonite normally has the highest water absorption capacity as well as swelling potential, followed by kaolinite and illite. ...
... The lamellar structure and high cation exchange capacity of the free metallic ions in the crystal lattice endow clay minerals with a high water absorption capacity, which would induce substantial swelling [9,[18][19][20]. According to Hatch [9] and Norvell [4], montmorillonite normally has the highest water absorption capacity as well as swelling potential, followed by kaolinite and illite. Generally, clay containing a higher proportion of minerals with high water absorption capacity and expansion potential would impose a greater effect on the plastic shrinkage cracking of cementitious materials. ...
Article
Clay-like substances in manufactured sand significantly impact the shrinkage of cementitious materials. This study investigated the effect of clay content on autogenous shrinkage, drying shrinkage, hydration rate, internal relative humidity (IRH), elastic modulus and pore structure of cementitious materials. The water content and self-contraction of clay during desorption were also studied to clarify the underlying mechanism of its influence on shrinkage. The results indicate that the clay slightly alleviated the autogenous shrinkage while significantly aggravated the drying shrinkage. Pronounced self-contraction of clay occurred as RH dropped, but the conversion ratio of the self-contraction of clay to the shrinkage of mortar was very low. It is concluded that the self-contraction of clay obviously influences the pore structure and the evolution of the various performance of mortars. Furthermore, the initial swelling of clay and the gentle decline of IRH are account for the reduction in autogenous shrinkage. Meanwhile, the coarsened pore structure accelerates the drying shrinkage and the self-contraction of clay intensifies the drying shrinkage.
... 63 The Freundlich model, in contrast, does not assume uniform surface adsorption but accounts for heterogeneity. 1 The Freundlich equation is shown by eq 2. This empirical equation is used to model the adsorption of gas molecules on a heterogeneous surface with an exponential energy distribution of adsorption 75 ...
... The Freundlich equation has been applied over a wide variety of adsorption reactions, and it is applicable for both solid−liquid and solid−gas interfaces. 1,5,76,77 The Freundlich equation was applied to the two linear regions in the low RH region (0− 20%) and high RH range (25−60%). ...
... The Freundlich and FHH models describe the transition from monolayer adsorption and multilayer adsorption to capillary condensation for water vapor adsorption on porous media [21,25,[48][49][50]. This section combines the two models to determine the relative pressure points corresponding to the turning points. ...
... where p/p 0 is the relative pressure; m Freu represents adsorption volume, mmol/g; n Freu is adsorption strength, g/mmol; and µ is adsorption capacity, mmol/g. It is believed that the Freundlich model can reflect the transition of water molecules from multilayer adsorption to capillary condensation under high humidity conditions [25,48]. Figure 7 is a diagram based on Inm Freu as the vertical axis and Inp/p 0 as the horizontal coordinate, and these two different regions represent two different adsorption methods. ...
Article
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The study on the adsorption and micropore filling of water vapor in coal is significant for predicting coalbed methane content in coal seams. The primary purpose of this study is to explain the effects of coal pore structure and its surface chemistry on water vapor monolayer adsorption, micropore filling, and diffusion coefficient. First, X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) analyzed inorganic mineral components of two kinds of coal samples and pore fissures structures. Then, we divide pores and fissures according to the theory of fractal dimensions. Furthermore, we carried out the water vapor adsorption and desorption experiments on two kinds of coal; in particular, we set 14 points of relative pressure between 0 and 0.2. Guggenheim–Anderson–de Boer (GAB), Frenkel–Halsey–Hill (FHH), and Freundlich models were used to analyze the data of water vapor adsorption to obtain the boundary pressure points of the monolayer, multilayer adsorption, and capillary condensation. Finally, the parameters of the models were obtained by fitting the adsorption data of water vapor according to the combined GAB, Freundlich, DA, and bidisperse adsorption (BDA) models to analyze the interaction mechanism between coal and water. We explain why the strongly adsorbed water minerals, such as pyrite, illite, and nacrite coal, can improve water vapor’s adsorption and diffusion capacity in coal pore fissures.
... 19,20,31,60−63 Fewer studies have been conducted on illite clay minerals and indicate much larger water uptake (>20−30 wt %). 64,65 As discussed below, these are in disagreement with the smaller values of surface Langmuir pubs.acs.org/Langmuir Article area and pore volume reported for illite clay (and the lack of interlayer expansion), further indicating that the trend in the total uptake amount from IMt-2 to STx-1b shown in Figure 1a is correct. ...
... Adsorption of water on Na-montmorillonite has been shown to occur first on the external surface at low water content (RH < 0.25) followed by stepwise hydration of the interlayer at higher RH. 19,65,78,82 The similarity in the uptake amounts between SWy-2 and ISCz-1 in the low RH region (Figure 1b) is the result of their similar external surface area (approximately 30 m 2 /g, see Table 1) and confirms that water adsorption on SWy-2 up to RH ≈ 0.25 is dominated by the external surface (interlayer sorption of water is limited for ISCz-1 over the entire RH range). The onset of water sorption inside the SWy-2 interlayer is manifested in the sharp increase in the uptake amount at RH ≈ 0.3, producing a departure from the isotherms of ISCz-1 and IMt-2. ...
Article
Understanding the long-term confinement of supercritical fluids in the clay pores of subsurface rocks is important for many geo-energy technologies, including geological CO2 storage. However, the adsorption properties of hydrated clay minerals remain largely uncertain because competitive adsorption experiments of supercritical fluids in the presence of water are difficult. Here, we report on the sorption properties of four source clay minerals-Ca-rich montmorillonite (STx-1b), Na-rich montmorillonite (SWy-2), illite-smectite mixed layer (ISCz-1), and illite (IMt-2)-for water at 20 °C up to relative humidity of 0.9. The measurements unveil the unsuitability of physisorption analysis by N2 (at 77 K) and Ar (at 87 K) gases to quantify the textural properties of clays because of their inability to probe the interlayers. We further measure the sorption of CO2 and CH4 on swelling STx-1b and nonswelling IMt-2, both in the absence (dehydrated at 200 °C) and the presence of sub-1W preadsorbed water (following dehydration) up to 170 bar at 50 °C. We observe enhanced sorption of CO2 and CH4 in STx-1b (50 and 65% increase at 30 bar relative to dry STx-1b, respectively), while their adsorption on IMt-2 remains unchanged, indicating the absence of competition with water. By describing the supercritical adsorption isotherms on hydrated STx-1b with the lattice density functional theory model, we estimate that the pore volume has expanded by approximately 6% through the formation of sub-nanometer pore space. By presenting a systematic approach of quantifying the smectite clay mineral's hydrated state, this study provides an explanation for the conflicting literature observations of gas uptake capacities in the presence of water.
... Clay minerals have layered silicate structures, some of which can expand through hydration of exchangeable cations between the layers. This hydration ability combined with the small particle size and therefore high surface area is why clays have a relatively high water adsorption capacity (Deer et al., 2013;Hatch et al., 2012). Hydrophilic sites present on clay minerals provide more opportunities for water cluster formation and growth, hence a higher water adsorption capacity for samples containing such minerals (Chen et al., 2021). ...
... This means some stronger electrostatic bonds (such as hydrogen bonds) or even covalent bonding has taken place between the adsorbed water and the rock samples. The layered structure of clays and their hydrophilic nature arising from their ability to sustain charged surfaces means these minerals are highly likely to be susceptible to chemisorption mechanisms (Deer et al., 2013;Hatch et al., 2012;Lahn et al., 2020;Sang et al., 2019;Seemann et al., 2017;Zolfaghari et al., 2017). ...
Article
This thesis aims to examine whether andesitic rock samples are likely to be good targets for permanent carbon sequestration via mineral trapping, as an alternative to basaltic-type reservoirs which have been proven to be successful. The CarbFix project in Iceland and the Wallula Basalt Pilot Scale project both reported results from field scale studies that suggested carbonation reactions had occurred within just two years in basaltic-type reservoirs, which is a significant improvement on the thousands of years needed for other geological carbon storage methods to be considered permanent. Carbon dioxide was successfully sequestered in these systems, after mineral dissolution reactions with the injected acidic fluids, which released divalent cations able to combine with the dissolved CO2 and precipitate carbonate minerals. However, there is a significant lack of research examining whether alternative volcanic rocks such as andesite may also be suitable. If alternative volcanic rocks can also be utilised as targets for permanent carbon sequestration in short timescales, this would expand the accessibility of the CarbFix project to more global locations and help mitigate the impacts of rising CO2 concentrations in the atmosphere. Rock samples from the region of Rantau Dedap on the Island of Sumatra, Indonesia, were first characterised in detail to examine their mineralogical and chemical compositions, with results indicating they were of andesitic composition. Batch reactor experiments were conducted under elevated temperatures of 100oC and pH values close to 3 using crushed andesite type rock samples, to simulate carbon sequestration conditions close to the site of injection. The release of silicon into the experimental fluids was used to calculate a bulk rock dissolution rate of the order 10-11 mol/m2/s for the andesite type rocks, which is roughly 1-2 orders of magnitude slower than reported basaltic dissolution rates. Mineral dissolution in basaltic systems is considered to be the rate limiting step in the permanent carbon sequestration via mineral trapping process, and so these results indicate that permanent sequestration of CO2 in andesitic systems may take slightly longer than the basaltic systems which saw sequestration in just two years. However, significant divalent cation release was observed as a result of mineral dissolution, which suggests andesitic samples may still have a good carbon sequestration potential. To expand on these findings, batch experiments were conducted using resin embedded andesite rocks, at temperatures of 100oC and increased concentrations of CO2 and calcium, to simulate conditions further from the site of injection. Some mineral dissolution was observed as well as divalent cation release. Evidence from electron microscope and energy dispersive x-ray techniques indicated two of the samples which had a feldspar composition with a higher anorthite content had an increased amount of calcite minerals present at the end of the 3-day experiments. These results give a positive indication that andesite samples are likely to support relatively rapid carbon sequestration via mineral trapping under conditions relevant to CO2 injection. The two samples also had a higher content of alteration minerals present compared to the third sample which indicates that the presence of calcic-plagioclase and/or alteration minerals increase the potential for permanent carbon sequestration in andesitic-type reservoir systems. Batch experiments were conducted to examine the impact of using fluids with increase NaCl concentrations up to 2.1 M, instead of freshwater, on the dissolution of feldspar minerals. If saline type fluids can be used as well as freshwater to dissolve CO2 for subsurface injection in volcanic rock systems, the feasibility of using this technique for carbon sequestration will be made more accessible in new locations worldwide. Silicon and aluminium release into the fluids in all experiments of a similar magnitude with varying NaCl concentrations indicates that using saline fluids is unlikely to have a negative impact on the carbon sequestration potential of a volcanic rock reservoir. Comparison between two feldspar mineral compositions indicates that a sample with a higher anorthite content may be more effective at buffering the acidity of acidic saline fluids, which is essential for initiating carbonation reactions, and so targeting such mineralogy’s is likely to be most effective. The water adsorption isotherms of samples before and after use in rock-fluid experiments were collected for andesitic rock samples, to determine whether a change in mineralogy as a result of acidic fluid dissolution has an impact on the water adsorption capacity of the rocks. The results indicate the andesitic samples have a water adsorption capacity of roughly 5.0 – 9.2 mg/g, which is comparable to previous studies using rock samples from other geothermal reservoir systems. The collected isotherms indicate that the water adsorption capacity of the samples increases after reaction with representative geothermal fluids, particularly if acidic fluids are used. The authors interpret this is a result of increased reactive surface areas after reaction and gives some indication that the water adsorption capacity of a reservoir is unlikely to be negatively impacted as a result of changing mineralogy during injection of acidic fluids. Overall, the results from this whole project indicate that andesitic rock samples should be further examined as potential targets for permanent carbon sequestration and that utilising seawater instead of freshwater for CO2 injection is likely to be a viable alternative and make the technique more globally accessible. However, significant research is still needed in these areas, to examine more long-term impacts of such suggestions and in particular, the impact of inducing such precipitation reaction will have on the overall permeability of a volcanic rock reservoir system. The impact of alterations minerals on the carbon sequestration potential in terms of possible cation release on dissolution, and permeability reducing properties on precipitation should be examined particularly closely.
... This model has been successfully applied for predicting the sorption onto a surface from an aqueous media and gas adsorption on porous surfaces. The key aspect of this model is that it accounts for intermolecular interactions between adsorbates and indicates the heterogeneity of adsorption sites [174]. Temkin isotherm model is able to predict the interaction between adsorbent and adsorbing particle, and, thus, it was successfully used to analyze the equilibrium sorption of the phosphoric acid modified rice husk [169]. ...
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Marine pollution is one of the biggest environmental problems, mainly due to single-use or disposable plastic waste fragmenting into microplastics (MPs) and nanoplastics (NPs) and entering oceans from the coasts together with human-made MPs. A rapidly growing worry concerning environmental and human safety has stimulated research interest in the potential risks induced by the chemicals associated with MPs/NPs. In this framework, the present review analyzes the recent advances in adsorption and desorption studies of different contaminants species, both organic and metallic, on MPs made of poly (ethylene terephthalate). The choice of PET is motivated by its great diffusion among plastic items and, unfortunately, also in marine plastic pollution. Due to the ubiquitous presence of PET MPS/NPs, the interest in its role as a vector of contaminants has abruptly increased in the last three years, as demonstrated by the very high number of recent papers on sorption studies in different environments. The present review relies on a chemical engineering approach aimed at providing a deeper overview of both the sorption mechanisms of organic and metal contaminants to PET MPs/NPs and the most used adsorption kinetic models to predict the mass transfer process from the liquid phase to the solid adsorbent.
... He et al. described already in 1995 that the water demand depends on type of clay mineral: montmorillonite > mica > non-expandable clays [7]. The specific surface area (SSA) [7,8] and the water adsorption behavior [9] decrease due to a smaller contribution of interlayer surface area in the following order: montmorillonite > illite > kaolinite. ...
Conference Paper
Synopsis: Calcined clays represent a promising future supplementary cementitious material (SCM) because of the worldwide availability of suitable clays and low material-related CO2 emissions during calcination. The application of superplasticizers is inevitable for a secured workability of cementitious systems with calcined clays due to their specific chemophysical properties. For their prospective use as SCM, a sound knowledge is elementary about the interaction of calcined clays with superplasticizers depending on clay and polymer structure. An ordinary Portland cement is replaced by 20 wt% of calcined clays. Four different calcined materials are used: one calcined clay mixture, industrial metakaolin, a metaillite and a metamuscovite. One polycondensate and one polycarboxylate-based polymer, both industrial products, are chosen as superplasticizers. The required dosages are adjusted by the same slump flow, so a similar dispersing behavior for all systems is given immediately after water addition. Over a period of two hours after water addition, the rheological behavior is evaluated via mini slump test and by rotational viscometer. The impact of different velocities during measurements with the viscometer provides further information related to the viscosity of these systems.
... On average, one kaolinite particle contains ~ 50 strata, with an interlayer distance of 7.2 Å. Compared to other phyllosilicates, it possesses a lower specific surface area and reduced affinity to water (Hatch et al., 2012). In alkaline environment, the aluminol and silanol groups are deprotonated and consequently kaolinite develops negatively charged basal as well as edge surfaces (Zhang et al., 2012). ...
Article
Polycarboxylate (PCE) comb polymers were selected as potential dispersant for suspensions prepared from individual calcined clay samples. It was anticipated that mechanistically their dispersing effect relies on adsorption onto positively charged surfaces of the meta clays which was to be proven. Furthermore, the structural differences between two specifically selected PCE kinds were assumed to result in different dispersing performance. Using spread flow tests, the dispersing effectiveness of the PCEs on four different meta clay samples (meta kaolin, meta muscovite, meta illite and meta montmorillonite) was assessed. Moreover, the surface chemistry of the meta clays dispersed in synthetic cement pore solution (SCPS) was captured via zeta potential and sorption measurements to elucidate the interaction of the superplasticizers with the calcined clay samples. In accordance to common knowledge, the results confirmed the high water demand of calcined clays which made them asking for superplasticizers when used in mortar and concrete. It was found that the zeta potential (surface charge) of the meta clays initially was negative, but converted to positive via uptake of Ca²⁺ ions from the pore solution, especially in Ca²⁺-rich cementitious systems. Sorption measurements revealed that the PCE superplasticizers adsorbed onto these positively charged surfaces and thus achieved dispersion. The methallyl ether (HPEG) based PCE vastly outperformed the methacrylate ester (MPEG) based PCE. Surprisingly, meta illite could not be dispersed satisfactorily, in spite of high PCE adsorption. The results contribute to understand at a glance the dispersing mechanisms of PCE superplasticizers in naturally occurring calcined clays with various clay mineral compositions and to select the adequate superplasticizer easily.
... The use of clay soils in the manufacturing of ceramic products for a wide range of applications requires knowledge of all their properties, including the features of hydration [4]. The importance of studying the adsorption of water by clay particles in environmental problems is evident from the fact that in the Earth's atmosphere, aerosols of mineral dust account for up to 45% of the total aerosol load of the atmosphere [5]. ...
Article
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The hydration of the basal surfaces of kaolinite is studied by theoretical methods. The cluster method was used to simulate the positions of atoms. The positions of the atoms of the basal surfaces of dry and hydrated minerals are optimized by minimizing the total energy in the Hartree–Fock approximation. The adsorption energies of water molecules were calculated taking into account the fourth-order correlation corrections of Møller–Plesset perturbation theory. The formation of the IR spectrum of kaolinite in the range of wave numbers 2500–4500 cm−1 is studied. The experimentally observed effect of the change in relative intensity and position of the band with a change in the moisture content of the sample is interpreted.
... This might be attributed to the water adsorption on (calcined) clay minerals. Such water adsorption behaviors of kaolinite, illite and montmorillonite clays have been comprehensively studied by Hatch et al. [81]. Additionally, mixtures with 2% SP + 0.24% VMA showed very close water retention value compared to mixtures with 1.5% SP + 0.24%VMA. ...
Article
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This paper aims to investigate the influences of high Portland cement substitutions (>60 wt%) by low-grade calcined clay (CC) and limestone (LF) on 3D concrete printability, stiffness evolution and early-age hydration. Results show that, with the same dosage of admixtures (superplasticizer and viscosity modifier), increasing LF and CC content reduced the slump, flowability and initial material flow rate, and significantly improved the buildability of fresh mixtures, which can be attributed to the reduced water film thickness (WFT). Furthermore, the stiffness evolution and SSA total development up to the first 3 h were accelerated by increasing CC content, which can also be linked to the change of WFT, and consumption of superplasticizer for the dispersion induced by hydration products. Additionally, the dilution effect on compressive strength and hydration caused by the high cement replacement was observed.
... For smectite, the high valence cations can be replaced by the low valence cations inside the crystals (i.e., crystalline substitution), which results in more negative charges on the surface of crystal cell, adsorbing more water vapor molecules. 72,81 Besides, the weak van der Waals force is the main attraction in smectite interlayer, which would allow more water vapor molecules entering the interlayer space. In contrast, other clay minerals form tight connections between interlayers because of the existence of the strong hydrogen bond force and electrostatic force, resulting in the interlayer space being inaccessible for water vapor molecules. ...
... This could indicate that the threshold soil water content occurred at a specific matric potential, i. e., -40 MPa, and the number of water molecules absorbed would then be dependent on the soil texture and its SSA, as discussed above. Moreover, other studies found that more than a monolayer of water can exist at this matric potential (Hatch et al., 2012;Orfanus et al., 2017), suggesting a monolayer of water molecules is not responsible for the increasing SWR with soil water content. Such a finding also implies that a waterrepellent soil in the field, with extended exposure to matric potential above -40 MPa or relative humidity above 75%, could reach this threshold soil water content, and any further increases could result in a linear increase in SWR. ...
Article
Soil water repellency (SWR) is problematic in rainfed cropping soils as it decreases plant water use efficiency. The occurrence of SWR is often dependent on the prevailing soil water content, but the response of SWR to soil water content varies among studies. We undertook three experiments to investigate how the (i) drying method prior to experimentation (oven-dried at 105 °C or vacuum-dried at 20 °C), (ii) incubation temperature (4 °C, 20 °C and 40 °C), and (iii) specific surface area (SSA) of four sieved soil fractions (0.49 m2 g−1, 0.59 m2 g−1, 0.65 m2 g−1 and 1.61 m2 g−1) influenced the response of SWR to soil water content. In all experiments, SWR (measured by molarity of ethanol droplet) remained constant up to a ‘threshold soil water content’, and then responded linearly with increasing soil water content. However, oven-dried soil at 105 °C had lower SWR than soil dried anoxically at 20 °C, which remained constant up to a threshold soil water content. The SWR response rate to soil water content above the threshold was also lower in the 105 °C oven-dried soil than the 20 °C anoxically vacuum-dried soil. Whereas, increasing the incubation temperature increased the SWR response rate to soil water content above the threshold. The four sieved soil fractions had increasing threshold soil water contents with increasing SSA, which could be related to the total carbon content of the soil. In conclusion, the same drying method and incubation temperature should be used throughout an experiment and between studies when investigating the response of SWR to soil water content to avoid methodological errors.
... Raw LQK samples A, D, F and G were obtained from clay mines in Central Florida registered by Florida's Department of Environmental Protection Agency's Integrated Habitat Network (IHN) [40]. The IHN considers these samples as clay for containing fine-sized phyllosilicate minerals including 1:1 structured clay minerals such as those of the kaolinite group: kaolinite, dickite and nacrite in addition to absorbable 2:1 structured clay minerals such as illite and those of the smectite group [41][42][43]. However, despite the IHN's classification of these LQK as clays, a previous study showed that they coexist in mines with large quantities of sand and small quantities of metal oxides, hydroxides and aluminosilicate gels [10]. ...
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Low quality kaolins (LQK) were used as supplementary cementitious materials to investigate their influence on paste rheological performance. Flow properties incorporating 20 wt% calcined clay with/without fine aggregate were determined. Flow properties were significantly affected by metakaolin content rather than material particle size, surface area or porosity. Accurately analyzing paste rheology following the Reiner-Riwlin procedure allows for the construction of a linear yield stress model based on all solids’ Particle size distribution (PSD) and raw LQK kaolinite content. Models of this sort offer insight for mix design addressing the negative rheological influences caused by LQK with mineralogical and microstructural heterogeneity.
... Furthermore, the strong relationship between SSA s and clay fraction indicates that this soil CO 2 uptake was related to clay particles. Even if clays were not abundant at this site (ranging from 0.6 to 4.3% in the measured samples), they contained highly adsorbent smectite (Hatch et al., 2012;Michels et al., 2015). Although smectite could have contributed to a certain extent to adsorption, its contribution was probably limited since it was only present in minor amounts (<5% of the clay fraction) (Solé-Benet et al., 1997). ...
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Water vapor adsorption (WVA) by soil is a potential contributor to the water cycle in drylands. However, continuous in-situ estimates of WVA are still scarce and the understanding of its coupling with carbon cycle and ecosystem processes remains at an incipient stage. Here we aimed to (1) identify periods of WVA and improve the understanding of the underlying processes involved in its temporal patterns by using the gradient method; (2) characterize a potential coupling between water vapor and CO2 fluxes, and (3) explore the effect of soil properties and biocrusts ecological succession on fluxes. We assumed that the nocturnal soil CO2 uptake increasingly reported in those environments could come from WVA enhancing geochemical reactions involving calcite. We measured continuously during ca. 2 years the relative humidity and CO2 molar fraction in soil and atmosphere, in association with below- and aboveground variables, over the biocrusts ecological succession. We estimated water vapor and CO2 fluxes with the gradient method, and cumulative fluxes over the study. Then, we used statistical modelling to explore relationships between variables. Our main findings are (1) WVA fluxes during hot and dry periods, and new insights on their underlying mechanisms; (2) a diel coupling between water vapor and CO2 fluxes and between cumulative fluxes, well predicted by our models; and (3) cumulative CO2 influxes increasing with specific surface area in early succession stages, thus mitigating CO2 emissions. During summer drought, as WVA was the main water source, it probably maintained ecosystem processes such as microbial activity and mineral reactions in this dryland. We suggest that WVA could drive the nocturnal CO2 uptake in those moments and discuss biogeochemical mechanisms potentially involved. Additional research is needed to monitor soil water vapor and CO2 uptake and separate their biotic and abiotic components as those sinks could grow with climate change.
... However, when the clay content in the soil media decreased from 10% to 5%, or the water content decreased from 100 to 75 or 50, the magnitude of T r decreases. T r behavior of different soil media with 10% clay content could be due to the small particle size (<2 µm), high surface area, which alters the internal structure of the different soil matrix, and greater water adsorption [45,46]. ...
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Abstract: Agricultural systems are facing the negative impacts of erosion and water scarcity, directly impacting the hydro-mechanical behavior of soil aggregation. Several technologies have been proposed to reduce hydro-mechanical soil-related problems in agriculture. Biopolymer-based hydrogels have been reported to be a great tool to tackle these problems in soils. In this study, we investigated the hydro-mechanical behavior of different soils media treated with Ca-bacterial alginate hydrogel. We used an unconfined uniaxial compression test, aggregate stability test and hydraulic conductivity measurements to investigate the mechanical and hydraulic behavior of treated soils media. Our results from unconfined uniaxial compression test showed that yield stress (i.e., strength) increased in treated soils with higher kaolinite and water content (i.e., HCM3), compared with untreated coarse quartz sand (i.e., CM1). Furthermore, we found that temperature is an important factor in the gelation capacity of our hydrogel. At room temperature, HCM3 displayed the higher aggregate stability, almost 5.5-fold compared with treated coarse quartz sand (HCM1), while this differential response was not sustained at warm temperature. In general, the addition of different quantities of kaolinite decreased the saturated hydraulic conductivity for all treatments. Finally, bright field microscopy imaging represents the soil media matrix between sand and clay particles with Ca-bacterial alginate hydrogel that modify the hydro-mechanical behavior of different soils media. The results of this study could be helpful for the soil-related problems in agriculture facing the negative effects of climate change.
... Even, when deactivated, these fossil fault zones are potentially excellent discontinuities for triggering large landslides. From another viewpoint, existing clay minerals in the fossil fault zones can absorb huge amounts of water (e.g., Barshad 1952;Hatch et al. 2012; Nabih and Shinawi 2020) during raining periods, expand and promote slope instabilities by swelling effect in place. The swelling clay-bearing layers is a known factor for landslide occurrence (e.g., Prior and Ho 1972;Azañón et al. 2010;Schulz et al. 2018;Kassou et al. 2020). ...
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Rainfall-induced landslides are among the most fatal and destructive geological hazards in the mountainous regions where active faulting is a major geological process. So far, many studies have been conducted on the various factors that influence or trigger rainfall-induced landslides; however, lesser attention has been paid to the proximity of rainfall-induced landslides to major faults. First time, this paper is going to discuss the concepts of fault damage zone and fault zone processes that interact and influence the occurrence of rainfall-induced landslides. This is done by introducing the concept of fault damage zone and its architecture and then presenting several examples from high mountains of Alborz and Zagros in which fault zones interact proactively with mass movement processes. Fault zone processes control the rainfall-induced landslides by three ways: (1) increasing fracture density near major faults that produces more debris and reduces rock strength, (2) weak minerals growing in fault zones in which clay minerals grow and (3) topographic features produced by active faulting. Presented examples show how active faulting can influence localization of rainfall-induced landslides. Intensely weathered rocks in the fault zone are a major source of sediment flux combined with the water to form mudflows. Additionally, fault mechanism and movement direction of fault blocks influence on internal geometry and attitude of minor structures is fault zone that controls properties of rock materials in the fault zone and therefore influence on slope strength. The interaction and connectivity among tectonic faults, river systems and erosion is a complex feature that should be considered in modeling landslides in the mountainous regions.
... Freundlich model points out that the adsorption process is multimolecular layer adsorption, and its equation is expressed as [44,45] ln q e � ln K F + ln C e n , ...
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In this study, amino-functionalized magnetic graphene-based composite TEPA-GO/CoFe2O4 (TGOM) was prepared by a simple one-step hydrothermal reaction and applied to the removal of Cr (VI) from wastewater. The removal of Cr (VI) by TGOM has the characteristics of high removal efficiency and excellent cycle performance. The maximum adsorption capacity is 114.81 mg/g, and the adsorption efficiency can still reach 62% after four cycles. The mass percentage of amino in TGOM material is about 1.97% according to thermogravimetric analysis. The modification by TEPA increased the adsorption sites and improved the adsorption capacities due to the synergistic effect of chelation with Cr (VI). The effects of pH, contact time, and temperature on the removal of Cr (VI) were studied. The removal process accorded with the pseudo-second-order kinetics and Langmuir isotherm model, and the thermodynamic parameters showed that the adsorption process was exothermic and spontaneous. The characterization analysis before and after adsorption showed that there were complexation reaction, electrostatic adsorption, and reduction mechanism in the removal process. The above results indicate that TGOM is an effective adsorption material for the removal of Cr (VI) in wastewater.
... Soil water vapour sorption encompasses the processes of adsorption and condensation (Hatch et al., 2012;Chen et al., 2021). The adsorption process can be further separated into monolayer and multilayer adsorption. ...
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Understanding the controlling factors of soil water vapour sorption at different water activities (a w) is essential for accurate estimation of soil properties, such as cation exchange capacity (CEC) and specific surface area (SSA). The objective of this study was to identify the role of CEC and soil pore system in water vapour sorption and sorption hysteresis over a range of a w values. The CEC, SSA, pore volume, and water and nitrogen adsorption/ desorption isotherms for eight soils with different clay contents and mineralogies were measured. Irrespective of a w and sorption direction, there was a significant correlation between water content and CEC, and the correlation varied with a w. The water content change was mainly related to CEC and SSA H2O for a w <~0.6, and to SSA N2 and pore volume for a w >~0.6. Similar to the forced closure phenomenon of the soil nitrogen desorption branch at a relative pressure (P/P0) of ~ 0.45, the soil water vapour desorption branch also exhibited a sudden drop in the range of 0.2 < a w < 0.4. The water vapour sorption hysteresis for a w <~0.75 was mainly due to the difference in cation hydration during the adsorption and desorption process, and the hysteresis phenomena for a w >~0.75 was attributed to the different sizes of narrow pore necks and the connected pores.
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When a fracturing fluid invades a nanoscale shale pore structure, it will inevitably affect the ad-/desorption behavior of methane adsorbed on a shale pore wall, impacting the overall methane production of a well. In this work, methane ad-/desorption experiments were conducted on the Longmaxi formation shale with varying levels of relative humidity (0, 0.1, 0.2, 0.3). In addition, the mechanisms and efficiency of methane replacement by water molecules were analyzed. The results indicate that water molecules occupy the adsorption sites of methane molecules in shale nanopores, thus reducing the methane adsorption volume and increasing the difficulty of adsorption. With an increase in the water content, the Langmuir volume of methane adsorption decreases linearly. At high pressures (greater than 8 MPa), a higher water content results in a lower hysteresis index, while at pressures less than 8 MPa, the hysteresis index increases and results in increasing methane desorption compared to dry shale samples. The efficiency of methane replacement by water molecules increases with an increase in the water content and decreases with an increase in pressure. The results of calculating the disjoining pressure of a shale surface-methane adsorption layer-water film system show that the stability of a water film on a shale surface is far greater than that of a methane adsorption layer on a shale surface. These insights will be helpful for analyzing the influence of an imbibition fracturing fluid on shale gas production under in situ conditions.
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The formulation of a drilling fluid is mostly defined by the type of formation to drill. Ensuring drilling mud's effectiveness before throughout a drilling process implies monitoring its physico–chemical properties, including cake filtration. Cake filtration of a drilling mud can be either good or poor (loss filtration or fluid drag effect) depending on the mud swelling efficiency. A drilling mud made of bentonite (or Barite) still needs the assistance of appropriate additives to carry it to its optimum performance. The present study aims at monitoring the cake filtration of a water-based drilling mud using polyvinyl alcohol (PVA), which is known and used for its swelling abilities. The mud samples were formulated by blending two different types of PVAs (standard & synthetic PVAs) with deionized water at various concentrations (0.0%–0.3%) and 7% of bentonite. pH and density of muds were measured before filtration tests. The cake filtration was evaluated by injecting 10 mL of mud samples at constant pressure into a stainless steel Millipore sigma filter holder 90 mm at a constant pressure of 1.2 MPa. Results show that the addition of PVA increases the mud's acidity with the concentration of polyvinyl alcohol. The observed higher reliable content of the samples with standard PVA was confirmed by their higher density values, leading to lower filtrate productions than the muds samples with synthetic PVA.
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Natural porous materials such as nanoporous clays are used as green and low-cost adsorbents and catalysts. The key factors determining their performance in these applications are the pore morphology and surface activity, which are typically represented by properties such as specific surface area, pore volume, micropore content and pH. The latter may be modified and tuned to specific applications through material processing and/or chemical treatment. Characterization of the material, raw or processed, is typically performed experimentally, which can become costly especially in the context of tuning of the properties towards specific application requirements and needing numerous experiments. In this work, we present an application of tree-based machine learning methods trained on experimental datasets to accelerate the characterization of natural porous materials. The resulting models allow reliable prediction of the outcomes of experimental characterization of processed materials (R 2 from 0.78 to 0.99) as well as identification of key factors contributing to those properties through feature importance analysis. Furthermore, the high throughput of the models enables exploration of processing parameter-property correlations and multiobjective optimization of prototype materials towards specific applications. We have applied these methodologies to pinpoint and rationalize optimal processing conditions for clays exploitable in acid catalysis. One of such identified materials was synthesized and tested revealing appreciable acid character improvement with respect to the pristine material. Specifically, it achieved 79% removal of chlorophyll-a in acid catalyzed degradation.
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This study aims to investigate the hydrocarbon potential and storage capacity of five shale samples collected from Barren Measure Formation of Damodar Valley in India. Characterization of source rocks was performed using rock eval pyrolysis and, pore volumes were measured using the MICP and low pressure CO2 adsorption methods. Results of pyrolysis show excellent TOC content ranging between 4.24% and 9.78%. Variation in Tmax values from 437 to 447⁰C indicates that the thermal maturity is within the oil window range. Values of HI (110 to 211 mg HC/gm TOC) and OI (3 to 36 mg HC/gm TOC) indicate a mixture of Type II and Type III kerogen which, can be a good source rock for oil and gas. Pore spaces present within the rock act as storage for the generated hydrocarbons. Pore volume and pore-size are the major influential factors for the storage and production capacities of hydrocarbon reservoirs. Results of MICP experiments show high porosity values (>=13%) for all the samples. Macro and mesopore volumes calculated using the MICP method are varying within the range between 0.074 to 0.17 cc/mg. Low-pressure adsorption using CO2 gas was adopted to estimate the micropore volume of the samples. The volumes of micropores are varying between 2.3 cc/gm and 4.1 cc/gm. Pore volumes measured using both techniques were arithmetically summed up to calculate the total pore volume of the samples. Source rock characters shows a change in trend below 475 m. High pore volumes indicate a good storage capacity for the studied samples. Having the potential to be a good source rock for hydrocarbon and also containing higher pore volume to store hydrocarbon, Barren Measure shale can be considered as a good source as well potential hydrocarbon reservoir rocks among Indian shale formations.
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The Atterberg limits are empirical indices of the critical water contents defining mechanical states of soil-water mixtures between the semisolid state and plastic state (the plastic limit or wP), and between the plastic state and liquid state (the liquid limit or wL). They reflect semiquantitatively a fine-grained soil’s ability to resist external loading. They are controlled by four fundamental factors: soil mineralogy, particle size distribution, pore fluid chemistry, and pore structure. However, general quantitative relationships among the Atterberg limits and these controlling factors are yet to be established. The authors hypothesize that the total amount of adsorptive water content for a given soil is directly related to the soil’s wL and wP. A broad suite of 35 soils with measured soil-water retention (SWR) and the Atterberg limits from the literature were synthesized to explore these relationships. Using the measured SWR data and interpreting them through a generalized SWR model, the adsorptive water contents of all 35 soils were quantified. The authors demonstrate that the Atterberg limits, including wP, wL, and plasticity index IP(=wL−wP), were all correlated to mechanisms of soil-water interaction, specifically to a soil’s total adsorptive water content in terms of gravimetric water content, confirming the hypothesis. Further, the correlation between the Atterberg limits and a soil’s volumetric water content was poor, indicating the Atterberg limits’ independence from capillary water retention mechanism. The correlations provide a new pathway to move beyond the Atterberg limits to classify soil directly using more representative soil physical properties like adsorption suction stress, which could be linked to all four fundamental factors of soil mineralogy, particle size distribution, pore fluid chemistry, and pore structure.
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In this study, a photoreversible graphene oxide (GO) - coumarin (GC) composite is fabricated by electrostatic self-assembly of positively charged nitrogenous coumarin surfactant and negatively charged GO. It is found that the introduction of coumarin not only results in a large amount of micropores and mesopores on the surface of GO, but photo-regulates its structure transformation between close-packed structure and 3D pleat-like structure, solves the separation problem, improves and reversibly controls its adsorption capacity, under 365/254 nm light irradiation. The maximum adsorption capacity of the GC composite and the Irradiated GC composite (the GC composite irradiated by 365 nm light for 30 min) for Pb²⁺ are 403.97 and 492.51 mg/g, respectively, under room temperature at pH 6. The adsorption kinetic processes of these two composites are described by pseudo-second-order kinetic model, and the equilibrium data are well fitted with the Langmuir isotherm model. Furthermore, adsorption-desorption experiments show that these two composites have effective reusability, and display desirable adsorption capacities toward Cd²⁺, Cu²⁺ and Zn²⁺ heavy metal ions. The results indicate that the GC composite provide theoretical and experimental basis for structurally photocontrollable materials, and can be served as photoreversible adsorbents for effective removal of heavy metal ions from wastewater.
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Adsorption is one of the most important forms of storage of gas in shale reservoirs. Shale gas adsorption in the actual reservoir is not only affected by individual factors such as water content, temperature, and pressure but also by the synergetic effect of these factors. In this study, we conducted laboratory experiments on methane adsorption in dry and wet shale at different pressures and temperatures. The synergetic effect of water content, temperature, and pressure on shale gas adsorption is explored. The results show that increasing temperature weakens the interaction between methane and shale and reduces adsorption capacity due to the exothermic nature of adsorption. Water reduces methane adsorption capacity by occupying adsorption sites and blocking pores in the shale system. Although temperature and water reduce methane adsorption individually, the effect of these two factors weakens each other. Temperature has a more significant effect on methane adsorption in shales with low water content, while water has a more remarkable impact on methane adsorption at a low temperature. Furthermore, the increase in pressure reduces the negative influence of water and temperature on methane adsorption. By quantitatively analyzing the relationship between methane adsorption in dry and wet shales, a predictive adsorption model for wet shale considering the influence of in situ conditions is proposed and validated. Validation shows that the proposed model has high accuracy and broad applicability to shales with different properties.
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The self-assembly of 1-dimensional nanorods into free-standing multi-dimensional (2D and 3D) nanostructures is a considerable challenge. Here, 2D β-FeOOH nanobundles (NBs) and 3D spiky particles (SPs) were prepared without a substrate using a one-pot hydrothermal method. The oriented aggregation of nanoparticles (NPs) induced at the initial stage an unusual growth pathway beyond a reversed crystal growth route, forming spindle-like or spiky structure, which was confirmed by structural analyses. Then, with a surface-to-core extension of crystallization and nanorod self-assembly, 2D NBs with ultrathin and well-aligned nanorods and 3D SPs were finally generated. The reduction of the surface free energy served as a primary driving force for the oriented self-assembly. The initial concentrations of sodium sulfate and polyethyleneimine, which are used as reducing reagent and electrostatic stabilizer, are crucial adsorption parameters. The adsorption capacity of the NBs and SPs for Cr(VI) was 68.3 mg g⁻¹ and 83.4 mg g⁻¹, respectively. The adsorption mechanism study showed that electrostatic interaction and reduction concomitantly affected the adsorption. The molecular dynamic simulation indicated that the adsorption performance depends on the crystallographic surface of the materials. The suggested synthesis route provides an atypical strategy to prepare 2D and 3D nanostructures with promising sorbent characteristics.
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The expression of specific crystal facets in different nanostructures is known to play a vital role in determining the sensitivity toward the photodegradation of organics, which can generally be ascribed to differences in surface structure and energy. Herein, we report the synthesis of hematite nanoplates with controlled relative exposure of basal (001) and edge (012) facets, enabling us to establish direct correlation between the surface structure and the photocatalytic degradation efficiency of methylene blue (MB) in the presence of hydrogen peroxide. MB adsorption experiments showed that the capacity on (001) is about three times larger than on (012). Density functional theory calculations suggest the adsorption energy on the (001) surface is 6.28 kcal/mol lower than that on the (012) surface. However, the MB photodegradation rate on the (001) surface is around 14.5 times faster than on the (012) surface. We attribute this to a higher availability of the photoelectron accepting surface Fe3+ sites on the (001) facet. This facilitates more efficient iron valence cycling and the heterogeneous photo-Fenton reaction yielding MB-oxidizing hydroxyl radicals at the surface. Our findings help establish a rational basis for the design and optimization of hematite nanostructures as photocatalysts for environmental remediation.
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The interactions between CO2 and coals during CO2-ECBM (CO2 sequestration in deep coal seams with enhanced coal-bed methane recovery) could change pore morphology and chemistry property of coals, thereby affecting adsorption, diffusion and flow capability of CO2 and CH4 within coal reservoirs. To simulate CO2-ECBM process more practically, the dynamic interactions of supercritical CO2 (scCO2) and moisture-equilibrated coals were performed at temperature of 318.15 K, pressure of 12.00 MPa, and duration of 12.00 h. The impacts of the interactions on physicochemical properties of coals were investigated. Results indicate that scCO2/H2O exposure shows minor effect on micropores of coals. However, the exposure significantly decreases the mesopore surface area of bituminous coals, while increases that of anthracites. The mesopore volume and the average mesopore diameter of all the coals after scCO2/H2O exposure decrease. The multi-fractal analysis verifies that the scCO2 exposure can enhance the pore connectivity of various rank coals. Apart from the pore morphology, the exposure of scCO2/H2O also affects the oxygenic functional groups on coal surface. Particularly, the exposure of scCO2/H2O reduces the content of C-O and C=O of coals. The content of COOH of low rank coals including Hehua-M2# coal, Zhongqiang-4# coal, Buliangou-9# coal and Tashan-5# coal decreases, while the high rank Laochang-11# coal and Kaiyuan-9# coal witness a growth in COOH. The content of total oxygenic functional groups of all coals after interaction with scCO2/H2O decreases; on the contrary, that of C-C/C-H of all coals after scCO2/H2O exposure increases. In summary, the interaction with scCO2/H2O significantly changes the pore system and oxygenic functional groups of various rank coals, which needs further attention regarding CO2-ECBM.
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The interaction between water/gas and rock plays an important role in evaluating initial fluid storage in shale gas reservoirs. It is challenging to understand the co-occurrence relationships of water, chemical structure, and nanopore in shale kerogen due to the fact that both pore-forming material and water adsorption are related to the chemical structure. In this study, we did water vapor adsorption (WVA) experiments on seven Longmaxi Formation shale kerogen, and then analyzed the vapor-liquid equilibrium process. Results show that water is preferentially adsorbed in micropores (< 2 nm) through monolayer coverage when the relative humidity (RH) is less than 75%, while mesopores (2-50 nm) contribute dominantly to the total water adsorption when the RH is greater than 75%. Furthermore, based on grand canonical Monte Carlo simulations, we constructed water-contained molecular models with the same adsorption amounts as the WVA experiments to simulate the water adsorption process. Simulation results show that water can exist in hydrophilic oxygen-containing structures in the form of monolayer coverage, and in hydrophobic carbon structures in the form of water clusters. Under low RH, the narrow ultra-micropores (mainly < 0.35 nm) within the hydrophilic oxygen-containing structures are the primary adsorption centers for water adsorption, which results in a monolayer coverage of water molecules. With increasing RH, the hydrophobic carbon structures can adsorb water molecules because the residual oxygen-containing structures bonded to aliphatic/aromatic carbons provide connecting sites for the formation and growth of water clusters. Based on the acquired results, a molecular model showing the co-occurrence relationships among water, chemical structure, and nanopore was constructed, which helps to understand the microscopic mechanism of fluids-rock interactions.
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The bound water in soil directly controls the special physical, chemical, and mechanical properties of clay. This paper carries out isothermal adsorption tests on a series of artificially mixed clays and explores the relationship between bound water content and clay mineral composition (montmorillonite content). On this basis, three common empirical models of adsorption were adopted to fit the isothermal adsorption data separately, and their applicability to bound water adsorption by clay was evaluated in turn. The results show that by the isothermal adsorption method, the relatively humidity (RH) of 0.9 is the boundary between strong and weak bound waters, and the RH of 0.98 is the boundary between weak bound water and free water; For the mixed clays with the same mineral composition, the bound water content linearly increases with the growing content of montmorillonite; GAB model works excellently at RH = 0 ~ 100%, with a good fitting effect (R2>0.90); the parameters of GAB model have clear physical meanings, and change in line with the trend of the hydration process of bound water adsorption by clay. Therefore, GAB model is the most suitable model for fitting the isothermal adsorption data on bound water of clay.
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At present, the stimulation technique involving soaking after fracturing of shale gas reservoirs has received increasing attention. In this study, gas-water displacement experiments were carried out to simulate the contact state between the fracturing fluid and the shale during the soaking stage after hydraulic fracturing of the shale gas reservoir. By using low-field nuclear magnetic resonance to dynamically monitor the occurrence state of the methane in shale cores, the changes in the masses of the methane in different occurrence states were calculated. Furthermore, the displacement of the adsorbed methane in the shale by the fracturing fluid was studied. In addition, the influences of the fracturing fluid's salinity and the shale clay content and type on the displacement process were also analyzed. The results of this study show that the fracturing fluid has a stronger adsorption on clay minerals than that of methane, so it can replace the adsorbed methane in the shale. Compared with pure fracturing fluid solution, the high salinity fracturing fluid solution containing cations has a stronger adsorption on the clay minerals in the shale, and thus, it has a stronger displacement ability. The mineral composition of the shale reservoir also has an important influence on the displacement efficiency. The higher the content of clay minerals with high adsorption capacities, the more adsorbed methane is replaced. The results of this study are important for gaining a better understanding of the stimulation technique involving soaking after fracturing of shale gas reservoirs and for optimizing the design of soaking.
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A monolithic porous composite was synthesized by sol–gel process, containing the maximum and significant amount of bentonite that allows its use as a filter bed in aqueous effluents treatment. This process is able to apply on an industrial scale. The bentonite used was an efficient adsorbent for various contaminant molecules in aqueous media when is operated in a batch stirred tank, but presents difficulty in the separation stage of suspended particles. In this laboratory-scale work, cylindrical monoliths of 9 cm length by 2 cm diameter were made that can be used as a filter bed. The primary composite, silica-resin, was prepared by the sol–gel precursor mixture of the partially hydrolyzed tetraethylorthosilicate and a phenol-formaldehyde resin. Bentonite was added to the pre-gelling, obtaining the silica-resin-bentonite composite, made up the gel which is then dried and cured at 270 °C. The different composites mineralogical and structurally were evaluated. The preliminary performance of the developed bentonite filter bed showed almost 90% adsorption of diphenylamine, a commercial agrochemical widely used as anti-antiscaldant in postharvest treatment of fruit, and showed that the bentonite conserves its adsorption capacity and controls the swelling of the interlayer space which encourages further research studies applied to water treatment.
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Methane is the main component of natural gas and a greenhouse gas. It usually coexists with water in geological formations. Methane adsorption onto shale has been studied extensively, but there is no report on the Simultaneous Adsorption of Water vapor and Methane (SAWM). This paper reports a new experimental method for studying SAWM onto shale. During the experiment, liquid water, water vapor and methane coexist in an adsorption cell. Water vapor is produced via evaporation of liquid water, and the processes of liquid water evaporation and water vapor and methane adsorption onto shale occur simultaneously. The rate of liquid water conversion into vapor and the free water vapor content in the gas mixture depend on Relative humidity (Rh). Changes in Rh are monitored with a humidity-sensor. In SAWM, the amount of water vapor adsorbed greatly exceeds that of methane. The adsorption of water vapor took longer to reach equilibrium than that of methane. The amount of water vapor adsorbed at equilibrium decreased with total pressure, while the opposite situation occurred with methane adsorption. Compared to Pure Methane adsorption onto Dry Shale (PMDS), the amount of methane adsorbed was lower by 10-59% in SAWM. The equilibrium time for methane adsorption was higher, and t50 and t80 (t50 and t80 represented the times required for adsorption of 50% and 80% of the equilibrium adsorption amount, respectively) increased 12.0-108.0 and 9.0-115.2 times, respectively. In the two experiments, the declines in the level of methane adsorption were equal when a critical threshold Equilibration Degree (Ed) was reached. Before reaching Ed, the rate of methane adsorption in SAWM was higher than that in PMDS. After reaching Ed, the phenomenon was reversed.
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The isothermal adsorption curves for water vapor on montmorillonite were measured by a gravimetric adsorption system. Dent's model was employed to estimate the adsorption behaviors of water vapor on primary adsorption sites and secondary adsorption sites. The thermodynamics analysis of water vapor adsorption was performed. At low vapor pressure region, primary adsorption predominates, and with increasing vapor pressure, secondary adsorption becomes notable. Primary adsorption sites have an evidently stronger adsorption affinity than secondary adsorption sites. With increasing vapor pressure, Gibbs free energy variation rapidly increases and then reduces slowly. Although increasing vapor pressure raises adsorption spontaneity on primary adsorption sites, the enhancement in vapor pressure decreases the spontaneity of water vapor adsorption on secondary adsorption sites. As adsorbed loading increases, isosteric heat of adsorption and entropy loss decrease first and then increase quickly. The gradually growing water clusters are responsible for the increase of entropy loss at late stage. This article is protected by copyright. All rights reserved.
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Increasing metal demand is accelerating the mining and processing of minerals, however to ensure sustainable growth innovative approaches are required to better manage associated effluents. Biochar from the fast pyrolysis of residues from fishery and forestry operations has been studied as a low-cost, environmentally and economically friendly method for treating mine tailings and processing effluents. However, the bulk of the studies focus on terrestrial biomass (e.g. wood) and do not include potential inhibition/enhancement of adsorption due to pH controlling compounds. In this work biochar generated from snow crab (Chionoecetes Opilio) processing was studied as an adsorbent for copper solutions containing sulfate (a key compound in sulfide ore mining waters) with the objective of assessing adsorption capacity and the impact of sulfate on copper adsorption. The biochar, a porous structure comprised of calcite (CaCO3), was alkaline and has a negative zeta potential under neutral and basic conditions. The crab biochar removed over 99% of Cu²⁺ from a 100 mg/L solution (sourced as CuSO4) at a dosage of 5 g/L, which was higher than lignocellulosic biochar at the same biochar dosage. While metal adsorption can often be impacted at acidic conditions, Cu²⁺ adsorption was not impacted by initial acidic pH due to the biochar's buffering capacity. The Pseudo-Second Order (PSO) model fit the adsorption rate with maximum adsorption achieved in approximately 2 h. The maximum adsorption isotherm capacity was 184.8 ± 10.2 mg/g for Cu²⁺, much higher than existing commercial activated carbons and previously studied lignocellulosic biochars and followed the Freundlich isotherm. The adsorption mechanism responsible for removal of Cu²⁺ was found to be precipitation, in the form of the mineral posnjakite (Cu4[(OH)6SO4]·H2O). These results indicate for the first time that crab-based biochars are capable of adsorbing large quantities of Cu²⁺ from sulfate-rich solution, while also buffering solution pH, demonstrating promise as an acid mine drainage treatment for removal of harmful metals and reduction of acidity.
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Coalbed methane not only is a new clean energy source, but also has potential damage to ecological environment. Water and methane coexist in coal reservoir; understanding the adsorption of water on coal and its impact on pore structure and methane adsorption of coal is vital to evaluate the reserves and productivity of coalbed methane. In the paper, water adsorption characteristics of various rank coals are firstly investigated by ten mathematical models. The modified Dent model provides a best fit, followed by GAB and Dent models. For GAB model, the primary site adsorption is more difficult to reach saturation, and the contribution rate of the secondary site adsorption is surprisingly high at P/P0 approaching 0, which can be attributed to the possible overestimation of GAB monolayer adsorption capacity and secondary site adsorption. Besides, the low-rank coal sample YZG2 exhibits more prominent hysteresis than middle- to high-rank coals. The low-pressure hysteresis can be attributed to the water-water interactions over the primary site and the strengthened binding forces of water molecules in the water desorption process. In contrast, the high-pressure hysteresis largely depends on pore structure of coal such as ink-bottle pores, especially for the studied sample YZG2. Besides, pore analyses by low-temperature nitrogen adsorption method show that the pre-adsorbed water has remarkable influence on micropores smaller than 10 nm, and the micropores smaller than 4 nm almost disappear for water-equilibrated coals, which is closely related to the formed water clusters and capillary water in pore throats. This finding reveals that more methane gas can only be adsorbed in the larger pores of moist coal, and provides an explanation for water weakening methane adsorption capacity.
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Oxygen is an important factor in food deterioration; thus, packaging, with an in‐built oxygen indicator, has been widely developed. Here, a safer, natural product‐based, colorimetric oxygen indicator film based on β‐cyclodextrin grafted chitosan/montmorillonite with methylene blue/glucose system was fabricated. Methylene blue in the activated films was reduced to leuco‐form (colourless) by glucose and reverted to blue with oxygen exposure. Glucose, as well as the reducing agent for methylene blue, crosslinked the chitosan. In addition, the grafting of β‐cyclodextrin onto chitosan and the addition of montmorillonite as well as humidity led to the faster colour changes of the films. The colour recovery of films could delay by covering them with a poly(ethylene terephthalate) (PET) film. The activated films showed good storage stability at low temperature which is suitable for the package of refrigerated food products. The films had the potential to be used as natural‐based colorimetric oxygen indicators for food packaging. Colorimetric oxygen indicator film based on β‐cyclodextrin grafted chitosan/montmorillonite with methylene blue/glucose system was fabricated. Methylene blue in the activated films was reduced to leuco‐form (colourless) by glucose and reverted to blue with oxygen exposure. The films had the potential to be used as natural‐based colorimetric oxygen indicators for food packaging.
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The interaction of retained water and clay minerals after the hydraulic fracturing process has a remarkable influence on the adsorption and transport behaviors of shale gas. To better understand the underlying adsorption mechanisms of water molecules on various clays, the detailed adsorption thermodynamics analysis is necessary. In this paper, we research the thermodynamics of adsorption of water molecules on swelling clay of motmorillonite and non-swelling clay of illite. First, the adsorption isotherms of water molecules on montmorillonite and illite at 293-313 K were measured by gravimetric method. Then, D’Arcy and Watt model was applied to deal with gained adsorption isotherms, and the key thermodynamic variables, including entropy change (ΔS), surface potential (Ω), isosteric heat of adsorption (Qst) and variation of Gibbs free energy (ΔG), were analyzed. Results illustrate that the adsorption amount for water molecules on illite is one order of magnitude smaller than that on montmorillonite, suggesting that swelling clay plays a dominant role in water molecules adsorption process. For water molecules adsorption on montmorillonite, the contribution of secondary adsorption to total adsorption (a2/a) is always less than 30%. For water molecules adsorption on illite, the contribution of primary adsorption to total adsorption (a1/a) is greater than a2/a at the low pressure region, while a2/a can exceed 60% at the high pressure region. The difference in the uptakes of water molecules adsorption on non-swelling and swelling clays is mainly resulted from the difference in primary adsorption on two clays. The Henry’s constant (KAA) for montmorillonite is in the range of 21.37-75.08 mmol/g/kPa, which is evidently larger than the KAA values of 0.34-0.98 mmol/g/kPa for illite. Swelling clay has the significantly stronger adsorption affinity for water molecules than non-swelling clay. Qst, ΔG, Ω and ΔS for montmorillonite are all greater than those for illite. Compared with non-swelling clay, the adsorption spontaneity degree for water molecules on swelling clay is higher, and the interaction of swelling clay-water molecules is stronger. Meanwhile, the movement of adsorbed water molecules in swelling clay is more confined than that in non-swelling clay.
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It is essential to understand the law by which coal adsorbs water to prevent coal and rock disasters in the mining process. However, the hydration of coal containing inorganic minerals is seldom studied. In this study, X-ray diffraction (XRD), low-pressure nitrogen adsorption (LPNA), and low-temperature carbon dioxide adsorption (TCA) experiments were performed on coal samples to obtain inorganic mineral compositions and pore structure characteristics. Then, vacuum vapor sorption analyzer (VVS) experiments were carried out on coal samples. GAB and Freundlich models were used to classify the strong adsorption region, weak adsorption region, and critical humidity for monolayer adsorption. The relationship between the amount of adsorbed water and the coal's pore structure and surface chemical properties was discussed. Then, the reason for the difference in specific surface area between N2 and H2O adsorbents was elucidated. Finally, we discuss the significance of coal-water adsorption by pyrite and clay minerals in preventing coal and dynamic rock disasters.
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This study reports laboratory measurements of cloud condensation nuclei (CCN) activity and droplet activation kinetics of aerosols dry generated from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. Based on the observed dependence of critical supersaturation, s <sub>c</sub>, with particle dry diameter, D <sub>dry</sub>, we found that FHH (Frenkel, Halsey and Hill) adsorption activation theory is a far more suitable framework for describing fresh dust CCN activity than Köhler theory. One set of FHH parameters ( A <sub>FHH</sub> ∼ 2.25 ± 0.75, B <sub>FHH</sub> ∼ 1.20 ± 0.10) can adequately reproduce the measured CCN activity for all species considered, and also explains the large range of hygroscopicities reported in the literature. Based on a threshold droplet growth analysis, mineral dust aerosols were found to display retarded activation kinetics compared to ammonium sulfate. Comprehensive simulations of mineral dust activation and growth in the CCN instrument suggest that this retardation is equivalent to a reduction of the water vapor uptake coefficient (relative to that for calibration ammonium sulfate aerosol) by 30–80%. These results suggest that dust particles do not require deliquescent material to act as CCN in the atmosphere.
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The swelling of some well-defined Mg-, Ca-, Sr- and Ba- homoionic montmorillonites was studied in the domain of water relative pressures lower than 0.95. This involves the expansion of the crystal lattice itself, commonly known as the "interlamellar expansion" or "inner crystalline swelling". The initial freeze-dried clays were characterized by nitrogen adsorption-desorption volumetry and controlled transformation rate thermal analysis. The evolution of the structural and textural properties of these different clays at different stages of hydration and dehydration was investigated using water adsorption gravimetry, immersion microcalorimetry at different precoverage water vapor relative pressures and X-ray diffraction (XRD) under controlled humidity conditions. Large textural variations are observed in the dry state depending on the exchangeable cations. The 2-layer hydrate exhibits the most ordered layer stacking. Water is mainly adsorbed in the interlamellar space. With increasing water pressure, each homoionic species leads to a 1-layer hydrate and, with the exception of Ba-montmorillonite, to a predominant 2-layer hydrate. The relative pressure corresponding to the formation of the 2-layer hydrate decreases with increasing hydration energy of the interlayer cation. For Ca-, Sr- or Mg-montmorillonites, simulation of XRD patterns leads to the definition of successive homogeneous states corresponding to the 2-layer hydrate. Furthermore, it yields the water filling ratio corresponding to the different hydration states during adsorption and desorption of water vapor.
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Hydration of the <1 μm size fraction of SWy-1 source clay (low-charge montmorillonite) was studied by modeling of X-ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Li-, Na-, K-, Mg-, Ca-, and Sr-saturated specimens. The quantitative description of smectite hydration, based on the relative proportions of different layer types derived from the fitting of experimental XRD patterns, was consistent with previous reports of smectite hydration. However, the coexistence of smectite layer types exhibiting contrasting hydration states was systematically observed, and heterogeneity rather than homogeneity seems to be the rule for smectite hydration. This heterogeneity can be characterized qualitatively using the standard deviation of the departure from rationality of the 00l reflection series (ξ), which is systematically larger than 0.4 Å when the prevailing layer type accounts for ~70% or less of the total layers (~25% of XRD patterns examined). In addition, hydration heterogeneities are not distributed randomly within smectite crystallites, and models describing these complex structures involve two distinct contributions, each containing different layer types that are interstratifed randomly. As a result, the different layer types are partially segregated in the sample. However, these two contributions do not imply the actual presence of two populations of particles in the sample. XRD profile modeling also has allowed the refinement of structural parameters, such as the location of interlayer species and the layer thickness corresponding to the different layer types, for all interlayer cations and RH values. From the observed dependence of the latter parameter on the cation ionic potential (v/r; v = cation valency and r = ionic radius) and on RH, the following equations were derived: which allow the quantification of the increase of layer thickness with increasing RH for both 1W (one water) and 2W (two water) layers. In addition, for 2W layers, interlayer H2O molecules are probably distributed as a unique plane on each side of the central interlayer cation. This plane of H2O molecules is located at ~1.20 Å from the central interlayer cation along the c* axis.
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Sorption isotherms for four gases (N2, A, Kr and CO2) , commonly used in specific surface area and pore structure measurements, have been accurately determined on a number of clay mineral and oxide systems. Specific surface areas obtained by application of the BET theory to these isotherms illustrate the extent to which the apparent cross-sectional areas for these sorbed gases vary with surface structure, ex- changeable cation and microporosity. V-n plots for nitrogen adsorption on these materials using nitrogen adsorption on crystalline materials of large crystal size as a standard isotherm provide appreciable ranges of linearity in each case. The specific surface areas obtained from these straight line plots agree well with the corresponding BET values. The linearity of these plots for illite clays indicates the absence of capillary condensation and that adsorption in slit-shaped pores takes place largely by the formation of physically adsorbed layers on the surfaces. Much larger BET specific surface areas were obtained from carbon dioxide sorption at 196K on goethite, hematite and gibbsite than from nitrogen, argon and krypton sorption at 78"K. It is suggested that enhanced sorption of CO2 into microporous regions of the oxides, inaccessible to the other gases, occurs in a similar fashion to that frequently observed for coal and charcoal materials. V-n plots for CO2 sorption in these materials using that for an illite clay as a standard isotherm, support this conclusion. Considerably lower BET specific surface areas were obtained for CO 2 sorption on kaolinite than were obtained for nitrogen, argon and krypton sorption. The shape of the V-n plots for CO., sorption on kao- linite compared with illite suggest that an initial specific adsorption of CO2 on the kaolinite is followed by a change in state with the completion of this layer, allowing normal multilayer formation to proceed.
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Clouds composed of both ice particles and supercooled liquid water droplets exist at temperatures above ~236 K. These mixed phase clouds, which strongly impact climate, are very sensitive to the presence of solid particles that can catalyse freezing. In this paper we describe experiments to determine the conditions at which the clay mineral kaolinite nucleates ice when immersed within water droplets. These are the first immersion mode experiments in which the ice nucleating ability of kaolinite has been determined as a function of clay surface area, cooling rate and also at constant temperatures. Water droplets containing a known amount of clay mineral were supported on a hydrophobic surface and cooled at rates of between 0.8 and 10 K min-1 or held at constant sub-zero temperatures. The time and temperature at which individual 10-50 mum diameter droplets froze were determined by optical microscopy. For a cooling rate of 10 K min-1, the median nucleation temperature of 10-40 mum diameter droplets increased from close to the homogeneous nucleation limit (236 K) to 240.8 ± 0.6 K as the concentration of kaolinite in the droplets was increased from 0.005 wt% to 1 wt%. This data shows that the probability of freezing scales with surface area of the kaolinite inclusions. We also show that at a constant temperature the number of liquid droplets decreases exponentially as they freeze over time. The constant cooling rate experiments are consistent with the stochastic, singular and modified singular descriptions of heterogeneous nucleation; however, freezing during cooling and at constant temperature can be reconciled best with the stochastic approach. We report temperature dependent nucleation rate coefficients (nucleation events per unit time per unit area) for kaolinite and present a general parameterisation for immersion nucleation which may be suitable for cloud modelling once nucleation by other important ice nucleating species is quantified in the future.
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Continuous daily aerosol sampling carried out at a coastal site in Miami, Florida, for the past 23 years shows that large quantities of African mineral dust are periodically carried into Florida every summer, yielding daily concentrations in the range of about 10 mug m-3 to 100 mug m-3. Dust events typically last several days or longer. The maximum dust concentration occurs in July (monthly mean, 16.3 mug m-3), but relatively high concentrations are also observed in June (8.4 mug m-3) and August (9.8 mug m-3). There is considerable year-to-year variability that is apparently linked to various meteorological factors including climate conditions in North Africa as manifested by drought. Satellite data show that African dust incursions are synoptic-scale events; consequently, they will impact a large region of the southern and eastern United States. The incursion of dust events over this large region, coupled with inputs from local emissions, could have important implications regarding regional air quality.
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Infrared (IR) spectroscopy has a long and successful history as an analytical technique and is used extensively (McKelvy et al., 1996; Stuart, 1996). It is mainly a complementary method to X-ray diffraction (XRD) and other methods used to investigate clays and clay minerals. It is an economical, rapid and common technique because a spectrum can be obtained in a few minutes and the instruments are sufficiently inexpensive as to be available in many laboratories. An IR spectrum can serve as a fingerprint for mineral identification, but it can also give unique information about the mineral structure, including the family of minerals to which the specimen belongs and the degree of regularity within the structure, the nature of isomorphic substituents, the distinction of molecular water from constitutional hydroxyl, and the presence of both crystalline and non-crystalline impurities (Farmer, 1979). The interpretation of the absorption spectra of the Source Clays in the middle-IR (MIR) region (4000–400 cm−1) given here follows those of Farmer and Russell (1964), Farmer (1974a, 1979) and Russell and Fraser (1994). In addition, reflectance spectra in the near-IR (NIR) region (11,000–4000 cm−1), where overtones and combination vibrations occur, are included. These spectra provide information on structural OH groups and H2O in clay minerals (Bishop et al., 1994; Frost and Johansson, 1998; Petit et al., 1999a) which may not be clearly observed in the MIR spectra. Small changes in stretching and bending band positions are additive in the combination bands, thereby making them more readily differentiated (Post and Noble, 1993). Dispersive IR spectrometers are slowly being replaced by quicker and more sensitive Fourier transform (FT) instruments (Rintoul et al., 1998). The greater sensitivity of the FTIR spectrometers is related to the continuous detection of the entire transmitted energy …
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Sequential cation-exchange capacity (CEC) measurements were obtained from standard clays using a mechanized, variable-rate leaching device. The device consists of a motorized screwjack and as many as 24 leaching tubes coupled to 60-ml plastic syringes. Controlled withdrawal of the syringe plungers produces a vacuum that permits samples in the leaching tubes to be extracted at a uniform rate. A single, 8-hr leaching of clays with 35 ml of salt solution was found to be comparable to multiple saturations or displacements using a centrifuge. CECs consistent with published values were obtained for reference 2:1 clay minerals using both acetate and chloride salts of Na, Ca, and Mg. Potassium-exchange capacities were also successfully measured following in situ thermal treatment of samples in the leaching tubes. Variations in measured CECs for kaolin-group minerals due to salt intercalation were minimized by using chloride rather than acetate salts and by washing with a dilute aqueous solution of the saturating cation following initial saturation. The mechanical extractor significantly reduced the effort required to perform conventional CEC determinations without sacrificing analytical precision.
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Imeraction of water with montmorillonite exchanged with Na +, K +, Co 2+, and Cu 2+ cations as a function of water content was examined using an FTIR/gravimetric cell designed to collect spectro- scopic and sorption data simultaneously. Correlation of water desorption isotherms with infrared spectra of the clay-water complex showed that the position of the HOH bending band of water decreased as a function of water content. The largest decreases in frequency were observed for Cu 2+ and Co 2 +; smaller decreases were found for Na + and K + . In addition, the molar absorptivity of sorbed water increased upon decreasing the water content. The decrease in frequency and the concomitant increase in molar absorptivity were attributed to polarization effects on the sorbed water molecules by exchangeable cations. The in- terference fringes of a self supporting clay film permitted d-spacings to be determined optically and, therefore, changes in frequency, molar absorptivity, and water sorption behavior to be related directly to changes in interlayer spacing. The d-spacings obtained from the interference fringes were consistently larger by approximately 0.5 ~ than those determined using powder XRD.
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Adsorption isotherms for water vapor, c-spacing and heat of immersion in water of Na- and Ca-montmorillonite were measured at 25~ at various r.h. The amount of water adsorbed as a function of the r.h. increased gradually, whereas the c-spacing increased, and the heat of immersion (per mole of adsorbed water) decreased in steps. There was good agreement between the calorimetric data, the heat calculated from the isotherms by use of BET equation, and the calculations from the ion-dipole model. A model is presented to describe the hydration of sodium and calcium mont- morillonite.
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Testing shows that many of the present commercially available bentonite products used for clay liner/soil sealant applications may be susceptible to chemical degradation by certain contaminants. Testing also confirms that a recently developed contaminant resistant clay (CRC) is resistant to various contaminants that would otherwise attack and degrade the present commercially available products. The tests that were used to determine its effectiveness were American Petroleum Institute (API) fluid loss, rigid wall hydraulic conductivity, flexible wall hydraulic conductivity and a newly developed top loading filter press (TLFP) test (LSK method).
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This paper concerns the hydration and swelling behavior of four synthetic sodium saponite samples with general formula Nax(Si4–x,Alx)(Mg3)O10(OH)2, where x = 0.4, 0.5, 0.6, and 0.7. The combination of gravimetric water adsorption measurements and X-ray diffraction experiments under controlled water pressure allows us to analyze the inß uence of layer charge on swelling mechanisms. When the layer charge increases, swelling occurs for lower values of the chemical potential, i.e., at lower relative pressure. In parallel, as the cohesion between layers increases with increasing layer charge, a greater amount of water is needed to initiate swelling for higher-charged samples. In this last case, due to the proximity of interlayer cations, the transition between the one layer and two-layer hydrate occurs before the sodium cations are surrounded by a complete hydration sphere. This study also shows that the “one-layer” or “two-layer” hydrates cannot be considered as deÞ ned states as they appear to be modiÞ ed with both layer charge and relative pressure.
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It is becoming increasingly clear that the heterogeneous chemistry of mineral dust aerosol is a function of relative humidity (f(RH)) as water on the surface of the mineral dust particles can enhance or inhibit its reactivity depending on the reaction. Since clay minerals make up a significant component of the mineral dust aerosol, it is important to understand water uptake on this large fraction of dust present in the Earth's atmosphere. In this study, bulk and surface properties of several types and sources of clay minerals are characterized using a variety of techniques, including surface area measurements, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) analysis, X-Ray diffraction (XRD), Mössbauer spectroscopy, and X-ray photoelectron spectroscopy (XPS). For these well-characterized clays, ATR-FTIR spectroscopy is combined with quartz crystal microbalance (QCM) mass measurements to investigate water uptake as a f(RH). Similar measurements were also done for alpha-Al2O3 and synthetic NaY zeolite for comparison. Water uptake on the clay minerals, although variable and dependent on both the type and source of the clay, is greater than that found for alpha-Al2O3, a metal oxide, and in many cases similar or greater than NaY zeolite, a crystalline porous material. The presence of cations with large hydration energies significantly increases the water uptake capacity for the clay minerals. The atmospheric implications of these results are discussed.
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Hygroscopicity and cloud condensation nucleus (CCN) activity were measured for three mineral dust samples: one from the Canary Islands, representing North African dust transported across the Atlantic; one from outside Cairo, representing North African dust transported to the eastern Mediterranean; and Arizona Test Dust, representing dust in the southwestern United States. To reaerosolize bulk samples, dust samples were either suspended in high purity water and particles generated by atomization, or samples were resuspended in dry air using a fluidized bed. Only the Canary Island sample generated from aqueous suspension showed appreciable hygroscopic growth at subsaturated conditions; all other samples exhibited diameter growth factors of less than 1.1 for relative humidities
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Individual particles were sampled in Beijing during the unusually strong dust storm of 20 March 2002 (DS) and a nondust day (NDS) and in Duolun, Inner Mongolia (DL), on a nondust day. Fourteen elements were measured in 500 particles of each by SEM-EDX. The main components were clay, quartz, calcite, and sulfur. The mineral aerosol compositionally resembled loess. X-Y plots of SiO2 versus SO3 and Al2O3 revealed a central core of clay, with lines radiating outward toward quartz, calcite, salts, and alumina. The core represented externally mixed clay particles, and the lines represented internally mixed clays and other components. Externally mixed particles (mostly clays) amounted to 65% of the total in DS, 60% in DL, and 50% in NDS. Saline minerals contributed considerable amounts of S, P, and Cl, especially in DS and DL, and could have come from dried salt lakes or saline soils in northern China and southern Mongolia. The strongest correlations of the 14 elements measured were within these salts, not within the aluminosilicate elements. Most Ca existed as calcite in DS and DL, but as CaSO4 in NDS. S was very abundant in many of the particles in NDS, while a few of these were unambiguously pollution S in DS. High CuO and Al2O3 were found in Duolun, probably from nearby pollution sources. Dust storm aerosol can interact with pollution gases and pollution aerosol during transport to Beijing, although such interactions appear to require longer transport times to observe. SEM photos showed that calcite could serve as a substrate for adsorbing SO2 or sulfuric acid and ammonium sulfate and allowing them to react and produce gypsum or mixed sulfates.
Article
This paper concerns the hydration and swelling behavior of four synthetic sodium saponite samples with general formula Na x (Si4− x ,Al x )(Mg3)O10(OH)2, where x = 0.4, 0.5, 0.6, and 0.7. The combination of gravimetric water adsorption measurements and X-ray diffraction experiments under controlled water pressure allows us to analyze the influence of layer charge on swelling mechanisms. When the layer charge increases, swelling occurs for lower values of the chemical potential, i.e., at lower relative pressure. In parallel, as the cohesion between layers increases with increasing layer charge, a greater amount of water is needed to initiate swelling for higher-charged samples. In this last case, due to the proximity of interlayer cations, the transition between the one layer and two-layer hydrate occurs before the sodium cations are surrounded by a complete hydration sphere. This study also shows that the “one-layer” or “two-layer” hydrates cannot be considered as defined states as they appear to be modified with both layer charge and relative pressure.
Article
The Clay Minerals Society published a complete characterization scheme for its 'Source Clays' but not for its 'Special Clays'. To address this issue, the specific surface areas (SSAs) of the 16 special clays from The Clay Minerals Society were determined using the Brunauer, Emmett and Teller (BET) method of adsorption of an inert gas. Two BET measurements were performed for each of the 16 special clays, and the average BET SSA of each of the special clays was determined. The BET SSA of cookeite is reported for the first time. In the present study, special clays from The Clay Minerals Society are classified under three groups based on their BET special surface area values as Group-I special clays, with BET values of 0.1–10 m2/g, Group-II special clays, with BET values of 10–100 m2/g, and Group-III special clays, with BET values >100 m2/g. Comparisons which proved interesting were the those involving the mixed-layer clays and the synthetic clays. The systematic approach employed in this paper will allow for better comparisons to be made between different clays and will provide a comprehensive database for future applications of such material (e.g. as catalyst carriers, as adsorbents in waste treatments, etc.).
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From swelling and surface area measurements, it was found that the swelling of a montmorillonite depends linearly on the fraction of its layers that fully expand in water and that this fraction, in turn, depends linearly on the b dimension of the unit cell. Therefore, swelling is a linear function of the b dimensioin. However, the specific surface area of a montmorillonite is a linear function of its b dimension only if no partially expanded layers exist. It was also found that the distance between fully expanded layers at a given applied pressure is the same for all montmorillonites. Refs.
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Using optical microscopy, we investigated the heterogeneous nucleation of ice in aqueous (NH4)2SO4-H2O particles containing two types of mineral dusts, kaolinite and montmorillonite. The efficacy of montmorillonite and kaolinite to nucleate ice in (NH4)2SO4-H2O particles is similar. The difference in freezing temperatures, compared to the homogeneous freezing temperatures, is found to vary from 8-20 K and it is larger for particles with concentrations greater than 27 wt %. Our freezing data shows that for temperatures ranging from 239 K to 198 K, ice super-saturations between 1.35 and 1.51 are required for ice to heterogeneously nucleate in NH4SO4-H2O particles containing mineral dust immersions. Based on our results, we conclude mineral dust is an efficient nuclei for ice in NH4SO4-H2O aerosols and as a result, it can initiate the formation of upper tropospheric ice clouds at warmer temperatures and lower super-saturations in comparison to homogeneous freezing.
Article
Field studies have shown that mineral dust particles can act as ice nuclei in cirrus clouds. Here, we present a laboratory investigation of heterogeneous ice nucleation on surrogates of mineral dust particles, in particular pure Arizona test dust (ATD) particles, and ATD particles coated with sulfuric acid. The experiments have been performed using a new apparatus in which ice formation on the particles is determined by optical microscopy at temperatures between 197 and 260 K and relative humidities up to water saturation. The experiments reveal that pure and sulfuric acid coated ATD particles nucleate ice at considerably lower relative humidities than required for homogeneous ice nucleation in liquid aerosols. Nucleation occurred over a broad relative humidity range indicating that the different minerals contained in ATD have different ice nucleation thresholds. No significant difference in the ice nucleation ability of pure and H2SO4 coated ATD particles was observed. Below 240 K, ice nucleated on ATD particles apparently by deposition nucleation. Preactivation of ATD particles, that is, a reduction in supersaturation, required for heterogeneous ice nucleation after a previous ice nucleation event on the same particle, has been observed for temperatures as low as 200 K. Differences of 10-30% in the onset RHice values were obtained for particles with or without preactivation. The results indicate that pure and sulfuric acid coated mineral dust particles may act as efficient ice nuclei in the atmosphere. Preactivation of the particles should be considered when modeling long-range transport of mineral dust particles and their impact on cloud formation.
Article
The long-range transport of North African dust to the Middle East, Europe, South America, and the Caribbean has been well documented during the past 25 years. With the advent of routine collection and analysis of fine aerosols at national parks, monuments, and wilderness areas in the continental United States, these North African dust incursions can now be tracked, characterized, and quantified across much of the eastern half of the United States. Identification of the North African source of these dust episodes is confirmed by mass distribution measurements, a characteristic Al/Ca ratio, isentropic backward air mass trajectories, and sequential plots of the spatial distribution of the dust plumes. North African dust incursions into the continental United States persist for ∼10 days and occurred, on average, 3 times per year from 1992 to 1995. Fine soil mass usually exceeds 10 μg m−3 during these dust episodes and dominates local fine soil dust by an order of magnitude or more, even in the so-called “dust bowl” states of the central United States. Size-resolved measurements of elemental composition taken during July 1995 indicate that the mass mean diameter of the transported North African dust is
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Water activities, densities, and refractive indices over extended concentration ranges at 25°C are reported for solution droplets containing a single salt of either (NHâ)âSOâ, NHâHSOâ, (NHâ)âH(SOâ)â, NaâSOâ, NaHSOâ, or NaNOâ, which are common constituents of atmospheric aerosols. The extensive data reported are obtained from experiments using the single-particle levitation technique recently developed for measuring the thermodynamic and optical properties of microdroplets. These data should find application in mathematical models predicting the dynamic behavior, visibility reduction, and radiative effects of atmospheric sulfate and nitrate aerosols. 32 refs., 13 figs., 3 tabs.
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Clays have been and continue to be one of the more important industrial minerals. Clays and clay minerals are widely utilized in many facets of our society. They are important in geology, agriculture, construction, engineering, process industries, and environmental applications. Traditional applications are many. Some of the more important include ceramics, paper, paint, plastics, drilling fluids, foundry bondants, chemical carriers, liquid barriers, decolorization, and catalysis.Research and development activities by clay scientists in academia, government, and industry are continually resulting in new and innovative clay products Many of these new applications are the result of improved processing, which provides clays of higher purity, more precise particle size and distribution, whiter and brighter color, modified surface chemistry, and other physical and chemical modifications. Some new and improved clay products include tailored or engineered paper coating kaolins, enhanced paint thickeners, nanocomposites for plastics, pillared clays as special absorbents and catalysts, clays for liquid fertilizer suspensions, clays for absorption of animal wastes, calcined kaolins with high brightness and low abrasion, faster casting clays, and clays with a very high modulus of rupture.Improvement of mining and processing techniques will lead to the continued growth of traditional clay applications and to the development of new and innovative clay products. Value added products are the wave of the future for the traditional industrial clay minerals.
Article
The swelling of some well-defined Mg-. Ca-, Sr- and Ba-homoionic montmorillonites was studied in the domain of water relative pressures lower than 0.95. This involves the expansion of the crystal lattice itself, commonly known as the "interlamellar expansion" or "inner crystalline swelling". The initial freeze-dried clays were characterized by nitrogen adsorption-desorption volumetry and controlled transformation rate thermal analysis. The evolution of the structural and textural properties of these different clays at different stages of hydration and dehydration was investigated using water adsorption gravimetry, immersion microcalorimetry at different precoverage water vapor relative pressures and X-ray diffraction (XRD) under controlled humidity conditions. Large textural variations are observed in the dry state depending on the exchangeable cations. The 2-layer hydrate exhibits the most ordered layer stacking. Water is mainly adsorbed in the interlamellar space. With increasing water pressure, each homoionic species leads to a 1-layer hydrate and, with the exception of Ba-montmorillonite, to a predominant 2-layer hydrate. The relative pressure corresponding to the formation of the 2-layer hydrate decreases with increasing hydration energy of the interlayer cation. For Ca-, Sr- or Mg-montmorillonites, simulation of XRD patterns leads to the definition of successive homogeneous states corresponding to the 2-layer hydrate. Furthermore, it yields the water filling ratio corresponding to the different hydration states during adsorption and desorption of water vapor.
Article
Testing shows that many of the present commercially available bentonite products used for clay liner/soil sealant applications may be susceptible to chemical degradation by certain contaminants. Testing also confirms that a recently developed contaminant resistant clay (CRC) is resistant to various contaminants that would otherwise attack and degrade the present commercially available products. The tests that were used to determine its effectiveness were American Petroleum Institute (API) fluid loss, rigid wall hydraulic conductivity, flexible wall hydraulic conductivity and a newly developed top loading filter press (TLFP) test (LSK method).