Clay Mineral Groups Research Articles

Variations in Spectral Signals of Heavy Metal Contamination in Mine Soils Controlled by Mineral Assemblages

This paper illustrates a spectroscopic analysis of heavy metal concentration in mine soils with the consideration of mineral assemblages originated by weathering and mineralization processes. The mine soils were classified into two groups based on the mineral composition: silicate clay mineral group (Group A) and silicate–carbonate–skarn–clay mineral group (Group B). Both soil groups are contaminated with Cu, Zn, As, and Pb, while the contamination level was higher for Group A. The two groups exhibit different geochemical behaviors with different heavy metal contamination. The spectral variation associated with heavy metal was highly correlated with absorption features of clay and iron oxide minerals for Group A, and the absorption features of skarn minerals, iron oxides, and clay minerals for Group B. It indicates that the geochemical adsorption of heavy metal elements mainly occurs with clay minerals and iron oxides from weathering, and of skarn minerals, iron oxides, and clay minerals from mineralization. Therefore, soils from different secondary mineral production processes should be analyzed with different spectral models. We constructed spectral models for predicting Cu, Zn, As, and Pb in soil group A and Zn and Pb in soil group B using corresponding absorptions. Both models were statistically significant with sufficient accuracy.

Designing nanoarchitecture for environmental remediation based on the clay minerals as building block

Nanoarchitecture of hybrids materials based on clay minerals as nano building blocks for the environmental remediation is summarized with the emphasis on the utilization of layered clay minerals, especially smectite group of clay minerals, as nano building blocks for designing functional nanostructures for the adsorption of molecular contaminants from the environments. Smectites are well-known adsorbents of cationic contaminants, while surface modification of smectites with organoammonium ions has given hydrophobic and microporous characters to uptake nonionic organic contaminants from environments. Not only on the designed interactions between adsorbent-adsorbate for efficient and higher capacity adsorption, the states of the adsorbed nonionic organic compounds have been altered and varied by the modification of smectites as shown by the controlled release and specific catalytic reactions. The organically modified clays are classified from the nanoarchitecture, and the functions derived from the nanoarchitectures are discussed based on the structure-property relationship.

A novel method to calculate the gas adsorption of mixed minerals

Five groups of methane isotherm adsorption tests were carried out at 61 °C under a pressure range of 0–25 MPa, including four groups of pure clay minerals (illite, montmorillonite, chlorite, kaolinite, for brief they are expressed as Ill, Mont, Chl, and Kaol respectively) and a group of mixed minerals by four pure clay minerals in equal mass ratio. The experimental results showed the order of methane adsorption of pure clay minerals: Kaol > Ill > Mont > Chl. And the composition of clay minerals was obtained by XRD experiments. The result showed that the four samples were of high purity, both of which were greater than 90%. In addition, the results of low-pressure nitrogen adsorption experiments showed the order of specific surface area: Kaol > Ill > Mont > Chl, which is consistent with the order of methane adsorption. The methane adsorption is positively correlated to the specific surface area. The adsorption data was fitted to the Langmuir–Freundlich model to establish the method to calculate the adsorption of mixed minerals. The result showed that the parameters of the adsorption model of mixed clay minerals can be obtained by summing the parameters of the adsorption model of the pure minerals contained in the mixture according to their constituent mass ratio and the feasibility of this result was also verified by literature data. Overall, once the mass ratio in mixed clay minerals gets known, its theoretical adsorption can be calculated.

The integration of grain-size distribution and plasticity parameters for characterizing and classifying unconsolidated fine-grained sediments

Grain-size distribution (GSD) characteristics are often used to classify different types of sediment and to understand how variations in depositional processes affect mechanical behavior. However, the current grain-size-based classification systems have not been able to distinguish fine-grained sediments with varying silt and clay content. In addition, the current classification systems do not consider mineralogy in the classification scheme or the subsequent implication of mineralogy in the mechanical behavior of the sediment. This study proposes a new grain-size-based scheme to classify unconsolidated inorganic sediments that cover a wide range of natural depositional environments with a special emphasis on fine-grained deposits. The proposed classification assumes a linear relationship between percent fines and the silt fraction. This relation describes the behavior of the GSD curve, which analysis showed to be controlled by the ratio of the clay fraction to the silt fraction. The proposed scheme allows the clay mineral composition to be included, and allows the mechanical behavior to be inferred as well. The classification scheme shows that plasticity indices (i.e. liquid limit and plasticity index) are reliable proxies for clay mineralogy. In addition, the study uses the activity of clay as a quantifiable factor that discriminates between the major clay-mineral groups. By combining grain-size characteristics and plasticity, the proposed classification extends the utility of the scheme beyond simply classifying the sediment class, towards inferring the potential mechanical behavior of sediments having various GSD characteristics and mineralogy.

Effect of salinity on rheological and strength properties of cement-stabilized clay minerals

This paper presents an experimental investigation into the effect of salinity on Atterberg limits, flowability, viscosity and strength properties of cement-stabilized clay minerals. Three groups of clay minerals (illite, kaolinite and montmorillonite) were obtained. Specimens with different porewater salinities were prepared by mixing the air-dried clays with sodium chloride (NaCl) at various salt concentrations (i.e., 0%, 2% 4%, 6% and 8%). Atterberg limits test results indicated that liquid limit and plasticity index decreased insignificantly with increasing salinity for Kaolinite and illite but significantly for montmorillonite. Flow test results indicated that of all specimens of three groups of clay minerals with or without adding cement consistently increase with increasing salinity. The flow value of montmorillonite increased more significantly than kaolinite and illite. Viscosity test results indicated that all the specimens tested behave as Bingham plastic. Flow value consistently decreased with increasing dynamic viscosity or yield stress, regardless of clay mineralogy, porewater salinity and cement amount. Strength test results indicated that all cement-stabilized specimens exhibit strain softening behavior. Unconfined compressive strength for three groups of clay minerals stabilized with cement consistently decreased with increasing salinity indicating that the presence of salt had an adverse effect on the development of strength.

Al (III) removal from wastewaters by natural clay and coconut shell

<p>This paper describes the adsorption of Al3+ ions from aqueous solutions, by natural clay (from Sakarya's Yenigün district) and coconut shell modified by means of acid treatment. Batch experiments were carried out to determine the effect of various factors such as initial pH (4-9), temperature (20, 40, 70 oC), initial concentration (10 to 200 mg L-1) and contact time (1-120 minute) on the adsorption process. The adsorption experiments were performed at a temperature of 20 ±2 oC), at 200 rpm agitation rate, with an adsorbent level of 1 g L-1, produced 98.95% (at pH 6) and 92.83% (at pH 7) maximum Al3+ removal efficiency for clay and coconut shell based adsorbents respectively. Furthermore, the process was found to be exothermic for clay and endothermic for coconut. XRF and XRD analyses of the clay variety used in adsorption analyses revealed it to be saponite clay, within the larger group of smectite clay minerals. The application of Langmuir revealed maximum adsorption capacity of 149.25 mg g-1 for natural clay adsorbent (NCA), and 120.482 mg g-1 for coconut shell adsorbent (CSA). Moreover, adsorption kinetics were found to be consistent with the second order kinetics (R2 > 0.95). The result shows that, natural clay and coconut shell adsorbents are effective adsorbents to remove Al3+ from aqueous solutions with good adsorption rate (>92.8%).</p>

Use of TEM-EDX for structural formula identification of clay minerals: a case study of Di Linh bentonite, Vietnam

Transmission electron microscopy linked with energy-dispersive X-ray spectroscopy (TEM-EDX) was applied to characterize mineralogical signals of weathering processes in the Di Linh bentonite deposit (Vietnam) and to visualize the effects of Na activation on the smectitic phases. Modelling of X-ray diffraction patterns (oriented mount) was applied in order to refine the computed structural formula. X-ray diffraction, X-ray fluorescence and Fourier-transform infrared spectroscopy (FT-IR) methods were also applied to verify the TEM-EDX results. AnExcel-based routine has been developed in this research to allow fast computation of structural formulae and classification of the investigated clay particles. This routine supports the acquirement of 100–300 TEM-EDX analyses as a representative set of individual particles for each sample. TheExcel-based routine involves end members of different clay-mineral groups and interstratifications with two or three members (e.g.illite–smectite interstratifications – IS-ml; dioctahedral vermiculite–smectite interstratifications – diVS-ml; and kaolinite–montmorillonite–dioctahedral vermiculite interstratifications – KSV-ml). The routine is now freely available. According to the identification procedure, the <2 µm fraction of the Di Linh bentonite (Vietnam) is composed mainly of K- and charge-deficient illite–smectite interstratifications (or diVS-ml): montmorillonite-rich randomly ordered (R0) type and illite-rich regularly ordered (R1) type. Additionally, Fe-poor KSV-ml was identified. Industrial Na activation of the Di Linh bentonite resulted in an increase of the R1 diVS-ml portion and dissolution of a large part of the smectite-rich phases. The TEM-EDX approach also gave analytical proof of a sedimentary process for Di Linh smectite. The parent muscovite was altered in two different environments: (i) K-leaching and layer-wise alteration into kaolinite (weathering), and (ii) further edge-controlled alteration of mica into lath-like montmorillonite particles associated with a dissolution of kaolinite layers from the former kaolinite–mica intergrowths by heat impact (basalt flow).

A study of stereoselective adsorption in smectites using thin-layer chromatography

The stereoselective center in a group of smectite-layered clay minerals was investigated to determine chiral discrimination at either the crystal edge of the smectite or in the interlayer space. In this study, thin-layer chromatography (TLC) was used to probe the stereoselective adsorption site in the smectites. Because uniform-sized particles are crucial for facile, homogeneous, and reproducible production of a TLC plate, core-shell type particles were used, in which a hectorite-like layered silicate was directly grown on monodisperse silica spheres with a 2.6 μm diameter. The core-shell microspheres prepared by the hydrothermal reaction of lithium fluoride, magnesium chloride, and silica in the presence of urea at 373 K for two days were deposited on a glass plate using a splendor. The formation of the resulting layered silicate on the TLC plate was achieved via ion-exchange reactions with enantiomeric Δ-tris(1,10-phenanthroline)nickel(II). The intercalated Ni complex formed pores at the molecular level in the interlayer spaces. The optical resolution of tris(acetylacetonato)ruthenium(III) using methanol as a mobile phase was found to be influenced by the size of the pores and could be adjusted by changing the negative-layer charge density that was varied according to the molar ratio of the Li/Mg added into the hydrothermal reactions. Two split TLC spots attributed to the Δ- and Λ-isomers of the acetylacetonato Ru complex were observed with no tailing when the TLC plate included the layered silicate with a greater density of charged layers. These findings indicated that an increase in the spatial density of the interlayer Ni complex (a narrower pore) enhanced interactions between the Ru complex and the intercalation compound, leading to optical resolution. The TLC experiments showed that the interlayer void space plays an important role when stereoselective adsorption sites are located in the interlayer space.

Fines quality assessment in all-in aggregates for pavement layers related to different standard procedures

During the construction of the unbound pavement layers of Corridors X and XI in Serbia, a problem was detected regarding the evaluation of cleanliness of the available materials. The European standard for the sand equivalent from 1999 to 2015 had significant changes related to the test procedure. A mass correction has been taken into account. It consists of replacing a part of the fines with rinsed material (0.063/2 mm) when the percentage of fines exceeds 10% in a tested fraction. Thus, the test sample usually yields high values of the sand equivalent, which often exceeds the limits of 50% and 60%. From the standpoint of the technical specifications, aggregates are considered clean, while using other methods like methylene blue or a plasticity index, the presence of clay particles above the limits can be confirmed. This paper presents the results of research on 63 laboratory-prepared test samples of limestone aggregate with small quantities of the smectite group of clay minerals, where the fines content in the unbound aggregate, 0/31.5 mm, gradually increased up to 20%. It was found that the sand equivalent values are continuously decreasing from 84 to 14% in the fraction 0/2 mm and from 87 to 18% in the 0/4 mm fraction, with increasing of the methylene blue value of the all-in aggregate (MBA) from 0.4 to 4.5 g/kg. Correlations of different methods and fractions, as well as with the content of fines were found. There are no correlations with SE10 because of grouping the test data around one point.

Insights on the role of organic matters of some Egyptian clays in methyl orange adsorption: Isotherm and kinetic studies

The role of organic matters (OM) of some Egyptian clay in Methyl Orange (MO) adsorption from aqueous solutions was tested for the first time. To elaborate this role, the raw Organic Matters-Rich Clays (OMRC) was calcinated at 500 °C/4 h to remove their associated OM by oxidation. Then the MO removal efficiency by both OMRC and its calcinated derivative (COMRC) was tested at different experimental parameters. The adsorption of MO by the studied adsorbents was pH- and time-dependent process and the equilibrium was attained after 60 min. The pseudo-second-order model with high determination coefficients (R2 > 0.999) fitted well the adsorption kinetics, while the intra-particle diffusion was not the rate governing step in MO adsorption by both adsorbents. The MO adsorption characteristics revealed that equilibrium data of OMRC and COMRC fitted well to the Freundlich and Langmuir models, respectively. Electrostatic interaction was the primary but not the only governing mechanism for MO adsorption by the investigated adsorbents; participation from hydrogen bonding mechanism was involved, with some preference for COMRC. The superiority of OMRC over COMRC in MO adsorption can be attributed to the involvement of oxygen- and nitrogen-bearing groups of both OM and clay minerals in the adsorption process on the contrary of COMRC in which only oxygen-bearing groups of the clay minerals were incorporated.

Potential shale resource plays in southeastern Nigeria: Petroleum system modelling and microfabric perspectives

Nigeria is witnessing significant increase in energy demand as a result of rising population and economic growth; as more focus on clean energy take hold. These challenges have triggered the search for shale gas and shale oil in the inland basins of Nigeria. The aim of the study is to carry out an integrated study that incorporates petroleum systems modelling, field studies and advanced analytical programs in order to define the hydrocarbon prospectivity of Upper Cenomanian-Lower Turonian Eze-Aku Shale and Ekenkpon Shale as potential shale gas/oil plays in southeastern Nigeria. Available subsurface information which includes exploration wells and proprietary Oil Company archive data were used to calibrate and simulate 1-D basin models. Amount of silica content, major clay mineral group and microfabric of the potential shale resource plays were determined using Energy Dispersive X-ray Fluorescence analysis, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy respectively. The simulated models showed that deeply buried Eze-Aku Shale and Ekenkpon Shale have undergone episodic generation of hydrocarbon. Significant amount of silica content (>30%) in Eze-Aku and Ekenkpon Shale samples suggested a brittle nature of the samples and the possibilities of the samples to capture portion of expelled hydrocarbon. Identification of non-swelling clay mineral group in the analyzed shale samples indicated that the samples have the potential for shale gas/oil. The SEM images of analyzed samples showed differences in cementation. This study recommends that deeply buried Eze-Aku Shale and Ekenkpon Shale are potential exploration targets for shale gas/oil in Abakaliki Fold Belt and Calabar Flank of the southeastern Nigeria.

Characteristics of clay minerals in soil particles from an argillic horizon of Alfisol in central China

The soil particles (<2000, 450–2000, 100–450 and 25–100nm) in an Alfisol were studied using inductively coupled plasma-optical emission spectroscopy (ICP-OES), conventional and synchrotron X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG) to investigate the mineral composition of clays and changes in crystalline structure in the particles of an argillic horizon. The results showed that the clay minerals in the particle fractions (<2000, 450–2000 and 100–450nm) were illite, kaolinite, vermiculite and a trace amount of hydroxy interlayered vermiculite and chlorite. In the nanoparticles (25–100nm), the main clay minerals were illite and kaolinite. The molar ratios of SiO2 to Al2O3 and SiO2 to R2O3 (Al2O3 and Fe2O3) were higher in the nanoparticles compared to other particle fractions. With decreasing particles size, kaolinite and vermiculite decreased gradually and illite increased. The Al-Mg-OH and Si–O–Si (Al) stretching modes of vermiculite were broadened in the 100–450nm particles and disappeared in nanoparticles while the hydroxyl group (OH) of clay minerals in the samples was reduced with decreasing particle fractions. The broadening of the band characteristics of clay minerals, the dehydration and dehydroxylation were less pronounced in particle fractions from the argillic horizon comparing to the topsoil. Clay minerals from 450 to 2000 and 100–450nm particle fractions were well ordered whereas illite and kaolinite were poorly ordered in nanoparticles of the argillic horizon. The “crystallinity” of clay minerals was weakly affected in the particle fractions of argillic horizon compared to topsoil.

Mechanochemically activated saponite as materials for Cu2 + and Ni2 + removal from aqueous solutions

Saponites are nanosized layered aluminosilicates from the smectite group of clay minerals, which can be further functionalized to prepare low-cost materials for water purification. Mechanochemical activation of saponite was achieved by high-energy grinding in a planetary ball mill. X-ray diffraction, infrared spectroscopy, scanning electron microscopy, thermal analysis, and the determination of cation-exchange capacity and specific surface area were used to characterize parent and functionalized solids. Prepared adsorbents were used for Cu2+ and Ni2+ removal from aqueous solutions. Compared to the untreated sample, activated saponites had significantly increased capacity to take away metal cations. The equilibrium data showed the maximum of Cu2+ and Ni2+ uptake of 295 and 129mg/g, respectively. In comparison with the pristine material, the measured values increased by 764% and 170% for Cu2+ and Ni2+ respectively. The formation of reactive Mg(OH)2 as the saponite decomposition product was also discussed.

NOVEL SUPERABSORBENT HYDROGEL COMPOSITE BASED ON POLY(ACRYLAMIDE-CO-ACRYLATE)/NONTRONITE: CHARACTERIZATION AND SWELLING PERFORMANCE

A novel superabsorbent hydrogel (SH) composite based on a poly(acrylamide-co-acrylate) matrix filled with nontronite (NONT), a Fe(III)-rich member of the smectite group of clay minerals, is described in this manuscript. A variety of techniques, including FTIR, XRD, TGA, and SEM/EDX, were utilized to characterize this original composite. Experimental data confirmed the SH composite formation and suggested NONT was completely dispersed in the polymeric matrix. Additionally, NONT improved the water uptake capacity of the final material, which exhibited fast absorption, low sensitivity to the presence of salt, high water retention and a pH sensitive properties. These preliminary data showed that the original SH composite prepared here possesses highly attractive properties for applications in areas such as the agriculture field, particularly as a soil conditioner.

Inhibitory effect of kaolin minerals compound against hepatitis C virus in Huh-7 cell lines.

BackgroundHepatitis C virus (HCV) is estimated to infect 200 million individuals in the globe, including approximately 10 million in Pakistan causing both acute and chronic hepatitis. The standard treatment against HCV is pegylated interferon therapy in combination with a nucleoside analogue ribavirin. In addition, several herbal extracts and phytochemicals derivatives are used traditionally in the treatment of liver diseases as well as HCV infection. The present study determines the inhibitory effect of kaolin minerals compound against hepatitis C virus in Huh-7 cell lines.MethodsHuh-7 cell lines were used for the in vitro HCV replication by using HCV positive sera from different patients with known HCV genotypes and viral titer/load. Total RNA was extracted from these infected cells and was quantified by real-time polymerase chain reaction (Real-time PCR). The viral titer was compared with the control samples to determine the anti-HCV activity of kaolin derived compounds. Kaolin is a group of clay minerals, with the chemical composition Al2 Si2O5 (OH)4.ResultsThe results showed promising effectiveness of local kaolin derived anti-HCV compounds by causing 28% to 77% decrease in the HCV titer, when applied to infected Huh-7 cell lines. This study provides the basis for future work on these compounds especially to determine the specific pathway and mechanism for inhibitory action in the replicon systems of viral hepatitis.ConclusionsKaolin mineral derivatives show promising inhibitory effects against HCV genotypes 3a and 1a infection, which suggests its possible use as complementary and alternative medicine for HCV viral infection.

Applicable Fine Stream Sediments from Upper Chi River Produced Fired Clay Bricks

Stream sediments from the upper Chi River basin, including Chi and Nam Phong sub-watershed, are applicable to be a source of raw materials to produce fired clay bricks. The sampling locations of clay materials are generally found along the river terrace where are covering three different regions (upper-, mid-and lower sub-watershed) nearby brickyards. Quartz is the main mineral of all samples. Moreover, mainly clay mineral groups consist of mica, kaolinite, and chlorite group composing totally around 5%. Other mineral compositions, such as carbonate, evaporite, corundum, hematite and pyrolusite are normally found both in fine stream sediments and fired clay bricks. Additional minerals in fired bricks are forsterite, zircon and mullite group which are less than 0.2%. Their strength in submersion test expressed in the air-dried to pure water both 1 day and 5 days is revealed that their strength and strain intend to increase with the submersed brick. Besides, prism compressive strength decreases in half related to a fired brick unit. Their impact resistances are significantly distinctive by mineral composition of clay mineral group and silica. The compressive strength of air-dried fired brick at the ultimate stress and strain corresponding by time in water absorption test show that water filled in void or pore can enhance their strength and strain. Thus, fired clay bricks are capable to resist compressive force than the normal condition.

Nanoscale Elastic Properties of Montmorillonite upon Water Adsorption

Smectites are an important group of clay minerals that experience swelling upon water adsorption. This paper uses molecular dynamics with the CLAYFF force field to simulate isothermal isobaric water adsorption of interlayer Wyoming Na-montmorillonite, a member of the smectite group. Nanoscale elastic properties of the clay-interlayer water system are calculated from the potential energy of the model system. The transverse isotropic symmetry of the elastic constant matrix was assessed by calculating Euclidean and Riemannian distance metrics. Simulated elastic constants of the clay mineral are compared with available results from acoustic and nanoindentation measurements.

Adsorption of phenanthrene on Na-montmorillonite: A model study

The role of clay minerals in the fate of polycyclic aromatic hydrocarbons (PAHs) in soil still remains an unresolved and controversial issue. Recent experimental studies report on PAH sorption capacity of clay minerals, which is either much smaller than or comparable to that of soil organic matter with water either inhibiting or not inhibiting PAH sorption. We studied adsorption of phenanthrene – a prominent PAH representative – on Na-montmorillonite – a common member of the smectite group of clay minerals and often dominating component of soil inorganic matter – by means of molecular simulations incorporating free energy calculations. The study also included the effect of surface hydration on sorption. Phenanthrene adsorption site featured by Na +− π bonding was identified as the most favorable one on the dehydrated montmorillonite surface with other inner-sphere adsorption sites being less favorable by 23–32 kJ/mol and the desorption state being less favorable by 74 kJ/mol on the free energy scale. Upon montmorillonite hydration by a water film with a thickness of ~ 1 nm, however, phenanthrene desorption from the montmorillonite surface to the water–air interface becomes more favorable than phenanthrene direct adsorption. Our results support, therefore, experimental studies suggesting that PAHs adsorption on clays predominates in the dry soils but is negligible in the presence of water. Still, a consideration of higher phenanthrene surface coverages (to account for possible aggregation effect) or other exchangeable cations (to account for possible stronger cation − π bonding) in the future model studies may provide additional arguments pro or contra of this suggestion.

DFT calculation of crystallographic properties of dioctahedral 2:1 phyllosilicates

AbstractThe low-charge dioctahedral 2:1 phyllosilicates are an important group of clay minerals that have a low degree of cation substitution and very weak interlayer interatomic interactions which are difficult to reproduce with quantum mechanical calculations. In order to study the crystallographic properties of these compounds with density functional theory (DFT) quantum-mechanical methods, an optimization of norm-conserving pseudopotentials of Al, Si, O, H and Na atoms has been carried out, and an optimization of the cutoff radii of the basis sets has been accomplished. Crystallographic properties and vibrational stretching frequencies of the OH groups, ν(OH), have been calculated, being consistent with previous computational and experimental results. All frequencies can be related to the different molecular environment of the OH groups. The effect of octahedral Fe3+ substitution on the ν(OH) frequency is reproduced. Several configurations of cation substitutions and interlayer cation (IC) positions are studied in low-charge dioctahedral 2:1 phyllosilicates, such as Al4(Si7–xAlx)O20(OH)4Nax, with x = 0.25, 0.50 and 0.75, indicating that the IVAl3+ is highly dispersed and the IC tends to be in the substituted ditrigonal hole. For the Al4(Si7Al)O20(OH)4Na composition, the trans-vacant form is more stable than the cis-vacant one.

The surface properties of sepiolite

Some surface properties of sepiolite were determined for a natural sample and after surface charge saturation with sodium cations. The values obtained are: water/solid contact angle 70.9° and 71.4°, spreading pressure at monolayer coverage 119.2 and 120.3 mJ m −2, spreading pressure at saturation 144.1 and 142.4 mJ m −2 amounts of water adsorbed at monolayer coverage 74.48 and 78.06 mg g −1, surface energy 243.3 and 241.4 mJ m −2, water/solid interfacial energy 7.4 and 7.4 kJ mol −1, enthalpy of water adsorption 52.4 and 52.24 kJ mol −1 respectively. These values are similar to those reported in the literature for palygorskite which is the other member of the clay mineral group.