Micro-structure differences in kaolinite suspensions

SEM observations of the aqueous suspensions of kaolinite from Birdwood (South Australia) and Georgia (USA) show noticeable differences in number of physical behaviour which has been explained by different micro-structure constitution. Birdwood kaolinite dispersion gels are observed at very low solid loadings in comparison with Georgia KGa-1 kaolinite dispersions which remain fluid at higher solids loading. To explain this behaviour, the specific particle interactions of Birdwood kaolinite, different from interaction in Georgia kaolinite have been proposed. These interactions may be brought about by the presence of nano-bubbles on clay crystal edges and may force clay particles to aggregate by bubble coalescence. This explains the predominance of stair step edge-edge like (EE) contacts in suspension of Birdwood kaolinite. Such EE linked particles build long strings that form a spacious cell structure. Hydrocarbon contamination of colloidal kaolinite particles and low aspect ratio are discussed as possible explanations of this unusual behaviour of Birdwood kaolinite. In Georgia KGa-1 kaolinite dispersions instead of EE contact between platelets displayed in Birdwood kaolinite, most particles have edge-to-face (EF) contacts building a cardhouse structure. Such an arrangement is much less voluminous in comparison with the Birdwood kaolinite cellular honeycomb structure observed previously in smectite aqueous suspensions. Such structural characteristics of KGa-1 kaolinite particles enable higher solid volume fractions pulps to form before significantly networked gel consistency is attained.     

Partitioning of clay colloids at air-water interfaces

Colloid sorption onto air-water interfaces in a variety of natural environments has been previously recognized, but better quantification and understanding is still needed. Affinities of clay colloids for the air-water interface were measured using a bubble-column method and reported as partition coefficients (K). Four types of dilute clay suspensions were measured in NaCl solutions under varying pH and ionic strength conditions: kaolinite KGa-1, illite IMt-2, montmorillonite SWy-2, and bentonite. The K values of three types of polystyrene latex particles with different surface-charge properties were also measured for comparison. Kaolinite exhibited extremely high affinity to the air-water interface at pH values below 7. Illite has lower affinity to air-water interfaces than kaolinite, but has similar pH dependence. Na-montmorillonite and bentonite clay were found excluded from the air-water interface at any given pH and ionic strength. Positively and negatively charged latex particles exhibited sorption and exclusion, respectively, at the air-water interface. These results show the importance of electrostatic interactions between the air-water interface and colloids, especially the influence of pH-dependent edge charges, and influence of particle shape.     

Quantitative mineralogical properties (morphology-chemistry-structure) of pharmaceutical grade kaolinites and recommendations to regulatory agencies

The physical and chemical characteristics of kaolinite (kaolin) may be variable, and minor amounts of other clay minerals, nonclay minerals, and other impurities may affect the properties of kaolinites. Thus specific technical properties of pharmaceutical grade kaolinites become very important because these clays are used in medical applications, e.g., as pharmaceutical excipients, and will be consumed by humans. Seven pharmaceutical grade kaolinite specimens were used in this study: K1004, KA105, 2242-01, K2-500, Acros, Acros-mono, and KX0007-1. In addition, two kaolinites from the Clay Minerals Society Source Clays, KGa-1b and KGa-2, were used for comparison purposes. The Acros-mono and 2242-01 kaolinites contained minor amounts of illite, which was demonstrated both compositionally and structurally by using inductively coupled plasma spectroscopy and powder X-ray diffraction. The KX0007-1 kaolinite powder was found to be heavily contaminated with quartz, cristobalite, and alunite. Crystal structure computations also showed excess Si in its tetrahedral site, and the mineral no longer has the typical kaolinite crystal structure. These widely-used industrial standards should be quantitatively characterized morphologically, compositionally, and structurally. Results of the mineralogical characteristics should be clearly labeled on the pharmaceutical grade kaolinites and reported to the relevant regulatory agencies.     

Heterogeneous reactions of gaseous HNO3 and NO2 on the clay minerals kaolinite and pyrophyllite

Airborne clay mineral particles have long atmospheric lifetimes due to their relatively small size. To assess their impact on trace atmospheric gases, we investigated heterogeneous reactions on prototype clay minerals. Diffuse reflectance infrared spectroscopy identified surface-adsorbed products formed from the uptake of gaseous nitric acid and nitrogen dioxide on kaolinite and pyrophyllite. For kaolinite, a 1:1 phyllosilicate, HNO3 molecularly adsorbed onto the octahedral aluminum hydroxide and tetrahedral silicon oxide surfaces. Also detected on the aluminum hydroxide surface were irreversibly adsorbed monodentate, bidentate, bridged, and water-coordinated nitrate species as well as surface-adsorbed water. Similar adsorbed products formed during the uptake of NO2 on kaolinite at relative humidity (RH) of 0%, and the reaction was second order with respect to reactive surface sites and 1.5 +/- 0.1 for NO2. Reactive uptake coefficients, calculated using Brunauer, Emmett, and Teller surface areas, increased from (8.0 +/- 0.2) x 10(-8) to (2.3 +/- 0.4) x 10(-7) for NO2 concentrations ranging from 0.56 x 10(13) to 8.8 x 10(13) molecules cm(-3). UV-visible spectroscopy detected gaseous HONO as a product for the reaction of NO2 on wet kaolinite. The uptake of HNO3 on pyrophyllite, a 2:1 phyllosilicate, resulted in stronger signal for nitric acid molecularly adsorbed on the silicon oxide surface compared to kaolinite. Monodentate, bridged, and water-coordinated nitrate species bound to aluminum sites also formed during this reaction indicating that reactive sites on edge facets are important for this system. The uptake of NO2 on pyrophyllite, gammaBET = (7 +/- 1) x 10(-9), was significantly lower than kaolinite because NO2 did not react with the dominant tetrahedral silicon oxide surface. These results highlight general trends regarding the reactivity of tetrahedral silicon oxide and octahedral aluminum hydroxide clay surfaces and indicate that the heterogeneous chemistry of clay aerosols varies with mineralogy and cannot be predicted by elemental analysis.     

Computer simulations of particle-bubble interactions and particle sliding using Discrete Element Method

Polymer coatings on nano-sized remediation agents and subsurface heterogeneity will affect their transport, likely in a pH-dependent manner. The effect of pH on the aggregation of polymer-coated nanoscale zerovalent iron (nZVI) and its deposition onto sand and clay (kaolinite) surfaces was studied. nZVI coatings included a high molecular weight (90 kg/mol) strong polyanion, poly(methacrylic acid)-b-(methy methacrylate)-b-(styrenesulfonate) (PMAA-PMMA-PSS) and a low molecular weight (2.5 kg/mol) weak polyanion, polyaspartate. Aggregation and deposition increased with decreasing pH for both polyelectrolytes. The extent was greater for the low MW polyaspartate coated nZVI. Enhanced deposition at lower pH was indicated because the elutability of polyaspartate-modified hematite (which did not aggregate) also decreased at lower pH. The greater deposition onto clay minerals compared to similar sized silica fines is attributed to charge heterogeneity on clay mineral surfaces, which is sensitive to pH. Heteroaggregation between kaolinite particles and nZVI over the pH range 6-8 confirmed this assertion. Excess unadsorbed polyelectrolyte in solution (100mg/L) enhanced the transport of modified nZVI by minimizing aggregation and deposition onto sand and clay. These results indicate that site physical and chemical heterogeneity must be considered when designing an nZVI emplacement strategy.     

恶臭假单胞菌与土壤矿物的界面反应及其对甲基对硫磷降解影响

研究了恶臭假单胞菌在蒙脱石、高岭石和针铁矿表面的吸附特征,探讨了细菌在不同粘粒矿物存在下的生长代谢活性,及对甲基对硫磷的降解动力学.结果表明, 三种矿物对细菌的吸附强度为针铁矿>高岭石>蒙脱石.当甲基对硫磷浓度较低时(10 mg/L), 游离菌的降解能力始终比固定菌强;在高浓度(20～40 mg/L)下, 固定菌对农药的降解能力起初(前9 h)高于游离菌, 随后渐渐低于游离菌.不同矿物固定的细菌, 其降解能力为蒙脱石>高岭石>针铁矿.蒙脱石对细菌的亲和力最弱, 但它对细菌的代谢活性有促进作用, 有利于农药的生物降解; 而针铁矿与细菌的结合强度最大, 细菌活性受到抑制, 不利于农药的降解.     

Interaction of Pseudomonas putida with kaolinite and montmorillonite: a combination study by equilibrium adsorption, ITC, SEM and FTIR

Equilibrium adsorption along with isothermal titration calorimetry (ITC), Fourier transform infrared spectra (FTIR) and scanning electron microscopy (SEM) techniques were employed to investigate the adsorption of Pseudomonas putida on kaolinite and montmorillonite. A higher affinity as well as larger amounts of adsorption of P. putida was found on kaolinite. The majority of sorbed bacterial cells (88.7%) could be released by water from montmorillonite, while only a small proportion (9.3%) of bacteria desorbed from kaolinite surface. More bacterial cells were observed to form aggregates with kaolinite, while fewer cells were within the larger bacteria–montmorillonite particles. The sorption of bacteria on kaolinite was enthalpically more favorable than that on montmorillonite. Based on our findings, it is proposed that the non-electrostatic forces other than electrostatic force play a more important role in bacterial adsorption by kaolinite and montmorillonite. Adsorption of bacteria on clay minerals resulted in obvious shifts of infrared absorption bands of water molecules, showing the importance of hydrogen bonding in bacteria–clay mineral adsorption. The enthalpies of −4.1 ± 2.1 × 10⁻⁸ and −2.5 ± 1.4 × 10⁻⁸ mJ cell⁻¹ for the adsorption of bacteria on kaolinite and montmorillonite, respectively, at 25 °C and pH 7.0 were firstly reported in this paper. The enthalpy of bacteria–mineral adsorption was higher than that reported previously for bacteria–biomolecule interaction but lower than that of bacterial coaggregation. The bacteria–mineral adsorption enthalpies increased at higher temperature, suggesting that the enthalpy–entropy compensation mechanism could be involved in the adsorption of P. putida on clay minerals. Data obtained in this study would provide valuable information for a better understanding of the mechanisms of mineral–microorganism interactions in soil and associated environments.     

Influence of the particle-size reduction by ultrasound treatment on the dehydroxylation process of kaolinites

Kaolinites from well-known sources (KGa-1 and KGa-2) were used to study the influence of the particle-size reduction on the dehydroxylation process. Size reduction of particles was obtained by ultrasound treatment to avoid the effect of the progressive amorphization of the structure, which takes place with the traditional grinding treatment.The particle-size reduction causes an increase of the mass loss between 140 and 390°C attributed to the loss of the hydroxyl groups exposed on the external surface of kaolinite; a shift to lower temperatures of the endothermic effect related with the mass loss between 390 and 600°C and a shift of the end of dehydroxylation to lower temperatures. The first modification can be explained by an increase of the number of hydroxyls exposed on the external surface of kaolinite which is proportional to the new surface generated in the particle reduction process, whereas the shift of the dehydroxylation to lower temperatures is related to the reduction of the dimensions of the particles which favour the diffusion controlled mechanisms.Comparing between the DTA curves to the TG curves of the studied samples shows that the observed modifications in the thermal properties induced by the particle-size reduction are greater for the low-defect kaolinite. The intensity of these modifications depends on the effectiveness of the ultrasound treatment.The authors are grateful to S. Yariv, I. Lapides and S. Shoval for carefully reviewing this paper and making helpful comments. This research has been supported by Research Project MAT 2002-03774 from the Spanish Ministry of Science and Technology and Research Groups FQM-187 and RNM-0199 of the Junta de Andalucia.     

Adsorption of dicarboxylic acids by clay minerals as examined by in situ ATR-FTIR and ex situ DRIFT

The adsorption of dicarboxylic acids by kaolinite and montmorillonite at different pH conditions was investigated using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) and ex situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The sorption capacity of montmorillonite was greater than that of kaolinite. Adsorption of dicarboxylic acids (succinic acid, glutaric acid, adipic acid, and azelaic acid) was the highest at pH 4 as compared with those at pH 7 and 9. These results indicate that sorption is highly pH-dependent and related to the surface characteristics of minerals. The aliphatic chain length of the dicarboxylic acids highly influenced the sorption amount at acidic pH, regardless of the clay mineral species: succinic acid [HOOC(CH2)2COOH] < glutaric acid [HOOC(CH2)3COOH] < adipic acid [HOOC(CH2)4COOH] < azelaic acid [HOOC(CH2)7COOH]. With in situ ATR-FTIR analysis, most samples tend to have outer-sphere adsorption with the mineral surfaces at all tested pHs. However, inner-sphere coordination between the carboxyl groups and mineral surfaces at pH 4 was dominant from DRIFT analysis with freeze-dried complex samples. The complexation types, inner- or outer-sphere, depended on dicarboxylic acid species, pH, mineral surfaces, and solvent conditions. From the experimental data, we suggest that organic acids in an aqueous environment prefer to adsorb onto the test minerals by outer-sphere complexation, but inner-sphere complexation is favored under dry conditions. Thus, organic acid binding onto clay minerals under dry conditions is stronger than that under wet conditions, and we expect different conformations and aggregations of sorbed organic acids as influenced by complexation types. In the environment, natural organic material (NOM) may adsorb predominantly on positively charged mineral surfaces at the aqueous interface, which can convert into inner-sphere coordination during dehydration. The stable NOM/mineral complexes formed by frequent wetting-drying cycles in nature may resist chemical/microbial degradation of the NOM, which will affect carbon storage in the environment and influence the sorption of organic contaminants.     

Absolute aggregation rate constants in aggregation of kaolinite measured by simultaneous static and dynamic light scattering

The aggregation rate was determined for the < 0.2 microm size fraction of kaolinite (KGa-2) using simultaneous static and dynamic light scattering at pH 9.5. It was found that method suggested by Holthoff et al. [Langmuir 1996, 12, 5541] is suitable for determination of the absolute aggregation rate constant of a clay dispersion without using the particle optical factors. The determined fast aggregation rate constant is k11,fast = (3.7 +/- 0.2) x 10(-18) m3 s(-1). Stability behavior of kaolinite colloids was studied as a function of concentration of sodium chloride by simultaneous static and dynamic scattering. The critical aggregation concentration was found to be 0.085 +/- 0.005 mol dm(-3). When calculating the relationship between the stability ratio and the electrolyte concentration using the DLVO theory, the best fit to the experimental data was achieved with a Hamaker constant of A = (4.7 +/- 0.2) x 10(-20) J.     

Benzene–kaolinite interaction properties

In this work, we present a theoretical study of interaction of benzene with kaolinite and an analysis of the vibrational spectra, electrostatic potential maps, and self consistent field (SCF) orbitals. B3LYP and MP2 benzene–kaolinite results indicate a preferential interaction of benzene on kaolinite octahedral surface. Population analysis indicates that the atoms modified their charges when the monoaromatic molecule and clay mineral are close to tetrahedral and octahedral surface of kaolinite, which suggests that the adsorbed molecule becomes slightly positive. Infrared vibrational data show the reduction in the band frequencies related to the kaolinite external hydroxyls, indicating a weak interaction of benzene with clay mineral. It also was verified, from the potential electrostatic maps, a change in electron density in both benzene and kaolinite. Electron localization function analysis was also carried out for this interaction. © 2011 Wiley Periodicals, Inc.     

Structural characterization of U(VI) surface complexes on kaolinite in the presence of humic acid using EXAFS spectroscopy

To determine the influence of humic acid (HA), pH, and presence of atmospheric CO2 on the sorption of U(VI) onto kaolinite, the structure of the surface complexes was studied by U L III-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The best fits to the experimental EXAFS data were obtained by including two uranium coordination shells with two axial (O ax) and five equatorial (O eq) oxygen atoms at 1.77+/-0.02 and 2.34+/-0.02 A, respectively, and two coordination shells with one Al/Si atom each at 3.1 and 3.3 A. As in the case of the binary system U(VI)-kaolinite, uranium forms inner-sphere surface complexes by edge sharing with aluminum octahedra and/or silicon tetrahedra. HA and atmospheric CO2 as well as pH had no influence on the EXAFS structural parameters in the pH range of 5-8. Despite the presence of HA, U(VI) prefers to sorb directly onto kaolinite and not to HA that is bound to the clay surface. X-ray photoelectron spectroscopy (XPS) measurements of kaolinite particles that had been exposed to HA suspensions showed that significant parts of the kaolinite surface are not covered by HA.     

Relation between aggregation kinetics and the structure of kaolinite aggregates

Dynamic and static light scattering were applied to the determination of the stability ratio and fractal dimension of kaolinite (KGa-2) at different kaolinite or/and electrolyte concentrations at pH 9.5. Dynamic light scattering was used to measure the kinetics of early stage aggregation to determine the stability ratio, W, as well as the cluster sizes which determine the fractal regime. Static light scattering was used to measure the fractal dimension, D(f). Results show that the two classes of "universality" (Lin et al. Nature 1989, 339, 360) characterizing the diffusion- and reaction-limited regimes of cluster-cluster aggregation do apply to colloidal kaolinite as limit cases when W approximately 1 or W > 100, respectively. In the intermediate regime where 5 < W < 100, the growth of the aggregate radius showed a power-law behavior similar to diffusion-limited cluster aggregation. For the intermediate aggregation regime, a scaling relation between fractal dimension and stability ratio, reflecting a continuous increase in particle packing density in the aggregate as the sticking probability of particles was reduced, was demonstrated.     

New polymeric based materials: terpoly(aniline,diphenyl amine,and o‐anthranilic acid) / kaolinite composites

Terpolymers of aniline, diphenyl amine and o‐anthranilic acid (PANIDPAA) / kaolinite clay composites were synthesized by 1:1:1 molar ratios of the respective monomers with different percentages of kaolinite clay particles via in situ chemical terpolymerization. The spectral characteristics upon incorporation of o‐anthranilic acid and diphenyl amine units into the polyaniline backbone in presence of kaolinite clay were investigated. The results were justified by measuring the UV–Vis absorption spectra, FT‐IR for PANIDPAA emeraldine base (EB), and PANIDPAA EB / kaolinite clay composite. Also, the thermal gravimetric analyses for the isolated terpolymer powder in the bulk in absence and in presence of kaolinite clay were carried out. Moreover, the morphology of the polymer clay composites system was studied by the scanning electron microscope micrographs at different magnifications. X‐ray diffraction was used to measure the nature of polymer and extent of crystallinity present in the neat terpolymer and terpolymer / kaolinite composite materials. Copyright © 2016 John Wiley & Sons, Ltd.     

Modeling the adsorption of Cd(II) onto Muloorina illite and related clay minerals

The adsorption of Cd(II) onto goethite, kaolinite, and illite was measured as a function of pH (adsorption edges) and concentration (adsorption isotherms) at 25 degrees C. As the pH was increased, adsorption onto goethite occurred mainly in the pH range 5.5-8, whereas adsorption onto kaolinite occurred in two stages, separated by a plateau in the pH region 5.5 to 7. Adsorption onto illite increased steadily as the pH was increased, with far less Cd(II) adsorbing onto illite than onto goethite or kaolinite per m(2) of mineral surface area. Potentiometric titrations of suspensions of each mineral, with and without Cd(II) present, were also completed. Results from all three types of experiments were modeled using an extended constant- capacitance surface complexation model. The reactions [Formula: see text] [Formula: see text] and [Formula: see text] best described Cd(II) adsorption onto goethite, while [Formula: see text] and [Formula: see text] best described Cd(II) adsorption onto kaolinite. A combination of the first, second, and fourth of these reactions best fitted the data for Cd(II) adsorption onto illite. In each case the model fitted all experimental data well. The results suggest that adsorption onto the variable charge (SOH) sites on illite more closely resembles adsorption onto goethite than onto kaolinite.     

Transmission X-ray microscopy reveals the clay aggregate discrete structure in aqueous environment

The utilization of new transmission X-ray microscopy (TXM) using the synchrotron photon source enable for the first time the study in three dimensions microsize clay particles in aggregates in their natural aqueous environment. This technique makes possible remarkable accurate images of nanosize mineral interparticle structure which forms a new nanocomposite. The Birdwood kaolinite/LDH aggregates observed in the TXM are much more compact than observed before in pure Birdwood kaolinite suspension and similar to aggregates formed after treatment by positively charged surfactant. Kaolinite/LDH aggregates in water reveal complex structure of larger kaolinite platelets connected together by gelled nanoparticles which are most probably LDH colloidal plates. Comparisons of the transmission electron microscope (TEM) and TXM techniques show similarities in particle morphology. The ability to study particles and aggregates in their natural aqueous environment and in 3-dimensions make this technique superior to the TEM technique.     

Synthesis and characterization of silver nanoparticle/kaolinite composites

Ag nanoparticles were synthetized in the interlamellar space of a layered kaolinite clay mineral. Disaggregation of the lamellae of non-swelling kaolinite was achieved by intercalation of dimethyl sulfoxide. The kaolinite was suspended in aqueous AgNO₃ solution and, after adsorption of Ag⁺, the ions were reduced with NaBH₄. The interlamellar space limits particle growth (d_ave=3.8–4.2 nm); however, larger silver particles may be formed on the exterior surface of kaolinite with d_ave=5.6–10.5 nm diameter. The diameter of the particles prepared in this way is depending on the initial AgNO₃ concentration. The silver nanoparticles prepared were characterized by UV–vis spectroscopy, X-ray diffraction (XRD), Small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM).     

Thermo-X-ray-diffraction analysis of dimethylsulfoxide-kaolinite intercalation complexes

DMSO-kaolinite complexes of low- and high-defect Georgia kaolinite (KGa-1 and KGa-2, respectively) were investigated by thermo-XRD-analysis. X-ray patterns showed that DMSO was intercalated in both kaolinites with a d(001)-value of 1.11 nm (type I complex). The samples were gradually heated up to 170°C and diffracted by X-ray at room-temperature. With the rise in temperature, due to the thermal evolution of the guest molecules, the relative intensity of the 1.11 nm peak decreased and that of the 0.72 nm peak (neat kaolinite) increased indicating that the fraction of the non-intercalated tactoids increased. The 1.11 peak disappeared at 130–140°C. During the thermal treatment of both complexes two additional peaks appeared at 110 and 120°C, respectively, with d-values of 0.79–0.94 and 0.61–0.67 nm in DMSO-KGa-1 and 0.81–0.86 and 0.62–0.66 nm in DMSO-KGa-2, indicating the formation of a new phase (type II complex). The new complex was obtained by the dehydration of type I complex and was composed of intercalated DMSO molecules which did not escape. The new peaks disappeared at 150–160°C indicating the complete escape of DMSO.     

Metal nanoparticle formation on layer silicate lamellae

Nanoparticles (Ag, Pd) were prepared by heterogeneous nucleation on the interlayer space of layered montmorillonite and kaolinite minerals in aquatic dispersion. Interlamellar incorporation of nanoparticles was monitored by X-ray diffraction and verified by transmission electron microscopy (TEM). After the reduction of adsorbed metal ions, a new Bragg reflection appeared, proving the formation of nanoparticles in the interlamellar space of clay mineral. Lamellar structure of layered silicates is partly destroyed by the particle formation. TEM images showed that larger nanoparticles were formed by UV irradiation and hydrazine hydrate than in the case of reduction by NaBH₄. Aqueous solutions of polyvinyl pyrrolidone and clay minerals were used for the stabilization of Pd° nanoparticles. The size of particles generated on the surface of clay minerals by heterogeneous nucleation increased with increasing metal concentration. When polymer is added to this system, particle size can be decreased by increasing polymer concentration. In this case, the particles are stabilized by the concerted action of the support and the macromolecule. The polymers promoted intercalation of nanoparticles into the clay mineral. In the absence of nanoparticles, the intercalation of polymers was significantly less extensive.     

Thermal behavior and immersion heats of selected clays from Turkey

Four clays (two bentonites and two kaolinites) from Turkey were investigated by X-ray diffraction (XRD), thermal analysis (DTA/TG-DSC) and surface area measurement techniques. Mineralogically bentonite samples were characterized low concentration of montmorillonite and high level of impurities. Both kaolinite samples mainly contained kaolinite and quartz as major mineral. TG-DTA curves of all clay samples were measured in the temperature range 30–1200 °C. The total % weight losses for the bentonite samples (B1 and B2) and the kaolinite samples (K1 and K2) were determined as 14.50, 13.42, 5.55 and 11.85%, respectively. Differential Scanning Calorimeter (DSC) analyses of samples were carried out by heating the samples from 30 to 550 °C. The immersion heats of clay samples were measured using with a Calvet-type C-80 calorimeter. The higher exothermic Q_imm values were determined for bentonite samples compared to kaolinite samples.