Dehydroxylation Temperature Research Articles

Micropores formation and effects in the magnetization roasting of limonite ore

As an abundant iron ore resource, limonite (mainly composed of goethite, hematite, lepidocrocite and other iron minerals) ore is seldom utilized due to its complex compositions, which has led to it lack mature processing methods. Magnetization roasting and magnetic separation is a promising method to process limonite ore. In this paper, the influence of microscopic pores on the reduction roasting of limonite ore was studied. X-ray diffraction, vibrating sample magnetometry, optical microscope, scanning electron microscopy, and the Brunauer-Emmett-Teller method of surface area analysis were used to study the dehydroxylation mechanism. The results indicated that goethite transformed into hematite, and the crystal structure of partly hematite probably changed when the dehydroxylation temperature increased from 600 °C to 1000 °C, making the sample more magnetic, the saturation magnetization increases significantly from 0.29 to 3.20 A·m2·kg−1. Simultaneously, SEM and BET showed the surface property has a big difference after roasting, more and more pores were generated with the temperature increased, then the specific surface area of the sample decreased from 75.94 to 0.59 m2·g−1. The reduction experiment results showed the dehydroxylation temperature has a significant effect on the reduction efficiency, the reduction time increased from 4 to 12.5 min with the temperature increased. This study has implications for the utilization of limonite ore using magnetization roasting technology.

Carboxymethyl Scleroglucan Synthesized via O-Alkylation Reaction with Different Degrees of Substitution: Rheology and Thermal Stability.

This paper presents the methodology for synthesizing and characterizing two carboxymethyl EOR-grade Scleroglucans (CMS-A and CMS-B). An O-Alkylation reaction was used to insert a hydrophilic group (monochloroacetic acid-MCAA) into the biopolymer's anhydroglucose subunits (AGUs). The effect of the degree of the carboxymethyl substitution on the rheology and thermal stability of the Scleroglucan (SG) was also evaluated. Simultaneous thermal analysis (STA/TGA-DSC), differential scanning calorimetry (DSC), X-ray Diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (SEM/EDS) were employed to characterize both CMS products. FTIR analysis revealed characteristic peaks corresponding to the carboxymethyl functional groups, confirming the modification. Also, SEM analysis provided insights into the structural changes in the polysaccharide after the O-Alkylation reaction. TGA results showed that the carboxymethylation of SG lowered its dehydroxylation temperature but increased its thermal stability above 300 °C. The CMS products and SG exhibited a pseudoplastic behavior; however, lower shear viscosities and relaxation times were observed for the CMS products due to the breakage of the SG triple helix for the chemical modification. Despite the viscosity results, the modified Scleroglucans are promising candidates for developing new engineering materials for EOR processes.

Dehydroxylation of Kaolinite and Halloysite-Rich Samples: An In Situ Study of the Texture and Structural Evolutions

Halloysite and kaolinite are dioctahedral TO phyllosilicates that drive the interest of scientists for formulating environmentally friendly materials, and consequently in the field of ceramics. The main scope of this study was the understanding of the texture evolution upon the dehydroxylation reaction and the influence of the presence of halloysite. In situ synchrotron (002) and (111) poles figures were recorded on the DiffAbs beamline at SOLEIL Synchrotron, from room temperature to 1000 °C, on kaolinite and/or halloysite-rich samples shaped by tape casting. Commercial kaolins and halloysite provided by Imerys company were used. The samples were labeled KRG100, KCS100, H100, KRG50H50 and KRG59H50 in relation with the wt. % of kaolin (KRG, KCS) or halloysite (H) clays. In samples KCS100 and KRG100, a strong texture was observed until in situ annealing at 700 °C, with respect to the c-axis of kaolinite. On the contrary, the texture with respect to the c-axis of halloysite for the sample H100 was weak whatever the temperature was. Moreover, this weak texture disappeared before the complete dehydroxylation of halloysite. This is due to the opening of some halloysite tubes. When considering the samples KRG50H50 and KCS50H50, a significant texture was observed with the c-axis preferentially oriented perpendicular to the sample surface. The presence of kaolinite platelets predominated onto the alignment of halloysites tubes. Furthermore, it was noted that the halloysite influenced the (002) diffracted intensity into the temperature range 20 °C to 400 °C. Above 400 °C, the behavior obtained for the (002) reflection in samples KRG50H50 and KCS50H50 was similar to the behavior noticed for pure kaolins KRG100 and KCS100, respectively. The dehydroxylation temperature range appeared to be relevant with combined effect of kaolinite and halloysite transformations arising from KRG100 or KCS100 and H100 samples. Therefore, the onset point of dehydroxylation is 550 °C ± 25 °C for KRG100, KCS100, KRG50H50 and KCS50H50. For the pure halloysite H100 sample, the dehydroxylation starts at the lower temperature 475 °C. It was also noted that during the dehydroxylation of kaolinite, the characteristic portion of ring related to the diffracted intensity of the (111) reflection located at χ = 45° tended to disappear above 550 °C and led to the formation of a new transitory phase with a (111) reflection with perpendicular alignment to the c-axis. Indeed, an epitaxial relationship with the (111) kaolinite reflection could be assumed. Further X-ray scattering experiments allowed highlighting the effective offset temperature of the dehydroxylation, which was identified as close to 720 °C. The metakaolinite achieved structural transformation to another transitory phase at 1000 °C.

State and forms of water in dispersed aluminum oxides and hydroxides

The state and forms of water in dispersed aluminum oxides and hydroxides and products obtained during their treatment are investigated in this paper. It has been found that particles of dispersed aluminum oxides and hydroxides of various water forms are present on surface and in volume. Their classification based on the state of water and the values of ΔH of evaporation has been introduced: “surface-bound” water, “structural” water, and “single OH groups”. For micron particles, the presence of predominantly “structural” water is exemplified for gibbsite (Al(OH)3) and boehmite (AlOOH). For the defective structure of products of heat treatment of gibbsite in air at 250 and 800°С, a low dehydroxylation temperature and high values of ΔH of water evaporation have been found: 71.13 kJ/mol and 67.27 kJ/mol, respectively. For the γ-Al2O3 nanopowder and the products of its treatment, the presence of “surface-bound”, “structural” water, and water represented by “single OH groups” has been detected. It has been shown that the treatment of gibbsite or aluminum oxide in a supercritical aqueous fluid at a water/Al2O3 molar ratio of less than 1.5 leads to the formation of tohdite 5Al2O3•H2O, the composition of which is characterized by a low content of structural water in the stable state over a wide temperature range.

Porous dehydroxyl cobalt phytate as electrocatalyst for high-efficiency water oxidation

Phytic acid (PA) is a six-fold dihydrogenphosphate ester of inositol with cost-effective, environmentally friendly, and safe properties. Here, we successfully synthesize the dehydroxyl cobalt phytate (PA-Co-400) using PA as phosphorus sources by a one-pot wet-chemistry strategy to prepare the precursor PA-Co and then heat treatment at 400 °C under an N2 atmosphere for dehydroxylation. The average diameter, specific surface area, surface element distribution, and catalytic activity of the catalyst are significantly affected by dehydroxylation temperature. The specific surface area increasesfirstandthendecreases with the treatment temperature from 200 °C to 600 °C. The SEM results indicate that the average diameter of PA-Co-400 particle is 68.90 nm. The as-prepared samples are used as an anode catalyst for electrocatalytic oxygen evolution reaction (OER). The PA-Co-400 exhibits splendid OER performances with an overpotential of 310.31 mV at j10 (η50 = 349.35 mV, η100 = 367.20 mV), which are even comparable to commercial RuO2 (η10 = 310.54 mV, η50 = 389.80 mV, η100 = 450.60 mV). Moreover, the PA-Co-400 has a small Tafel slope of 53.27 mV dec−1, which is lower than commercial RuO2 (81.71 mV dec−1). The ultra-long durability of PA-Co-400 was tested for over 80 h at current densities of 10 mA cm−2 without a significant reduction in 1 M KOH.

High‐Field NMR, Reactivity, and DFT Modeling Reveal the γ‐Al2O3 Surface Hydroxyl Network**

AbstractAluminas are strategic materials used in many major industrial processes, either as catalyst supports or as catalysts in their own right. The transition alumina γ‐Al2O3 is a privileged support, whose reactivity can be tuned by thermal activation. This study provides a qualitative and quantitative assessment of the hydroxyl groups present on the surface of γ‐Al2O3 at three different dehydroxylation temperatures. The principal [AlOH] configurations are identified and described in unprecedented detail at the molecular level. The structures were established by combining information from high‐field 1H and 27Al solid‐state NMR, IR spectroscopy and DFT calculations, as well as selective reactivity studies. Finally, the relationship between the hydroxyl structures and the molecular‐level structures of the active sites in catalytic alkane metathesis is discussed.

High-Field NMR, Reactivity, and DFT Modeling Reveal the γ-Al2 O3 Surface Hydroxyl Network.

Aluminas are strategic materials used in many major industrial processes, either as catalyst supports or as catalysts in their own right. The transition alumina γ‐Al2O3 is a privileged support, whose reactivity can be tuned by thermal activation. This study provides a qualitative and quantitative assessment of the hydroxyl groups present on the surface of γ‐Al2O3 at three different dehydroxylation temperatures. The principal [AlOH] configurations are identified and described in unprecedented detail at the molecular level. The structures were established by combining information from high‐field 1H and 27Al solid‐state NMR, IR spectroscopy and DFT calculations, as well as selective reactivity studies. Finally, the relationship between the hydroxyl structures and the molecular‐level structures of the active sites in catalytic alkane metathesis is discussed.

Thermal Properties of Illite-Zeolite Mixtures up to 1100 °C.

Illitic clays are the commonly used material in building ceramics. Zeolites are microporous, hydrated crystalline aluminosilicates, they are widely used due to their structure and absorption properties. In this study, illitic clay (Füzérradvány, Hungary) was mixed with natural zeolite (Nižný Hrabovec, Slovakia) with up to 50 wt.% of zeolite content. The samples were submitted to thermal analyses, such as differential thermal analysis, differential scanning calorimetry, thermogravimetry, and dilatometry. In addition, the evolution of thermal diffusivity, thermal conductivity, and specific heat capacity in the heating stage of firing were measured and discussed. The amount of the physically bound water in the samples increased along with the amount of zeolite. The temperature of the illite dehydroxylation (peak temperature) was slightly shifted to lower temperatures, from 609 °C to 575 °C (for sample IZ50). On the other hand, the mass loss and the shrinkage of the samples significantly increased with the zeolite content in the samples. Sample IZ50 reached 10.8% shrinkage, while the sample prepared only from the illitic clay contracted by 5.8%. Nevertheless, the temperature of the beginning of the sintering (taken from the dilatometric curves) decreased from 1021 °C (for illitic clay) to 1005 °C (for IZ50). The thermal diffusivity and thermal conductivity values decreased as the amount of zeolite increased in the samples, thus showing promising thermal insulating properties.

Effects of vermiculite on in-situ thermal behaviour, microstructure, physical and mechanical properties of fired clay bricks

Vermiculite is a hydrous clay mineral that occasionally occurs in raw materials for brickmaking. The presence of vermiculite affects the drying and firing processes of brick production; thus, the functions of this clay mineral should be clarified. In this study, vermiculite from 0 wt% to 30 wt% have been added to clay mixtures for brick button firing. Through effective integration of in-situ XRD, thermogravimetric and dilatometric analyses, the real-time thermal behaviours have been interpreted, and the microstructure, physical and compressive characteristics of brick buttons have been investigated. The incorporation of vermiculite has changed the temperatures of kaolinite dehydroxylation and rutile formation. Enstatite, cordierite and amorphous contents increased in fired brick buttons, while mullite, quartz and cristobalite decreased. Vermiculite retained a partial sheet-like morphology at 1150 °C firing. From 25 to 1150 °C, five weight loss steps have been defined with six shrinkage/expansion processes observed. Cracks appeared on brick button surfaces when 30 wt% of vermiculite was added. The colour of fired brick buttons changed from “light camel” to “black olive”. Drying shrinkage, firing shrinkage and bulk density increased with an increased proportion of vermiculite. The maximum compressive strength reached 150.94 MPa (a rise of 21.6% towards the control sample) when 5 wt% of vermiculite was added.

Property modifications of low‐grade clay through physical treatments and its incidence in the pozzolanic activity

AbstractIn the cement industry, it is usual to use calcined clays due to structural changes caused by thermal activations; however, there are other activation methods, such as mechanical activation by grinding. This method is not so common and has been relegated to the second level. Thus, in this work, the physical and mechanical changes in the structure of clays, induced by comminution processes, of standard clays and a low‐grade kaolinitic multicomponent clay, derived from weathering of metamorphic rock, were evaluated. These changes were measured using X‐ray fluorescence, X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, specific surface area (SSA) by Brunauer–Emmett–Teller method, and lime fixing as a measure of pozzolanic activity. It was found that the milling process modified the structure of the clays and the pozzolanic activity, since the main reflection (001) disappeared, the dehydroxylation temperature decreased to a maximum differential of 150°C with 120 s of milling time, especially in T:O:T clays, and the SSA increased along with the lime fixing to a maximum of 119 m2/g and 46%, respectively. In this way, the milling process is effective for the mechanical activation of the clay, especially in multicomponent clay, making it interesting for use as supplementary cementitious material.

Fabrication and Characterization of Clay-Polyethylene Composite Opted for Shielding of Ionizing Radiation

This study fabricated and characterized a self-sustaining hydrogenous content clay-polyethylene composite opted for ionizing radiation shielding. Composites designated A–G were fabricated each containing 0–30 wt% of recycled low density polyethylene (LDPE), respectively. To know the effects of the incorporated LDPE on the morphology, microstructural, compressive strength, thermal property and displacement effect on the vital elements were studied using scanning electron microscopy (SEM), X-ray diffractometry (XRD), universal mechanical testing machine, differential thermal analysis (DTA), Rutherford backscattering (RBS) technique and particle induced X-ray emission (PIXE), respectively. The bulk densities of the clay composites ranged between 1.341 and 2.030 g/cm3. The samples’ XRD analysis revealed similar patterns, with a sharp and prominent peak at angle 2θ equals ~26.11°, which matched with card number 16-0606 of the Joint Committee on Powder Diffraction Standards (JCPDS) that represents Aluminum Silicate Hydroxide (Al2Si2O5(OH)4), a basic formula for Kaolin clay. The compressive strength ranged between 2.52 and 5.53 MPa. The ratio of Si to Al in each composite is about 1:1. The dehydroxylation temperature for samples ranged between 443.23 °C and 555.23 °C.

Effect of Montmorillonite Layer Charge on the Thermal Stability of Bentonite

AbstractThe thermal stability of bentonite is vitally important for its application in the casting field and the layer charge of montmorillonite (Qm) is one of its central crystal-chemical parameters. As the main component of bentonite, the influence of Qm on montmorillonite properties and behavior needs to be considered if bentonite is to be used in high-temperature environments. The objective of the current study was to investigate the relationship between Qm and the thermal stability of Chinese bentonite samples collected from Wuhu, Anhui Province (marked as WH); Xinyang, Henan Province (marked as XY); and Santai, Sichuan Province (marked as ST) below. The values of Qm were obtained using the O (11) method, and the structural properties of the bentonite samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TG-DSC), and field emission scanning electron microscopy (FESEM). The results showed that, in the samples investigated, Qm was inversely related to the thermal stability of bentonite. The Qm value (electrons per half unit cell, e/huc) was greatest for sample ST (0.725 e/huc), followed by sample XY (0.470 e/huc), and by sample WH (0.354 e/huc). The dehydroxylation temperature changed related to Qm; the sample with the largest Qm value was WH (701°C), followed by sample XY (684°C), and sample ST (630°C). After the samples were calcined at 600°C, sample WH had the best montmorillonite structural integrity with the greatest degree of reusability (78.21%); while the montmorillonite structures of samples XY and ST were destroyed, and their reusabilities were only 9.48 and 6.01%, respectively.

The thermal dehydroxylation of kaolinite using thermogravimetric analysis and Controlled rate thermal analysis

The aim of this work was to identify parameters that could influence the conversion of kaolinite into metakaolinite. To this end, the dehydroxylation of four kaolinites, using controlled rate thermal analysis (CRTA) and thermogravimetric analysis (TGA), was investigated. X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) were used to confirm the kaolinitic nature of the samples. Their crystallinity was evaluated using the Hinckley index from the XRD patterns and transmission electron microscopy (TEM) was used for morphological observation of the clay platelets. The thermal analyses of the samples indicate, for all samples, low defects as revealed by the low amount of adsorbed water on the clay surface. The dehydroxylation temperature from both techniques was influenced by the sample crystallinity and particle size. It was observed from both techniques that increase crystallinity resulted in highdehydroxylation temperature. Also, the influence of the clay platelets size on the dehydroxylation temperature, is proposed. All the results indicate that crystallinity and particle size are parameters that could be used to control the temperature for the conversion of kaolinite to metakaolinite.
 Keywords: Kaolinite; Crystallinity, Dehydroxylation; Thermal analysis

DMSO Deintercalation in Kaolinite–DMSO Intercalate: Influence of Solution Polarity on Removal

This study focused on the deintercalation of dimethyl sulfoxide (DMSO) from a kaolinite–DMSO complex in various solvents. The use of kaolinite as filler in polymer–clay composite generally faced the difficulty of kaolinite dispersion due to its high cohesion. For improved dispersion of kaolinite within a given matrix, previous intercalation of small polar molecules is usually done prior to its displacement during composite-making. The influence of the solvent polarity on the deintercalation in analyzed here to understand its role during the deintercalation process. The intercalation of the DMSO was done by solution-mixing and its displacement was done in distilled water, ethyl acetate, and acetone. The products of deintercalation were analyzed using Fourier transform infra-red (FTIR), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The weakening of the kaolinite cohesion after DMSO intercalation is demonstrated through the broadening of the diffraction peak associated with the kaolinite on XRD patterns. From FTIR spectra, the weakening is associated with the displacement to low wavenumbers of the Si–O or Al–O vibration bands within the kaolinite–DMSO complex. The kaolinite dehydroxylation temperatures from DSC show that the rate of DMSO displacement affects the ordering of the recovered kaolinite. The crystallite size of the kaolinite is reduced from the raw to the recovered kaolinite after DMSO displacement, indicating an exfoliation of the kaolinite. From these results, it is found that the removal of the DMSO from the kaolinite–DMSO complex is influenced by solvent polarity. The higher the polarity, the greater the removal of the DMSO from the complex. Solvent polarity affects the rate of DMSO displacement, which influences the ordering of the recovered kaolinite. It is suggested that solvent polarity can be used to control the removal rate of DMSO, which may be key to the dispersion of the kaolinite platelets.

Origin of dioctahedral smectites in Lower Eocene Lulehe Formation paleosols (Qaidam Basin, China)

Smectites affecting water and soil exchangeable cations, especially potassium and ammonium related to plants, are common swelling clay minerals in sediments and paleosols that can record paleoenvironmental and paleoclimatic information. Paleoenvironmental and paleoclimatic interpretations are potentially ambiguous, because smectite minerals may have either detrital or pedogenic origins. This study analyzes smectites in Lower Eocene paleosols of the Qaidam Basin, China, with the goal of determining their origin and paleoclimatic significance. Twelve smectite-rich vertisol samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma-mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) in the Dahonggou (DHG) section of the Lulehe Formation. The samples from DHG section contained predominant dioctahedral smectites (60–65%) in the <2 μm clay fractions. Minor dioctahedral illites, dioctahedral interstratified illite-smectite (I-Sm), kaolinite, and traces of dioctahedral chlorites and palygorskites were present. The chemical data and FTIR spectra revealed both tetrahedral substitutions (i.e., Al for Si) and octahedral substitutions (i.e., Mg and minor Fe for Al) in the dioctahedral smectites. Montmorillonite comprised the dominance of the fine-clay fractions (< 0.2 μm) with minor contributions of beidellite, as determined by the Greene-Kelly test (GK-test), geochemical and FTIR analyses. SEM observations revealed two morphological types of dioctahedral smectites, the less abundant one with typical ‘honeycomb’ structure, interpreted as neoformed, and the other occurring as thin, well-defined plates and irregular masses considered to be detrital. DSC revealed two dehydroxylation temperatures (500–550 °C and 600–700 °C), indicating the presence of trans-vacant (tv) and cis-vacant (cv) layers, respectively. The cv layers were attributed to montmorillonite originating as catchment-delivered detritus, as the study Lulehe Formation exhibited no evidence of volcanic ash layers or diagenesis that would have promoted formation of montmorillonite with high dehydroxylation temperatures. The tv layers represented pedogenic beidellite formed via solution crystallization in a floodplain pedogenic environment. The accumulation of abundant inherited montmorillonite and neoformed beidellite in paleosols of the Lulehe Formation was probably promoted by a relatively warm climate with alternating wet-dry seasons during the Early Eocene. Admixture of detrital montmorillonite makes paleoclimatic reconstructions based on bulk-smectites concentrations and isotopic compositions unreliable, showing that integrated clay mineralogical analyses of the type undertaken in this study are necessary to identify the provenance and paleoclimatic significance of smectites in sediments.

Effect of acid activation on structural evolution and surface charge of different derived kaolinites

Acid activation plays an important role in modifying the microstructure and improving the surface properties of clay minerals. Herein, the microstructural evolution characteristics and surface charge properties of different derived kaolinites were investigated and the relevant mechanism was discussed. Acid activation could gradually expand the interlayer distance of both kaolinite and coal-bearing kaolinite due to the leaching of cations and the following weakened interlayer forces. The structure of kaolinite has a better resistance to acidic attack. Most of the frame structures and functional groups are retained when the acid concentration is 2 mol/L and the treatment time is up to 72 h at room temperature. Acid activation has little effect on dehydroxylation temperature but a greater effect on transformation temperature of ~3–7 °C. The relatively rapid changes of zeta potential indicate stronger protonation and deprotonation reactions in coal-bearing kaolinite. The process could release more acidic sites while maintaining the layered structure, proved the gradual evolution process of macroscopic properties, and complemented that in harsh chemical conditions such as high temperature and acid concentration.

Bonding mechanism and performance of rectorite/ball clay bonded unfired high alumina bricks

In this study, the bonding mechanism and normal/high temperature performance of rectorite clay or ball clay bonded unfired high alumina bricks were investigated by using different techniques (XRD, TG-DSC, SEM, particle size distribution and rheology). The results showed that clay particles are separated into layer structural units in water due to the hydration swelling and electrostatic repulsive force, and rectorite layer structural units have larger aspect ratio than ball clay. Rectorite layer structural units form band-type structure with “face to face” after drying results in better bonding performance than ball clay (card-house structure with “edge to face”). The cold crushing strength of 9% rectorite/ball clay bonded unfired high alumina bricks after firing at the dehydroxylation temperature for 3 h reach 71 MPa and 50 MPa, respectively, and which can satisfy the strength requirement for the transportation and use of most high alumina bricks. The secondary mullitization and lower liquid phase content of ball clay bonded unfired high alumina brick under high temperature cause it has higher refractoriness under load and lower linear shrinkage than rectorite clay bonded brick. The T0.6 refractoriness under load of 9% rectorite/ball clay bonded unfired high alumina brick are 1262.6 °C and 1580.3 °C, respectively. Thus, the 9% ball clay bonded unfired high alumina bricks have wider service temperature range than 9% rectorite bonded bricks.

DMSO Intercalation in Selected Kaolinites: Influence of the Crystallinity

The present study deals with the relation between crystalline order in kaolinites and their ability to intercalate DMSO. Raw clays and kaolinite–DMSO complexes are analyzed using FTIR, XRD powder diffraction and differential scanning calorimetry and thermogravimetric analysis (DSC-TGA). The crystallinity is accessed using the Hinckley index (HI) from the raw clays’ XRD patterns and the p2 factor from their FTIR spectra. The intercalation ratio is evaluated from XRD and compared among the samples. The thermal analyses show a decrease in the dehydroxylation temperature in the DMSO–kaolinite complexes, indicating a decrease in the interlayer cohesion that may be useful to improve the delamination of kaolinite. The analysis of the coherent scattering domain size in the raw and the DMSO-intercalated samples indicates that the ordering is not affected during the DMSO intercalation. From these results, it is deduced that DMSO intercalation is favored by an increased crystallinity, as revealed by the intercalation ratio from XRD and the DSMO release during DSC-TGA analysis.

Potential Applications in Relation to the Various Physicochemical Characteristics of Al-Hasa Oasis Clays in Saudi Arabia

In this work, various physicochemical characteristics, e.g., surface properties and mineralogical compositions, of five clays collected from different sites in the Al-Hasa oasis in Saudi Arabia have been investigated. Analysis of the mineralogical compositions of the clays in the study by X-ray diffraction indicated the coexistence of palygorskite, montmorillonite, illite, kaolinite, chlorite, calcite and quartz in different percentages. Thermogravimetric analysis indicated that all studied clays exhibited dehydroxylation temperatures higher than 470 °C. On the other hand, pore size distribution analysis of clays from N2 adsorption indicated the presence of micro- and narrow mesopores (of 1.3–2.8 nm). Furthermore, the capability of the different clays for removal of Pb (II) from aqueous solution has been studied. The adsorption process was described through the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models. The Langmuir model was the most suitable compared to the other models in the case of palygorskite- and montmorillonite-rich clays. However, the Temkin model better represented the adsorption process of Pb (II) on calcite-rich clay. The clay sample with 61.0 wt% of palygorskite was found to be the most effective at removing Pb (II), with a maximum removal capacity of 74.07 mg/g at pH 6, with a contact time of 6 h and at 25 °C. Generally, the adsorption mechanism of lead over all the studied clays followed the pseudo-second-order kinetics. On the other hand, the catalytic activity of clays in the study has been tested in methanol conversion. The acidic clays, those containing high amounts of montmorillonite, showed higher selectivity to ethylene, viz., 78.9%, with a methanol conversion of 39.1% at 350 ° C and 0.1 MPa.

Thermal behaviors and kinetic analysis of two natural kaolinite samples selected from Qingshuihe region in Inner Mongolia in China

The thermal characteristic behaviors of two kaolinite samples selected from Qingshuihe region in Inner Mongolia in China were studied through thermogravimetry, derivative thermogravimetry, and differential scanning calorimetry (TG–DTG–DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The activation energies of dehydroxylation for the two kaolinite samples (determined as Kaol-1 and Kaol-2) were calculated based on KAS and FWO methods. The XRD results indicated that Kaol-1 and Kaol-2 both were determined as kaolinite, and a small amount of quartz, but the Kaol-2 presented many amorphous organic matters. The TG–DSC results displayed the adsorbed water desorption and dehydroxylation with the temperature increased from 200 to 1100 °C. The dehydroxylation is followed as the intensities decrease in the bands at 3690 cm−1, 3620 cm−1 and 914.0 cm−1 attributing to the stretching mode of inner surface hydroxyls, and which disappeared when the temperature reached at 600 °C. The endothermic peak temperature of dehydroxylation for Kaol-2 presented higher than that of Kaol-1, which may be attributed to present of amorphous organic matter and was in agreement with the XRD data. The maximum endothermic temperature of dehydroxylation increased both for Kaol-1 and Kaol-2 with the increase in heating rate, which was attributed to more sufficient decomposition as the decrease in heating rate. The thermal kinetic analysis indicated that the dehydroxylation reaction of Kaol-1 should be a single kinetic mechanism, but the E of Kaol-2 decreased as α increasing from 0.2 to 0.5 and then gradually increased with the increase of α. The average E of dehydroxylation for Kaol-2 both was lower than that of Kaol-1 based on Kissenger–Akahira–Sunose and Flynn–Wall–Ozawa methods, which was attributed to the relatively higher organic carbon content in Kaol-2.