Aluminium ions at polyelectrolyte interfaces. I. Mechanism of polyacrylic acid/aluminium oxide and humic acid/kaolinite complex formation

Understanding adsorption phenomena involving humic acids and clays is a difficult challenge owing to their complex nature. Thus, to progress in the study of such systems, attempts were made to replace natural systems by polyacids and oxides of simpler chemical and morphological structure. Since the present investigation was dedicated to determine some characteristics of acidic soils which contain traces of aluminium ions, these ions were added to the adsorbent/polyacid systems as trace constituents. Phenomena related to the interactions of humic or polyacrylic acid with aluminium oxide and kaolinite clay have been investigated and the well-differentiated interfacial behaviour of the oxide and kaolinite was determined and discussed. The results of electrophoretic mobility measurements demonstrated the huge time-dependent effect of polymeric layers adsorbed on oxides and modified clays. Received: 24 July 2000 Accepted: 20 December 2000     

Thermal analysis to assess pozzolanic activity of calcined kaolinitic clays

The use of calcined clays as partial replacement of cement is encouraged since it promotes the reduction of the green-house gas emission and the energy requirement of cement-based material, maintaining or enhancing the mechanical properties and the durable performance of these materials. In this paper, the use of thermal methods—DTA/TG and calorimetry—to select and to evaluate two kaolinitic clays for their use as pozzolanic materials was explored. The content and crystallinity of kaolinite in clays can be determined by DTA/TG analysis, and this technique is also suitable to select the calcination temperature for complete kaolinite dehydroxylation. Calorimetric analysis on blended cements (30 % by mass of replacement) can differentiate the reactivity of calcined kaolinitic clays. Results show that more reactive calcined kaolinitic clay develops the second and third peaks earlier than those of PC with great intensity and high acceleration. The reactivity of calcined clays is associated to raw materials containing kaolinite with high structural disorder that determines calcined clays with large specific surface area, high grindability, and small mean particles size (d ₅₀) for the same grinding objective. Finally, the DTA/TG analysis can determine the type and the amount of hydrated phases obtained at different ages to evaluate the pozzolanic reaction of calcined clay in accordance with the standardized pozzolanic activity index.     

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.     

Thermal behaviour of sericite clays as precursors of mullite materials

Thermal analysis of some sericite clays, from several deposits in Spain, which are not exploited at this time, has been studied. The samples have been previously characterized by mineralogical and chemical analysis. Sericite clays have interesting properties, with implications in ceramics and advanced materials, in particular concerning the formation of mullite by heating. According to this investigation by differential thermal and thermogravimetric analysis (DTA-TG), the sericite clay samples can be classified as: Group (I), sericite–kaolinite clays, with high or medium sericite content, characterized by an endothermic DTA peak of dehydroxylation of kaolinite with mass loss, which overlapped with dehydroxylation of sericite, and Group (II), sericite–kaolinite–pyrophyllite clays, with broader endothermic DTA peaks, in which kaolinite is dehydroxylated first and later sericite and pyrophyllite with the main mass loss, appearing the peaks overlapped. X-ray diffraction analysis of the heated sericite clay samples evidenced the decomposition of dehydroxylated sericite and its disappearance at 1050 °C, with formation of mullite, the progressive disappearance of quartz and the formation of amorphous glassy phase. The vitrification temperature is ~ 1250 °C in all these samples, with slight variations in the temperatures of maximum apparent density (2.41–2.52 g mL^?1) in the range 1200–1300 °C. The fine-grained sericite content and the presence of some mineralogical components contribute to the formation of mullite and the increase in the glassy phase by heating. Mullite is the only crystalline phase detected at 1400 °C with good crystallinity. SEM revealed the dense network of rod-shaped and elongated needle-like mullite crystals in the thermally treated samples. These characteristics are advantageous when sericite clays are applied as ceramic raw materials.     

Interactions in clay/electrolyte systems

The sorption of cesium and cobalt on kaolinite and montmorillonite were followed by radiotracer method. The sorption of cesium can be described by a Freundlich isotherm. Cobalt sorption on clays equilibrated in cesium chloride solutions significantly differs for kaolinite and montmorillonite due to their differences in sites available for cation sorption and changes in solution chemistry.Heterogeneous exchange of cesium ions between clay and the surrounding electrolyte was performed in order to obtain information about clay/electrolyte systems equilibration. An interplay of different processes included in the attainment of true chemical equilibria of clay/electrolyte systems are responsible for the change of clay surface properties and total exchange capacity.     

Non-isothermal crystallization kinetics of some aventurine decorative glaze

Thermal and structural properties of three clays (sepiolite and two kaolinites) from Turkey were studied by thermal analysis (TG–DTA), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FT-IR), and surface area measurement techniques The adsorption of sulfur dioxide (SO₂) gas by these clays was also investigated. SO₂ adsorption values of K1, K2, and S clay samples were measured at 20 °C and pressures up to 106 kPa. Sepiolite sample (S) primarily consists of pure sepiolite, only dolomite present as accompanying mineral. Both kaolinite samples, K1 and K2, mainly contain kaolinite as the major clay mineral and quartz as impurity. In K2 sample, muscovite phase is also present. Simultaneous TG–DTA curves of all clay samples were obtained at three different heating rates 10, 15, and 20 °C min⁻¹ over the temperature range 30–1200 °C. It was found that the retention value of SO₂ by S clay (2.744 mmol/g) was higher than those of K1 (0.144 mmol/g) and K2 (0.164 mmol/g) samples.     

Surface activation of air oxidation of hydrazine on kaolinite. 2. Consideration of oxidizing/reducing entities in relationship to other compositional, structural, and energetic factors

The rates (previously reported) for the air oxidation of hydrazine on kaolinite and substituent oxides of kaolinite showed a complex dependence on the relative amounts of several structural oxidizing/reducing entities within the reaction-promoting solids. The rates indicated an important role of the clay but no dominant role of any one of the oxidizing/reducing entities. In this paper we review (a) the reaction-promoting activity of these centers as studied in other systems, (b) various spectroscopic results showing interaction between these entities in clays, and (c) reported spectroscopic studies of the complexation between hydrazine and aluminosilicate surfaces as a whole, in an effort to propose a mechanism for the reaction. Whereas some uncertainties remain, the present synthesis concludes that a mechanism operating through single electron/hole transfers and hydrogen atom transfers by discrete centers is adequate to explain the observed rate behaviors including the observed second order dependence of the oxidation rate on catalyst amount. The effects of these operations on the catalyst can result in no alteration of, or complete or partial electronic relaxation of its contingent of trapped separated charge pairs. The degree to which surface complexation as a whole, intercalation, or luminescent processes may also be associated with the reaction cannot be adequately assessed with the information in hand.     

Adsorption of thymine and uracil on 1:1 clay mineral surfaces: comprehensive ab initio study on influence of sodium cation and water

This computational study performed using the density functional theory shows that hydrated and non-hydrated tetrahedral and octahedral kaolinite mineral surfaces in the presence of a cation adsorb the nucleic acid bases thymine and uracil well. Differences in the structure and chemistry of specific clay mineral surfaces led to a variety of DNA bases adsorption mechanisms. The energetically most predisposed positions for an adsorbate molecule on the mineral surface were revealed. The target molecule binding with the surface can be characterized as physisorption, which occurs mainly due to a cation-molecular oxygen interaction, with hydrogen bonds providing an additional stabilization. The adsorption strength is proportional to the number of intermolecular interactions formed between the target molecule and the surface. From the Atoms in Molecules analysis and comparison of binding energy values of studied systems it is concluded that the sorption activity of kaolinite minerals for thymine and uracil depends on various factors, among which are the structure and accessibility of the organic compounds. The adsorption is governed mostly by the surface type, its properties and presence of cation, which cause a selective binding of the nucleobase. Adsorbate stabilization on the mineral surface increases only slightly with explicit addition of water. Comparison of activity of different studied kaolinite mineral models reveals the following order for stabilization: octahedral-Na-water > octahedral-Na > tetrahedral-Na > tetrahedral-Na-water. Further investigation of the electrostatic potentials helps understanding of the adsorption process and confirmation of the active sites on the kaolinite mineral surfaces. Based on the conclusions that clay mineral affinity for DNA and RNA bases can vary due to different structural and chemical properties of the surface, a hypothesis on possible role of clays in the origin of life was made.     

In situ oxidative copolymerization and characterization of new poly(benzidine-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="Italic">o</Emphasis>-phenylenediamine)/kaolinite microcomposites

Copolymers of benzidine and o-phenylenediamine/kaolinite clay composites with different percentages of kaolinite clay particles were synthesized via in situ oxidative copolymerization. The spectral characteristics upon incorporation of o-phenylenediamine units into the polybenzidine backbone in presence of kaolinite clay were investigated by means of UV–Vis and FTIR spectroscopy. The copolymer in the absence and in the presence of kaolinite clay was studied by thermal gravimetric analysis under non-oxidative conditions. The morphology of the copolymer kaolinite composites system was investigated by the scanning electron microscopy.     

Characterization and assessment of Saudi clays raw material at different area

The general characteristics of three types of clays obtained from the different locations in Saudi Arabia have been investigated. These clays were compared with those of pure kaolin samples. Clays were analyzed by DTA, TGA, SEM, X-ray diffraction, chemical composition (XRF) and optical properties. Three clays are white clay (WC), red clay (RC) from Jeddah area and grey clay (GC) from Elmadina area. The comparison made with Spain clay as pure kaoline (KA). The clays contain kaolinite, illite, montmorillonite and quartz. Quartz is present in every class and varies between 45% and 20%. Montmorillonite is found mainly in the WC (50%) and are lacking only in sample RC and GC. Another important aspect with respect to the chemical composition of the clays is the low amounts of Na₂O and K₂O. The clay deposits (WC, RC, and GC) are suitable for use in industrial ceramics due to the low whiteness, high yellowness and high content of impurities as montmorillonite and iron. This is an important technological aspect that renders possible use of clay RC and GC in the fabrication of products with a cream tonality, especially in roofing tiles and rustic floor tiles. The results also, showed that the studied clays have adequate characteristics for ceramics wall, floor, roof tiles, tableware, earthenware and brick fabrication.     

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.     

Sequestered carbon on clay mineral probed by electron paramagnetic resonance and X-ray photoelectron spectroscopy

This paper describes the interaction among soil organic matter components with kaolinite, an important clay mineral present in tropical soils, especially in Brazil. XPS data show that the soil organic matter adsorbed on kaolinite has aromatic and aliphatic structures, with phenolic and/or alcoholic functions and carbonyl carbons (CO) of amide and/or carboxylic groups. The N1s spectrum of the kaolinite shows an asymmetric peak that is assigned to amide and protonated ammines probably from humin. The interaction between them is strong enough to resist chemical oxidative or reductive attack besides loose amide functionalities. EPR data show that reductive treatment reduces some Fe3+ of the kaolinite structure, loosing organic components. A schematic representation of the reduction of structural Fe3+ in the concentrated domains and consequently increased concentration of Fe3+ ions in diluted domains of the spectrum is presented. This reinforces the hypothesis that humin is a stable carbon sink in soils when adsorbed to clays.     

Preparation and thermal stability of Al2O3-clay and Fe2O3-clay nanocomposites, with potential application as remediation of radioactive effluents

In the last years metal/clays, aluminosilicates with properties and characteristics of microporous materials, have received more attention, due to the possibility of their use as matrix for nanoparticles encapsulation and stabilization processes. Some types of clays were comparatively evaluated for treating the simulated radioactive wastewater. The raw clay from Valea Chioarului Romania and its pillared forms with Al, Fe, pillars for decontamination of waste-waters with medium and low radioactivity were used. Characterization of the obtained materials was carried out using techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, BET analyses and thermogravimetric analysis (DTG-TG), respectively. Also, the thermal stability of nanocomposites was highly superior to native clay due to the presence of the well-dispersed clay nanolayer, which has a barrier property in a composite system. Clay nanocomposite sample materials were obtained with good thermal stability after calcination. Clay nanocomposites samples were evaluated for remediation of radioactive effluents by treating the radioactive wastes streams. The ion-exchange characteristics and the abilities to uptake radioisotopes of indigene clay from Valea Chioarului area-Romania were examined. The results showed that the precursor used in sample preparation influenced the structural and textural properties of nanocomposites and also capability of prepared modified clay samples by pillaring to be potential candidates for use in connection with environmental protection, remediation of radioactive effluents, respectively.     

Assessment of the surface areas of silica and clay in acid-leached clay materials using concepts of adsorption on heterogeneous surfaces

Two clays of the areas of Kaélé and Kousseri (extreme North Cameroon) containing mainly smectites and minor amounts of kaolinite were activated with sulfuric acid (1 to 8 N). Crystal-chemical properties were studied using X-ray diffraction, Fourier transform infrared spectroscopy, and chemical analysis, while textural properties were analyzed by step-by-step nitrogen adsorption at 77 K and low-pressure quasi-equilibrium argon adsorption at 77 K. As is generally observed, smectite is more sensitive to acid leaching than kaolinite. As a result of smectite decomposition, amorphous Al-containing silica forms, leading to an increase in the specific surface area of the leached materials. The content of the clay minerals and amorphous silica can be estimated on the basis of changes in the chemical composition of the samples upon acid leaching. As far as adsorption energy distributions derived from low-pressure argon derivative adsorption isotherms are concerned, the main modifications occur when 1 N sulfuric acid is used, due to the replacement of calcium and sodium compensating cations by protons. When higher acid concentrations are used, variations in adsorption energy distribution can be assigned to the presence of amorphous silica. It was possible to model experimental adsorption energy distributions as weighted sums of argon adsorption energy distributions obtained on (i) 1 N samples representing protonated clays and (ii) a silica gel used as a reference aluminous silica. Using such an approach, increasing acid concentration results in an increase in the surface area of silica, whereas the surface area of the remaining clay minerals remains roughly constant.     

New synthesis strategies for effective functionalization of kaolinite and saponite with silylating agents

Functionalization of Brazilian São Simão kaolinite and Spanish Yunclillos saponite with the alkoxysilanes 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane is reported. The resulting hybrids were characterized by X-ray diffraction, thermal analysis, infrared absorption spectroscopy, and scanning electron microscopy, which demonstrated the effectiveness of the interlamellar grafting process. The X-ray diffractograms revealed incorporation of the alkoxide molecules into the interlayer space of the clays. The displacement of the stretching bands of interlayer hydroxyls in the infrared spectra of the modified kaolinites and the increased intensity of the Mg–OH vibrations in the spectra of the modified saponites confirmed the functionalization of the clays. The thermal behavior of the organoclays confirmed the stability of the hybrids, which was dependent on the clay used for preparation of the materials.     

Aluminium ions at polyelectrolyte interfaces. III. Role in polyacrylic acid/aluminium oxide and humic acid/kaolinite aggregate cohesion

Understanding the formation and breakup of humic acids and clays agglomerates is a difficult challenge owing to their complex nature. Thus, to progress in the study of the stability of such systems, attempts were made to replace the humic acid/kaolinite natural system by the polyacrylic acid/aluminium oxide synthetic system. Since the present investigation was dedicated to determine some characteristics of acidic soils which contain traces of aluminium ions, these ions were added to the adsorbent/polyacid systems as trace constituents. Initial and short-term phenomena related to the adsorption of humic and polyacrylic acids on aluminium oxide and kaolinite clay have been presented elsewhere. Here we present long-term phenomena regarding the formation and cohesion of oxide and clay aggregates formed in the presence of polyacrylic and humic acids, respectively. The results of electrophoretic mobility measurements demonstrated the amphipathic character of polymeric layers adsorbed on aluminium oxide and the amphoteric character of humic acid layers adsorbed on kaolinite. The long-term stability of the two colloidal systems was determined to evolve similarly despite the existence of the these typical characteristics. Received: 24 July 2000 Accepted: 20 December 2000     

The effect of inorganic particulates on the ASV signals of Cd, Pb and Cu

The potential influence of inorganic particulates on the ASV response of < 100-microg/l. levels of Cd, Pb and Cu, at a thin film mercury electrode, was examined by adding various weights of the solids to the acetate background electrolyte solution. Materials added included the hydrous oxides of Mn(IV), FE(III) or Al(III), clay minerals (kaolinite, illite, montmorillonite) and some contaminated sediments. Abrasion of the mercury film was minimized by deaerating the turbid solutions before their transfer to the measuring cell. The hydrous oxides specifically sorbed all three metal ions, resulting in peak-size changes that varied in magnitude with pH. With the clays, only sorption of Pb by illite or montmorillonite was detected. The presence of the solids had little effect on the peak position or half-peak breadth of the Cd or Pb signals, but the Cu peak parameters changed, indicating some hydroxy-species formation at higher pH. Some contaminated sediment samples released a significant fraction of their total metal content into acetate buffer solutions. Shielding the mercury film with a semipermeable membrane had a similar effect to filtering the suspension before analysis, but diffusion equilibrium was only slowly achieved (> 12 hr).     

Sorption of neptunium on clays

Batch sorption experiments with²³⁷Np using kaolinite and molasse clays were carried out under oxic conditions. The sorption kinetics and the effects of particle size of clay samples, concentration of neptunium in the solutions and the pH below and above the point of zero charge of the clays on the sorption coefficients were studied. The sorption coefficients of neptunium, on kaolinite were between 23 and 1100 ml/g at pH 1.5 and 7.6, respectively, whereas, sorption on the molasse clay was not affected significantly by pH (R_d600 ml/g).     

用于制备聚氨酯纳米复合物的高岭石粒子的表征

Clay such as kaolinite， is commonly used as an additive to modify the thermal properties of polymer. In this paper， the morphology， composition， shape and structure of kaolinite was characterized by various advanced techniques. The TEM/ EDX data showed that the kaolinite had a larger particle size and a Si/Al ratio of 1.8. The individual particle of kaolinite was a single crystalline. TEM also showed that these particles were always stacked together due to the presence of electrostatic cohesive energy and hydrogen bond between plaletes. The PAS-FTIR spectra showed that no absorbance of hydroxyl group for hydration water in hydrogen bond region or at 1650cm^-1 was observed at room temperature. It meant a little ability to adsorb water for kaolinite particle. Kaolinite clay also showed no change for its PAS-FTIR spectra with increasing temperature. The TGA results revealed that kaolinite almost doesn′t lose weight at 60℃ due to loss of dehydration of absorbed water， however， it will decomposed around 510℃ and lose its hydroxyl functional group in the form of water (dehydroxylation). The result is consistent with that of PAS-FTIR analysis. This suggests that the structural hydroxyl group on the surface of individual kaolinite clay particle is very stable below 500℃， and the kaolinite composed polymer could be got by the reaction of its stable structural hydroxyl group with isocynate group of polyurethane prepolymer.     

Thermal characterization of the clay binder of heritage Sydney sandstones

Thermal analysis has been employed in a study of the degradation of heritage Sydney sandstone used in St Mary’s Cathedral in Sydney, Australia. TG and DSC have been used to characterise the clay components removed from weathered and unweathered sandstone. Two types of kaolin clays — kaolinite and its polymorph, dickite — have been identified. A higher amount of dickite present in the clay of weathered sandstone indicates that a kaolinite-to-dickite transformation occurs upon weathering. XRD hot stage analysis was also used to demonstrate the presence of a more thermally stable polymorph of the kaolinite.