Physico-chemical Properties Of Clay Minerals Research Articles

Physicochemical Variation of Clay Minerals and Enrichment of Rare Earth Elements in Regolith-hosted Deposits: Exemplification from The Bankeng Deposit in South China

AbstractThe wide application of rare earth elements (REEs) in the development of a carbon–neutral society has urged resource exploration worldwide in recent years. Regolith-hosted REE deposits are a major source of global REE supply and are hosted mostly in clay minerals. Nonetheless, the ways in which changes in the physicochemical properties of clay minerals during weathering affect the concentrations of REEs in the regolith are not well known. In the current study, a world-class regolith-hosted REE deposit (Bankeng, South China) has been studied to illustrate further the effect of clay minerals on sorption and fractionation of REEs during weathering to form economic deposits. In the weathering profile, halloysite and illite are abundant in the saprolite due to weathering of feldspars and biotite from the bedrock. During weathering, halloysite and illite transform gradually to kaolinite and vermiculite. The large specific surface area, pore volume, and cation exchange capacity of the clay mineral assemblages are favorable to the sorption of REEs, probably because of the formation of vermiculite. The abundance of vermiculite could explain the enrichment of REEs in the upper part of the lower pedolith. For the saprolite-pedolith interface, halloysite is probably the main sorbent for the REEs, as indicated by the distinctive appearance of pore sizes of 2.4–2.8 nm characteristic of halloysite. The progressive transformation of halloysite to kaolinite reduces the pores and desorbs the REEs, causing REE depletion in the shallower soils. As a result, REEs were mobilized downward and re-sorbed in the lower pedolith-upper saprolite causing gradual enrichment and formation of these regolith-hosted deposits.

Physico-chemical characterization of clay mineral mixtures from Boyacá-Colombia

An adequate identification of physico-chemical properties of clay minerals is an important step to develop technological applications. In Colombia, a common issue is that the evaluation of raw materials with the preparation of the final product depend on empirical knowledge, it is common not to use any kind of technological tool to conduct any analysis. In contrast, the clay mixtures for this study were prepared and characterized by following a careful procedure to evaluate and control the qualities such as color of the final product. For this purpose, differential scanning calorimetry, magnetization, scanning electron microscopy, X-rays analysis, and positron annihilation lifetime spectroscopy techniques were applied. It is possible to conclude that the implementation scientific techniques in the sector of clay minerals may serve as a powerful tool, since preparing samples in an empirical way have been proved to lead to different qualities in the final product.

One-pot synthesis of the reduced-charge montmorillonite via molten salts treatment

Layer charge is a critical factor determining the structural characteristics and physicochemical properties of clay minerals, and fixing small cations (e.g., Li+) into the tetrahedral/octahedral sheets of clay minerals is a feasible way for reducing their layer charges. However, conventional methods for preparing reduced-charge clay minerals are usually quite complex and time-consuming. Herein, a facile one-pot treatment method for preparing reduced-charge clay minerals was successfully developed using molten salts. In particular, montmorillonite (Mt) was mixed with mono LiNO3 or LiNO3-NaNO3 mixture, which was then heated above the melting points of salts. The obtained results showed that the cation exchange capacity (CEC) of Mt decreased evidently after being treated with molten LiNO3, and the CEC value was reversely related to the heating time. The X-ray diffraction results demonstrated that Mt layers collapsed upon treatment with molten LiNO3. On the other hand, the partial replacement of LiNO3 by NaNO3 could restrict the collapse of Mt layers, as the larger ionic radius of Na+ (than Li+) helped in maintaining the interlayer spaces of Mt during the process of charge reduction. As indicated by the Fourier transform infrared spectroscopy, the structural OH stretching vibration shifted to a higher wavenumber (from 3623 to 3632 cm−1) after the molten LiNO3 treatment, which suggested that some Li+ ions migrated into the hexagonal cavities in the tetrahedral sheets of Mt, and the new band at 3670 cm−1 indicated that some Li+ ions even further migrated into the octahedral vacancies of Mt. The locations of fixed Li+ ions were further confirmed by the X-ray photoelectron spectroscopy characterization. Due to the migration of Li+ ions into the layers of Mt, the Li1s peak shifted to lower binding energy. The above results showed that the molten salt treatment might be a cost-effective and environmentally friendly approach for synthesizing reduced-charge clay minerals, and using mixed molten salts can help in maintaining the interlayer structure.

Physico-Chemical Properties of Clay Minerals and Their Use as a Health Promoting Feed Additive.

Simple SummaryFeeds contaminated by mycotoxins cause organ damage, immune suppression and health disorders, limiting growth and performance of farm animals. One of the most practical approaches to minimizing the negative effect of these substances in livestock diets is by the use of different feed additives, preventing their absorption from the gastrointestinal tract. Growing interest in particular is applied to mineral additives, such as clays and clay minerals. These materials are not digested but bind toxic metabolites and mycotoxins, moving them through the digestive tract, without detrimental influence on the animal body. Apart from the binding capacity, clay minerals show other activity which could positively affect animal welfare and productivity. However, each type of clay has its own specific binding capacity that can greatly vary according to its origin deposit and treatment. Moreover, clays may bind with not only noxious substances but also some nutrients, causing a nutritional imbalance for animals. Therefore, the aim of the review was to present the available knowledge on the properties and use of clays in feedstuff decontamination as well as to discuss the resulting potential benefits for animal health and safety of human food.The contamination of feeds with microbiological or toxicological agents can affect health, productivity and safety of livestock animals and their products. The treatment of feedstuffs to lower the content of undesired substances before feeding is expensive and labor intensive, therefore an alternative is to reduce their gastrointestinal absorption. Different feed additives are available, however the use of clays and clay minerals are ideal for this purpose due to their high specific surface area, adsorption capacity, low or null toxicity for the animal and low cost. A large number of clays available to producers have different structures that are dependent on their mining source, causing difficulty in proper categorization. For this reason properties of phyllosilicates with 1:1 layers (one sheet of SiO4 tetrahedra joined to one sheet of Al- or Mg-octahedra), 2:1 layers (one sheet of Al- or Mg-octahedra between two sheets of Si-tetrahedra), and 2:1:1 layers (a basic 2:1 structure with an interlayer brucite (with cations Mg2+ or Fe2+) or gibbsite (with cation Al3+) sheet) and tectosilicates are described. The role of clay minerals in animal production shows a reduction in diarrhea, better feed conversion ratio, and improved health of many livestock species due to their specific adsorption potential of many feed mycotoxins. Overall, there is growing interest in the use of clays due to their beneficial characteristics, absence of primary toxicity and success in research to reduce animal disease and improve animal production and safety of animal products.

Effects of charge density on the hydration of siloxane surface of montmorillonite: A molecular dynamics simulation study

Abstract The physicochemical properties of clay minerals strongly depend on their hydration characteristics which therefore have drawn great concerns from different research communities. In the present work, the effects of charge density of montmorillonite (Mt) on the hydration characteristics of its interlayer spaces, particularly the siloxane surface, were studied using classical molecular dynamics (MD) simulations. Four Mt. models with various octahedral charges are established, and these charges are compensated with tetramethylammonium cation (TMA). The simulation results showed that water molecules within the hydration layer of siloxane surface will donate hydrogen atoms to form H-bond with the surface oxygen atoms, while those surrounding TMA only slightly have their oxygen atoms point towards TMA. In addition, water molecules prefer to first hydrate the siloxane surface and then the TMA as the water content increases. These findings indicate that water molecules have stronger hydration interaction with siloxane surface than with TMA, and TMA can be ideal counterbalance cation in terms of studying the hydration characteristics of siloxane surface. Charge density can significantly influence the hydration of TMA-Mt. Although increasing charge density will not lead to the formation of stronger H-bond (i.e., no obvious reduction of H-bond length) between water molecules and siloxane surface, water molecules are more likely to be drawn to the siloxane surface and form more H-bonds between them. Subsequently, the hydration energy increases and the mobility of water molecules decreases as the charge density rises. These findings show that charge density can evidently influence the hydrophobicity of siloxane surface, which may further influence its interaction with organic species, e.g., the adsorption of organic contaminants.

팽창성 점토광물 내 층간수의 확산특성분석을 위한 수치해석학적 방법

The numerical modeling and simulation have been used increasingly as tools for examining and interpreting the bulk structure and properties of materials. The use of molecular dynamics (MD) simulations to model the structure of materials is now both widespread and reasonably well understood. In this research, we introduced the numerical method to calculate the physico-chemical properties such as a diffusion coefficient and a viscosity of clay mineral. In this research, a series of MD calculations were performed for clay mineral and clay-water systems, appropriate to a saturated deep geological setting. Then, by using homogenization analysis (HA), the diffusion coefficients are calculated for conditions of the spatial distribution of the water viscosity associated with some configuration of clay minerals. This result of numerical analysis is quite similar to the previous experimental results. It means that the introduced numerical method is very useful to calculate the physico-chemical properties of clay minerals under various environmental conditions.

Radiation-induced defects in clay minerals: A review

Extensive information has been collected on radiation effects on clay minerals over the last 35years, providing a wealth of information on environmental and geological processes. The fields of applications include the reconstruction of past radioelement migrations, the dating of clay minerals or the evolution of the physico-chemical properties under irradiation.The investigation of several clay minerals, namely kaolinite, dickite, montmorillonite, illite and sudoite, by Electron Paramagnetic Resonance Spectroscopy has shown the presence of defects produced by natural or artificial radiations. These defects consist mostly of electron holes located on oxygen atoms of the structure. The various radiation-induced defects are differentiated through their nature and their thermal stability. Most of them are associated with a π orbital on a Si–O bond. The most abundant defect in clay minerals is oriented perpendicular to the silicate layer. Thermal annealing indicates this defect in kaolinite (A-center) to be stable over geological periods at ambient temperature. Besides, electron or heavy ion irradiation easily leads to an amorphization in smectites, depending on the type of interlayer cation. The amorphization dose exhibits a bell-shaped variation as a function of temperature, with a decreasing part that indicates the influence of thermal dehydroxylation. Two main applications of the knowledge of radiation-induced defects in clay minerals are derived: (i) The use of defects as tracers of past radioactivity. In geological systems where the age of the clay can be constrained, ancient migrations of radioelements can be reconstructed in natural analogues of high level nuclear waste repositories. When the dose rate may be assumed constant over time, the paleodose is used to date clay populations, an approach applied to fault gouges or laterites of the Amazon basin. (ii) The influence of irradiation over physico-chemical properties of clay minerals. An environmental application concerns the performance assessment of the engineered barrier of nuclear waste disposals. In case of a leakage of transuranic elements from the radioactive waste form, alpha recoil nuclei can amorphize smectite after periods of the order of 1000years according to a worst case scenario, whereas amorphization from ionizing radiation is unlikely. As amorphization greatly enhances the dissolution kinetics of smectite, the sensitivity of the smectites must be taken into account in the prediction of the long term behavior of engineered barriers.

Influence of the physicochemical properties of clay minerals on the degree of darkening via polycondensation reactions between catechol and glycine

Polycondensation reactions between amino acids and phenols are an important pathway for humification, and clay minerals are able to catalyze these reactions. In the present study, we investigated the influence of the physicochemical properties of some clay minerals on polycondensation reactions between catechol (CT) and glycine (Gly). The polycondensation of CT and Gly was evaluated using the specific absorbance at 600 nm ( E 600) as a measure of the degree of darkening. The following materials were used in the present study: kaolin, bentonite, zeolite, Kanuma soil (allophanic soil) and aluminum silicate. In the presence of Kanuma soil, bentonite and zeolite, the degree of darkening was significantly enhanced, compared to the control (CT + Gly without clay), clearly showing that these clay minerals are able to serve as effective catalysts. The characteristics of these clay minerals were as follows: higher levels of specific surface area, and higher Fe, Ti and Ca contents. Transition metals (Fe and Ti) in the clay minerals can serve as Lewis acids, and divalent alkaline-earth metals (Ca) can contribute to the appearance of Brønsted acid sites. Therefore, contents of such metals in clay minerals are important factors in terms of enhancing darkening via polycondensation reactions between amino acids and phenols.

Irradiation effect on physico-chemical properties of clay minerals

The purpose of the present work was to study the exposure of various doses of γ-irradiation (10 5, 10 6, 10 7, 3×10 7 Gy) on types and concentration of radiation-induced defects, deuteration, changes in specific surface and solubility of minerals irradiated in D 2O solution in closed capsules. Some clay minerals (perfect and imperfect kaolinites, palygorskite, montmorillonite), muscovite, synthetic gibbsite and brucite were investigated. A sharp increase of the A- (Si–O −) and B-centres (Al VI–O −–Al VI bridge) concentration in the dose interval 10 5–10 7 Gy in both investigated kaolinites has been established. These concentrations are higher both in the initial and irradiated samples of well-ordered kaolinite. In irradiated palygorskite, montmorillonite and muscovite, such concentration is considerably lower than in kaolinites. The concentration of the A-centres and their stabilization are determined by the composition of the tetrahedral structural fragment of a mineral: kaolinite ([Si 4O 10])>montmorillonite, palygorskite ([Al 0.5Si 3.5O 10])>muscovite ([AlSi 3O 10]), and also by the presence of mobile water molecules on the surface and in the interlayer space of a mineral: perfect kaolinite (water molecules are practically absent)>imperfect kaolinite>montmorillonite (the maximum amount of water molecules). Concentration of the B- and B′-centres is even more sensitive in the presence of mobile water molecules in mineral like the A-centres concentration. In irradiated montmorillonite, the B′-centre was not found. The B-centre model has been refined: an unpaired electron in the B-centre in kaolinite (1:1 structure) is located on an oxygen ion of an outer OH-group, and in the B′-centre in minerals with 2:1 structure—on an inner OH-group. The deuteration begins at lower irradiation doses in those minerals, in which the maximum amount of the radiation-induced centres appears. The lower limit of the beginning of deuteration at small irradiation doses rises in the following sequence: brucite<kaolinite<montmorillonite<palygorskite<gibbsite. The irradiation dose growth leads to the increase of specific surface and change of solubility of the irradiated samples of clay minerals: the going out degree of the Al 3+ ions from kaolinite increases, but that of Si 4+ ions—decreases, for montmorillonite and palygorskite the inverse dependence takes place. It can be explained by the increase in the amount of the different types of radiation-induced defects in these minerals.

Physico-Chemical Properties of Clay Minerals from Alluvial Soil Sediment of West Bengal

The X-ray, DTGA and chemical analyses of clay fractions isolated from alluvial soil clays (pond sediments) were carried out. The results indicated the presence of illite (2: mical type) as the dominant clay mineral with traces of kaolinite. The X-ray basal spacings and the DTGA peak temperatures were observed to be lower than the standard samples (cf. fithian illite). The molar ratios of SiO2/Al2O3 were also found be lower. All these indicated the presence of minerals (cf. kaolinite) other than illite as the only constituent.