Study on the differences of Na- and Ca-montmorillonites in crystalline swelling regime through molecular dynamics simulation

Emerging Trends of Computational Chemistry and Molecular Modeling in Froth Flotation: A Review

Froth flotation is the most versatile process in mineral beneficiation, extensively used to concentrate a wide range of minerals. This process comprises mixtures of more or less liberated minerals, water, air, and various chemical reagents, involving a series of intermingled multiphase physical and chemical phenomena in the aqueous environment. Today's main challenge facing the froth flotation process is to gain atomic-level insights into the properties of its inherent phenomena governing the process performance. While it is often challenging to determine these phenomena via trial-and-error experimentations, molecular modeling approaches not only elicit a deeper understanding of froth flotation but can also assist experimental studies in saving time and budget. Thanks to the rapid development of computer science and advances in high-performance computing (HPC) infrastructures, theoretical/computational chemistry has now matured enough to successfully and gainfully apply to tackle the challenges of complex systems. In mineral processing, however, advanced applications of computational chemistry are increasingly gaining ground and demonstrating merit in addressing these challenges. Accordingly, this contribution aims to encourage mineral scientists, especially those interested in rational reagent design, to become familiarized with the necessary concepts of molecular modeling and to apply similar strategies when studying and tailoring properties at the molecular level. This review also strives to deliver the state-of-the-art integration and application of molecular modeling in froth flotation studies to assist either active researchers in this field to disclose new directions for future research or newcomers to the field to initiate innovative works.

Effect of Temperature on the Diffusion and Sorption of Cations in Clay Vermiculite

The MD method for modeling vermiculite containing Na⁺, Rb⁺, Cs⁺, Mg²⁺, and Ba²⁺ cations shows the following: With a weak swelling of clay, the temperature has no significant effect on the diffusion of water and cations through vermiculite. With a high content of water in vermiculite, the effect of temperature on the diffusion coefficient of water is greater than that of cations. We studied the structure of RDF ions in Na⁺-vermiculite, in which some of the cations are replaced by Rb⁺, Cs⁺, Mg²⁺, and Ba²⁺. Cations of alkali and alkaline earth metals compete with Na⁺ ions for adsorption sites on the surface of the clay layer. The alkaline earth metal cations are in the middle between the clay layers due to their higher charge and stronger hydration. In this case, Na⁺ is localized at the surface of the clay layer. Thus, cations of alkaline earth metals have little effect on the temperature dependence of the diffusion coefficient Na⁺.

Combined effect of mineralogical and chemical parameters on swelling behaviour of expansive soils

Microlevel properties such as mineralogical and chemical compositions greatly control the macro behaviour of expansive soils. In this paper, the combined effect of mineral (i.e. montmorillonite, MMC) and chemical contents (i.e. Ca and Na in their total (T), leachable (L) and exchangeable form (CEC)) on swelling behaviour is investigated in a comprehensive way. Several 3-dimensional (3D) graphs correlating MMC and Ca/Na ratio, together, with swelling property (swelling potential, S_a, and swelling pressure, S_p) are developed. 3D plots, in general, portrayed a non-linear relationship of S_a and S_p with MMC and Ca/Na ratio, together. It is hypothesized that swelling initially is triggered by chemical parameters due to their quick and rapid ionization capability, but the overall swelling phenomenon is largely controlled by MMC. It is importantly found that expansive soils are dominant with divalent Ca⁺⁺ ions up to MMC of 67% and beyond this percentage, monovalent Na⁺ ions are prevalent. From the interpretation of results, the maximum S_a of 18% and S_p of 93 kPa is measured at MMC of 43%, (Ca/Na)_T of 10-14 and (Ca/Na)_L of 2-7. It is concluded from study that total CEC + MMC for determining S_a and (Ca/Na)_T + MMC for determining S_p are superior parameters to be considered. The findings of the study also excellently endorsed the results of Foster³², who stated that ionization of Na or Ca depends on the constituent mineral contents. The findings presented herein are unique, interesting and bear very practical significance, as no earlier research work reported such findings by accounting for chemical and mineralogical parameters impact, in tandem, on swelling properties.

A review on clay wettability: From experimental investigations to molecular dynamics simulations

Clay is one of the most important mineral components in geological formations, and it is widely used in many industrial applications. One clay property, which is of key importance in many areas, e.g. mineral processing, agriculture, fundamental geologic understanding, hydrology, oil/water separation and multi-phase fluid flow, is clay wettability. However, clay wettability is a complex parameter which is determined by clay surface chemistry, in-situ aqueous and non-aqueous fluid chemistries, and geo-thermal conditions. Thus, a systematic review of published results on the wettability of six different clay minerals (kaolinite, montmorillonite, illite, mica, talc and pyrophyllite) is provided here, spanning from experimental studies to molecular dynamics simulations. This is integrated with a critical discussion to elucidate the origin of significant inconsistencies in the reported data. Finally, a range of conclusions is clearly established and a future outlook is given. This review will thus advance the understanding of clay wettability and provide guidance for the various applications discussed.

Optimal Synthesis of Environment-Friendly Iron Red Pigment from Natural Nanostructured Clay Minerals

A series of environment-friendly clay minerals-α-Fe₂O₃ iron-red hybrid pigments-were prepared by a simple one-step hydrothermal reaction process using natural nanostructured silicate clay minerals as starting materials. The influence of structure, morphology and composition of different clay minerals on the structure, color properties, and stability of the pigments was studied comparatively by systematic structure characterizations with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmittance electron microscope (TEM), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS) and CIE-L*a*b* Colorimetric analyses. The results showed that the clay minerals act as green precipitants during the hydrothermal reaction to induce in-situ transformation of Fe(III) ions into Fe₂O₃ crystals. Meanwhile, they also act as the "micro-reactor" for forming Fe₂O₃ crystals and the supporter for inhibiting the aggregation of Fe₂O₃ nanoparticles. The color properties of iron-red hybrid pigments are closely related to the surface charges, surface silanol groups, and solid acid sites of clay minerals. The clay minerals with higher surface activity are more suitable to prepare iron-red pigments with better performance. The iron-red hybrid pigment derived from illite (ILL) clay showed the best red color performance with the color values of L* = 31.8, a* = 35.2, b* = 27.1, C* = 44.4 and h° = 37.6, and exhibited excellent stability in different chemical environments such as acid, alkaline, and also in high-temperature conditions.

Impact of Clay Minerals on the Dewatering of Coal Slurry: An Experimental and Molecular-Simulation Study

The cleaning process of coals is challenging due to the existence of clay minerals. The overall objective of this study is to investigate how the dewatering of coal slurry is impacted by the presence of clay minerals, i.e., kaolinite and montmorillonite. Filtration tests were first conducted to investigate the effect of kaolinite and montmorillonite on the dewatering efficiency of coal. Specifically, we measured the filtration velocity, moisture, average specific resistance, and porosity of filter cakes for six slurry samples, in which different amounts of kaolinite and montmorillonite were contained. Filtration tests show that a small amount of kaolinite and montmorillonite leads to a significant reduction in the filtration velocity and porosity, and a big increase in the average specific resistance and the moisture of the filter cake. We observe that most kaolinite existed in the top and middle layers of the filter cake, while most montmorillonite existed in the top layer; on the contrary, little montmorillonite is observed in the middle and bottom layers of the filter cake. Montmorillonite results in a much more deteriorative effect than kaolinite. Considering that the interactions between clay minerals and water may play a key role, we then further investigate the effect of such interactions using molecular simulations. Simulation results show that water molecules could hardly diffuse into kaolinite from the edge, while they could readily penetrate into the montmorillonite layers from the edge surface. This result can be explained by the hydrated cation in montmorillonite. The adsorption density of water on the octahedral surface of kaolinite is higher than that of water on the tetrahedral surface of kaolinite. Furthermore, the adsorption density of water on the double surfaces of kaolinite is higher than that of water on the montmorillonite surface. This research is expected to provide benefits or contributions to the dewatering of clay-rich coal tailings.

Preparation and characterization of self-assembly hydrogels with exfoliated montmorillonite nanosheets and chitosan

Novel montmorillonite-nanosheet/chitosan (MMTNS/CS) hydrogels fabricated via the self-assembly of exfoliated MMTNS and CS chains were investigated. The exfoliation of MMTNS, self-assembly mechanism and structure of MMTNS/CS hydrogels were characterized by an atomic force microscope, scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscope, energy-dispersive x-ray spectroscope and Brunauer-Emmett-Teller analyzer, respectively. The results indicated that MMT could be easily exfoliated to nanosheets with a thickness of 1 ∼ 5 nm in aqueous solution by an ultrasonic base upon interlayer hydration. The formation mechanism of the self-assembly hydrogels was due to the hydrogen bond (-OH ··· ⁺NH₃-) and electrostatic interaction between the MMTNS and CS. The MMTNSs were connected consecutively by CS in-plane to form a huge slice. The porous structure of the hydrogels was controllable by adjusting the MMTNS/CS mass ratio. The hydrogels could be used as adsorbents for sewage treatments, carriers for drugs, microorganisms and catalyzers due to their controllable porous structure and tremendous specific surface area which were derived from the completely exfoliated MMTNS.

Correlation of montmorillonite exfoliation with interlayer cations in the preparation of two-dimensional nanosheets

Varying exfoliation properties of Na– and Ca–MMTs were first investigated through AFM and molecular dynamics simulation.