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In this work, hydrophobic agglomeration of fine talc particles in aqueous solutions under mechanical conditioning and without any addition of surfactants has been experimentally studied. A method of in-situ measurement of turbidity of flocs suspension in the settlement process has been applied, and the turbidity as a function of settling time has been attempted to fit a certain function so as to assess the hydrophobic agglomeration behaviors. Effects of kerosene dosages, stirring rate, and wettability of talc particles on the hydrophobic agglomeration behaviors have been investigated. The results show that the addition of kerosene can greatly enhance the aggregation of colloidal talc in aqueous suspensions. Besides, the stirring strength and duration make an enormous influence on the aggregation through providing the kinetic energy for overcoming the energy barrier between the approaching particles. It is also found that the wettability of talc is closely related to the aggregation degree. More hydrophobic talc particles show a much stronger aggregation behaviors. [ABSTRACT FROM AUTHOR]

In this work, the effect of the exfoliation degree of montmorillonite (MMT) platelets on their electrophoretic mobility distributions in aqueous suspensions was investigated in order to approach into the correlation of MMT exfoliation with electrokinetic property. The experimental results have shown that the negative mobility increased with the increase of exfoliation degree or with the decrease of MMT thickness. This observation might be attributed to the “exposing” of permanent layer negative charge during the exfoliation processing and the “spillover” of electrostatic potential from basal surfaces onto edges. The former would increase the permanent negative charge of the MMT platelets because of the large amounts of layer charge; the latter would decrease the positive edge charge. It is demonstrated that MMT exfoliation would change the electrokinetic property, which might be helpful of the applications of MMT in the related industries. [ABSTRACT FROM AUTHOR]

Montmorillonite (MMT) is easily exfoliated into two-dimensional(2D) nanosheets, which are widely used to prepare functional composites. However, there are few studies on the differences in the performance of MMT nanosheets (MMTNS) with different exfoliation degrees, which seriously limits the further breakthrough in the preparation of high-performance MMTNS based materials. In this work, some representative performance of MMTNS with different exfoliation degrees was investigated, and the performance was closely related with making functional composites. The exfoliation degrees of MMTNS were controlled by different ultrasonic exfoliation powers. The performance of MMTNS was studied by the measurements of atomic force microscopy (AFM), Zeta potential, turbidity, viscosity, scanning electron microscopy (SEM) and molecular dynamics simulation. The results show that MMTNS with high exfoliation degree had more negative electrical sites exposed and stronger repulsive potential energy between particles, which exhibited high surface negative electricity and excellent dispersion stability. Moreover, the MMTNS with high exfoliation degree had better gelling property. It can be seen that the "house-of-cards" structure in the structure after gelation of MMTNS with high exfoliation degree was more intensive. Also, with the increase of MMTNS exfoliation degree, its adsorption capacity for organic matter was better and its reaction with organic was more active. These findings might be helpful to select the suitable MMTNS for making functional composites by controlling its exfoliation degree. [Display omitted] • MMTNS with different exfoliation degree had different properties for making materials. • Highly exfoliated MMTNS had high surface electrical property and dispersion stability. • High exfoliation degree helps MMTNS show excellent gelling property. • The reaction of highly exfoliated MMTNS with organic was more active. [ABSTRACT FROM AUTHOR]

As a new type of separation material, two-dimensional membrane has attracted wide attention due to its special transport mechanism. However, due to the hydration swelling of montmorillonite nanosheets, there are still challenges in preparing two-dimensional membrane with stable channel structure and fixed interlayer spacing. In order to overcome the problems caused by swelling, this study used polyvinyl alcohol and polyacrylic acid to stabilize the channel structure of two-dimensional membranes. Moreover, the crosslinking between Fe3+ and montmorillonite nanosheets was proposed to fix the interlayer spacing of two-dimensional membrane. It is found that various polymers had different effects on the mechanical property of two-dimensional membrane. The addition of polyvinyl alcohol and polyacrylic acid can significantly improve the tensile strength of the membrane. And the introduction of them reduces the hydrophilicity of the membrane surface, thus improving the stability of the membrane in water. In addition, the interlayer cations affect the stability of interlayer spacing of the membrane in water. After crosslinking the membrane with Fe3+, the interlayer spacing is fixed and can be maintained at about 0.94 nm in water for a long time. When a certain dosage of polyvinyl alcohol and PAA are added into the membrane and the crosslinking conditions are suitable, two-dimensional membrane has good selectivity to Li+ and Mg2+ in high Mg/Li ratio brine. Inspired by the natural ion exchange properties of montmorillonite, this study found a new method for inhibiting the hydration swelling of two-dimensional membrane and realizing precise control of interlayer spacing. [Display omitted] • A new method to inhibit hydration swelling of 2D MMT membrane was developed. • Fe3+-crosslinking inhibited the hydration swelling of 2D MMT membrane. • Stability of channel structure realized by cooperation of polymer and metal cation. [ABSTRACT FROM AUTHOR]

The slurry pH shows significant effects on flotation, but the root cause of pH affecting flotation in the presence of clay is still not fully understood. In this work, the mechanisms of protonation and deprotonation reactions of clays at weakly acidic (pH = 4.5) and alkalescent (pH = 9.0) environment affecting pyrite flotation were investigated. The pyrite flotation in the presence of clays (montmorillonite (Mt), kaolinite (Kaol) and illite (I)) was improved with the deprotonation reactions at pH 9.0 compared with the protonation at pH 4.5. The protonation reactions made the edge surfaces of all the clays and the O basal surface of Kaol positively charged. Hence, the "house-of-cards" structure of Mt and the slime coating of Mt and Kaol occurred, which depressed the pyrite flotation. However, the deprotonation of clay took place at pH 9.0, and thus the face-to-face associations of clay were clearly observed by scanning electron microscopy (SEM). In addition, the negative potential of clay also increased with the deprotonation of clay, which affected the DLVO total interaction energy, making the attraction turning into the repulsive tendency between pyrite and clay. However, pyrite grade showed a little or no increase in the presence of I, which was ascribed to the 2:1 structure and non-swelling nature of I. Such findings can not only help understand the protonation and deprotonation of clay on regulating flotation in the presence of clay, but are expected to provide guidance for mitigating the negative effects of clay during the flotation in the future work. [ABSTRACT FROM AUTHOR]

In this work, the exfoliation of montmorillonite related with electric charges on the layers in aqueous solutions were investigated through the measurements of zeta potential, turbidity and atomic force microscopy, as well as molecular dynamics simulation. The charge amount on montmorillonite layers was adjusted by blocking or neutralizing the layer charges with tetraethylenepentaminecopper (II) ([Cu(tetren)] 2+ ) through cation exchange reaction. The experimental results have shown that the exfoliation closely correlated to the amount of the layer charges. The larger are the charge amount on montmorillonite layers, the more easily the montmorillonite is exfoliated. This observation might be attributed to the repulsive energy (electrostatic and hydration repulsion) was stronger between the high charged montmorillonite layers than low charged ones. [ABSTRACT FROM AUTHOR]

In this work, a method for the quantitative determination of isomorphous substitutions on clay mineral or nanosheet surfaces has been presented in order to provide accurate, reliable and quantitative information for the isomorphous substitutions on clay mineral surfaces. It was based on the selective adsorption of a specific organic ion (benzyltrimethylammonium ions, BTMA + ) on the substitution sites on clay mineral surfaces, and the atomic force microscopy (AFM) imaging of the adsorption. The adsorption behaviors of BTMA + at the substitution sites were verified by molecular dynamic simulations. By means of an image processing software, the AFM images could be analyzed and the areas as well as area percentages of the substitution sites on the clay mineral surfaces could be determined. The case of mica, one kind of clay minerals, was showed for example in this study. [ABSTRACT FROM AUTHOR]

The flotation separation of sylvite (KCl) and halite (NaCl) had drawn much attention, but the mechanism is still controversial. In this work, the atomic insights into the flotation separation of KCl and NaCl was conducted using molecular dynamics simulation (MDs). A novel concept that the hydration layer on minerals surface has been introduced. The molecular dynamic calculation shows that the adsorption energy between the octadecylamine (ODA, the most common collector for KCl flotation) and NaCl is smaller than the cohesive energy in the hydration layers on NaCl surface. However, the adsorption energy of ODA/KCl is much larger than the cohesive energy of the hydration layers on KCl surface. Hence, the collector ODA can pass through the hydration layers and then be adsorbed onto the KCl surface, but that cannot do occur on the NaCl surface, which perfectly explains the mechanism of the separation of KCl and NaCl by ODA. Notably, the new viewpoint of hydration layer may open up a new path to explain the behavior of flotation separation. The flotation experiment results also show the KCl is easily floated while the NaCl hardly floated by ODA, which agrees well with the calculation results. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Due to the very hydrophobic characteristic, silica tetrahedron (siloxane) structure on clay minerals surfaces was believed to affect many surface property of clay minerals, such as surface wettability, dispersion and agglomeration property. In this work, kaolinite and talc, with different number of siloxane surfaces, were chosen for studying how the siloxane structure affected hydrophobic agglomeration behaviors in aqueous solution. In-situ turbidity measurement of flocs suspension in the settlement progress had been applied to characterize the agglomeration behaviors of clay minerals. Through molecular dynamics simulation (MDs) results, it was found that the hydroxyl surface of kaolinite was very hydrophilic, while the siloxane surface of kaolinite (on the Si-tetrahedral side) and talc (both basal surfaces) showed a strong hydrophobicity due to the highly symmetrical siloxane structure. As a result, the talc and kaolinite showed vast differences on hydrophobic agglomeration behaviors. Because of the much more exposed siloxane structures on talc surface, the hydrophobic agglomeration degrees are far stronger than that of kaolinite due to the both hydrophobic basal surfaces. Besides, the sizes of talc flocs are also far larger than that of kaolinite due to the formation of layer by layer floc structure. Therefore, the siloxane structure on clay minerals surface has a significant influence on the agglomeration behaviors, including the agglomeration degree and the size of resulted flocs. It is the first time that the hydrophobic agglomeration behaviors were correlated to the siloxane structure on clay mineral surfaces, which has profound guiding significance on the study of dispersion stability of colloidal clay minerals. [ABSTRACT FROM AUTHOR]

In this work, the influence of different cations (Na + , K + , Ca 2+ and Mg 2+ ) on the surface tension of electrolyte solution was investigated using molecular dynamics simulations (MDs). The structure of the water-ion system was discussed in terms of ion-oxygen, ion-hydrogen radial distribution function (RDF) and hydration numbers of different electrolyte ions. It was found that the water-ion system existed in the form of ionic hydration shells. Besides, the interactions between the ions and water molecules were illustrated by the hydration energy, which provided the extra driving force to enlarge the surface tension of the ionic solution compare to the water. These results commendably explained the phenomenon that the greater the hydration energy of the ions, the greater the surface tension of these ionic solution. [ABSTRACT FROM AUTHOR]

The adsorption of Pb 2+ at the rutile/water interface has been studied for the activation of rutile flotation with salicyl hydroxamic acid (SHA) as a collector in this work. This study was performed through measurement of the zeta potential, adsorption capacity, calorimetry and X-ray photoelectron spectroscopy. The experimental results showed that the adsorption of SHA on rutile and the flotability of rutile were significantly improved by the addition of Pb 2+ . This improvement was attributed to the specific adsorption of Pb 2+ in the form of PbOH + , which interacted with the Ti-OH at the rutile surface and formed a surface Ti-O-Pb + complex. This adsorption followed the Langmuir model. It reversed the zeta potential sign of rutile at pH 5.5–6.8 and had a heat of adsorption of −46.71 kJ/mol, suggesting the occurrence of a chemiosorptive process. [ABSTRACT FROM AUTHOR]

[Display omitted] Montmorillonite (MMT), having special property of hydration expansion, can be easily exfoliated into two-dimensional (2D) nanosheets, which are the promising blocks for making multifunctional nanocomposites. In this work, the exfoliation performances of MMTs from different region including Inner Mongolia (IM), Zhejiang (ZJ) and Liaoning (LN) were investigated from the perspective of layer charge density. All the MMTs were prepared as Na-MMTs first to avoid the effect of the interlaminar ion. Atomic force microscope (AFM) measurements indicated that the exfoliation performance increased as: IM-MMT < ZJ-MMT < LN-MMT. Alkyl ammonium ion exchanged method was applied to study the layer charge density of the MMTs. It was found that the exfoliation performance decreased with the layer charge density of MMT increased. The characterizations of zeta potential, swelling index and BET specific surface area were used to reveal the effects of layer charge density on the exfoliation performance of MMT. The results showed that with increasing the layer charge density, MMT was with more negative zeta potential, thus leading to the stronger binding forces between the layers. The swelling index of LN-MMT was the highest who had the lowest layer charge density, demonstrated by the largest specific surface area and pore diameter after hydration swelling, which explained the best exfoliation behavior of LN-MMT. This study correlates the exfoliation performances with the layer charge density of MMT, and it will provide a guidance to prepare much thinner and larger MMT nanosheets. [ABSTRACT FROM AUTHOR]