Interaction forces between coal and kaolinite particles measured by atomic force microscopy

The Use of Kaolin as a Prophylactic Treatment to Prevent Columnaris Disease (Flavobacterium covae) in Commercial Baitfish and Sportfish Species

Aquaculture farms in Arkansas, USA routinely battle columnaris disease caused by Flavobacterium covae. Columnaris is prevalent during stressful events such as feed training and when fish are stocked at high densities in holding vats before sale. Kaolin clay was effective in laboratory trials as a treatment for columnaris in catfish. As a result, fish farmers are interested in applying kaolin products but were hesitant as they feared that the high doses of kaolin clay in vats might negatively affect the gills and overall health of fish. Therefore, we evaluated potential clay concentrations that might be used to prophylactically treat fish in vats. The effects of low to excessively high doses (0, 1, 2, 4, or 8 g/L) of kaolin clay (AkuaPro^TM, Imerys, GA, USA) were evaluated using a 72 h bioassay conducted in static tanks using Micropterus salmoides, Pomoxis nigromaculatus, Lepomis macrochirus, Ictalurus punctatus, Notemigonus crysoleucas, and Pimephales promelas. Results of these trials revealed a 100% survival rate across all six fish species exposed to kaolin clay at concentrations of up to 8 g/L for 48 h (followed by a 24 h recovery period in clean water) with no adverse effects to eyes, skin, gastrointestinal tract, or liver histology noted at any treatment. In addition, Micropterus salmoides analyzed for heavy metals due to exposure to the clay indicated that concentrations did not differ from control fish.

Modeling the Breakup of Oil-Particle Aggregates in Turbulent Environments for Projectile Penetration

After an oil spill incident, the spilled oil slicks are observed to migrate to the shoreline area. Under the turbulent conditions, they break into small droplets and are suspended in the water column. The dispersed droplets are expected to interact with the suspended particles and form the oil-particle aggregates (OPAs), which significantly changes the transport of the oil. Instead of an earlier assumption that particles cover the oil surface, thus preventing further breakage or aggregation of OPAs, recent studies demonstrated that particles act like projectiles penetrating the oil droplets, resulting in the breakage of OPAs over a longer period of time. A model looking into the OPA breakup through two breakup mechanisms was proposed for the first time. The first method depicted the breakup of one large OPA into two daughter droplets owing to the turbulent nature, while the second method demonstrated the tear of the OPA surface layer caused by particle uprooting. The model was then calibrated by an experimental study targeting crude oil with varied viscosities, along with previous experimental investigations. Three key factors were identified accounting for the breakage of OPAs, where the increase in particle concentration in the natural environment and the increase in turbulent energy of the surrounding flows benefited the breakage of OPAs, and the increase in oil viscosity suppressed the breakage due to large resistance to shear stress. Besides these elements, the impact of the particle shape on the penetration depth was discussed. The model serves as a fundamental theory to describe the evolution of OPAs for fragmentation behavior.

Density Functional Simulation Study of Surface Wettability of Coal Molecules with Different Degrees of Defects

To explore the adsorption mechanism of H₂O molecules on the surfaces of defective coal molecules and perfect bituminous coal molecules, the energy band structure, electronic density of states, electrostatic potential, and front orbitals on the surfaces of three coal molecule models were investigated using quantum chemical density functional theory (DFT) simulations. The adsorption energy and Mulliken charge layout of H₂O molecules with the surfaces of defective coal molecules and perfect bituminous coal molecules were similarly investigated. The results of the DFT calculations showed that the widths of the forbidden bands of the defective coal molecular surfaces were narrower, and the electrostatic potential values were smaller. In addition, they each had an increased conduction band near the Fermi energy level, a larger electronic density of states near the Fermi energy level, and a higher electron activity and electron density than those of the perfect bituminous coal molecular surface. While stable adsorption of H₂O molecules occurred on the surfaces of the single-vacancy-defective coal molecules, double-vacancy-defective coal molecules, and perfect bituminous coal molecules, the adsorption energy values were -39.401, -30.002, and -29.844 kJ/mol for the more stable configurations, corresponding to -0.022, -0.013, and -0.011 electrons gained by H₂O molecules, respectively. Wettability improved with the appearance of defects, and the order of improvement was single-vacancy-defective coal molecule > double-vacancy-defective coal molecule > no-defect coal molecule.

DFT Study on the Adsorption of Monomeric Hydroxyl Aluminum on Fe(II)/Mg Replacement Kaolinite (001) Surfaces

In the natural environment, Al and Si in the kaolinite crystal structure are likely to form lattice defects or be replaced by low-valence positive ions so that the base surfaces have permanent negatively charged sites. It is therefore very important to investigate the adsorption process and adsorption mechanism of adsorbates on the replaced surfaces. In this paper, two types of surface models formed by replacing Al atoms in the alumina octahedron of kaolinite (001) surface with Fe(II) and Mg were selected as the adsorption surfaces, these being the kaolinite Fe(II)_Al-(001) and Mg_Al-(001) surfaces, respectively. Then, we used density functional theory (DFT) to simulate the adsorption of three monomeric hydroxy aluminum models (i.e., Al(OH)₂ ⁺, Al(OH)₃, and Al(OH)₄ ^-) on the two replaced surfaces. Results show that, when compared to the adsorption on the ideal kaolinite (001) surface, the adsorption energies of the three adsorbates adsorbed on the replaced surfaces are lower and the adsorption is more stable. When the three adsorbates are adsorbed on the kaolinite Fe(II)_Al-(001) surface, adsorption stability increases with the number of hydroxyl groups, and hydrogen bonding and electrostatic adsorption play a major role. Conversely, when they were adsorbed on the kaolinite Mg_Al-(001) surface, the stability of the adsorption deteriorated as the number of hydroxyl groups increased. Moreover, the decisive roles are the interaction between the aluminum atoms in the adsorbates and the oxygen atoms on the replaced surface and the electrostatic adsorption.

A Review on Coagulation/Flocculation in Dewatering of Coal Slurry

Coal slurry is an essential component of mining operations, accounting for more than half of operating costs. Dewatering technology is simultaneously confronted with obstacles and possibilities, and it may yet be improved as the crucial step for reducing the ultimate processing cost. Coagulation/flocculation is used as a dewatering process that is reasonably cost-effective and user-friendly. This paper reviews application of different coagulants/flocculants and their combinations in dewatering mechanisms. In this context, various polymeric flocculants are discussed in the coal slurry in depth. Many operational parameters that influence the performance of coal slurry flocculation are also presented. Furthermore, a discussion is provided on the mechanism of flocculants’ interaction, the strategy of combining flocculants, and efficient selection methods of flocculants. Finally, coagulation/flocculation remaining challenges and technological improvements for the better development of highly efficient treatment methods were highlighted, focusing on the intricate composition of slurry and its treatment difficulties.

Effects of flotation and acid treatment on unburned carbon recovery from atmospheric circulating fluidized bed coal gasification fine ash and application evaluation of residual carbon

The high carbon content (20-60%) in coal gasification fine ash (CGFA) makes CGFA unable to be directly used in the building materials and ceramic industries, and can only be dissipated in landfills, which brings serious environmental safety problems. This paper uses physical (flotation method) and chemical (multi-stage pickling method) methods to treat CGFA, analyze the separated carbon, and evaluate its application. The carbon content of the filter cake ash (FCA) residual carbon recovered by the flotation method is slightly increased, and the carbon ash separation effect for the water-containing CGFA is poor. The carbon content of dry ash (DA) recovered carbon in acid treatment increased from 16.33% to 89.97%. The specific surface area of the acid-washed recovered carbon is 6-34 times that of the original sample, and the specific surface area of dry ash-HCl/HF/HCl (DA-CFC) is as high as 425.31 m²/g, and its pore structure network is more developed than before deashing. After pickling treatment, the microcrystalline structure changes, the carbon skeleton becomes looser, the degree of crosslinking decreases, and the reaction activity increases. The relative content of CC in the acid-washed recovered carbon increased by 6.4-46.3%, and the relative content of functional group CH bonds increased by 48.5-89.5%. Compared with the activation energy of the original sample, the activation energy E of the sample after flotation and acid treatment is reduced, and the reaction activity is enhanced. Flotation and pickling methods can improve the grade of fuel, and multi-stage pickling methods to obtain high specific surface area carbon can be used as a precursor for the preparation of activated carbon. Carbon-ash separation of DA by flotation method can be applied to fuel combustion, fine chemical industry, and road filling. However, for FCA, it is necessary to use a pickling scheme for carbon-ash separation to realize resource utilization and harmlessness.

Determination and modulation of the typical interactions among dispersed phases relevant to flotation applications: A review

Flotation is a process involving multi-components, multi-scales, and gas-liquid-solid three phases, where the material separation is achieved based on the difference in surface hydrophobicity of various constituents. In a flotation system, fluids are usually regarded as the continuous phase, while the dispersed phases refer to scattered particles, bubbles, and droplets with low solubility as a dispersion that is surrounded by the aqueous environment. Fundamentally, the interactions among dispersed phases exist throughout the flotation process, and play distinct roles during different periods. For example, the liquid collector-solid, solid-solid, bubble-bubble and gas bubble-solid interactions are closely associated with the particle surface modification, particle behavior, bubble size evolution and separation in flotation, respectively. Therefore, the influences of each stage are all worthy of concern, and should be spared sufficient attention, which requires to formulate a horizontal writing structure. In this review, instead of summarizing all available characterization techniques or measurements, certain typical examples or methods were consciously chosen to perform analysis or comparison, aiming to summarize recent studies on the determination and modulation of dispersed phase interactions. The determination on the interactions among dispersed phases is helpful for fundamentally understanding the microcosmic process connotations, and their modulation contributes to firmly providing macroscopic optimization schemes for practical applications. By integrating some typically available theoretical calculations and experimental measurements related to the dispersed phase interactions, the present article is devoted to revealing the influential factors, finding out the current challenges or knowledge gaps, and affording certain references or suggestions for future investigations.

Electrokinetic potential reduction of fine particles induced by gas nucleation

Electrokinetic potential of particles has been extensively studied in colloidal systems over the past century, while up to date, the influence of gas on electrokinetic behaviors of particles has not been fully understood yet. In this study, the electrokinetic response of particles to gas nucleation was systematically investigated with coal as the object. The results showed that the nucleation of gas (both on particle surfaces and in water) significantly changed the particle' electrokinetic behaviors. Higher gas content and particle's surface hydrophobicity normally trigger more intensive gas nucleation, thus inducing more significant reduction of particle zeta potential. After gas nucleation, numerous nanobubbles (NBs) appear in the suspensions mainly in two forms: NBs adhering onto solid surfaces (ANBs) and NBs stagnating in bulk solutions (BNBs). ANBs not only enhance the surface heterogeneity, but also cause the "steric hindrance" effect, and electric double layer (EDL) overlapping and associated ions shielding towards charged particles, which significantly decrease their electrokinetic potentials. Although BNBs can also reduce the zeta potential of particles by EDL compressing, their functions are rather limited.

Mechanism-Independent Manipulation of Single-Wall Carbon Nanotubes with Atomic Force Microscopy Tip

Atomic force microscopy (AFM) based nanomanipulation can align the orientation and position of individual carbon nanotubes accurately. However, the flexible deformation during the tip manipulation modifies the original shape of these nanotubes, which could affect its electrical properties and reduce the accuracy of AFM nanomanipulation. Thus, we developed a protocol for searching the synergistic parameter combinations to push single-wall carbon nanotubes (SWCNTs) to maintain their original shape after manipulation as far as possible, without requiring the sample physical properties and the tip-manipulation mechanisms. In the protocol, from a vast search space of manipulating parameters, the differential evolution (DE) algorithm was used to identify the optimal combinations of three parameters rapidly with the DE algorithm and the feedback of the length ratio of SWCNTs before and after manipulation. After optimizing the scale factor F and crossover probability Cr, the values F = 0.4 and Cr = 0.6 were used, and the ratio could reach 0.95 within 5-7 iterations. A parameter region with a higher length ratio was also studied to supply arbitrary pushing parameter combinations for individual manipulation demand. The optimal pushing parameter combination reduces the manipulation trajectory and the tip abrasion, thereby significantly improving the efficiency of tip manipulation for nanowire materials. The protocol for searching the best parameter combinations used in this study can also be extended to manipulate other one-dimensional nanomaterials.

The Interaction Force between Scheelite and Scheelite/Fluorite/Calcite Measured Using Atomic Force Microscopy

The mechanism of the formation of the hydrophobic agglomerate in fine scheelite flotation was studied using zeta potential measurement, contact angle measurement, optical microscope measurement, and atomic force microscopy (AFM) colloid probe technology. Zeta potential measurement results confirmed the adsorption of sodium oleate on scheelite, fluorite, and calcite surface and surface potential difference at different pH values of ultrapure water. Contact angle measurement results confirmed the surface of nature scheelite, fluorite, and calcite was hydrophilic, and the surface after thread by sodium oleate solution was hydrophobic. The optical microscope measurement results confirmed the agglomerates could really form in ultrapure water of pH 8 or 10 and in 1 mM sodium oleate solution of pH 10. The agglomerations were empty and not tight in ultrapure water. On the contrary, the hydrophobic agglomerations were larger and denser after treated with sodium oleate solution than that of in ultrapure water. According to the AFM experiment results, the interaction forces on hydrophilic scheelite-scheelite and scheelite-fluorite were repulsive at pH 5.6 and attractive at pH 8 or 10. However, the interaction forces on hydrophilic scheelite-calcite were attractive at pH 5.6, 8 or 10. The interaction forces on hydrophobic scheelite-scheelite, scheelite-fluorite, and scheelite-calcite were attractive strongly due to the existence of hydrophobic force. The measurement results of the interaction forces were in good agreement with the changes of zeta potential and contact angle at different conditions. The combined results could be beneficial to understand the interaction force in fine scheelite flotation.

A Study of Bubble Mineralization by Modified Glass Microspheres Based on a High-Speed Dynamic Microscopic Test System

The microscopic study of bubble mineralization is an important means of flotation theory research. In order to visualize the research process, it is required that the particles have certain optical properties and the amount of bubbles is controllable. In this paper, the particles were glass microspheres modified with trimethylchlorosilane (TMCS). The modification effect was confirmed by Fourier-transform infrared spectroscopy (FTIR), contact angle measurements, and a flotation test. The FTIR analysis and flotation test verified that the functional group (-OH) of glass microspheres reacted with the functional group (-Si-Cl) of TMCS and that the glass microsphere surface was successfully modified. The results also showed that the contact angle and hydrophobicity of the glass microspheres of a given size increased with the increase of TMCS. A small glass microsphere required more TMCS during the modification step in order to have the same contact angle as a large glass microsphere. The microscopic process of bubble mineralization was captured by a high-speed dynamic analysis system. The probability of collision between large glass microspheres and bubbles was high, but so was the probability that the microspheres would detach from the bubble. Both the collision probability and the detachment probability between small glass microspheres and bubbles were small, and small glass microspheres were easily affected by the flotation fluid. Besides, small bubbles and fine glass microspheres had a higher flotation recovery than coarse glass microspheres and large bubbles.

Measurement of Radial Elasticity and Original Height of DNA Duplex Using Tapping-Mode Atomic Force Microscopy

Atomic force microscopy (AFM) can characterize nanomaterial elasticity. However, some one-dimensional nanomaterials, such as DNA, are too small to locate with an AFM tip because of thermal drift and the nonlinearity of piezoelectric actuators. In this study, we propose a novel approach to address the shortcomings of AFM and obtain the radial Young's modulus of a DNA duplex. The elastic properties are evaluated by combining physical calculations and measured experimental results. The initial elasticity of the DNA is first assumed; based on tapping-mode scanning images and tip⁻sample interaction force simulations, the calculated elastic modulus is extracted. By minimizing the error between the assumed and experimental values, the extracted elasticity is assigned as the actual modulus for the material. Furthermore, tapping-mode image scanning avoids the necessity of locating the probe exactly on the target sample. In addition to elasticity measurements, the deformation caused by the tapping force from the AFM tip is compensated and the original height of the DNA is calculated. The results show that the radial compressive Young's modulus of DNA is 125⁻150 MPa under a tapping force of 0.5⁻1.3 nN; its original height is 1.9 nm. This approach can be applied to the measurement of other nanomaterials.

Porous Alumina Ceramics Obtained by Particles Self-Assembly Combing Freeze Drying Method

An innovative approach for fabricating porous alumina ceramics is demonstrated in this paper. The distinguished feature is that the construction of the porous structure stems from the interaction between ceramic particles, which is a poorly explored area. By tailoring the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy to the second minimum, the dilute ceramic slurry would be gelled by the weakly assembled particle network, and the assembled structure is conserved via a freeze drying strategy. The DLVO theoretical analyses revealed that the second minimum of interaction energy could be obtained when the counter-ion concentration in colloidal suspension is 1.5 × 10⁻² mol/L. The properties of the as-assembled samples were compared with one produced by the conventional freeze drying method. Results showed that the self-assembly of alumina particles has a positive influence on micro structures. Unlike the laminar pores generated by the traditional freeze drying procedure, the assembled samples show homogeneously interconnected and hierarchical open pores which were stable even after a 24 h dwell time at 950 °C (open porosity is 79.19% for the slurry of vol 20% solid loading). Particularly, after sintering at 1550 °C for 2 h, open porosity (67.01%) of the assembled samples was significantly greater than that of their un-assembled counterparts (39.97%). Besides, the assembled sample shows a narrower pore size distribution and a relatively higher cumulative pore volume.

Study on the aggregation behavior of kaolinite particles in the presence of cationic, anionic and non-ionic surfactants

Aggregation behaviors of kaolinite particles with different surfactants were studied in this paper. Aggregation settling yield and fractal dimension analysis were used to determine the aggregation results. Zeta potential measurements, adsorption tests, Infrared spectroscopy analysis and scanning electron microscope measurements were conducted for further investigation into the mechanism. Experimental results showed that much better aggregation results was obtained in the presence of cationic surfactant than that in the presence of anionic and non-ionic surfactants. 98% aggregation setting yield was obtained in the presence of dodecylamine. Adsorption tests indicated that the adsorption capacity of dodecylamine on kaolinite surface was larger than that of sodium oleate and Tween80. Zeta potential measurements confirmed that dodecylamine was more beneficial to the aggregation of kaolinite particles. Infrared spectroscopy analysis revealed that the adsorption of dodecylamine on kaolinite surface was attributed to electrostatic and hydrogen-bonding interactions. Sodium oleate was adsorbed by chemical adsorption. However, Tween80 can hardly be adsorbed by kaolinite surface.

The application of atomic force microscopy in mineral flotation

During the past years, atomic force microscopy (AFM) has matured to an indispensable tool to characterize nanomaterials in colloid and interface science. For imaging, a sharp probe mounted near to the end of a cantilever scans over the sample surface providing a high resolution three-dimensional topographic image. In addition, the AFM tip can be used as a force sensor to detect local properties like adhesion, stiffness, charge etc. After the invention of the colloidal probe technique it has also become a major method to measure surface forces. In this review, we highlight the advances in the application of AFM in the field of mineral flotation, such as mineral morphology imaging, water at mineral surface, reagent adsorption, inter-particle force, and bubble-particle interaction. In the coming years, the complementary characterization of chemical composition such as using infrared spectroscopy and Raman spectroscopy for AFM topography imaging and the synchronous measurement of the force and distance involving deformable bubble as a force sensor will further assist the fundamental understanding of flotation mechanism.

Anisotropic surface chemistry properties and adsorption behavior of silicate mineral crystals

Anisotropic surface properties of minerals play an important role in a variety of fields. With a focus on the two most intensively investigated silicate minerals (i.e., phyllosilicate minerals and pegmatite aluminosilicate minerals), this review highlights the research on their anisotropic surface properties based on their crystal structures. Four surface features comprise the anisotropic surface chemistry of minerals: broken bonds, energy, wettability, and charge. Analysis of surface broken bond and energy anisotropy helps to explain the cleavage and growth properties of mineral crystals, and understanding surface wettability and charge anisotropy is critical to the analysis of minerals' solution behavior, such as their flotation performance and rheological properties. In a specific reaction, the anisotropic surface properties of minerals are reflected in the adsorption strengths of reagents on different mineral surfaces. Combined with the knowledge of mineral crushing and grinding, a thorough understanding of the anisotropic surface chemistry properties and the anisotropic adsorption behavior of minerals will lead to the development of effective relational models comprising their crystal structure, surface chemistry properties, and targeted reagent adsorption. Overall, such a comprehensive approach is expected to firmly establish the connection between selective cleavage of mineral crystals for desired surfaces and designing novel reagents selectively adsorbed on the mineral surfaces. As tools to characterize the anisotropic surface chemistry properties of minerals, DLVO theory, atomic force microscopy (AFM), and molecular dynamics (MD) simulations are also reviewed.

The pH dependent surface charging and points of zero charge. VII. Update

The pristine points of zero charge (PZC) and isoelectric points (IEP) of metal oxides and IEP of other materials from the recent literature, and a few older results (overlooked in previous searches) are summarized. This study is an update of the previous compilations by the same author [Surface Charging and Points of Zero Charge, CRC, Boca Raton, 2009; J. Colloid Interface Sci. 337 (2009) 439; 353 (2011) 1; 426 (2014) 209]. The field has been very active, but most PZC and IEP are reported for materials, which are very well-documented already (silica, alumina, titania, iron oxides). IEP of (nominally) Gd₂O₃, NaTaO₃, and SrTiO₃ have been reported in the recent literature. Their IEP were not reported in older studies.

Separation Process of Fine Coals by Ultrasonic Vibration Gas-Solid Fluidized Bed

Ultrasonic vibration gas-solid fluidized bed was proposed and introduced to separate fine coals (0.5–0.125 mm fraction). Several technological methods such as XRF, XRD, XPS, and EPMA were used to study the composition of heavy products to evaluate the separation effect. Results show that the ultrasonic vibration force field strengthens the particle separation process based on density when the vibration frequency is 35 kHz and the fluidization number is 1.8. The ash difference between the light and heavy products and the recovery of combustible material obtain the maximum values of 47.30% and 89.59%, respectively. The sulfur content of the heavy product reaches the maximum value of 6.78%. Chemical state analysis of sulfur shows that organic sulfur (-C-S-), sulfate-sulfur (-SO₄), and pyrite-sulfur (-S₂) are confirmed in the original coal and heavy product. Organic sulfur (-C-S-) is mainly concentrated in the light product, and pyrite-sulfur (-S₂) is significantly enriched in the heavy product. The element composition, phase composition, backscatter imagery, and surface distribution of elements for heavy product show concentration of high-density minerals including pyrite, quartz, and kaolinite. Some harmful elements such as F, Pb, and As are also concentrated in the heavy product.

Recent experimental advances for understanding bubble-particle attachment in flotation

Bubble-particle interaction is of great theoretical and practical importance in flotation. Significant progress has been achieved over the past years and the process of bubble-particle collision is reasonably well understood. This, however, is not the case for bubble-particle attachment leading to three-phase contact line formation due to the difficulty in both theoretical analysis and experimental verification. For attachment, surface forces play a major role. They control the thinning and rupture of the liquid film between the bubble and the particle. The coupling between force, bubble deformation and film drainage is critical to understand the underlying mechanism responsible for bubble-particle attachment. In this review we first discuss the advances in macroscopic experimental methods for characterizing bubble-particle attachment such as induction timer and high speed visualization. Then we focus on advances in measuring the force and drainage of thin liquid films between an air bubble and a solid surface at a nanometer scale. Advances, limits, challenges, and future research opportunities are discussed. By combining atomic force microscopy and reflection interference contrast microscopy, the force, bubble deformation, and liquid film drainage can be measured simultaneously. The simultaneous measurement of the interaction force and the spatiotemporal evolution of the confined liquid film hold great promise to shed new light on flotation.