Improved dewatering behavior of clay minerals dispersions via interfacial chemistry and particle interactions optimization

Effect of electrostatic repulsion on barrier properties and thermal performance of gelatin films by carboxymethyl starch, and application in food cooking

Carboxymethyl starch (CST) was introduced to improve gelatin films and its practical application as edible high-performance films for food packaging and cooking was also investigated. The gelatin films modified by carboxymethyl starch exhibited the transparent appearance, tensile strength, barrier properties (oxygen, water vapor and UV light), and thermal performance (TGA, thermal shrinkage and heat-sealing strength). Resulting from the effect of electrostatic interaction modes on the properties of films, electrostatic repulsion could surpass electrostatic attraction in improving the tensile strength, oxygen barrier property and thermal stability of the films probably due to extensive physical entanglement without aggregation. Analysis of FTIR, zeta potential, interfacial dilatational rheology, shear rheological properties, XRD, Raman, SEM and AFM suggested that hydrogen bonding and electrostatic repulsion contributed to the excellent performance. The packaged food could also be cooked with the prepared film for porridge; and the film slightly influenced the shear rheological properties of porridge and imposed little effect on the odors (Electronic-Nose) of porridge. Hence, the gelatin films modified by carboxymethyl starch could potentially work as the edible inner packaging or the edible quantitative packaging for food, offer convenience for consumers, reduce the packaging waste and avoid an extra burden on environment.

Dewatering behavior and regulation mechanism of montmorillonite nanosheet in aqueous solution

Two-dimensional montmorillonite nanosheet (MMTNS) is desirable building block for fabricating multifunctional materials as due to its extraordinary properties. In practical applications, however, the concentration of MMTNS prepared by exfoliation is normally too low to be used for material assembling. The general thermal-concentration method is effective, however, it can be time-consuming and require a lot of energy. In this case, the remarkable dispersion stability of MMTNS is worth noting. Herein, the extraordinary dispersion stability of MMTNS derived from electrostatic and hydration repulsion was firstly revealed by molecular dynamics (MD) simulation, which caused the poor dewatering of MMTNS. Further, based on the surface and structural chemistry of MMTNS, a series of strategies, involving charge and cross-linked structure regulation on the edge surface, as well as electrical double-layer modulation and calcification modification based on the electrolytes, were proposed to inhibit the dispersion and enhance the aggregation of MMTNS. Intriguingly, a novel chemical, Tetraethylenepentamine (TEPA) was applied in the dewatering of MMTNS. The TEPA not only act as a cross-linker to bond with MMTNS into an easy-to-dewatering 3D network structure, but also act as a switch for effortless viscosity tuning. Meanwhile, the dual function of electrolytes for electrical double layer compression and calcification modification of MMTNS was investigated by DLVO theory and structural analyses. This work offers explicit directions for improving the dewatering performance of MMTNS to meet the requirements of practical implementation.

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

Surfaces are often characterized by their points of zero charge (PZC) and isoelectric points (IEP). Different authors use these terms for different quantities, which may be equal to the actual PZC under certain conditions. Several popular methods lead to results which are inappropriately termed PZC. This present review is limited to zero-points obtained in the presence of inert electrolytes (halides, nitrates, and perchlorates of the 1st group metals). IEP are reported for all kinds of materials. PZC of metal oxides obtained as common intersection points of potentiometric curves for 3 or more ionic strengths (or by means of equivalent methods) are also reported, while the apparent PZC obtained by mass titration, pH-drift method, etc. are deliberately neglected. The results published in the recent publications and older results overlooked in the previous compilations by the same author are reported. The PZC/IEP are accompanied by information on the temperature and on the nature and concentration of supporting electrolyte (if available). The references to previous reviews by the same author allow to compare the newest results with the PZC/IEP of similar materials from the older literature.

Response of Floc Networks in Cemented Paste Backfill to a Pumping Agent

Cemented paste backfill is critical for the development of green mines, the safe exploitation of mineral resources deep underground, and the efficient disposal of solid wastes produced by mining. In this paper, the mechanism underpinning how the pumping agent works was studied. The number, area, and fractal dimension of pores in the microstructure of fresh paste were quantitatively analyzed using scanning electron microscopy (SEM), image processing, and fractal theory, and the response of flocs was investigated. The results show that floc networks disintegrated and the liquid network became the dominant structure under the action of the pumping agent, which enhanced the lubrication and promotion of multi-scale particles. In addition, the force chains became fragile and scattered, diminishing the yield stress of the paste. The pores had a more homogenized dimension and the porosity was 15.52% higher. The increase in the fractal dimension of the pores indicated that there was a higher self-similarity, in terms of microstructure, with a strengthened liquid network. The migration of floc structures contributed to the enhancement of the fluidity and rheology of the paste. This study provides insights into the effects of floc and liquid networks on the performance of paste, and it is of engineering significance in terms of realizing safe and efficient CPB operations.

Modelling and Experimental Investigation on the Settling Rate of Kaolinite Particles in Non-Ideal Sedimentation Stage under Constant Gravity

We compared the catalytic effects of two polymers (soluble starch and apple pectin) on the flocculation of kaolinite suspension. Moreover, the relationship between the zeta potential value and the time when kaolin particle sedimentation occurred was verified, and the mechanism of flocculation was analyzed. Additionally, a constitutive model was proposed to simulate the non-ideal sedimentation of clay particles in an aqueous system under constant gravity. This model not only considers the inhomogeneity of the solute but also simulates the change in clay concentration with time during the deposition process. This model proposes a decay constant (α) and sedimentation coefficient (s). The model can also be used to calculate the instantaneous sedimentation rate of the clay suspensions at any time and any depth for the settling cylinder. These sedimentary characteristics were simulated by adopting the established deposition model. The results show that the model is capable of predicting the time required for the complete sedimentation of particles in the aqueous system, suggesting the feasibility of engineering wastewater treatment, site dredging, etc.

Use 3-D tomography to reveal structural modification of bentonite-enriched clay by nonionic surfactants: Application of organo-clay composites to detoxify aflatoxin B1 in chickens

Although nonionic surfactants are relatively eco-friendly compared with cationic and anionic surfactants, few studies have investigated their application in modified clay. Herein we prepared organo-clay composites (OCCs) by mixing bentonite-enriched clay (BEC) with nonionic surfactants (Brij 30 and Igepal CO-890) and determined if these modifications would enable chickens to detoxify aflatoxin B1 (AFB1). For the first time, in situ three-dimensional (3-D) microstructures of modified BEC was characterized in suspension using transmission X-ray microscopy. Although X-ray diffraction patterns indicated the expansion in the spacing between planes of atoms (basal spacing) of surfactant-modified BEC, 3-D images indicated shrinkage in its microscale porous framework with increasing surfactant additions from 1 to 30 wt%. Such declining trends in porous dimensions caused by the dehydration in interlayer galleries of clays positively correlated with sorption amounts of AFB1 on OCCs. After chickens had consumed amended feeds for 11 weeks, AFB1 concentrations in liver, kidney, and plasma were significantly lower than in the control treatment. Thus, we suggest using BEC with 1 wt% surfactant addition, an amendment to chicken feeds, to detoxify AFB1. Modifying BEC with nonionic surfactants show the promise in mitigating AFB1 accumulation in chickens, which should improve food safety and reduce environmental contamination.

A novel carboxyl-rich chitosan-based polymer and its application for clay flocculation and cationic dye removal

Due to the complexity of contaminants, the effectiveness of traditional flocculants toward water purification is insufficient. To break the limitation, a novel polymer flocculant [chitosan grafted poly (acrylamide-itaconic acid), CS-g-P(AM-IA)] was synthesized via ultraviolet-initiated graft copolymerization reaction. Characterization results revealed that the graft copolymers were successfully synthesized and with rougher surface structure. The solubility of CS-g-P(AM-IA) and chitosan grafted polyacrylamide (CS-g-PAM) were greatly improved and they can dissolve in the wide pH range of 2.0-12.0. CaCl₂ was used as a source of cation bridge to enhance the flocculation of kaolin particles, and its optimum dosage was 150 mg·L^-1. At dosage of 30 mg·L^-1 and pH of 5.0, the turbidity removal efficiency of CS-g-P(AM-IA) reached the maximum of 93.8%, whereas those of CS-g-PAM and CS were 96.7% and 76.9%, respectively. The patchwise adsorption of ionic groups embedded in the molecular chain on Ca²⁺-clay complexes took effect to generate flocs with larger particle size. Besides, the decolorization ability of cationic dyes by CS-g-P(AM-IA) was greatly enhanced due to the role of abundant carboxyl groups. In the crystal violet (CV) adsorption experiment, the maximum CV dye removal efficiency for CS-g-P(AM-IA) reached the maximum of 81.6% at dosage of 0.7 mg·mL^-1 and pH of 9.0, while those for CS-g-PAM and CS were 51.7% and 36.5%, respectively.

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.

Experimental and numerical characterization of floc morphology: role of changing hydraulic retention time under flocculation mechanisms

The formation, breakage, and re-growth of flocs were investigated by using modified flocculation tests and numerical simulation to explore the evolution of floc morphology for different hydraulic retention times. The shorter the aggregation time was, the smaller the flocs produced for the same hydraulic conditions were. Another interesting discovery was that broken flocs that formed in shorter aggregation time had the capacity to completely recover, whereas those formed in a longer amount of time had rather worse reversibility of broken flocs. With the addition of the maximum motion step in the representative two-dimensional diffusion-limited aggregation (DLA) model, there was a transition for flocs from isotropic to anisotropic as the maximum motion step increased. The strength of flocs was mainly affected by the distribution of particles near the aggregated core rather than distant particles. A simplified breakage model, which found that broken flocs provided more chances for diffused particles to access the inner parts of flocs and to be uniformly packed around the aggregated core, was first proposed. Moreover, an important result showed that the floc fragments formed with a larger value of the maximum motion step had more growing sites than did those with a smaller msa value, which was a benefit of following the re-forming procedure.

Microstructure of bentonite in iron ore green pellets

Sodium-activated calcium bentonite is used as a binder in iron ore pellets and is known to increase strength of both wet and dry iron ore green pellets. In this article, the microstructure of bentonite in magnetite pellets is revealed for the first time using scanning electron microscopy. The microstructure of bentonite in wet and dry iron ore pellets, as well as in distilled water, was imaged by various imaging techniques (e.g., imaging at low voltage with monochromatic and decelerated beam or low loss backscattered electrons) and cryogenic methods (i.e., high pressure freezing and plunge freezing in liquid ethane). In wet iron ore green pellets, clay tactoids (stacks of parallel primary clay platelets) were very well dispersed and formed a voluminous network occupying the space available between mineral particles. When the pellet was dried, bentonite was drawn to the contact points between the particles and formed solid bridges, which impart strength to the solid compact.

Interaction forces between silica surfaces in aqueous solutions of cationic polymeric flocculants: effect of polymer charge

Three cationic polymers with molecular weights and charge density of 3.0 x 10(5) g/mol and 10% (D 6010), 1.1 x 10(5) g/mol and 40% (D6040), and 1.2 x 10(5) g/mol and 100% (D6099) were investigated in aqueous NaCl solutions in the presence of silica. The atomic force microscope (AFM) colloidal probe technique was used to determine silica interparticle interaction forces, which were compared to macroscopic information on the strength of interactions such as compressive yield stress measurements. It was found that in 30 mM NaCl solution the 10% charged polymer produced steric repulsion upon approach and long-range adhesion with multiple pull off events upon retraction at the optimum flocculation concentration. This suggests that the polymer was adsorbed in a conformation where segments extend from the surface, resulting in bridging flocculation. The 40 and 100% charged polymers produced attraction upon approach and strong adhesion with snap out from contact upon separation at optimum polymer dosages. This suggests that these polymers are adsorbed with flat conformations and is typical of charge neutralization or patch attraction. The attractions for 40 and 100% charged polymers measured with the AFM are significantly larger than for the 10% charged polymer. The polymer dose that produced the optimum flocculation and the maximum compressive yield stress typically corresponded to the polymer concentration that produced the maximum adhesion for each polymer. It was found that the magnitude of the adhesive force was more significant in determining the compressive yield stresses of the silica particle sediments than the aggregate size and structure.