Extended DLVO Theory Research Articles

A comparative study on aggregation and sedimentation of natural goethite and artificial Fe3O4 nanoparticles in synthetic and natural waters based on extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory and molecular dynamics simulations

Natural iron oxides nanomaterials have important roles in biogeochemical processes. In this study, the effects of pH, natural organic matter, and cations on aggregation and sedimentation of natural goethite and artificial Fe3O4 nanoparticles in water were investigated to learn more about the environmental behaviors of engineered and natural nanomaterials and how they differ. In addition, a novel extended DLVO theory that considered steric, gravitational, and magnetic attraction forces concurrently was specifically developed to provide mechanisms explanations. Specifically, Fe3O4 NPs were more likely than bulk goethite to aggregate (because of magnetic attraction interactions) at low HA concentrations and disperse at high HA concentrations. Besides, goethite was less prone to settle with the same concentration of NaCl than Fe3O4 NPs, but the opposite trend was found for the same concentration of CaCl2 because of the difference in maximum net energy (barrier) and strong Ca2+ bridging effectiveness of goethite in CaCl2 solution. Statistical models were established to evaluate colloidal stability of the particles. XPS and molecular dynamics simulation results suggested that ions were adsorbed onto particles via ionic polarization and that the binding free energies at high coverage followed the order Ca2+ > Na+ > Cl- and presence of cation bridging between particles.

Effects of Organic Agriculture in Structure and Organic Carbon Adsorption at Colloidal Scale in Marginal Olive Groves, Characterized by the Extended DLVO Model

Relationship between macroscopic and microscopic behavior of soils is a difficult issue, especially when dealing with complex properties such as structure or carbon sequestration, but it is necessary for a suitable understanding of the agricultural soil quality. In this work, we used the extended-DLVO theory to compute total energy of interaction between particles (kT), of three soils over granodiorites. This parameter allows predicting the tendency to aggregate formation at the colloidal scale, being the basis of soil structure. Furthermore, we characterized the mechanism and adsorption capacity of humic molecules on mineral surfaces, and its influence in the interaction energy, by means of the adsorption isotherms. The aim was to compare first the effects of organic farming on conventionally managed soils and, second, to compare these with a non-cultivated forest soil under Mediterranean climate. When total energies are negative (particle attraction), or positive (particle repulsion) but near 0 kT (<100 kT), then particle flocculation occurs and the structure at colloidal scale can be developed. Total energy was less in the forest sample and greater in the soil of conventional groves, with intermediate values in organic farming soil. This indicates a tendency toward particle flocculation and more stability of the structure at colloidal scale in less disturbed soils, agreeing with other soil physical properties such as the total porosity (50, 41 and 37% in forest, organic and conventional plots, respectively) or the aggregate stability index (0.94, 0.73 and 0.66, respectively), which followed the same trend. Of the three components of the total energy of interaction, the acid-base force was a key factor. This component, related with the electron-donor component of surface free energy, γ−, yielded a strong attractive force (−150 kT at 3 nm) when calcium solutions were analyzed for the forest soil. This indicates a clear hydrophobic character of this sample. Because the mineralogical composition of the samples is quite similar, hydrophobicity should be attributed to the organic carbon content of the forest soil, which is much higher than that of the cultivated ones (12.03 vs. 1.44% and 0.88% in organic and conventional farms, respectively), proving to be an essential element for the development of the structure at the colloidal level.

Effect of modified microbial flocculant on membrane fouling alleviation in a hybrid aerobic granular sludge membrane system for wastewater reuse

Pre-coagulation is an excellent method for alleviating membrane fouling in aerobic granular sludge (AGS) membrane systems (AGSMSs) for wastewater reuse. However, little attention has been paid to modified microbial flocculants (MMFs) for membrane fouling mitigation. Herein, an MMF was prepared, and the effect of its dosage (5–30 mg/L) on membrane fouling mitigation was investigated. MMF pre-coagulation could effectively alleviate membrane fouling by utilizing electrical neutralization and adsorption bridging. When the MMF dosage was 10 mg/L, the membrane flux was increased by 79.4% and the total fouling resistance was reduced by 90.3%. The MMF dosage of 10 mg/L greatly inhibited the adhesion and accumulation of foulants, thereby forming a loose and porous cake layer on the membrane surface. Moreover, the extended Derjaguin–Landau–Verwey–Overbeek theory further clarified that the greatest energy barriers existed throughout the filtration process with an MMF dosage of 10 mg/L. Correlation analysis showed that the occurrence of membrane fouling was mainly related to total phosphorus, chemical oxygen demand, and polysaccharides in the raw wastewater. This study reveals the effects of different MMF dosages on membrane fouling and provides a novel approach for MMF pre-coagulation to mitigate membrane fouling.

Interactions of coal pitch with amphoteric polycarboxylate dispersant in coal pitch–water slurry: Experiments and simulations

As the main by-product of coal tar processing, large amounts of coal pitch (CP) are insufficiently utilized. In this study, to realize resource utilization, CP was used to prepare coal pitch–water slurry (CPWS) fuels with the addition of three amphoteric polycarboxylate dispersants (AAD-1, AAD-2, AAD-3). The effects of dispersants on the slurry characteristics were studied. The adsorption of dispersant and the surface properties of CP were also analyzed. Results showed that the AAD-2 with a moderate side-chain length had a better ability to increase the stability and reduce the apparent viscosity of CPWS than others. When the dosage of AAD-2 was 0.5 wt%, the maximum slurry concentration was 53.7 wt%. The adsorption behaviors of three dispersants could be fitted well by the Freundlich model, and the adsorption quantity of AAD-2 was greater than that of two other dispersants. The Zeta potential and wettability of CP were improved to the greatest for AAD-1. To explore the dispersion and stabilization mechanisms, the molecular dynamics simulation and extended DLVO theory were used to discuss the interactions between CP and dispersants, the interaction energy among CP particles. Results showed that the adsorption energy of AAD-2 with CP was the most prominent (-1520.29 kJ/mol), the mobility of water molecules was reduced. Furthermore, in the CPWS with AAD-2, the total interaction energy ΔET was more significant than that of other slurries, which was due to the larger steric hindrance energy from AAD-2. In sum, this research provided an experimental and theoretical basis for preparing slurry with CP and polycarboxylate dispersant.

Improvement of WET cleaning technique of CSP reflector mirrors using novel liquids

Concentrated solar power (CSP) plants are one of the most advanced technologies in terms of generating electricity from solar energy. However, this technology is facing many issues; one of their main issues is their high consumption of water in their daily operations. In this context, the purpose of this paper is to find a new solution that can be implemented in the CSP plants projects to reduce the water consumption during the washing operation of reflector mirrors. Based on the extended DLVO theory and the Good–van Oss model to describe the adhesion between the reflector mirrors and cleaning liquids during the process of cleaning. Additives are proposed to increase the spreading of water when in contact with the surfaces of CSP reflector mirrors. All the chosen additives that have a low work of adhesion are suggested to be mixed with water in order to increase the spreading and the wettability of water. In this research, the natural Ghassoul it’s highly recommended to be mixed with water. In fact, the natural Ghassoul contain both a hydrophilic side (water loving), and a hydrophobic side (water hating); one side contains positive charges and the other side contain negative charges. In addition to Natural Ghassoul, a list of additives has been proposed to increase the effectiveness of CSP plants by mixing with water for a good spreading in contact with the surfaces of reflector mirrors during the cleaning process.

A comprehensive insight on the impact of individual ions on Engineered Waterflood: With already strongly water-wet sandstone

Engineered Waterflood (EWF) has drawn increasing attention as an emerging economic-friendly technique. However, the underlying mechanisms still remain ambiguous. Wettability alteration has been claimed as the main reason to the additional oil recovery by EWF. In contrast, limited work was devoted to investigate the contribution of fluid-fluid interaction. To fill this gap, in the study, strongly water-wet rock samples (artificial clay-free sandstones) were used to minimize wettability alteration, thereby highlighting the fluid-fluid interaction. A high-salinity single-component NaCl solution (100 kppm) was used as a base line; three low salinity (1 kppm) brines (i.e., NaCl, CaCl2 and Na2SO4) were adopted in our experiments to explore the effect of brine salinity and ion types. Moreover, an offshore heavy oil was chosen in our study to emphasize fluid-fluid interfacial response. First, secondary EWFs were conducted to demonstrate the brine chemistry effect on core scale. Subsequently, oil/brine interfacial properties including IFT and IVE were analyzed at the interfacial film scale. Thereafter, visible micromodel experiments were performed to manifest the fluid-fluid interaction on pore-scale displacement events. On the other hand, zeta potential measurements along with the disjoining pressure isotherm calculation by the extended-DLVO theory were used to study the rock-fluid interaction. Our results show that both low salinity and the sulfate enrichment increase the interfacial visco-elasticity, which hinders the microscopic displacement events of both snap-off and coalescence. In addition, as engineered water is injected at secondary mode, the overall oil continuity is primarily improved by suppressing snap-off. Additionally, disjoining pressure calculation reveal that a lower brine salinity and an enrichment of sulfate can decrease the attraction force between oil and rock, imparting a lubricating effect on the flow of crude oil. Therefore, this work has shed light on EWF mechanisms by considering both fluid-fluid and fluid-rock interactions from multi-scales. It also clarifies the effect of sulfate on EWF in sandstone, unlike previous studies that mainly evaluated the performance of sulfate in carbonate.

Spindle-like-aggregating behavior of hydroxyapatite nanorods in polyacrylic acid aqueous system

The aggregating behavior of hydroxyapatite (HAP) nanorods plays a central role in the mechanism of biomimetic mineralization. In this study, the spindle-like aggregating behavior of hydroxyapatite (HAP) nanorods was studied by ultrasonically dispersing HAP in a polyacrylic acid (PAA) aqueous system. Unlike the quick aggregation and precipitation of HAP nanorods without PAA, the spindle-like primary aggregations formed herein could be suspended in water with good stability. The preferential adsorption of PAA on the side surface of HAP nanorods generated steric repulsion opposite to the van der Waals interaction in the radial direction. Accordingly, with an increase in the molar ratio of PAA[-COOH-]/HAP, the HAP nanorods showed a tendency to form spindle-like primary aggregations with decreased diameter and increased aspect ratio. The resulting aggregates possessed sufficient repulsion (steric repulsion and electric double layer repulsion) to overcome van der Waals interactions to remain suspended and dispersed. This study revealed the mechanism of aggregating HAP nanorods into spindle-like aggregates by extended Derjaguin–Landau–Verwey–Overbeek theory, including the steric stabilization mode. We believe that this study will facilitate the ordered structuring of minerals in hard-tissue mineralization processes.

Eco-friendly utilization of microplastics for preparing coal water slurry: rheological behavior and dispersion mechanism

Microplastics (MPs) are emergingly hazardous contaminants which ubiquitously exists in aquatic, terrestrial and atmospheric system, as well as in human system. Coal water slurry (CWS) is an important clean-coal-based liquid fuel with the characteristics of high-efficiency and low-pollution. This paper aims to implement the principles of clean production and prepare CWS by coblending coal particles and polyethylene terephthalate (PET) microplastics. It shows that the presence of PET particles significantly reduces the viscosity and increases the dispersion performance of CWS suspension. The apparent viscosity of CWS tends to decrease with the increase of PET content. Through the contact angle, surface morphology, and zeta potential analyses, particles with stronger hydrophobicity, more spherical shape and higher electronegativity, are more easily to form consistent and dispersed CWS suspensions. The extended DLVO theory demonstrates that the repulsion between solid particles becomes larger when PET particles are added to the slurry, which is beneficial to particle dispersion. In addition, the dispersant interfacial distribution differs between coal and PET particles, and significantly affect the rheological behavior and dispersion mechanism of CWS. This study proposes a potential approach to recycle the hazardous waste MPs and provides theoretical basis for enhancing CWS dispersion performance through coblending with PET microplastic particles.

Interactions between bubble and particles of key minerals of diasporic bauxite through the extended DLVO theory

The flotation of diasporic bauxite is to separate diaspore (valuable mineral) from aluminosilicate minerals (gangue minerals, mainly including kaolinite, illite and pyrophyllite), and the microscopic interaction force between the two types of minerals and air bubbles determines the separation efficiency. In this paper, based on the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the van der Waals, electrostatic and hydrophobic interaction between particles of the four minerals mentioned above and air bubbles in collectorless solution were calculated first, and then diaspore and kaolinite were taken as examples to analyze the influence of various factors such as electrolyte concentration, mineral particle size, air bubble size, collector type (dodecylamine hydrochloride (DAH) and sodium oleate (NaOL)) and concentration, and pulp pH on the interactions between the particles of valuable mineral and gangue minerals and air bubbles. The results showed that the total extended DLVO interactions between the four minerals and air bubbles were repulsive in most cases in collectorless solution. The increase in electrolyte concentration reduced the interaction force or even changed the direction of the force under certain circumstances. The addition of DAH and NaOL can reduce the adhesion energy barrier of kaolinite-bubble and diaspore-bubble respectively. Each type of minerals exhibited a specific interface interaction response with air bubbles in each collector with different pH values. The research results have theoretical guiding significance for the optimization and directional control of diasporic bauxite flotation conditions.

Formation of Supported Lipid Bilayers (SLBs) from Buffers Containing Low Concentrations of Group I Chloride Salts.

Supported lipid bilayers (SLBs) are a useful tool for studying the interactions between lipids and other biomolecules that make up a cell membrane. SLBs are typically formed by the adsorption and rupture of vesicles from solution. Although it is known that many experimental factors can affect whether SLB formation is successful, there is no comprehensive understanding of the mechanism. In this work, we have used a quartz crystal microbalance (QCM) to investigate the role of the salt in the buffer on the formation of phosphatidylcholine SLBs on a silicon dioxide (SiO2) surface. We varied the concentration of sodium chloride in the buffer, from 5 to 150 mM, to find the minimum concentration of NaCl that was required for the successful formation of an SLB. We then repeated the experiments with other group I chloride salts (LiCl, KCl, and CsCl) and found that at higher salt concentrations (150 mM) SLB formation was successful for all of the salts used, and the degree of deformation of the adsorbed vesicles at the critical vesicle coverage was cation-dependent. The results showed that at an intermediate salt concentration (50 mM) the critical vesicle coverage was cation-dependent and at low salt concentrations (12.5 mM) the cation used determined whether SLB formation was successful. We found that the successful formation of SLBs could occur at lower electrolyte concentrations for KCl and CsCl than it did for NaCl. To understand these results, we calculated the magnitude of the vesicle-surface interaction energy using the Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended-DLVO theory. We managed to explain the results obtained at higher salt concentrations by including cation-dependent surface potentials in the calculations and at lower salt concentrations by the addition of a cation-dependent hydration force. These results showed that the way that different cations in solution affect the 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)-SiO2 surface interaction energy depends on the ionic strength of the solution.

Interfacial Steric and Molecular Bonding Effects Contributing to the Stability of Neutrally Charged Nanoemulsions.

In cosmetic, pharmaceutical, and food applications, many active ingredients have limited bioavailability in an aqueous environment, and in that context, nanoemulsions provide a mechanism for encapsulation, protection, and transport. These dispersed oil droplets are on the order of 100s of nanometers in diameter and owe their long-term stability to emulsifiers that are commonly charged. More recently, applications have been utilizing nonionic species as stabilizing agents due to their enhanced biosafety. DLVO (named after Derjaguin, Landau, Verwey, and Overbeek) theory has been central in the description of colloid stability, which emphasizes repulsive electrostatic forces, while extended DLVO theory also accounts for steric effects. Past studies of nanoemulsions have largely employed charged surfactants and polyelectrolytes, making it difficult to decouple electrostatic and steric effects as they relate to droplet stability. To better understand steric and molecular factors contributing to the stability of "uncharged" droplets, we have created nanoemulsions with sodium dodecyl sulfate (SDS) and poly(N-vinylacetamide) (PNVA). Though SDS is anionic, with PNVA coating the droplet surfaces, the ζ-potentials of these nanoemulsions are ∼0 mV. Despite minimizing electrostatic contributions, these nanoemulsions are stable for upward of a month with interesting dynamics. By employing dynamic light scattering, vibrational sum frequency scattering spectroscopy, and calculating interaction pair potentials using extended DLVO theory, we learn that the thickness of the PNVA layer plays a critical role in stabilizing these "uncharged" nanoemulsions. Beyond the sterics, the molecular conformation of the PNVA strands also contributes to the droplet stability. The adsorbed PNVA strands are shown to form stratified, rigid polymer networks that prevent the nanoemulsions from rapid destabilization.

Modeling Bacterial Attachment Mechanisms on Superhydrophobic and Superhydrophilic Substrates.

Superhydrophilic and superhydrophobic substrates are widely known to inhibit the attachment of a variety of motile and/or nonmotile bacteria. However, the thermodynamics of attachment are complex. Surface energy measurements alone do not address the complexities of colloidal (i.e., bacterial) dispersions but do affirm that polar (acid-base) interactions () are often more significant than nonpolar (Lifshitz-van der Waals) interactions (). Classical DLVO theory alone also fails to address all colloidal interactions present in bacterial dispersions such as and Born repulsion () yet accounts for the significant electrostatic double layer repulsion (). We purpose to model both motile (e.g., P. aeruginosa and E. coli) and nonmotile (e.g., S. aureus and S. epidermidis) bacterial attachment to both superhydrophilic and superhydrophobic substrates via surface energies and extended DLVO theory corrected for bacterial geometries. We used extended DLVO theory and surface energy analyses to characterize the following Gibbs interaction energies for the bacteria with superhydrophobic and superhydrophilic substrates: , , , and . The combination of the aforementioned interactions yields the total Gibbs interaction energy () of each bacterium with each substrate. Analysis of the interaction energies with respect to the distance of approach yielded an equilibrium distance () that seems to be independent of both bacterial species and substrate. Utilizing both and Gibbs interaction energies, substrates could be designed to inhibit bacterial attachment.

Forward osmosis treatment of algal-rich water: Characteristics and mechanism of membrane fouling

Membrane fouling is an inevitable problem in forward osmosis (FO) treatment of algal-rich water (ARW). Natural ARW has a complex composition. Therefore, the coexisting components (Ca2+, natural organic humic acid [HA], and inorganic particulate kaolinite) in the influence of ARW on FO membrane fouling were studied. The analysis of extended Derjaguin–Landau–Verwey–Overbeek theory and the confocal laser scanning microscopy revealed that the addition of coexisting components increased the attraction between pollutants and membranes, as well as among pollutants to varying degrees, and promoted the development of membrane fouling. Furthermore, Ca2+ and HA aggravated irreversible membrane fouling. All coexisting components changed the distribution and thickness of the fouling layer, and the addition of Ca2+ increased the content of extracellular organic matter (proteins and polysaccharides). The present results enhance the understanding of the mechanism through which natural ingredients affect microalgal membrane fouling and provide a basis for membrane fouling control to treat ARW.

Population balance modeling of homogeneous viral aggregation

Viral aggregation is a natural process which helps viruses to survive in the environment and to resist to disinfection. Aggregation is a complex phenomenon controlled by the isoelectric point of the viral suspension. Previous models describe the energies of interaction between viruses using the extended DLVO theory. However, they do not allow us to predict the evolution of the viral aggregates size, which is critical for viral survival and transport.In this paper, we present a model for homogeneous viral aggregation based on the population balance equation (PBE) to describe the evolution of aggregate size. The PBE was coupled with the extended-DLVO theory to account for the energy of interaction between viral particles affected by virus type and physicochemical conditions. The model was verified with literature data and no parameter fitting was required as all the model parameters are based on the physicochemical properties of the system.Overall, this model can be an useful tool to simulate viral aggregate evolution in water and in sediments. It can be extended to describe heterogeneous viral aggregation and coupled with transport models for the prediction of virus migration and persistence in groundwater.

Measuring and modeling nanoparticle transport by foam in porous media

In this paper, an experimental study of nanoparticle transport by foam is presented. Bubbles made of N2-gas were stabilized with either a cationic surfactant (Cetyl Trimethyl Ammonium Bromide, CTAB), silica nanoparticles, or a combination of them. The concentrations of the surface active materials were selected upon foamability and stability tests. Column-flood tests were run until steady-state changing nanoparticle concentration, foam quality (fg), and flow rate. A synergistic behaviour of surfactant and nanoparticles help the formation of a strong foam. The measurements were used to validate a mechanistic model, presented in our earlier work (Li and Prigiobbe, 2020), which couples foam and nanoparticles transport with agglomeration and extended-DLVO theory. The model agrees well with the measurements and results show that an high-quality (ca. 90% gas fraction) can be used to carry nanoparticles and the efficient increases with flow velocity. This opens the opportunity for the application of foam as a carrier of nanoparticles in subsurface applications such as the remediation of contaminated sites and makes the model a valuable tool to design and predict such operations.

Influence of carbonate impurities on smartwater effect: Evaluation of wettability alteration process by geochemical simulation

Low salinity water flooding (LSWF) has been considered as a promising technique for enhanced oil recovery (EOR). The wettability alteration towards a more water-wet state is recognised as the main mechanism for the positive LSWF effect. Electrokinetic interactions occurring at crude oil/brine and rock/brine interfaces affect the wettability alteration. Most of the studies reported in the existing knowledge considered synthetic calcite to understand the electrokinetics of natural carbonate with brines. The mineral impurities present in natural carbonate could influence the electrokinetics and subsequently wettability alteration. In this study, the surface complexation model, thermodynamic equilibrium model, and extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory were combined to evaluate the effect of impurities (dolomite and anhydrite) in natural carbonate on wettability alteration. The surface complexation modelling parameters were first estimated by fitting the calculated zeta potential to that of measured value in various brines and then validated in smartwater. The thermodynamic equilibrium of impurities is largely insensitive to crude oil/brine interface properties. However, the calculated carbonate/brine surface or zeta potential changed from positive to negative with anhydrite equilibrium in the brines containing Ca2+ or Mg2+ ions. The attractive or repulsive forces between crude oil and carbonate were estimated from disjoining pressure using extended DLVO theory and compared with measured adhesion forces. The computed disjoining pressure was used as an indicator to evaluate wettability alteration. It is found that brine with SO42- ions can result in highest water-wet condition, followed by smartwater (brine with Ca2+, Mg2+, and SO42-) and brine with either Ca2+ ions or Mg2+ ions. The de-ionic (DI) water is unfavourable for wettability alteration. The effect of impurities equilibrium and the crude oil surface site densities on the disjoining pressure were also discussed.

Wavelet neural network modeling for the retention efficiency of sub-15 nm nanoparticles in ultrafiltration under small particle to pore diameter ratio

Ultrafiltration (UF) using membranes with a small ratio of particle to pore diameter (PPD) would be very desirable for energy saving. The nanoparticle (NP) retention efficiency of membranes with a small PPD ratio depends on various physical and chemical properties of NPs, membranes and solutions as well as the filtration conditions. Until now, no simple model is available for the calculation of NP retention efficiency in UF membranes, besides, it is unlikely to conduct experiments covering all conditions for obtaining the efficiency. The artificial neural network (ANN) has been attracting much attention for studying the performance of a highly nonlinear system. In this study, a wavelet ANN model was developed to predict the NP retentions in membranes for the dead-ended UFs under different conditions. A total of 13 parameters, including the membrane features, particle properties, water solution characteristics, operating conditions, etc., are considered as ANN inputs and the NP retention efficiency as the output. A total of 200 datasets with high quality from literature were selected, in which 50% were for the model training, 30% for the model validation and the remaining 20% for the model testing. A high correlation between the output and inputs was obtained and the significance of the 13 parameters on the NP retention was ranked. A case study was performed to further validate the trained ANN model in the prediction of the retention efficiency of 10 nm gold NPs in a 50 nm pore sized polycarbonate track etched (PCTE) membrane at different pH conditions (5–9). Focusing on the variation of pH, an excellent agreement between the model prediction and the calculation by the modified extended Derjaguin Landau Verwey Overbeek-Maxwell (MEDLVO-Maxwell) model originating from classical and extended DLVO theory was obtained. The interaction energy in the MEDLVO-Maxwell model was based on the separation distance calculated by a quench molecular dynamics (MD) simulation. This study illustrates and validates the application of ANN modeling on the NP retention efficiency prediction in the UF with small PPD ratios.

Uncovering the hydrophobic mechanism of a novel dithiocarbamate-hydroxamate surfactant towards galena

Flotation separation is determined by chemical additives which can enlarge the hydrophobicity difference of minerals. Herein, S-[(2-hydroxyamino)-2-oxoethyl]-N,N-dipropyl dithiocarbamate (HAPTC) was firstly developed for the flotation separation of galena and sphalerite. In situ AFM imaging elucidated a much stronger adsorption affinity of HAPTC towards galena (PbS) than that to sphalerite (ZnS) at pH 6.2 and 9.0. The AFM force findings and the extended DLVO theory analyses indicated that HAPTC adsorption promoted the hydrophobicity of galena surface more significantly than that of sphalerite. The micro-flotation results showed that HAPTC achieved a selective flotation separation of galena against sphalerite at pH around 9.0. FTIR and XPS uncovered that both dithiocarbamate and hydroxamate groups in HAPTC participated in the bonding interaction with Pb sites on galena surface with the formation of Pb-S and Pb-O bonds. The results provide implications on developing novel reagents, and the fundamental understanding of their adsorption and hydrophobization to minerals at nanoscale.

Hydrophobic agglomeration flotation of oxidized digenite fine particles induced by Na2S and butyl xanthate

Secondary copper sulfide mineral fine particles are easily oxidized, and their effective recovery by froth flotation is extremely challenging. This study investigated the roles of sodium sulfide (Na2S) and sodium butyl xanthate (SBX) in the hydrophobic agglomeration flotation of oxidized digenite fine particles. The microflotation experiments of the study showed that the simultaneous addition of Na2S and SBX is beneficial for improving the floatability of heavily oxidized digenite fine particles. In addition, the recovery at pH 7.0 was apparently higher than that of the unoxidized digenite fine particles, indicating that hydrophobic agglomeration of digenite fine particles may occur. The results of the zeta potential measurements, X-ray photoelectron spectroscopy analyses, and contact angle measurements suggested that negatively charged hydrogen sulfide ion and xanthate ion respectively hydrolyzed from Na2S and SBX adsorbed on the surface of digenite. Moreover, they significantly decrease the amount of hydrophilic copper sulfate and oxides/hydroxides on the surface, thus improving the surface hydrophobic degree of digenite. The results of the optical microscopy analysis, particle size analysis, and extended Derjaguin–Landau–Verwey–Overbeek theory calculations provided strong evidence for the roles of Na2S and SBX in promoting the hydrophobic agglomeration of the digenite fine particles. After treatment with Na2S and SBX, the total interaction energies between the digenite fine particles were negative, indicating that the strong hydrophobic attractive forces promote the formation of large-sized agglomerates, enabling the digenite fine particles to be more easily captured by bubbles than those without the treatment. Therefore, effective recovery of heavily oxidized digenite fine particles can be realized by the hydrophobic agglomeration flotation technology induced by Na2S and SBX.

Impact of pH on interaction between the polymeric flocculant and ultrafine coal with atomic force microscopy (AFM)

Solution pH plays a vital role in the interactions between polymer flocculants and solid colloid particles which determines the flocculation performance. The influence of solution pH on the flocculation of Magnafloc5250 on ultrafine coal suspension and the interactions between the polymers and solid surfaces were investigated by using atomic force microscopy (AFM), hydrodynamic radius measurements, particle floc size analyses, and flocculation dewatering tests. Our results revealed that the settling velocity and supernatant transmittance of ultrafine coal suspension without flocculant were low in alkaline conditions due to the strong repulsion, which agreed with the extended DLVO theory and direct force measurements by AFM. In the presence of Magnafloc5250, the highest transmittance was observed at pH 4 due to the compressed electric double layer among the coal particles, while the settling velocity reached a maximum value at pH 10, which was consistent with the largest average size of flocs (41.80 µm) and more extended conformation of flocculant. The adhesion force measured by AFM was divided into two parts: flocculation force and bare force. And the flocculation force reached a maximum value with the broadest range of action at pH 10, which supported the settling tests and floc size measurements well. The strengthened bridging interaction (e.g., via hydrogen bonding) with increasing solution pH is attributed to the increase of effective binding sites between more extended polymer chains and coal particles, thus contributing to an enhanced flocculation behavior.