Extended Derjaguin-Landau-Verwey-Overbeek Research Articles

Interfacial interactions of nanoscale zero-valent iron particles with clay minerals in the aquatic environments: Experimental and theoretical calculation study

The environmental transport and fate of nanoscale zero-valent iron particles (nZVI) in soil and groundwater can be altered by their hetero-aggregation with clay mineral particles (CMP). This study examines the interactions between bare or carboxymethyl cellulose (CMC)-coated nZVI with typical CMP, specifically kaolinite and montmorillonite. Methods include co-settling experiments, aggregation kinetic studies, electron microscopy, Derjaguin–Landau–Verwey–Overbeek (DLVO) and extended DLVO (EDLVO) energy analysis, and density functional theory calculations, focusing on the pH dependency of these interactions. The EDLVO theory effectively described the interactions between nZVI and CMP in aquatic environments. Under acidic conditions (pH 3.5), the interfacial interaction between bare nZVI and kaolinite is regulated by van der Waals forces, while complexation, van der Waals forces, and electrostatic attraction govern the interaction of bare nZVI with montmorillonite, primarily depositing on the Si-O face. In contrast, the positively charged Al-O face and edge of CMP are the main deposition sites for CMC-coated nZVI through hydrogen bonding, van der Waals forces, and electrostatic attraction. At neutral (pH 6.5) and alkaline (pH 9.5) conditions, both bare and CMC-coated nZVI predominantly attach to the Al-O face and edge, facilitated by complexation or hydrogen bonding, alongside van der Waals forces. The attachment of CMC-coated nZVI to CMP surfaces shows reversible aggregation or deposition due to the steric repulsion from the CMC coating. These findings hold significant implications for the environmental applications and risk of nZVI.

New insights into selective depression mechanism of Tamarindus indica kernel gum in flotation separation of fluorapatite and calcite

The similar floatability of fluorapatite (FAp) and calcite (Cal) lead to difficulty in their separation using fatty acid collectors alone. To effectively recover FAp from Cal, a biodegradable polysaccharide, called Tamarindus indica kernel gum (TIKG), was introduced as an efficient Cal depressant in this study, and its depression mechanisms were elucidated. Flotation tests suggested that in sodium oleate (NaOl) system, TIKG strongly depressed Cal but hardly affected FAp, significantly widening the difference in their floatability. Infrared spectroscopy (IR), zeta potential, and wettability analyses indicated that TIKG had strong adsorption interaction with Cal, hindered NaOl adsorption on Cal, and significantly weakened the hydrophobicity of Cal, while the opposite effect was observed for FAp. X-ray photoelectron spectroscopy (XPS) proved that intense interactions of TIKG with Ca sites of Cal enhanced its adsorption on Cal rather than FAp. Extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) calculations confirmed that TIKG reduced the hydrophobic attraction between Cal and bubbles and enhanced the electrostatic repulsion between them, thereby weakening Cal adhesion to bubbles and depressing Cal flotation. Consequently, TIKG achieved effective separation of FAp and Cal, in which 90.21% of Cal was efficiently removed in addition to 83.58% of FAp recovered. Based on these findings, TIKG serves as a Cal depressant for the purification of Cal-bearing phosphate ores by flotation.

A Chemical-Free Magnetophoretic Approach for Recovering Magnetic Particles in Microalgae Removal through Magnetic Separation

Magnetic separation can swiftly remove many substances (e.g., biomolecules, cells, and viruses) from water. In algal bloom mitigation and biomass dehydration, magnetic particles (MPs) with proper surface modifications could effectively attract and remove algae from the impaired water body. It has long been expected to recover and reuse magnetic nanoparticles or particles to reduce the algal removal cost and potential adverse effects on the environment. This study evaluated the use of a tunable magnetic field to remove algae using functionalized MPs coated with polymers: polyethyleneimine (PEI), chitosan (CTS), and cetyltrimethyl ammonium bromide (CTAB), whose recovery and reuse were examined. The results show that PEI-coated MPs and CTS-coated MPs at the coating density of 2.3 g-cationic polymers·g-MPs-1 achieved higher removal efficiencies of 88.61 ± 9.12% and 73.19 ± 0.37%, respectively, toward a model algal cell (i.e., Scenedesmus obliquus) within a 5-min separation time. In contrast, CTAB-coated MPs and pristine MPs exhibited lower removal efficiencies (47.46 ± 0.3% and 52.69 ± 0.44%, respectively). Furthermore, the removal efficiency of PEI-coated MPs was further improved to over 95% under pH 7, the highest magnetic field of 40 mT, and algogenic organic matter-free conditions. Adsorption kinetics and isotherm analysis revealed that chemical and physical interactions drive the adsorption of a monolayer of algal cells on the surface of magnetic particles. Atomic force microscopy and quartz crystal microbalance confirmed a strong adhesion force and rate between functionalized MPs and algae, which affect both algal removal efficiency and MPs recovery from algae-MPs aggregates. The extended Derjaguin−Landau−Verwey−Overbeek (EDLVO) theory predicted a strong attractive force between algae and cationic polymer-coated MPs, which supported the enhanced algal removal. Finally, almost 99% of the four MPs could be recovered from separated algae-MPs aggregates within 30 s under the strong magnetic field and exhibited excellent magnetic responsiveness and reusability in further separation cycles. This study establishes a foundation for coagulant-free algae removal and enables the potential sustainable separation processes.

Detachment dynamics of sessile droplets triggered by interaction forces between oil and wall in a microchannel

Understanding the detachment dynamics of droplets adhered to reservoir walls holds significant importance for the residual oil displacement process in high water-cut oilfields. Existing studies demonstrated that increasing mainstream shear by adjusting displacement flow and weakening wall adhesion by increasing contact angle can enhance droplet detachment. However, the complex physical and chemical oil–wall interactions, a crucial reservoir feature, cannot be solely relied on the macroscopic representation through contact angle. A deviation in understanding the process of crude oil droplet detachment would be resulted due to the change of wall adhesion. Considering the intricate physical and chemical interactions between oil and walls, in this paper, we employed the extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory to establish an oil–wall interaction forces system, and coupling computational fluid dynamics method to further explore the detachment dynamics of sessile oil droplets in a microchannel under varying EDLVO forces. The findings showed that (1) by increasing the Capillary number, the droplets gradually occur in four typical dynamic states: static, sliding, detachment, and pinch-off. (2) Static droplets are more prone to experience sliding behavior when influenced by EDLVO forces. (3) For droplets undergoing detachment and pinch-off, EDLVO forces inhibit entrainment behavior. These results contribute to an enhanced comprehension of droplet detachment dynamics in reservoirs, offering fresh insights for enhanced oil recovery strategies.

Selective adsorption analysis of BAPTA depressants on the surface of carbonate minerals: Insights into flotation behavior and adsorption mechanism

Flotation separation of magnesite and calcite, two carbonate minerals, poses a significant challenge due to their intrinsic surface similarities. In this study, 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA) was employed as a depressant to selectively regulate the mineral surface property in magnesite-calcite flotation. Micro-flotation experiments demonstrated that successful separation of magnesite-calcite mixtures could be achieved with 40 mg/L BAPTA and 100 mg/L sodium oleate (NaOL). Contact angle measurements and Ultraviolet-Visible absorption spectrum analysis revealed that pre-adsorption of BAPTA selectively hindered the adsorption of sodium oleate onto calcite surface, effectively eliminating the surface hydrophobicity of calcite induced by sodium oleate. The Extended-Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory further indicated a reduced attractive interaction energy between magnesite and calcite particles in the presence of BAPTA. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) simulation elucidated the stronger binding affinity of BAPTA towards calcium ions. Finally, a model was established for the selective formation of cage-like chelating structures on the calcite surface by BAPTA.

Flotation of lean coal using trisodium citrate dihydrate as a dispersant in the presence of sodium oleate

Flotation is a highly efficient method for purifying low-ash coal particles from high-ash fine slimes. Herein, the dispersion effect of trisodium citrate dihydrate (TCD) on the reduction of slime coating on low-ash lean coal particle surface was studied using flotation tests, scanning electron microscope–energy Dispersive Spectroscopy (SEM–EDS) observation, turbidity measurements, and extended Derjaguin–Landau–Verwey–Overbeek (E-DLVO) calculations. Flotation tests revealed that after adding of 2000 g/t TCD, the yield of clean coal increased by 1.09 % and the ash content of clean coal decreased by 1.45 % with 1000 g/t NaOL at pH 7.0, thereby increasing the combustible recovery and flotation perfect index by 2.50 % and 6.42 %, respectively. The SEM–EDS observation and turbidity measurements indicated that the coating of the high-ash fine slimes on the low-ash coal particle surface was significantly weakened in the presence of 2000 g/t TCD. Furthermore, the E-DLVO calculations verified that the addition of 2000 g/t TCD increased the energy barrier between the low-ash coal particles and high-ash fine slimes, providing theoretical evidence for flotation tests and SEM–EDS observation. Therefore, TCD served as an effective dispersant for the high-ash fine slimes to improve the flotation performance of lean coal.

Effects of carrier particles on flotation removal of unburned carbon particles from fly ash

Fly ash, a major by-product of coal-fired power plants, contains unburned carbon which poses challenges to its effective utilization. The flotation separation efficiency of unburned carbon from fly ash is limited due to the ultrafine size and poor hydrophobicity of the unburned carbon. This study introduces carrier flotation as an efficient method for removing unburned carbon from fly ash. Experimental results indicated that the use of carrier particles (low ash content coal particles) significantly enhanced the flotation removal efficiency of unburned carbon from fly ash compared to conventional methods. The enhancement mechanism was evaluated by examining the differences in flotation froth properties, particle aggregation behaviors, and extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) interaction energy in the presence and absence of hydrophobic carrier particles. Hydrophobic carrier particles were found to increase the stability of the flotation froth layer, facilitate the water recovery, and aid in the removal of fine unburned carbon particles. Focused beam reflectance measurement (FBRM) confirmed that the presence of hydrophobic carriers promoted the aggregation of fine unburned carbon particles, thereby increasing bubble-particle collision probability. Furthermore, EDVLO theory calculations revealed that the attractive interaction energy between carrier particles and unburned carbon particles was stronger than that between carrier particles and ash particles. Therefore, carrier flotation shows promise as a highly efficient method for removing unburned carbon from fly ash.

Influence of surface roughness of magnesite on bubble-particle energy barrier: Analysis based on a new simplified model

The surface roughness of mineral particles treated by different methods varies greatly, which will significantly affect flotation operations. In this investigation, magnesite particles with different surface roughness were obtained by ultrasonic treatment for different times. A new simplified mathematical model of rough particle-bubble interaction energy based on the extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory was formulated. Theoretical analysis shows that it is essentially consistent with the Wenzel wetting model. The parameters in the model were obtained by contact angle test, zeta potential test and AFM test. The interaction energy between a rough magnesite particle and a bubble at different NaOL concentrations was calculated. The results indicate that increasing the surface roughness of hydrophobic magnesite particles can significantly reduce the value of energy barrier (Em) that needed to be overcome for the adsorption between bubbles and magnesite particles. Meanwhile, it can push the location of energy barrier further away (that is, increase the critical hydration film thickness hcr when bubble-particle adhesion occurs), allowing magnesite particles to adhere to bubbles earlier and more easily, thereby improving the flotation performance of magnesite particles. However, the promoting effect of increasing surface roughness on the flotation of magnesite particles gradually weakened as the concentration of NaOL increased.

Oil–wall interaction induced droplet deformation dynamics in a capillary tube

Displacement of residual oil droplet in high water-cut oilfields can be optimized through the understanding of droplet deformation dynamics. The current studies demonstrated that the changing of capillary number or the radius ratio of droplet and tube can control the droplet deformation, but neglects the intricate interaction between the wall and droplet. Due to the complex physicochemical properties of the reservoir wall and crude oil, the interaction forces between them are very rich and unoverlooked. The current contact angle and atomic force microscope measurement are insufficient in accurately describing the oil–wall interaction forces system, resulting in discrepancies of droplet deformation dynamics with the actual reservoir conditions. We used the extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory to establish a system of oil–wall interaction forces. The deformation dynamics of high-viscosity droplets (plug and slug droplets) and low-viscosity droplets (tail-concaved droplets) in a capillary tube were studied under various EDLVO forces values. The results showed that: (1) for high-viscosity droplets, the influence of the EDLVO forces differs significantly between plug and slug droplets, with a greater tendency to suppress the deformation of slug droplets. (2) For low-viscosity droplets, the EDLVO forces cause an increased degree of droplet concavity and hinder the reconnection of the droplet tail. These findings significantly contribute to our understanding of droplet deformation dynamics within reservoir pores and hold great importance for optimizing droplet control strategies in enhance oil recovery processes.

Effective reverse flotation separation of siderite from hornblende using pentaethoxylated tallow amine as a selective collector

To effectively separate siderite from hornblende, pentaethoxylated tallow amine (PTA) was introduced as a hornblende collector for the first time and its selective collection mechanism was revealed. The flotation results indicated that PTA strongly collected hornblende but not siderite, which enlarged the differences in flotation performance. The measurements of contact angle and adsorption amount suggested that hornblende adsorbed much more PTA than siderite, which greatly enhanced the surface hydrophobicity of hornblende. The analysis of zeta potential and Fourier transform infrared (FTIR) proved that the strong adsorption of PTA on hornblende was attributed to hydrogen bonding and electrostatic attraction. Extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theoretical calculations confirmed that PTA enhanced attractive hydrophobic interaction and electrostatic attraction interaction between hornblende and bubbles, and promoted the adhesion of hornblende to the bubble surface, resulting in a high recovery of hornblende. However, the repulsive interaction between siderite and bubbles prevented siderite from adhering to the bubbles, resulting in poor flotation performance. Consequently, effective separation of hornblende from siderite was achieved by PTA, in which 90.46% of siderite was effectively recovered and 94.26% of hornblende was effectively removed. Thus, PTA can be used as an effective collector to separate siderite from hornblende.

Improving the rheological behavior of alkali-activated slag pastes by using low surface free energy mineral admixtures

This study investigates the effect of low surface free energy mineral admixtures (CaF2-dominated fluorite (FL) and fluorine-containing lithium slag (LS)) on the rheological behavior of alkali-activated slag (AAS) pastes. The fluidity, rheological behavior, surface charge properties and surface free energy properties were tested. The interparticle forces based on extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory were calculated to understand the mechanism for the rheological behavior improvement. The results revealed that both FL and LS could improve the fluidity and decrease the yield stress and plastic viscosity of AAS pastes. Furthermore, the attraction is manifested by the sum of electrostatic, van der Waals, and Lewis acid-base forces, and this value decreases with increasing LF or LS content, implying that the particle dispersion in AAS pastes is improved. Furthermore, observing flocculent structures captured by the metallographic microscope proves the better dispersion of AAS pastes after adding FL and LS. Moreover, incorporating LS or FL decreases the flexural and compressive strengths of AAS mortars.

Insights into the Dispersion Mechanism of Microfine Coal Particles Modified with Naphthalene Sulfonate Formaldehyde Based on EDLVO Theory

Coal water slurry (CWS) fuel prepared using microfine coal particles with a size distribution of 1–10 μm is a promising way to cleanly utilize solid resources in engines, even catering a popular application for clean coal technology. In an attempt to address the problems in coal aggregation in microfine coal water slurry (MCWS), dispersants are used to improve the dispersing status of microfine coal particles. Based on the experimental results and extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory calculations, the role of naphthalene sulfonate formaldehyde (NSF) in MCWS performance was explored. The measurement of the slurry ability of microfine coals demonstrated that the apparent viscosity and yield stress of MCWS were decreased significantly with 1.5% NSF addition, which was consistent with the saturated adsorption value of NSF on microfine coals. Furthermore, the ζ-potential and contact angle of microfine coals were both decreased as a function of the NSF dosage, indicating that a larger electrostatic repulsion force and better wetting ability of the coal surface would be obtained in the presence of NSF. The thickness calculation results showed that the thickness is increased with NSF addition, which is attributed to that the NSF molecule extends into the surrounding solution to form a hydrophilic film. The EDLVO calculations illustrated that the total interaction was turned from an attractive force into a repulsive force in the case of NSF, noting that the better dispersion of microfine coals mainly resulted from the better hydrophilicity of the coal surface modified with NSF. The findings might provide guidance for MCWS preparation by revealing the interaction mechanism of microfine coals modified with NSF.

Comparative study on effects of pH, electrolytes, and humic acid on the stability of acetic and polyacrylic acid coated magnetite nanoparticles

The poor colloidal stability of magnetite nanoparticles (MNPs) limits their mobility and application, so various organic coatings (OCs) were applied to MNPs. Here, a comparative study on the colloidal stability of MNPs coated with acetic (HAc) and polyacrylic acids (PAA) was conducted under varied pH (5.0–9.0) in the presence of different concentrations of cations and anions, as well as humic acid (HA). Comparing the effects of various cations and anions, the stability of both HAc/PAA-MNPs followed the order: Na+ > Ca2+and PO43− > SO42− > Cl−, which could be explained by their adsorption behaviors onto HAc/PAA-MNPs and the resulting surface charge changes. Under all conditions even with more anion adsorption onto HAc-MNPs (0.14–22.56 mg/g) than onto PAA-MNPs (0.04–18.34 mg/g), PAA-MNPs were more negatively charged than HAc-MNPs, as PAA has a lower pHIEP (2.6 ± 0.1) than that of HAc (3.7 ± 0.1). Neither the HAc nor PAA coatings were displaced by phosphate even at considerably high phosphate concentration. Compared with HAc-MNPs, the stability of PAA-MNPs was greatly improved under all studied conditions, which could be due to both stronger electrostatic and additional steric repulsion forces among PAA-MNPs. Besides, under all conditions, Derjaguin-Landau-Verwey-Overbeek (DLVO) explained well the aggregation kinetic of HAc-MNPs; while extended DLVO (EDLVO) successfully predict that of PAA-MNPs, indicating steric forces among PAA-MNPs. The aggregation of HAc/PAA-MNPs was all inhibited in varied electrolyte solutions by HA (2 mg C/L) addition. This study suggested that carboxyl coatings with higher molecular weights and pKa values could stabilize MNPs better due to stronger electrostatic and additional steric repulsion. However, in the presence of HA, these two forces were mainly controlled by adsorbed HA instead of the organic pre-coatings on MNPs.

Structural insights into mechanisms of rapid harvesting of microalgae with pH regulation by magnetic chitosan composites: A study based on E-DLVO model and component fluorescence analysis

Magnetic harvesting of microalgae depends on the interface interactions between microalgal cells and flocculants, and thus it is important to find a reasonable evaluation method understand these interface interactions. In this effort, we discussed the formation mechanism and pH regulation of microalgae magnetic harvesting via magnetic chitosan (Fe3O4@SiO2-CS) synthesized by a micro-emulsion method. The flocculation performances and mechanisms during the harvesting of microalgae by the novel flocculant were evaluated. The synthesis process and structure were determined by XRD, FT-IR, SEM and XPS, and the results indicated that Fe3O4@SiO2-CS was successfully prepared. The collection efficiency of 96.52 % was achieved for Chlorella vulgaris within 3 min using Fe3O4@SiO2-CS with the Fe3O4@SiO2 and CS mass ratio of 1:3 under pH 1.0. Moreover, this study introduced the two-dimension fractal dimension and extended Derjaguin-Landau-Verwey-Overbeek (E-DLVO) model to evaluate the harvesting performances and mechanisms of Fe3O4@SiO2-CS. Experimental results showed that a strong electrostatic interaction was formed under acidic conditions between Fe3O4@SiO2-CS and microalgae cells with D2 = 1.82 (fractal dimension value). The hydrophobic tryptophan-like amino acid was observed in the slime-extracellular polymeric substances (S-EPS) secreted by microalgae. S-EPS was found to be a significant substance to promote harvesting performance when the system was neutral or alkaline. This work provides deeper insights into microalgae harvesting by Fe3O4@SiO2-CS as well as reasonable mechanisms to illustrate the interaction of Fe3O4@SiO2-CS and microalgae under different pH values.

Study on the slurrying properties of semi-coke with dispersants and the interaction between semi-coke particles based on E-DLVO theory

It is essential to prepare the semi-coke water slurry (SCWS) using semi-coke powder in China. The preparation of SCWS can not only alleviate the oil demand, but can also provide a new way to utilize semi-coke powder. In this work, the effects of sodium methylene naphthalene sulfonate (NNO), sodium lignosulfonate (SLS), sodium humate (SH), polycarboxylate (PCE), and compound anion-anion (NNO/PCE), on the slurrying performance of semi-coke water slurry (SCWS) were studied. The results showed that the anionic dispersants increased the concentration of SCWSs, and the slurry exhibited the pseudoplastic rheological behavior of shear thinning. Adding PCE and NNO/PCE in the SCWS could improve its stability and fluidity. The absorbed capacity the microstructure of the particles, surface tension, contact angle, as well as Zeta potential of semi-coke powder were impacted by the addition of anionic dispersants in the SCWS. The results showed that anionic dispersants were adsorbed on the surface of semi-coke by a single-molecular layer. The developments of molecular dynamics simulation indicated that all dispersants should be spontaneously adsorbed on the surface of semi-coke, and the addition of anionic dispersants could reduce the contact angle and surface tension of the semi-char particle surface, increase the hydrophilicity and enhance the electronegativity. Finally, extended Derjaguin–Landau–Verwey –Overbeek (E-DLVO) theory calculations showed that adsorption of dispersants could significantly increase the total interaction energy between semi-coke particles. Finally, a model of the interaction mechanism of the anionic dispersants and semi-coke particles was proposed in this paper.

Is it possible to efficiently and sustainably remove microplastics from sediments using froth flotation?

Microplastics (MPs) contamination in sediments is becoming an intractable environmental issue. Numerous methods are proposed for removing microplastics from aqueous solution, however, the techniques developed for microplastic removal from sediments have been rarely reported. To target the dilemma, this work innovatively applied froth flotation to the MPs removal from beach and lake sediments. Interestingly, we found that the sediment particle adhered to the MPs surfaces resulted in unavailable attachment of air bubbles to MPs surfaces. The effects of pH, salinity, moisture, MPs property, sediment type, and incubation time on MPs flotation were systematically investigated. According to characterization, polyvinyl chloride (PVC) was only covered by aluminosilicate, while acrylonitrile butadiene styrene (ABS) interacted with aluminosilicate and quartz. Analysis of Extended Derjaguin Landau Verwey Overbeek (EDLVO) further confirmed that the stronger electrostatic repulsion between PVC and sediment contributed to the higher energy barrier. However, sediment particles were easier to adhere to ABS with less negative surface potential. Besides, metal ions adsorbed on MPs surfaces might serve as a bridge to link MPs and sediment particles. To improve the flotation performance, a flotation process combined 10 g/ton of sodium oleate could achieve approximately 100% removal of MPs. To further evaluate the applicability of froth flotation, we conducted life cycle assessment (LCA) and economic assessment. Froth flotation outperformed other separation methods in all environment categories. The cost of froth flotation, mostly electricity, was much lower than other removal technologies. Overall, this work provided an effective and sustainable candidate for MPs removal from the sediment environment.

Aggregation of varied organic coated magnetite nanoparticles: Adsorbed mass and thickness of coatings and interactions with natural organic matter

Magnetite nanoparticles (MNPs) with varied organic coatings (OCs) which improved their stability have broad environmental applications. However, the adsorbed amounts and layer thickness of varied OCs onto MNPs during the synthesis were generally not or poorly characterized, and their interactions with natural organic matter (NOM) were still in progress. In this study, acetic (HAc), citric (CA), and polyacrylic acid (PAA) were selected as model OCs, the adsorption behaviors of OCs on MNPs were characterized under varied aqueous C/Fe ratios, and the aggregation behaviors of MNPs with varied OCs (OC-MNPs) at neutral pH (7.0 ± 0.2) with NaCl (5–800 mM) in the presence/absence of NOM were systematically investigated. Under low aqueous C/Fe ratio, the adsorbed amounts of model OCs as –COOH/Fe ratio followed the order: CA ≈ PAA > > HAc. With high aqueous C/Fe ratio, the maximum adsorbed masses of OC-MNPs were similar. The adsorbed layer thicknesses of OC-MNPs were thoroughly characterized using three different methods, all showing that the adsorbed layer of PAA was thicker than that of CA and HAc. Derjaguin–Landau–Verwey–Overbeek (DLVO) and extended DLVO (EDLVO) calculations showed that electrostatic and van der Waals forces were dominant for CA-MNPs and HAc-MNPs stabilization; while steric repulsion played major roles in stabilizing PAA-MNPs, probably due to a thicker PAA layer. In the presence of NOM, stability behaviors of all OC-MNPs were similar, ascribing to the much greater amounts of NOM adsorbed than the OCs, causing greater steric repulsion. This study provides new mechanistic insights which could help better understand the effects of varied OCs on MNPs' colloidal stability.

Recovery of ultrafine scheelite particles by magnetic seeding flocculation and its mechanism

Froth flotation has been proven to be the most efficient mineral processing technology for fine particles. However, it cannot be applied to processing ultrafine particles, especially ultrafine scheelite with sizes of −10 µm, thereby wasting a lot of tungsten resources. In this study, positively-charged and hydrophobic magnetic seeds were fabricated and employed instead of bubbles to capture ultrafine scheelite particles, significantly improving the recovery of the ultrafine particles via magnetic separation. Here, a novel surfactant, lead complexes with benzohydroxamic acid (Pb–BHA), were developed to modify the magnetite. The zeta potential, Fourier-transform infrared (FT–IR) spectroscopy and surface hydrophobicity measurements indicated that Pb–BHA was adsorbed on the magnetite surface, inducing a positively-charged hydrophobic surface. Ultrafine scheelite (−10 µm) was treated with sodium oleate (NaOL) to impart it with negative charges and surface hydrophobicity. The flocculation of magnetite and scheelite is directly observable via scanning electron microscopy (SEM). The extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory was applied to analyse the mutual attraction of two kinds of particles, and the calculation results demonstrated that they aggregated mainly through electrostatic and hydrophobic interactions. This technology affords an alternative solution for processing ultrafine valuable particles.

Application and mechanisms of microalgae harvesting by magnetic nanoparticles (MNPs)

Magnetic harvesting of microalgae by magnetic nanoparticles (MNPs) depends on the interface interactions between microalgal cells and MNPs, therefore it’s important to understand these interface interactions. In this effort, we discussed the application and principles of microalgae magnetic harvesting via MNPs synthesized by the coprecipitation method. MNPs were capable of capturing Nannochloropsis maritima with a harvesting efficiency of 99.5% at a dosage of 0.33 g MNPs/g dry biomass, and the harvesting performance was less dependent on pH values in the range of 5.0–9.0. Treated with ultrasonic chloroform/methanol (2:1, v/v) solvent, the biomass was enriched and MNPs were reactivated and maintained ~60% harvesting effectiveness after 5 cycles. Regardless of the negative zeta potential for both MNPs and microalgae, MNPs-microalgae interactions were explained by surface-enhanced Raman spectroscopy (SERS) and extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory, and phospholipids over microalgal membrane were located as anchors for MNPs adhesion onto the microalgae. This work provided deeper insights into microalgae harvesting by MNPs and offered the powerful SERS technique for unlocking the door to MNPs-microalgae interface interactions.

Collecting behaviors of high internal phase (HIP) emulsion in flotation of ultrafine high-ash content coal slime

ABSTRACT In order to tackle the problems of high oily collector consumption and low separation efficiency associated with ultrafine coal slimes, a new collector named high internal phase (HIP) emulsion was prepared. The flotation results showed that the HIP emulsion could significantly reduce the oil consumption by 90% compared with kerosene. The superior performance of HIP emulsion compared to kerosene was attributed to its higher flocculation ability, which was supported by the kinetic flocculation experiment and the Extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory calculation. The preconditioning experiment showed that the high-shear pulping could greatly promote the overall flotation rate of HIP emulsion, which was due to the enhanced dispersion of the pasty HIP emulsion in the slurry as confirmed by the rheological measurement. The degradation of flocculation ability of HIP emulsion during high-shear stirring may be attributed to the microstructure damage as supported by the conductivity experiments. The HIP emulsions were proved as a potential economic and efficient collector for the beneficiation of ultrafine and high-ash content coal slimes.