Attachment Of Particles Research Articles

Dynamics of particle attachment in a model stirred cell: A new technique to characterize and quantify particle floatability

Floatability evaluation is critical to predicting flotation results and designing a flotation flowsheet. Laboratory-scale flotation cells are commonly used to study particle floatability, but differences in cell design and governing hydrodynamics make extrapolation to industrial scale operations difficult. In this work, a new experimental approach based on particle attachment dynamics is proposed to evaluate particle floatability. This method allows precise control of hydrodynamic conditions, visualization of attachment processes, and direct observation of the bubble surfaces. It is therefore ideal for studying attachment dynamics as a function of collector concentration, particle size and concentration, and propeller speed. In addition, it opens the possibility for future studies of the packing density of the particles at the interface and their selective attachment. By evaluating the time-dependent surface coverage as a function of bubble residence time, we illustrate its ability to predict flotation kinetics within a flotation cell. This innovative technique provides a faster, more versatile means of studying particle floatability and attachment dynamics with practical implications for flotation cell optimization.

Leveraging Crystallization Pathway to Control Structure in Hf0.5Zr0.5O2 Nanoparticles

Hf0.5Zr0.5O2‐based materials have garnered significant attention for applications requiring ferroelectricity at the nanoscale. This behavior arises due to the stabilization of metastable phases at room temperature. However, the synthesis of phase pure Hf0.5Zr0.5O2 remains a challenging problem in both thin films and nanoparticles. Herein, the crystallization of Hf0.5Zr0.5O2 nanoparticles from an as‐synthesized amorphous phase is studied. By tailoring the aggregate nature of the intermediate amorphous nanoparticles via different drying processes, the crystallization pathway can be altered, resulting in significant differences in crystal structure, crystallite size, and crystallite morphology after calcination. X‐ray diffraction (XRD) and Rietveld refinement show the dominant crystallographic phase changes from a monoclinic structure to a cubic structure for samples with decreased aggregation. Samples prepared via freeze drying exhibit the most aggregation control and correspond with the observation of single‐crystalline particle aggregates and branching structures attributed to a crystallization by particle attachment mechanism. Herein, differing crystallization pathways lead to unique crystal morphologies that stabilize the traditionally high‐temperature phases of Hf0.5Zr0.5O2‐based materials that are necessary for functional applications.

Influenza A virus hemagglutinin: from classical fusion inhibitors to proteolysis targeting chimera-based strategies in antiviral drug discovery

The influenza virus glycoprotein hemagglutinin (HA) participates in critical steps of the attachment of viral particles to the host cell membrane receptor and membrane fusion. Due to its crucial involvement in the initial phases of influenza A infections, HA emerges as a promising target in the search of novel drug-like candidates. Given its pivotal role in the early stages of influenza A infections, intense drug discovery efforts have been undertaken to target HA in the past decades. Drug discovery studies mainly rely on preventing the recognition of sialic acid units by the receptor binding site in the globular head (GH) domain, or the conformational rearrangement required for the fusion of viral and cell membranes. In this work, the aim is to summarize the progress made in HA-targeted development of small molecule fusion inhibitors. To this end, attention will primarily be focused on the analysis of the X-ray crystallographic structures of HA bound to fusion inhibitors. Furthermore, this study also aims to highlight the efforts made in exploiting the structural information in conjunction with molecular modeling techniques to discern the mechanism of action of the fusion inhibitors and to assist the design and interpretation of structure-activity relationships of novel lead compounds will be highlighted. The final section will be dedicated to elucidating novel and promising antiviral strategies proceeding from the transformation of known small molecule antivirals in proteolysis targeting chimera (PROTAC)-based targeted protein degradation. This knowledge will be valuable to assist the exploitation of classical and novel antiviral structure-based strategies, together with a deeper understanding of the mechanism of action and minimization of the impact of drug resistance.

Thin liquid film drainage mechanism for bubble − particle attachment interactions in the low-rank coal flotation in the presence of salt and surfactants

Bubble-particle interaction is a fundamental process in froth flotation, where the attachment of bubbles and particles is the crucial process in effective flotation. However, modeling bubble-particle attachment interaction is challenging. This is because advanced methods like AFM (Atomic Force Microscope) characterizations are difficult to quantify hydrophobic interactions reproducibly for air bubbles and non-spherical particles. This study presents a methodology to obtain the hydrophobic force constants for bubble-particle attachment interaction in the presence of salt (KCl) and surfactants (DTAC and SDS). The hydrophobic interaction constants of bubble-particle interactions were acquired from first principles with the Stefan − Reynolds theory and Glembotsky experimental device. The Stefan − Reynolds theory was successfully applied in the determination of the real hydrophobic constants for bubbles and particles interaction in DI water (deionized water). However, in the coexistence of salt and surfactants, the real hydrophobic constants for bubbles and particles interaction cannot be obtained while the fictive hydrophobic constants were acquired with a linear extrapolation method. The results showed that the addition of inorganic salt and surfactants compressed the electronic double layer’s thickness and presented a higher hydrophobic force constant, enhancing the interaction between a bubble and a low-rank coal particle. In addition, the evaluations of hydrophobic constants reveal that the hydrogen bond energy and salt ions destruction energy should be considered to the comprehension of attachment interaction mechanism and the hydrophobic force source for bubble − particle attachment interactions.

Exploring the mechanisms of calcium carbonate deposition on various substrates with implications for effective anti-scaling material selection

The unexpected scaling phenomena have resulted in significant damages to the oil and gas industries, leading to issues such as heat exchanger failures and pipeline clogging. It is of practical and fundamental importance to understand the scaling mechanisms and develop efficient anti-scaling strategies. However, the underlying surface interaction mechanisms of scalants (e.g., calcite) with various substrates are still not fully understood. In this work, the colloidal probe atomic force microscopy (AFM) technique has been applied to directly quantify the surface forces between calcite particles and different metallic substrates, including carbon steel (CR1018), low alloy steel (4140), stainless steel (SS304) and tungsten carbide, under different water chemistries (i.e., salinity and pH). Measured force profiles revealed that the attractive van der Waals (VDW) interaction contributed to the attachment of the calcium carbonate particles on substrate surfaces, while the repulsive electric double layer (EDL) interactions could inhibit the attachment behaviors. High salinity and acidic pH conditions of aqueous solutions could weaken the EDL repulsion and promote the attachment behavior. The adhesion of calcite particles with CR1018 and 4140 substrates was much stronger than that with SS304 and tungsten carbide substrates. The bulk scaling tests in aqueous solutions from an industrial oil production process showed that much more severe scaling behaviors of calcite was detected on CR1018 and 4140 than those on SS304 and tungsten carbide, which agreed with surface force measurement results. Besides, high salinity and acidic pH can significantly enhance the scaling phenomena. This work provides fundamental insights into the scaling mechanisms of calcite at the nanoscale with practical implications for the selection of suitable anti-scaling materials in petroleum industries.

Colloid Transport and Retention in Constricted Tube Pore Spaces With Diverse Geometries and Orientations

AbstractColloidal contaminants infiltrate and can be attached onto grain surfaces of soils and aquifers, where they may persist. In this study, Lagrangian particle tracking is used to investigate particle trajectories and attachment in pore and fracture spaces modeled as three‐dimensional constricted tubes with diverse geometries and orientations relative to gravity. A comprehensive force balance arising from hydrodynamic drag and lift, gravitational settling, Brownian motion, and attractive DLVO interactions is simulated. Results show that the collection efficiency η is primarily governed by the dimensionless settling number 𝑆, representing the relative dominance of gravitational over hydrodynamic forces experienced by the particles. High‐𝑆 scenarios have larger η and are more sensitive to pore orientation, while low‐𝑆 scenarios are more sensitive to pore geometry. For all scenarios but especially low‐S scenarios, the majority of colloid attachment occurs near pore extremities, where fluid velocities are low, such that mechanical remobilization of particles attached is improbable. In low‐𝑆 scenarios, particles may spread and become immobilized at greater distances from the contamination source owing to lower η, are harder to mechanically remobilize as they attach more disproportionately at pore extremities, and have trajectories more sensitive to minor forces, rendering their environmental fates complex. Characterizing the collection efficiency and deposition morphology for various pore space geometries and orientations is crucial in understanding particle fate and developing continuum‐scale models of colloid transport in real soils, where pore spaces are heterogeneous and advection paths are tortuous.

Methods for the Characterization of the Colloidal Properties of Bacterial Membrane Vesicles.

Bacterial membrane vesicles (BMVs) are extracellular vesicles secreted by either Gram-positive or Gram-negative bacteria. These BMVs typically possess a diameter between 20 and 250nm. Due to their size, when these BMVs are suspended in another medium, they could be constituents of a colloidal system. It has been hypothesized that investigating BMVs as colloidal particles could help characterize BMV interactions with other environmentally relevant surfaces. Developing a more thorough understanding of BMV interactions with other surfaces would be critical for developing predictive models of their environmental fate. However, this bio-colloidal perspective has been largely overlooked for BMVs, despite the wealth of methods and expertise available to characterize colloidal particles. A particular strength of taking a more colloid-centric approach to BMV characterization is the potential to quantify a particle's attachment efficiency (α). These values describe the likelihood of attachment during particle-particle or particle-surface interactions, especially those interactions which are governed by physicochemical interactions (such as those described by DLVO and xDLVO theory). Elucidating the influence of physical and electrochemical properties on these attachment efficiency values could give insights into the primary factors driving interactions between BMVs and other surfaces. This chapter details methods for the characterization of BMVs as colloids, beginning with size and surface charge (i.e., electrophoretic mobility/zeta potential) measurements. Afterward, this chapter will address experimental design, especially column experiments, targeted for BMV investigation and the determination of α values.

Surface Charging Characteristics of Rotating Asteroids in the Solar System

The attachment and movement of charged particles in the space plasma environment can result in observable potentials on the asteroid surface, this surface charging phenomenon has been extensively studied. However, the influence of asteroid's rotation on surface charging and the surrounding plasma is not yet fully understood. Traditional methods using numerical integration and PIC have slow computation speeds, and mainly focus on the charging mechanisms of static asteroids. In this study, we established a multi-scale model based on neural networks and the finite element method, improving simulation efficiency and enabling three-dimensional dynamic simulations of rotating asteroids. Simulation results for asteroids with different rotation periods indicate that the maximum and minimum surface potentials decrease as the rotation period increases. The minimum potential on the nightside decreases from -4.96V with one-hour period to -5.97V with one-week period. For asteroids with longer periods, this decreasing trend slows down, with the increase from one week to half a year causing changes of 0.001V in potential. Because strong electric field near the the terminator accelerates electrons and ions, electrons respond more promptly to the electric field because of their much higher mobility and diffusion coefficient, exhibiting a more severe accumulation phenomenon than ions, then decrease the surface potential. This phenomenon is most pronounced when the solar wind is obliquely incident, where the subsolar point is close to the terminator, resulting in the strongest electric field. This downward trend becomes more when the period exceeds one week, specifically, the asteroid and plasma have enough time to reach equilibrium at all angles. During the passage of solar storms, the surface potentials at different stages vary significantly, with potential differences caused by rotation periods reaching hundreds of volts. Surface minerals also play a role, plagioclase is the most sensitive mineral among those explored, while ilmenite appears indifferent to changes in rotation periods. Understanding the surface charging of asteroids under various rotation periods and angles is crucial for further research on solar wind plasma and asteroid's surface dust motion, providing a reference for the safe landing and exploration of asteroids.

Aluminosilicate colloidal gels: from the early age to the precipitation of zeolites.

Aluminosilicate hydrogels are often considered to be precursors for the crystallisation of zeolites carried out under hydrothermal conditions. The preparation of mechanically homogeneous aluminosilicate gels enables the study of these materials through bulk rheology and observation of the aging dynamics until the precipitation of crystalline zeolites. The first part of this study deals with the establishment of ternary state diagrams, in order to identify the range of chemical formulations that enable preparation of single-phase homogeneous gels. Then, by studying the viscoelastic moduli during the gelation reaction, and by yielding the gel under large deformation, we propose an empirical law considering the partial order of reaction on each chemical element, to predict the gelation time according to the chemical formulation. The scaling behavior of the elastic properties of this colloidal gel shows a transition from a strong link behavior to a weak link regime. Long term aging results in the shrinkage of the gel, accompanied by syneresis of interstitial liquid at the surface. Zeolites precipitate through crystallisation by a particle attachment mechanism, when thermodynamic equilibrium is reached. The stoichiometry of the precipitated zeolites is not only consistent with the concentration of the remaining species in the supernatant but, surprisingly, it is also very close to the partial order of the reaction of the chemical elements involved in the determination of the critical gel point. This indicates a strong correlation between the morphology of the soft amorphous gel network that is formed at an early age and those of the final solid precipitated crystals.

Carbon nanotube microbeads for enhanced gas heating in a fluidized bed solar air collector

A novel approach utilizing vertically-aligned carbon nanotube (VACNT) as solar heat absorbers is proposed for efficient gas heating in a concentrated fluidized bed solar air collector (FBSAC). The VACNT powder was fabricated into CNT beads suitable for fluidized bed applications through macronization and densification. The CNT bead showed an increase in size and a 6.8 times increase in apparent density. The increase in sphericity and a significant decrease in the repose angle indicated improved particle fluidity. The prepared CNT beads demonstrated an absorptivity similar to VACNT, along with increased thermal conductivity and specific heat capacity, indicating superior thermophysical properties compared to conventional CNTs. Moreover, the reduced electrostatic charge generation minimizes the issue of particle attachment on the transmission window. The heat absorption characteristics of air in FBSAC (50 mm i.d. × 150 mm height) with CNT microbeads were determined. The FBSAC achieved a maximum gas temperature of approximately 150 °C. The CNT bead achieved a higher temperature difference of the gas per irradiance and a more comprehensive operating range of gas velocities up to 0.16 m/s than VACNT. The FBSAC with CNT beads exhibited a maximum thermal efficiency of 30.3 % and higher efficiency of 8–21 % than CNT powders at gas velocity of 0.11 m/s. A correlation was proposed to predict the thermal efficiencies of the FBSACs with different particles from dimensionless numbers considering particles dynamics and thermophysical properties.

Spatio-temporally resolved dynamical transitions in flow of Pickering emulsions through porous media

Pickering emulsions, when formulated using suitable particles, can exhibit both droplet–droplet and droplet–grain attraction while flowing through porous media. Despite their potential impact on the flow behavior of Pickering emulsions, the underlying mechanisms and dynamics of these attractions are not yet fully understood. To address this, we developed a custom-built micro-sandpack apparatus coupled with confocal microscopy to simultaneously measure the pressure gradient and visualize the flow patterns of emulsions. Our results reveal that the flow of attractive Pickering emulsions displays large-amplitude oscillations in the pressure gradient which cannot be explained using traditional models (e.g. geometric straining, filtration, or continuum). We have identified localized flow patterns characterized by particle attachment and deposition to nearby grains, droplet deposition, jamming of droplets within the throat, and droplet release. These patterns occur cyclically, corresponding to the gradual and rapid changes in the overall pressure gradient. Photonic force microscopy confirmed the strength of droplet–droplet attraction and revealed the underlying cause of this flow dynamics: the formation of chains of nanoparticles that tether droplets together. Our work provides new insights into the mechanism for self-regulated morphological evolution of Pickering emulsion during flow through porous media, resulting from the combined effects of droplet jamming/straining (in line with prior observations of emulsion flow through porous media) and particle deposition (typically observed in the flow of particulate suspensions).

Molecular-level study of hydrophobic interactions during low-rank coal particle-bubble attachment

Particle-bubble attachment is a crucial part of coal and mineral flotation processes. The attachment of two different hydrophobic low-rank coal particles to bubble surface were simulated by a non-equilibrium molecular simulation method. Both particles were subjected to water film drainage resistance when approaching the bubble. Eventually, CPC (low-rank Coal Particle with mixed Collector adhered) jumped in and attached to bubble, but CP (low-rank Coal Particle) had only repulsive effect with bubble. The surface water film of CPC generated tiny hole under the entropy effect of water molecule rearrangement, and the presence of gas–water and oil–water interfacial tension promoted the rapid expansion of the hole until the water film rupture. The critical rupture thickness of the water film on CPC surface was about 1 nm and the rupture was completed in a very short time of 0.4 ns. The CPC jumped in and attached to the bubble surface under the action of oil–water interfacial tension. This suggests that the long-range hydrophobic force originates from the combined action of various interfacial tensions. Our results demonstrate the important role of interfacial tension in the attachment of hydrophobic particle to bubble, and contribute to the connection between microscopic and macroscopic mechanism of particle-bubble attachment.

Geometric frustration of hard-disk packings on cones.

Conical surfaces pose an interesting challenge to crystal growth: A crystal growing on a cone can wrap around and meet itself at different radii. We use a disk-packing algorithm to investigate how this closure constraint can geometrically frustrate the growth of single crystals on cones with small opening angles. By varying the crystal seed orientation and cone angle, we find that-except at special commensurate cone angles-crystals typically form a seam that runs along the axial direction of the cone, while near the tip, a disordered particle packing forms. We show that the onset of disorder results from a finite-size effect that depends strongly on the circumference and not on the seed orientation or cone angle. This finite-size effect occurs also on cylinders, and we present evidence that on both cylinders and cones, the defect density increases exponentially as circumference decreases. We introduce a simple model for particle attachment at the seam that explains the dependence on the circumference. Our findings suggest that the growth of single crystals can become frustrated even very far from the tip when the cone has a small opening angle. These results may provide insights into the observed geometry of conical crystals in biological and materials applications.

Rab32, a novel Rab small GTPase from orange-spotted grouper, Epinephelus coioides involved in SGIV infection

Rab32 is a member of the Rab GTPase family that is involved in membrane trafficking and immune response, which are crucial for controlling pathogen infection. However, the role of Rab32 in virus infection is not well understood. In this study, we focused on the regulation of Rab32 on virus infection and the host immunity in orange-spotted grouper, Epinephelus coioides. EcRab32 encoded a 213-amino acid polypeptide, which shared a high sequence identity with other Rab32 proteins from fishes to mammals. In healthy orange-spotted grouper, the mRNA of EcRab32 was expressed in all the detected tissues, with the more expression levels in the head kidney, liver and gill. Upon SGIV infection, the expression of EcRab32 was significantly up-regulated in vitro, indicating its potential role in viral infection. EcRab32 was observed to be distributed in the cytoplasm as punctate and vesicle-like structures. EcRab32 overexpression was found to notably inhibit SGIV infection, while the interruption of EcRab32 significantly promoted SGIV infection. In addition, using single particle imaging analysis, we found that EcRab32 overexpression prominently reduced the attachment and internalization of SGIV particles. Furthermore, the results demonstrated that EcRab32 played a positive role in regulating the interferon immune and inflammatory responses. Taken together, these findings indicated that EcRab32 influenced SGIV infection by regulating the host immune response, providing an overall understanding of the interplay between the Rab32 and innate immunity.

Study on Saccharide-Glucose Receptor Interactions with the Use of Surface Plasmon Resonance.

The aim of this study was to investigate the process of attachment of saccharide particles differing in degree of complexity to cell receptors responsible for transport of glucose across the cell membrane (GLUT proteins). This phenomenon is currently considered when designing modern medicines, e.g., peptide drugs to which glucose residues are attached, enabling drugs to cross the barrier of cell membranes and act inside cells. This study aims to help us understand the process of assimilation of polysaccharide nanoparticles by tumour cells. In this study, the interactions between simple saccharides (glucose and sucrose) and dextran nanoparticles with two species of GLUT proteins (GLUT1 and GLUT4) were measured using the surface plasmon resonance technique. We managed to observe the interactions of glucose and sucrose with both applied proteins. The lowest concentration that resulted in the detection of interaction was 4 mM of glucose on GLUT1. Nanoparticles were measured using the same proteins with a detection limit of 40 mM. These results indicate that polysaccharide nanoparticles interact with GLUT proteins. The measured strengths of interactions differ between proteins; thus, this study can suggest which protein is preferable when considering it as a mean of nanoparticle carrier transport.

Effect of particle shape on bubble-particle attachment behavior: Roles of surfaces, edges, and vertexes

It has been understood through many studies that particle shape is important in terms of particle adhesion to air bubbles in flotation. However, there are many questions yet to be answered. Whether the surface of the particle or its sharp corners is effective is only one of the issues that need to be better understood. Therefore, this study aims to delve deeper into the fundamental studies on the role of particle's geometry (surface, edges, and vertex) in their flotation behavior by investigating the attachment of spherical, cylindrical, triangular prismatic, and cubic particles to air bubbles based on their attachment efficiency, settling velocity, collision efficiency, and induction time. Bubble-particle attachment test results inferred that the attachment efficiency was in the order of cubic > triangular > cylindrical > spherical. In addition, it was found that the induction time of the spherical surface decreased from 37 ms to 15 ms with increasing collector concentration, while the induction time of the edged cubic particle decreased from 8 ms to 2 ms. This was attributed to the fact that the edge facilitates the drainage, thinning, and rupture of the water film between the bubble and the particle, thereby increasing the attachment efficiency. Finally, it has also been observed that the three-phase contact line of the cube particle is larger than that of the spherical particle, which improves the attachment stability and reduces detachment efficiency. The results obtained in this study shed light on the fact that the shape of the particles fed to flotation can be produced by using a suitable mill and thus higher flotation efficiency can be achieved with lower collector concentration.

PM2.5 and PM10 adsorption onto filters and surfaces functionalized with calcium carbonate particle assembly

Existing air-cleaning solutions more and more fail to tackle the escalating air pollution by particle manner. Here, a novel air-cleaning method is proposed based on assembled porous CaCO3 particle arrays on a glass surface and on air filter fibers. The composition and crystallographic structure of the CaCO3 particles are analyzed using advanced X-ray scattering techniques and Fourier transform infrared analysis. The strength of particle attachment to the glass surface under environmental conditions and the CaCO3 particles particulate matter (PM) interaction is studied by atomic force microscopy. The air cleaning process is studied by the exposure of these assembled particles to polluted air. It is shown that the adsorption of particulate matter is facilitated which affects the filtration efficiency. Biocompatible CaCO3 microparticle arrays effectively adsorb airborne particulate matter. CaCO3-coated air filters demonstrate over 10 times increased efficiency for particles smaller than 1 µm, enhancing the filters' quality factor by up to 22 times. Summarizing, this research offers a promising solution to combat air pollution and lays the groundwork to develop more advanced and efficient air purification technologies. SynopsisAssembled calcium carbonate particle arrays have been used to clean particulate matter from the air.

Surface-induced oxidation of Mn(II) and crystallization of manganese (hydr)oxides on clay minerals

The crystallization induced by foreign surfaces is crucial for various geological and geochemical processes on Earth’s surface, but the underlying mechanisms remain poorly understood. In this study, we investigated the oxidation of Mn(II) and crystallization of manganese (hydr)oxides (MnOx) on kaolinite (Kln) and montmorillonite (Mnt), two prevalent clay minerals in the nature with different structures and properties. Our results reveal that both Kln and Mnt surfaces can catalyze the heterogeneous oxidation of Mn(II) and crystallization of MnOx, but the crystallization pathways, as well as the morphologies and phases of the products, are distinct. The Mn(II) adsorbed by Kln’s outer surfaces were oxidized to Mn(III) and crystallized into MnOx, which were identified as hausmannite and manganite nanoaggregates. In contrast, the adsorption of Mn(II) and its oxidation to Mn(III) occurred both on the outer surfaces and interlayer spaces of Mnt, while the crystallization of MnOx only occurred on the outer surfaces, indicating that the confined volume of Mnt’s interlayer spaces can inhibit the crystallization of Mn(II/III) cations. Hausmannite emerged as the first MnOx product on Mnt, followed by groutite and manganite, all of which were well-dispersed fine nanoparticles. Additionally, the Si(IV) ions dissolved from Mnt participated in the formation of rhodonite with Mn(II), but this mineral phase was absent on Kln. Notably, MnOx nanoaggregates on Kln were assembled by a group of MnOx nanoparticles with slight misorientations among them, and the misorientations of these nanoparticles can gradually recover over time, indicating the contribution of crystallization by particle attachment (CPA). On the other hand, the strong electrostatic interactions between MnOx nanoparticles and Mnt surfaces reduced the mobility of nanoparticles, inhibiting their growth via CPA. Above results demonstrate the significant influence of the confinement effect and surface interactions on the surface-induced crystallization process of MnOx. These findings can also advance our knowledge about the role of clay minerals in Mn(II) oxidation and MnOx formation, and offer a possible explanation for the presence of various MnOx with diverse structures in the nature.

Effect of energy input on flotation of particles with different sizes: Perspective of hydrodynamics characteristics

By employing a torque sensor to measure energy input in a flotation machine, this paper investigates the flotation behavior of modified quartz particles with different sizes but similar surface hydrophobicity under various energy input conditions. Numerical simulations of the mechanical flotation machine were conducted to obtain the fluid dynamic characteristics including the flow velocity, turbulence kinetic energy, and turbulent eddy scale. With the flotation results and numerical simulations combined, the potential collision, attachment, and detachment behaviors of fine particles (―45 µm), intermediate particles (45―74 µm), and coarse particles (74―125 µm) were analyzed. The results demonstrate that under different conditions of energy input, the recovery of intermediate-sized particles was optimal for the above size fractions. As the particle size increases, the energy input required to achieve optimal recovery decreases. The flotation rate constants increase nearly linearly with energy input. Compared to the medium-sized particles in the range of 45―74 µm, finer and larger particles exhibit lower floatability. When the energy input exceeds a certain range, no stagnation zone is observed. The rupture of bubble-particle aggregates becomes more pronounced, which may be a reason why flotation recovery begins to decrease. Increasing energy input enhances turbulence energy dissipation and reduces the Kolmogorov turbulence length scale, in this study, the ―45 µm, 45―74 µm, and 74―125 µm particle sizes reached the optimal flotation performance at dp / η values of 1.35, 1.83, 2.54, respectively. The particle diameter-to-integral length scale ratio (dp/L) is also discussed as an important parameter for turbulent dispersion.

Microbial pyrite formation: mineral morphology and precipitation kinetics

Pyrite (FeS2) is a mineral of wide interest due to its importance in the biogeochemical cycling of Fe and S, which is tied to those of carbon and other trace metals and nutrients. The mineral itself has potential applications as biosignatures, for environmental remediation and as semiconductors. Despite being a common authigenic mineral in sedimentary environments, most laboratory-based experiments have failed to form pyrite in microbial cultures at ambient temperatures. To fill this knowledge gap, we have employed cultivation-based approaches, using different combinations of microorganisms (Fe(III)- and S0-reducers; S0-disproportionaters) and initial Fe and S sources to identify the conditions that are optimal for pyrite formation. Scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffraction (XRD) demonstrate that pyrite is not formed within ~3 years at circumneutral pH when oxidants (e.g., Fe(III) minerals, elemental sulfur, S0) are exhausted. In contrast, pyrite is formed within months when S0 and Fe(III) minerals are both present. The precipitation timescale is consistent with those expected in sedimentary environments Mansor and Fantle 2019), albeit some natural pyrite framboids are expected to form even faster Rickard 2019). The pyrite crystals formed in our experiments are in the low micrometer range, with either a spherical or euhedral morphology depending on the initial crystallinity of the supplied Fe(III) minerals. Framboids are not formed in our system, perhaps due to the relatively slow precipitation kinetics. Time-based sampling indicates mackinawite (FeS) as the first product, with rare (and minor) detection of greigite (Fe3S4) and vivianite [Fe3(PO4)2.8H2O]. We hypothesize that pyrite formation and growth proceed mainly from transformation of precursor minerals, with potential contributions via dissolution-precipitation and/or particle attachment pathways. Our preliminary study is the first step in optimizing a system for microbial pyrite formation, with the intention of investigating the properties and the reactivity of the mineral with implications for biosignatures, environmental remediation and industrial applications.