Simulation of solute transportation within porous particles during the bioleaching process

A mathematical model, accounting for the sulfuric acid and ferric ions diffusion and the copper sulfide mineral leaching process, was developed for an ore particle by considering its porous structure. It was simulated with the simulation tool COMSOL Multiphysics. The simulation results show that the highest acid and ferric concentrations near the particle surface are apparent, while the concentrations in the central particle increase slightly as the less-porous ore core with low permeability prevents the oxidation from penetrating. The extraction of the mineral near the particle surface is the maximum, mainly because of ample sulfuric acid, ferric ions, bacteria, and oxygen available for the leaching process. Because of low oxidation concentration in the central part of the particle, the reaction rate and copper sulphide conversion are small. The simulation shows good agreement with the experimental results.

Experimental Testing of Cellular Construction Materials Containing Flax Particles

The feasibility of a sustainable non-autoclaved cellular concrete,based on flax vegetable co-products,for the production of usable specimen in the lightweight construction field,has been investigated experimentally.The produced specimen,containing various volume ratios of flax particles with respect to preformulatd Tradical PF70 lime binder of 0,1,and 2,were lightened by creating a porous structure in the matrix through the addition of 0.3%wt.Aluminium powder(able to react with calcium hydroxide from the binder and result in microscopic air-bubbles).Fresh and hardened specimen properties,including hydration,fresh density,porosity,hardened density,compressive and flexural strengths,toughness energy,and dry thermal conductivity at different temperatures,were assessed for varying flax-to-binder ratios.Results have shown that the addition of Aluminum powder leads to restrain the setting time delay of binder-based lime.Moreover,the hardened material displays a significant decrease in specimen density,thereby resulting in a compressive strength level compatible with that required in the cellular construction materials sector.Results also highlighted the ability of added flax to induce a change in the specimen from brittle to ductile behavior.Moreover,a high degree of thermal insulation can be achieved,which makes the cellular specimen based on flax particle suitable as insulated-bearing walls material.

Kinetic performance comparison of fully and superfcially porous particles with sizes ranging between 2.7 lm and 5 lm: Intrinsic evaluation and application to a pharmaceutical test compound

The reintroduction of superficially porous particles has resulted in a leap forward for the separation performance in liquid chromatography. The underlying reasons for the higher efficiency of columns packed with these particles are discussed. The performance of the newly introduced 5 p.m superficially porous particles is evaluated and compared to 2.7 pm superficially porous and 3.5 and 5 p.m fully porous columns using typical test compounds （alkylphenones） and a relevant pharmaceutical compound （impurity of amoxicillin）. The 5 I.tm superficially porous particles provide a superior kinetic performance compared to both the 3.5 and 5 Ixm fully porous particles over the entire relevant range of separation conditions. The performance of the superficially porous particles, however, appears to depend strongly on retention and analyte properties, emphasizing the importance of comparing different columns under realistic conditions （high enough k） and using the compound of interest.

Continuum percolation of porous media via random packing of overlapping cube-like particles

The pore configuration in porous medium is assumed to be the randomly distributed cube-like particles which can overlap each other in the periodic cubic domain, and the impact of particle characteristics on the percolation property of these cube-like particle packing systems is analyzed.Firstly, by combining the percolation models and finite-size scaling analysis, three numerical parameters(i.e., percolation transition width △L, local percolation threshold ψ_c(L), and correlation length exponent v) for the cube-like particle systems with shape parameter s in[1.0, +∞] are derived successively. Then, based on the relation between the percolation thresholdψ_c in infinite space and the local percolation threshold ψ_c(L), the corresponding ψ_c with s in[1.0, +∞] are further determined. It is shown from the study that the characteristics of cube-like particles have significant influence on the global percolation threshold ψ_c of the particle packing systems. As the parameter s increases from 1.0 to +∞, the percolation threshold ψ_c will go down persistently. When the surface of cube-like particles is cubical and spherical, respectively, the minimum and maximum thresholds ψ_c,min and ψ_c,max are obtained.

Simulation of the relationship between porosity and tortuosity in porous media with cubic particles

Tortuosity is an important parameter used in areas such as vascular medicine,neurobiology,and the field of soil permeability and diffusion to express the mass transport in porous media.It is a function of the porosity and the shape and distribution of particles.In this paper,the tortuosity of cubic particles is calculated.With the assumption that the porous medium is homogeneous,the problem is converted to the micro-level over a unit cell,and geometry models of flow paths are proposed.In three-dimensional（3D） cells,the flow paths are too complicated to define.Hence,the 3D models are converted to two-dimensional（2D） models to simplify the calculation process.It is noticed that the path in the 2D model is shorter than that in the 3D model.As a result,triangular particles and the interaction are also taken into consideration to account for the longer distance respectively.We have proposed quadrate particle and interaction（QI） and quadrate and triangular particle（QT） models with cubic particles.Both models have shown good agreement with the experimental data.It is also found that they can predict the toruosities of some kinds of porous media,like freshwater sediment and Negev chalk.

Enhanced removal of ultra fi ne particles from kerosene combustion using a dielectric barrier discharge reactor packed with porous alumina balls

Ultrafine particles(UFPs)are harmful to human beings,and their effective removal from the environment is an urgent necessity.In this study,a dielectric barrier discharge(DBD)reactor packed with porous alumina(PA)balls driven by a pulse power supply was developed to remove the UFPs(ranging from 20 to 100 nm)from the exhaust gases of kerosene combustion.Five types of DBD reactors were established to evaluate the effect of plasma catalysis on the removal efficiency of UFPs.The influences of gasflow rate,peak voltage and pulse frequency of different reactors on UFPs removal were investigated.It was found that a high total UFP removal of 91.4%can be achieved in the DBD reactor entirely packed with PA balls.The results can be attributed to the enhanced charge effect of the UFPs with PA balls in the discharge space.The UFP removals by diffusion deposition and electrostatic attraction were further calculated,indicating that particle charging is vital to achieve high removal efficiency for UFPs.

Flow and Heat Transfer of a Dusty Williamson MHD Nanofluid Flow over a Permeable Cylinder in a Porous Medium

This study investigates the flow and heat transfer of dusty Williamson (MHD) Nanofluid flow over a stretching permeable cylinder in a porous medium. Dusty Williamson Nanofluid was considered due to its thermal properties and potential benefits of increasing the heat transfer rate. Firstly, partial differential equations are transformed into coupled non-linear ordinary differential equations through a similarity variables transformation. The resulting set of dimensionless equations is solved analytically by using the Homogony Perturbation Method (HPM). The effects of the emerging parameters on the velocity and temperature profiles as well as skin-friction coefficient and Nusselt number are publicized through tables and graphs with appropriate discussions. The present result has been compared with published papers and found to be in agreement. To the best of author’s knowledge, there has been sparse research work in the literature that considers the effect of dust with Williamson Nanofluid and also solving the problem analytically. Therefore to the best of author’s knowledge, this is the first time analytical solution has been established for the problem. The results revealed that the fluid velocity of both the fluid and dust phases decreases as the Williamson parameter increases. Motivated by the above limitations and the gaps in past works, therefore, it is hoped that the present work will assist in providing accurate solutions to many practical problems in science, industry and engineering.

Experimental and theoretical study of coupled influence of flow velocity increment and particle size on particle retention and release in porous media

Experimental and theoretical studies were carried out to investigate the coupled influence of flow velocity increment and particle size on the retention and release of particles in porous media. Particle release was examined through measurement of changes in effluent particle concentrations, and particle retention was assessed through measurement of the final spatial distribution of particles remaining in the soil columns after the experiments. Particle release curves were simulated using a convection-dispersion model that includes the instantaneous release of the line source. Fitted model parameters were used to gain insights into the mechanisms that control particle retention and release. When the flow velocity increment was 0.0435 cm/s, the peak concentration of particles decreased with increasing flow velocity until the latter approached a critical level, beyond which the particle concentration increased. Particle wedging and fouling were considered the primary mechanisms that controlled particle retention and release beyond the critical particle velocity. In experiments with large flow velocity increments, small particles exhibited lower particle mass fraction than large particles as particle wedging and fouling increased with particle size. The range of longitudinal dispersivity decreased with an increasing particle size and flow velocity increment. Moreover, the mean particle velocity increased with the mean interstitial fluid velocity. The mean particle velocity profile was highly sensitive to the particle size at low velocity increments. In general,particle release rates increased with both flow velocity and velocity increment. The mass of the released particles provides further evidence that particle wedging and fouling are the major factors that control particle release in sand columns.

Dynamic pore wetting and its effects on porous particle flotation:A review

The dynamic pore wetting plays an important role in the flotation of porous particle,such as coal,fly ash,gasification slag,etc.Water phase get into the pores and crevices on the surface and inside of the particles,creating a dense water layer that covers their surface and decreases their floatability.It is important to reduce the adverse impact of dynamic pore wetting on the flotation performance of porous particles.Thus,this review is to highlight the dynamic pore wetting behavior,and its role in the porous particle flotation as well as the proposed regulation methods to weaken the pore wetting.The characterization approaches of the dynamic pore wetting are discussed including the optical method for the capillary and the nuclear magnetic resonance(NMR)method for porous particles.The surface tension and viscosity of liquid significantly affect the pore wetting degree of porous particles during the 60 min wetting process.Pre-wetting time adjustment,pore compression,pore filling,and hydrophobic modifications are introduced to decrease the wetting percentage of pores in porous particles and further improve their flotation performance.This critical review will provide some guidance for studying the dynamic wetting behavior of pores and enhancing the floatability of porous particles.

STUDY ON PREPARATION OF UNIFORM POLYSTYRENE HOLLOW PARTICLES

Uniform polystyrene hollow particles were prepared successfully by employing SPG (Shirasu porous glass) emulsification technique. The oil phase composed of monomer [styrene (St) and N,N’-dimethylamino ethylmethacrylate (DMAEMA)], hexadecane (HD) and initiator was permeated through the uniform pores of SPG membrane into the aqueous phase (containing stabilizer, emulsifier and water-soluble inhibitor ) by a gas pressure to form uniform droplets. The droplets were then polymerized at 70℃. It was found that the hollow particles were obtained by adding a small amount of DMAEMA into the oil phase and by using NaNo2 as the water-soluble inhibitor, while only one-hole particles were obtained without adding DMAEMA, or when using diaminophenylene (DAP) or hydroquinone (HQ) as the inhibitor. The formation mechanism was discussed by the view of interfacial tensions between polymer and aqueous phase, HD and aqueous phase, and HD and polymer. Further more, it was found that hollow particles can be obtained even when DMAEMA content in the oil phase was very low, by increasing HD to high value.

INFLUENCES OF ACID POST-TREATMENT ON THE MORPHOLOGY OF SOAP-FREE P(MMA-EA-MAA)PARTICLES PREPARED BY SEEDED EMULSION POLYMERIZATION

Soap-free poly（methyl methacrylate-ethyl acrylate-methacrylic acid） latex particles with narrow size distribution were synthesized by seeded emulsion polymerization, and the porous particles were created by a stepwise alkali/acid treatment method. Effects of acid treatment conditions on the particle morphology were investigated. Results show that one to three pores were formed inside most of particles after post-treatment. At pH 7.0, when the treatment temperature was lower than 70℃, the size of particles and the volume of pores remained almost unchanged, and these two values increased significantly when the temperature was higher than 70℃. Both the particle size and the pore volume decreased with the increase of initial pH value and treatment time in the acid treatment. As the pH was below 4.0 and the treatment time was longer than 180 min, the particles shrunk in size.

Preparation of Porous Silicone Resin Sheet with Phase Inversion in Parallel with Non Solvent Induced Phase Separation and Application to Hollow Particle Formation

We have tried to prepare the porous silicone resin sheet with the phase inversion method in parallel with the non solvent induced phase separation method. In the experiment, ethyl acetate and water were adopted as a good solvent and a poor solvent for silicone resin, respectively and ethyl alcohol as an amphiphilic solvent was used to increase the solubility of ethyl acetate in water and decrease the interfacial tension by mass transfer from water to ethyl acetate. The concentration of silicone resin in ethyl acetate and the oil soluble surfactant species were changed. Increasing the concentration of silicone resin could depress coalescence between the water droplets in the (W/O) dispersion and increase the porosity and pore number density of silicone resin sheet. Span 80 among the oil soluble surfactant species made the porosity and pore number density larger. The effect of physical proparties of liquids concerned on the porosity and pore number density was discussed on the basis of dispersing behavior of liquid droplets in the liquid-liquid dispersion. The hollow silicone resin particles could be prepared by applying the preparation method presented here.

Deep bed filtration model for cake filtration and erosion

Many phenomena in nature and technology are associated with the filtration of suspensions and colloids in porous media. Two main types of particle deposition,namely, cake filtration at the inlet and deep bed filtration throughout the entire porous medium, are studied by different models. A unified approach for the transport and deposition of particles based on the deep bed filtration model is proposed. A variable suspension flow rate, proportional to the number of free pores at the inlet of the porous medium, is considered. To model cake filtration, this flow rate is introduced into the mass balance equation of deep bed filtration. For the cake filtration without deposit erosion,the suspension flow rate decreases to zero, and the suspension does not penetrate deep into the porous medium. In the case of the cake filtration with erosion, the suspension flow rate is nonzero, and the deposit is distributed throughout the entire porous medium. An exact solution is obtained for a constant filtration function. The method of characteristics is used to construct the asymptotics of the concentration front of suspended and retained particles for a filtration function in a general form. Explicit formulae are obtained for a linear filtration function. The properties of these solutions are studied in detail.

Microwave absorption performance of porous carbon particles modified by nickel with different morphologies

In this work,porous carbon particles were prepared from wheat flour by pyrolysis and activation.Through the subsequent coprecipitation and electroless plating,the surface and pores of carbon particles were modified by nickel-rich particles with different morphologies.Several loss mechanisms,including dielectric loss,magnetic loss,multiple reflection and scattering loss,were used to assess the attenuation ability to incident electromagnetic waves of these composite particles.The result shows that the chain-shaped morphology of nickel can provide the highest dielectric loss.Under the filler loading of 20 wt.%,the minimum reflection loss(RL min)reached-38.42 dB at 13.2 GHz,and the_(max)imum effective absorption bandwidth(EAB_(max))was 5.2 GHz with a matching thickness of 2 mm.The excellent performance of the composite particles is attributed to the synergistic effect of outstanding impedance matching and supe-rior electromagnetic loss ability caused by the chain structure.The result shows that the morphology of modifiers in carbon-based composites is important to improve microwave absorption performance,and this work provides inspiration for the design of high-performance porous carbon-based composites.

Fused-core particle technology in high-performance liquid chromatography: An overview

The advent of superficially porous particles （SPPs） for packed HPLC columns has changed the way that many practitioners have approached the problem of developing needed separations. The very high efficiency of such columns, combined with convenient operating conditions, modest back pressures and the ability to use conventional HPLC instruments has resulted in intense basic studies of SPP technology, and widespread applications in many sciences. This report contains an overview of the SPP technology first developed in 2006 by Advanced Materials Technology, Inc., for sub-3-11m particles, then expanded into a family of SPP products with different particle sizes, pore sizes and other physical parameters. This approach was designed so that each particle of the family could be optimized for separating a particular group of compounds, usually based on solute size.

Analysis of particulate behavior in porous media

In this work, we analyze the behavior of the particle phase in the flow of a particle-laden mixture through a porous medium. An attempt is made to model the diffusion and dispersion processes, and to quantify the deviation terms that arise when intrinsic volume averaging is used to derive the flow equations.

Application of Metaheuristic Algorithms for Optimizing Longitudinal Square Porous Fins

The objectives of this study involve the optimization of longitudinal porous fins of square cross-section using metaheuristic algorithms.A generalized nonlinear ordinary differential equation is derived using Darcy and Fourier’s laws in the energy balance around a control volume and is solved numerically using RFK 45 method.The temperature of the base surface is higher than the fin surface,and the fin tip is kept adiabatic or cooled by convection heat transfer.The other pertinent parameters include Rayleigh number(100≤Ra≤10^(4)),Darcy number,(10^(−4)≤Da≤10^(−2)),relative thermal conductivity ratio of solid phase to fluid(1000≤kr≤8000),Nusselt number(10≤Nu≤100),porosity(0.1≤φ≤0.9).The impacts of these parameters on the entropy generation rate are investigated and optimized using metaheuristic algorithms.In computer science,metaheuristic algorithms are one of the most widely used techniques for optimization problems.In this research,three metaheuristic algorithms,including the firefly algorithm(FFA),particle swarm algorithm(PSO),and hybrid algorithm(FFAPSO)are employed to examine the performance of square fins.It is demonstrated that FFA-PSO takes fewer iterations and less computational time to converge compared to other algorithms.

FORMATION OF MICRO-POROUS SPHERICAL PARTICLES OF CALCIUM SILICATE(XONOTLITE) IN DYNAMIC HYDROTHERMAL PROCESS

Stirring during hydrothermal synthesis plays an important role in the formation of porous spherical xonotlite particles. The size of spherical particles formed during dynamic hydrothermal process is related to the size of minimum vortices in the reaction slurry, which is determined by stirring speed. The kinetics of growth of xonotlite particles is de-termined by measuring the apparent viscosity of the reactant slurry at various reaction time and reaction temperatures. It is found that the growth of particles follows the contracting-volume equation, and the activation energies for nucleation and growth are 104 and 123 kJ.mol-1, respectively.

CONTROL OF POLYMER PARTICLE SIZE USING POROUS GLASS MEMBRANE EMULSIFICATION A REVIEW

Much attention has in recent years been paid to fine applications of polymer particles, e.g., carrier for enzyme, separation media for protein, DNA and cell, and carrier for drug in Drug Delivery System (DDS). Control of polymer particle size is especially important in such fine applications. For instance, when the particles are used as a carrier of anti-cancer agents, the locations of particles containing anti-cancer agents also depend on the size of the particles. In this paper, various techniques of controlling polymer particle size are described, with emphasis on Shirasu Porous Glass (SPG) membrane emulsification, as carried out in our research group.

Mass spectrometry detection of basic drugs in fast chiral analyses with vancomycin stationary phases

Current trends in chiral analysis of pharmaceutical drugs are focused on faster separations and higher separation efficiencies, Core-shell or superficially porous particles （SPP） based chiral stationary phases （CSPs） provide reduced analysis times while maintaining high column efficiencies and sensitivity. In this study, mobile phase conditions suitable for chiral analyses with electrospray ionization LC-MS were systematically investigated using vancomycin as a representative CSP. The performance of a 2.7 μm SPP based vancomycin CSP （SPP-V） 10 cm ×0.21 cm column was compared to that of a corresponding 5 μm fully porous particles based analogue column. The results demonstrated that the SPP-V column provides higher efficiencies, 2-5 time greater sensitivity and shorter analysis time for a set of 22 basic pharma- ceutical drugs. The SPP-V was successfully applied for the analysis of the degradation products of racemic citalopram whose enantiomers could be selectively identified by MS.