Separation Of Magnetic Particles Research Articles

High-Gradient Magnetic Separation of Ultrafine Particles with Rod Matrix

The matrix plays a key role in determining the performance of a high-gradient magnetic separator; it provides the carrier for the magnetic particles to be captured and transported to the nonmagnetic field as magnetic product. High-gradient magnetic separation (HGMS) of ultrafine hematite with the finest 1 mm rod matrix has been investigated on a pilot pulsating HGMS separator. The results of this investigation indicate that this matrix achieves a significantly improved performance for the ultrafine hematites, compared to the coarser 2 mm one which is now widely applied in industry, due to its stronger magnetic capture to ultrafine particles. It was concluded that the 1 mm matrix has a powerful manipulation over ultrafine particles in a pulsating HGMS process, and is capable of achieving a higher separation performance at a considerably lower energizing cost.

Magnetic separation of particles and cells in ferrofluid flow through a straight microchannel using two offset magnets

The separation of particles and cells is critical in many chemical and biological applications. This work presents a simple idea for utilizing a pair of permanent magnets to continuously separate diamagnetic particles and cells in ferrofluid flow through a straight microchannel. The first magnet is placed close to the microchannel for focusing the particle mixture to a single stream without the use of a sheath flow. The second magnet, which is offset from the first magnet and placed farther from the channel, is to displace the aligned particles to dissimilar flow paths for a continuous sorting. This idea is first demonstrated through the separation of 3μm- and 10μm-diameter polystyrene particles, where the effects of flow speed and magnet distance are both examined. The experimental data are found to fit well with the predictions of an analytical model. Furthermore, a continuous separation of live yeast cells from 10μm polystyrene particles is implemented in the same device.

Enhanced separation of magnetic and diamagnetic particles in a dilute ferrofluid

Traditional magnetic field-induced particle separations take place in water-based diamagnetic solutions, where magnetic particles are captured while diamagnetic particles flow through without being affected by the magnetic field. We demonstrate that replacing the diamagnetic aqueous medium with a dilute ferrofluid can significantly increase the throughput of magnetic and diamagnetic particle separation. This enhancement is attributed to the simultaneous positive and negative magnetophoresis of magnetic and diamagnetic particles, respectively, in a ferrofluid. The particle transport behaviors in both ferrofluid- and water-based separations are predicted using an analytical model.

High gradient magnetic separation of catalyst/wax mixture in Fischer–Tropsch synthesis: Modeling and experimental study

Separation of magnetic catalyst particles from the wax stream in Fischer–Tropsch synthesis (FTS) process is one of the most important challenges for exploring FTS slurry bubble column reactors. In the present work, we studied the separation efficiency of magnetic catalytic particles from FTS wax using high gradient magnetic separation (HGMS), and the three-dimensional mathematical models were established to describe the magnetic field and magnetic force distribution with multi-wires for HGMS. The calculation results indicated that the distributions of magnetic field and magnetic force in HGMS were significantly related to the matrix arrangement patterns and the background uniform external magnetic field strength. The wire interval, the axial distance between matrices, the arrangement angle between matrices and the external magnetic field strength were investigated using the established models. Based on the experimental optimization, the magnetic iron content of the catalyst/wax mixture can be reduced to less than 30ppm through HGMS, with the separation efficiency higher than 99.77% for iron particles.

Separation of magnetic particles in channel flows by BEM

AbstractIn‐line separation of suspensions can become difficult in case of particles with comparable values of densities. For flows in micro devices in such cases gravitational settling is inefficient, and other separation techniques must be applied. In case of magneto active particles, the action of Kelvin magnetic force in a non‐uniform magnetic field could be used in order to achieve a higher degree of particles separation. The contribution therefore deals with Euler‐Lagrangian formulation of dilute two‐phase flows. The Boundary element based computational algorithm solves the incompressible Navier‐Stokes equations written in velocity‐vorticity formulation. The non‐uniform magnetic field is defined analytically for the case of a set of long thin wires. The particle trajectories are computed by applying the 4th order Runge‐Kutta method. The computed test case consists of a narrow channel with laminar flow of suspension under Re = 1 − 10. Particle trajectories under the influence of a non‐uniform magnetic field are computed for the case of magnetite and aluminium particles suspended in water. The efficiency of separation on basis of particle trajectories for different values of Re number and magnetic field strength is performed, clearly indicating superior separation of magneto active particles. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stroma-dependent development of two dendritic-like cell types with distinct antigen presenting capability

Novel antigen presenting cells (APCs) have been described in the murine spleen. Cells have a distinct CD11c(lo)CD11b(hi)MHC-II(-)CD8α(-) phenotype as highly endocytic dendritic-like cells that cross-present antigen to CD8(+) T cells but fail to activate CD4(+) T cells. These cells are named "L-DCs" because they reflect dendritic cells (DCs) produced in long-term spleen cultures (LTC). Similar cells were produced when bone marrow progenitors were cocultured over the splenic stromal line 5G3. Cocultures continuously produced a majority of L-DCs and a transient population of cells reflecting conventional dendritic cells (cDCs). Both the L-DC and cDC-like subsets cross-present antigen to CD8(+) T cells, inducing their activation and proliferation. However, as MHC-II(-) cells, L-DCs are unable to activate CD4(+) T cells, while MHC-II(+) cDC-like cells present antigen for CD4(+) T cell activation. These results distinguish two APC subsets produced invitro: a transient population of cDC-like cells and L-DCs that are continuously produced, presumably from self-renewing progenitors. These subsets are not developmentally linked via a precursor or progeny relationship. L-DCs and cDC-like cells are also distinct in terms of cytokine expression, with 65 of 84 tested genes displaying greater than a twofold difference by quantitative reverse-transcriptase polymerase chain reaction. Splenic stroma supports production of two APC subsets reflecting different lineage origins.

Continuous sheath-free magnetic separation of particles in a U-shaped microchannel.

Particle separation is important to many chemical and biomedical applications. Magnetic field-induced particle separation is simple, cheap, and free of fluid heating issues that accompany electric, acoustic, and optical methods. We develop herein a novel microfluidic approach to continuous sheath-free magnetic separation of particles. This approach exploits the negative or positive magnetophoretic deflection to focus and separate particles in the two branches of a U-shaped microchannel, respectively. It is applicable to both magnetic and diamagnetic particle separations, and is demonstrated through the sorting of 5 μm and 15 μm polystyrene particles suspended in a dilute ferrofluid.

Centrifugo-magnetophoretic particle separation

There has been a recent surge of research output on magnetophoretic lab-on-a-chip systems due to their prospective use in a range of applications in the life sciences and clinical diagnostics. Manifold applications for batch-mode or continuous-flow magnetophoretic separations of cells, proteins, and nucleic acids are found in bioanalytics, cell biology, and clinical diagnostics. To ensure stable hydrodynamic conditions and thus reproducible separation, state-of-the-art magnetophoretic lab-on-a-chip systems have been based on pressure-driven flow (Gijs in Microfluid Nanofluid 1:22–40, 2004; Pamme and Manz in Anal Chem 76:7250–7256, 2004; Pamme in Lab Chip 7:1644–1659, 2007; Karle et al. in Lab Chip 10:3284–3290, 2010), which involves rather bulky and costly instrumentation. In a flow-based system, suspended particles are following the liquid phase as a result of the Stokes drag, thus being fully exposed to divergent flow lines around obstacles and pump-induced pressure fluctuations. To eventually achieve more stable hydrodynamic conditions, improved control of magnetic particles, a more compact instrumentation footprint, and integration of high-performance upstream sample preparation, this work introduces a novel two-dimensional particle separation principle by combining magnetic deflection with centrifugal sedimentation in a stopped-flow mode (i.e., mere particle sedimentation). The experimental parameters governing our centrifugo-magnetophoretic system are the strength and orientation of the co-rotating magnetic field, the rotationally induced centrifugal field, and the size-dependent Stokes drag of the various particles with respect to the (residual) liquid phase. In this work, the following set of basic functional modes is demonstrated as proof-of-concept: separation of magnetic from non-magnetic particles, routing of magnetic particles based on control of the spin speed, and size separation of various magnetic particles. Finally, a biomimetic application involving the separation of particles representing healthy cells from a very small concentration of magnetic particles of a similar size, mass and magnetization as a immuno-magnetically tagged target cell, for instance mimicking a circulating tumor cell.

Magnetic separation and SERS observation of analyte molecules on bifunctional silver/iron oxide composite nanostructures

We report the preparation of bifunctional silver–iron oxide composite nanostructures (Ag@Fe2O3) and demonstrate their magnetic separation with an analyte molecule from silver nanoparticles in a mixed solution. Magnetic and non‐magnetic plasmonic nanostructures and their separation are monitored by the surface‐enhanced Raman scattering (SERS) spectra of two different analytes attached to each kind of particles. In general, such separation experiments can provide insight into basic phenomena of adsorption and exchange of adsorbed molecules which are of strong interest in SERS. The formation of stable Ag@Fe2O3 nanoparticle–molecule complexes suggests small magnetic SERS labels without additional protective layers for application in analytical assays. The magnetic plasmonic nanostructures have great promise for targeted imaging and sensing in biological structures by directing nanosensors to places of interest using magnetic fields. The option of magnetic separation and collection of plasmonic particles improves the analytical capabilities of SERS. Copyright © 2012 John Wiley & Sons, Ltd.

High gradient magnetic particle separation in viscous flows by 3D BEM

The boundary element method was applied to study the motion of magnetic particles in fluid flow under the action of external nonuniform magnetic field. The derived formulation combines the velocity-vorticity resolved Navier---Stokes equations with the Lagrange based particle tracking model, where the one-way coupling with fluid phase was considered. The derived algorithm was used to test a possible design of high gradient magnetic separation in a narrow channel by computing particles trajectories in channel flow under the influence of hydrodynamic and magnetic forces. Magnetic field gradient was obtained by magnetization wires placed outside of the channel. Simulations with varying external magnetic field and flow rate were preformed in order to asses the collection efficiency of the proposed device. We found that the collection efficiency decreases linearly with increasing flow rate. Also, the collection efficiency was found to increase with magnetic field strength only up a saturation point. Furthermore, we found that high collection efficiently is not feasible at high flow velocity and/or at weak magnetic field. Recommendation for optimal choice of external magnetic field and flow rate is discussed.

Continuous-flow in-droplet magnetic particle separation in a droplet-based microfluidic platform

This paper presents a continuous-flow in-droplet magnetic particle separation in a droplet-based microfluidic device for magnetic bead-based bioassays. Two functions, electrocoalescence and magnetic particle manipulation, are performed in this device. A pair of charging metallic needles is inserted into two aqueous channels of the device. By electrostatic force, two different solutions can be merged to be mixed at a junction of droplet generation. The manipulation of magnetic particles is achieved using an externally applied magnetic field. The magnetic particles are separated by the magnetic field to one side of the droplet and extracted by splitting the droplet into two daughter droplets: one contains the majority of the magnetic particles and the other is almost devoid of magnetic particles. The applicability of the continuous-flow in-droplet magnetic particle separation is demonstrated by performing a proof-of-concept immunoassay between streptavidin-coated magnetic beads and biotin labelled with fluorescence. This approach will be useful for various biological and chemical analyses and compartmentalization of small samples.

Microstripes for transport and separation of magnetic particles.

We present a simple technique for creating an on-chip magnetic particle conveyor based on exchange-biased permalloy microstripes. The particle transportation relies on an array of stripes with a spacing smaller than their width in conjunction with a periodic sequence of four different externally applied magnetic fields. We demonstrate the controlled transportation of a large population of particles over several millimeters of distance as well as the spatial separation of two populations of magnetic particles with different magnetophoretic mobilities. The technique can be used for the controlled selective manipulation and separation of magnetically labelled species.

Magnetic Field and Fluid Flow Computation of Plural Kinds of Magnetic Particles for Magnetic Separation

Magnetic chromatography is an effective system for fine magnetic particle separation because of its strong magnetic field gradients. We have been developing the magnetic chromatography system to separate two or more kinds of fine magnetic particle with different sizes. To evaluate the performances of our developed system, we have also developed a simulation code with taking into account the fluid dynamics and magnetics. It is, however, difficult to consider two or more kinds of fine magnetic particles with different sizes in the simulation, because magnetic interferences between two or more kinds of magnetic particles need to be considered. Therefore, we have newly developed a simulation code to deal with magnetic interferences between two or more kinds of fine magnetic particles.

CFD simulation for biomagnetic separation involving dilute suspensions

AbstractFull‐Eulerian simulation of the separation of magnetic particles carried by a Newtonian fluid through a planar channel under the influence of a magnetic field is presented. The simulation is based on the application of the Navier–Stokes and concentration equations. The scheme for the magnetic separation of particles is achieved by applying an external magnetic dipole field. The hydrodynamic and magnetophoretic interactions between the particles and the carrier fluid are analysed. Analysis of the competing tendencies of mass transfer indicates that the magnetophoresis migration of magnetic particles is dominant over the molecular diffusion. This dominance becomes more evident at lower diffusivities leading to a drastic magnetic separation confined within a small region in the proximity of the magnetic field source. © 2012 Canadian Society for Chemical Engineering

Simulation of Magnetic Fluid to Develop the Magnetic Chromatography for Magnetic Particle Separation

A magnetic chromatography is a very useful system for an ion and/or fine magnetic particle separation. Recently, its performance has been enhanced using a superconducting magnet. The superconducting magnet can generate a high magnetic field and its strong magnetic field gradients in a very small flow channel. We have developed the magnetic chromatography system to separate the fine particles. However, its numerical simulation is difficult, since the scale of the fine magnetic particles in fluid is much different from the scale of the superconducting magnet generating the strong magnetic field. In order to accurately simulate the magnetic separation, it is necessary to develop the simulation code dealing with the multiscale. The performance of the developed magnetic chromatography is evaluated by the developed simulation tool, and it is clarified that it is unsuitable for magnetic particle separation. Therefore, a magnetic chromatography is newly designed and its performance is evaluated by the developed simulation tool.

Removal of magnetite particles and lubricant contamination from viscous oil by High-Gradient Magnetic Separation technique

This article presents investigations on the removal of particles from viscous lubricant oil by High-Gradient Magnetic Separation (HGMS). The study deals with the removal of magnetite particles (Fe3O4) and solid lubricant contamination from a mineral oil. The lubricant contamination particles are extracted from a used wind power plant (WPP) gear oil filter. Both particle systems are characterised regarding their particle size distribution, solid density and magnetisation. The WPP particles are analysed in terms of their chemical composition by Energy-Dispersive X-ray Spectroscopy (SEM-EDX) and Inductively-Coupled Plasma Optical Emission Spectroscopy (ICP-OES). In order to predict the separation efficiency of different matrices a theoretical approach is used. The theoretical calculation are also compared to experimental data. The experiments focus primary on the separation efficiency and grade efficiency of different matrix geometries. The concentration of the feed suspension is low (3mg/l), hence an laser particle counter is best suited for the online characterisation of the separation efficiency. In case of a single-stage arrangement, the removal of magnetite particles from lubricant oil showed that it is more successfully done with the fine matrix than with the coarse matrix. Using a multi-stage separation chamber, the removal is improved significantly compared to the single-stage processes. The investigation of magnetic separation of WPP particles was carried out with a multi-stage arrangement. Comparing the obtained separation efficiencies showed that the removal of WPP particles is not as good as that of magnetite particles. Nevertheless, the experiment showed that it is possible to separate solid lubrication contamination from an industrial gear oil to a high amount. The chemical analysis by ICP-OES of the WPP particles before and after HGMS treatment resolves that magnetically induced hetero-agglomeration occurs and that the agglomerated particles are captured on the HGMS wire mesh. The results of the experiments are compared to theoretical calculations. Their values are qualitatively in good agreement. Deviations are due to magnetic induced agglomeration, which involves particle growth and reduced magnetic susceptibility. Nevertheless, the calculation is a reliable tool in order to predict the separation efficiency and is used for the enhancement of the matrix geometry and stage number.

Investigation on Novel Magnetic Chromatography With Ferromagnetic Nano-Wires for Ion Separation

Magnetic chromatography is a very useful system for ion and/or fine magnetic particle separation due to strong magnetic field gradients in a very small flow channel. We have developed the magnetic chromatography system to separate the ions and fine particles. It is, however, difficult to separate the ions or the magnetic particles using the developed magnetic chromatography. It makes the strong magnetic field gradients in the flow channel, but the alternate direction of the gradient is not suitable for magnetic separation. Therefore, we have newly designed a novel magnetic column with ferromagnetic nano-wires. In this paper, the new magnetic column is presented, and the magnetic field and its gradients in the flow channel are investigated.

Field-flow fractionation of magnetic particles in a cyclic magnetic field

Although magnetic field-flow fractionation (MgFFF) is emerging as a promising technique for characterizing magnetic particles, it still suffers from limitations such as low separation efficiency due to irreversible adsorption of magnetic particles on separation channel. Here we report a novel approach based on the use of a cyclic magnetic field to overcome the particle entrapment in MgFFF. This cyclic field is generated by rotating a magnet on the top of the spiral separation channel so that magnetic and opposing gravitational forces alternately act on the magnetic particles suspended in the fluid flow. As a result, the particles migrate transversely between the channel walls and their adsorption at internal channel surface is prevented due to short residence time which is controlled by the rotation frequency. With recycling of the catch-release process, the particles follow saw-tooth-like downstream migration trajectories and exit the separation channel at velocities corresponding to their sedimentation coefficients. A retention model has been developed on the basis of the combined effects of magnetic, gravitational fields and hydrodynamic flow on particle migration. Two types of core–shell structured magnetic microspheres with diameters of 6.04- and 9.40-μm were synthesized and used as standard particles to test the proposed retention theory under varying conditions. The retention ratios of these two types of particles were measured as a function of magnet rotation frequency, the gap between the magnet and separation channel, carrier flow rate, and sample loading. The data obtained confirm that optimum separation of magnetic particles with improved separation efficiency can be achieved by tuning rotation frequency, magnetic field gradient, and carrier flow rate. In view of the widespread applications of magnetic microspheres in separation of biological molecules, virus, and cells, this new method might be extended to separate magnetically labeled proteins or organisms for multiplex analyte identification and purification.

Morphological and mineralogical forms of technogenic magnetic particles in industrial dusts

The morphology, mineralogy, and magnetic properties of technogenic magnetic particles (TMPs) were analysed in four kinds of industrial dust produced during high temperature technological processes of different branches of industry (lignite and hard coal burning, cement production, coke production). The study was carried out by means of magnetic susceptibility measurement, energy dispersive spectroscopy (EDS), scanning electron microscope (SEM), X-ray diffraction, Mossbauer spectroscopy, and thermomagnetic analysis. To assess the total content of the magnetic fraction in bulk dust samples, mass specific magnetic susceptibility (χ) was measured and then a physical separation of magnetic particles (mostly of technogenic origin) was conducted. The dusts revealed high diversity of the χ value, which was dependent on the magnetic particles’ concentration and mineralogical composition. Significant differences in the magnetic mineralogy of dusts coming from different branches of industry were observed. In fly ashes from coal combustion, spherical forms (typical ferromagnetic spherules) of magnetite, magnesioferrite, and maghemite were mostly observed. In dusts after lignite combustion a higher content of antiferromagnetic hematite and maghemite was observed due to the lower temperature of lignite combustion. In cement dusts a large variety of iron minerals were observed including magnetite, maghemite, hematite, ferrites, and goethite. The characteristic mineral forms for cement dusts were Ca-ferrites and co-occurrence of calcite, anhydrite, gypsum, and bassanite with a magnetic mineral fraction. The magnetic fraction produced by the coke industry was mostly in the form of tightly compacted aggregates with well-formed crystal structures where ferromagnetic pyrrhotite was characteristic feature. The TMPs could be distinctive for pollution source identification and serve as a tracer of dust origin and (if found in topsoil) identification of soil pollution sources.

Investigation of the process of diamagnetic particle separation in a high-gradient ordered-structure magnetic field

On the basis of the model of a flow-type magnetic filter with a transversely magnetized ordered system of long ferromagnetic rods of rectangular cross section, the process of high-gradient magnetic separation of microscopic diamagnetic particles (potato starch granules of sizes 8–30 μm) from a liquid suspension has been investigated. The registered laws of change in the concentration and size distribution of particles at the suspension outlet from the filter agree with the theoretical conclusions obtained from the analysis of the magnetic field structure and thecharacter of the particle motion in the filter volume.