High Gradient Magnetic Filtration Research Articles

Cleaning Aqueous Media from Iron Oxides by High-Gradient Magnetic Filtration (Review)

Cleaning Aqueous Media from Iron Oxides by High-Gradient Magnetic Filtration (Review)

Effect of particle size on the capture of uranium oxide colloidal particles from aqueous suspensions via high-gradient magnetic filtration

The effectiveness of High Gradient Magnetic Filtration (HGMF) in capturing uranium oxide particles from suspensions was investigated in this study. Two sets of experiments were performed to evaluate the importance of size on the capture of uranium oxide particles. The first considered two batches sieved into size bins of< 5, 5–10, 10–15, and 15–20 µm, while the second was performed using two suspensions with diameters smaller than 1.0 µm and between 1.0 and 1.5 µm. Iron oxide experiments, with particles between 0.3 and 0.8 µm, were performed for calibration purposes. In all experiments, a surfactant (Triton-X100 or sodium dodecyl sulfate) was used to prevent particle aggregation and limit the influence of non-magnetic capture mechanisms. A magnetic field of approximately 1.1 Tesla was generated using a water cooled electromagnet. HGMF was performed using tubular filters packed with ferromagnetic stainless-steel wool. Of the initial four uranium oxide particle sizes, magnetic capture was only observed for particles with a diameter of less than 5 µm, while larger particles experienced no magnetic and minimal total capture. For particles with diameters smaller than 1.0 µm and between 1.0 and 1.5 µm, capture efficiencies increased by 39 ± 9% and 34 ± 6% respectively, solely due to the magnetic field. Although the magnetic force is proportional to particle diameter, the capture efficiency decreased as diameter increased. These results suggest that Brownian diffusion, which is influential for micron sized particles and increases with decreasing particle size, is acting in conjunction with the magnetic force to influence the efficacy of HGMF for uranium oxide. This important finding underscores the effectiveness of Brownian diffusion in increasing the rate of collision between particles and collector fibers. A stochastic trajectory model was developed to incorporate the influence of Brownian motion on particle behavior and filter removal efficiency. Modeling results are discussed and compared for uranium and iron oxide particles.

Separation experiment and mechanism study on PVC microplastics removal from aqueous solutions using high-gradient magnetic filter

Microplastics have posed a threat to organisms and human health in the water environment. Seeking environmentally friendly and efficient method to remove microplastics from aqueous solution has garnered research interest. We studied the magnetic separation method of microplastics using a magnetic filter, and discussed the removal mechanism in the coupled field including the flow and magnetic fields. The results show that the Fe3O4 magnetic medium carrier can effectively combine and wrap itself onto the surface of microplastic particles (polyvinyl chloride, PVC) to form high strength magnetic aggregates, with strong magnetic characteristics. The designed magnetic filter has a high intensity magnetic field strength of 4–8 T near the magnetic matrices, and also has a stable separation flow field. The magnetic aggregates were firmly captured on the magnetic matrices to realize the effective separation of magnetic aggregates from the aqueous solution. The removal efficiency increased gradually and reached 100 % with the increase of reaction time. Furthermore, the Fe3O4 magnetic medium carrier was recovered by a tubular furnace and recycled experiments were subsequently conducted. The PVC removal rate after five cycles reduced due to the mass loss, but could still be maintained above 94 %. In this study, the easily prepared Fe3O4 was selected as the magnetic medium carrier and applied to the magnetic separation method to remove the microplastics in the aqueous solution, and was efficient, economically feasible, and environmentally friendly.

Removal of Iron Oxide Impurities from Water Using High-Gradient Magnetic Filtration

Removal of Iron Oxide Impurities from Water Using High-Gradient Magnetic Filtration

Numerical simulation of high-gradient magnetic filtration

We have reported on the results of a numerical simulation of high-gradient magnetic filtration of ultradisperse corrosion products from water coolants. These results have made it possible to establish optimal technical characteristics of high-gradient magnetic filters. The results have been used to develop test samples of high-gradient magnetic filters (HGMFs) with different magnetic systems to purify technological water media of atomic power plants from activated corrosion products.

Optimization of High Gradient Magnetic Separation Filter Units for the Purification of Fermentation Products

High gradient magnetic separation (HGMS) has been established since the early 1970s. A more recent application of these systems is the use in bioprocesses. To integrate the HGMS in a fermentation process, it is necessary to optimize the separation matrix with regard to the magnetic separation characteristics and permeability of the non-magnetizable components of the fermentation broth. As part of the work presented here, a combined fluidic and magnetic force finite element model simulation was created using the software COMSOL Multiphysics and compared with separation experiments. Finally, as optimal lattice orientation of the separation matrix, a transversal rhombohedral arrangement was defined. The high suitability of the new filter matrix has been verified by separation experiments.

Phosphate recovery from wastewater using engineered superparamagnetic particles modified with layered double hydroxide ion exchangers

An innovative nanocomposite material is proposed for phosphate recovery from wastewater using magnetic assistance. Superparamagnetic microparticles modified with layered double hydroxide (LDH) ion exchangers of various compositions act as phosphate adsorbers. Magnetic separation and chemical regeneration of the particles allows their reuse, leading to the successful recovery of phosphate.Based upon the preliminary screening of different LDH ion exchanger modifications for phosphate selectivity and uptake capacity, MgFe–Zr LDH coated magnetic particles were chosen for further characterization and application. The adsorption kinetics of phosphate from municipal wastewater was studied in dependence with particle concentration, contact time and pH. Adsorption isotherms were then determined for the selected particle system. Recovery of phosphate and regeneration of the particles was examined via testing a variety of desorption solutions. Reusability of the particles was demonstrated for 15 adsorption/desorption cycles. Adsorption in the range of 75–97% was achieved in each cycle after 1 h contact time. Phosphate recovery and enrichment was possible through repetitive application of the desorption solution. Finally, a pilot scale experiment was carried out by treating 125 L of wastewater with the particles in five subsequent 25 L batches. Solid–liquid separation on this scale was carried out with a high-gradient magnetic filter (HGMF).

Dipolar openable Halbach magnet design for High-Gradient Magnetic Filtration

High-Gradient Magnetic Filtration (HGMF) uses heavy electromagnets or c-shaped type permanent magnets in order to generate a magnetic field. When using electromagnets, permanent operation only is possible if an effective cooling system (e.g. water, air) is applied. The operation costs are high due to the electric power consumption. In order to reduce operation costs the use of permanent magnets thus is very advantageous. Most permanent magnet systems that are currently used for HGMF are of the c-shaped type equipped with pole caps and iron yoke which makes them big and heavy. In terms of magnet weight versus magnetic flux density, Halbach type permanent magnets are much more efficient. The present work deals with a dipolar Halbach magnet, called Mandhala (Magnetic Arrangement for Novel Discrete Halbach Layout) which consists of rings from identical magnet blocks that are stacked on top of each other and can be split at optimal angles. We developed a formula which allows to calculate the magnetic flux density along the bore axis for a series of equidistant stacked rings. An optimization program using the genetic algorithm (ga) of MATLAB supports the design and up-scale of the Halbach magnet for HGMF applications as it minimizes the magnet material amount for the user fixed minimum constraints of magnetic flux density and open area for filter introduction. The Halbach magnet that was constructed in this study generates a flux density of 0.37T in the center and offers a region of 160mm within the length of the bore axis in which the magnetic flux density does not fall below 0.29T. This field is sufficiently strong to separate submicron magnetic particles with high efficiency. The built Halbach magnet is more cost-effective, more compact and lighter than c-shaped permanent magnets.

Harvesting fresh water and marine algae by magnetic separation: Screening of separation parameters and high gradient magnetic filtration

In this study, the focus is on magnetic separation of fresh water algae Chlamydomonas reinhardtii and Chlorella vulgaris as well as marine algae Phaeodactylum tricornutum and Nannochloropsis salina by means of silica-coated magnetic particles. Due to their small size and low biomass concentrations, harvesting algae by conventional methods is often inefficient and cost-consuming. Magnetic separation is a powerful tool to capture algae by adsorption to submicron-sized magnetic particles. Hereby, separation efficiency depends on parameters such as particle concentration, pH and medium composition. Separation efficiencies of >95% were obtained for all algae while maximum particle loads of 30 and 77g/g were measured for C. reinhardtii and P. tricornutum at pH 8 and 12, respectively. This study highlights the potential of silica-coated magnetic particles for the removal of fresh water and marine algae by high gradient magnetic filtration and provides critical discussion on future improvements.

Superconducting Magnetic Filter: Performance, Recovery, and Design

Due to the development of superconducting magnets, the magnetic filtration process is now undergoing its biggest evolution since its conception. In Japan, the first industrial superconducting magnetic filter has been successfully applied for factory wastewater treatment. Much effort in both theory and practice is needed to further contribute to the new developments of this high gradient magnetic filtration process. In this substantial review, we have collected the most important theoretical and practical data about magnetic filtration, its recovery and design to establish a good framework for further development of this amazing technology.

Surfactant effects on the mechanism of particle capture in high-gradient magnetic filtration

This study investigates the effect of surfactants and key design parameters on the removal efficiency (RE) of paramagnetic colloidal particles by high-gradient magnetic filtration, and attempts to predict the effect of these parameters by a trajectory model. Magnetic filtration offers an advantage over conventional filtration in that it can achieve a reversible and selective separation. An aqueous suspension of paramagnetic colloidal ferric oxide (Fe 2O 3) particles was treated with sodium dodecyl sulfate (SDS) and delivered through a column containing a stainless steel wool filter matrix, which was mounted between the poles of an electromagnet. The RE of the surfactant-treated particles was measured by analyzing effluent samples for Fe 2O 3 concentration. The effect of the applied magnetic induction, fluid velocity, and radius of the stainless steel wires on the RE was tested and compared for both surfactant-treated and untreated particles. These three factors had a marked effect on the RE of surfactant-treated particles. An increase in applied magnetic induction from 0.2 to 0.5 T increased the RE from 79.9 to 93.4%, a decrease in wire radius from 49 to 15 μm increased the RE from 60.2 to 93.4%, and a decrease in fluid velocity from 0.5 to 0.1 cm/s increased the RE from 69.5 to 95.3%. In the absence of a magnetic field (0 T), the RE was 10.8%. The predictions of the trajectory model agreed closely with these results. The same factors had a negligible effect on the RE of untreated particles. Over the range of all three parameters, the RE varied from 90 to 99%, but these variations were not statistically significant. In the absence of applied magnetic induction, the RE was 90.1%. These results differed markedly from the trajectory model predictions and demonstrated that nonmagnetic filtration mechanisms are primarily responsible for the capture of particles without SDS. Regeneration experiments indicated that the particles were captured in the primary minimum of the potential energy. On the other hand, these results showed that the magnetic filtration mechanism is primarily responsible for the removal of particles treated with SDS and that these particles are captured in the secondary minimum of the potential energy. Therefore, surfactant adsorption onto colloidal particles can potentially preserve and enhance the advantages of magnetic filtration (e.g., reversibility and selectivity).

Synthesis and characterization of composite nanoparticles comprised of gold shell and magnetic core/cores

Nanoparticles comprised of gold shell and magnetite/maghemite inclusion were synthesized by overgrowing the gold shell onto magnetic seeds. Results from transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) indicate that there are two populations of well-dispersed nanoparticles: one is the small-diameter iron oxide particles with metallic gold shell, while the other is the moderately large gold particles containing magnetic core/cores. A close relation between the maximum optical absorbance of characteristic gold colloid and the magnetic field applied during performance of high-gradient magnetic filtration confirms further that nearly all the particles of Au character contain magnetic inclusion.

Study on a Water and Sludge Treatment Method Using Superconducting Magnetic Separation and Hydrothermal Decomposition

We studied a treatment method on beavy metal separation and sludge decomposition using a superconducting magnetic separation and a hydrothermal decomposition method. The experiment showed that the superconducting magnetic separation method to which a high gradient magnetic filter was applied proved to be practically used to remove 90% of heavy metal particles and that the hydrothermal decomposition method proved effective in dehydrating sludge and in minimizing the volume. The study also showed a well-posed hydrothermal condition on temperature and oxidation that matched the magnetic separation to remove heavy metal in sludge.

Removal System of Arsenic From Geothermal Water by High Gradient Magnetic Separation-HGMS Reciprocal Filter

We have developed a high gradient magnetic separation (HGMS) system to remove arsenic from geothermal water and to supply hot water for public use by using a superconducting magnet. We attained the reduction of arsenic concentration to 0.015 mg/L that is less than the standard for discharge of 0.1 mg/L and slightly larger than the environmental standard of 0.01 mg/L in Japan. The system consists of a pretreatment process that adds extra magnetization to arsenic by chemical reaction, and a reciprocal HGMS filter using a superconducting magnet that extracts magnetized arsenic from the geothermal water. We present the experimental results of the removal system.

Electrocoagulation for magnetic seeding of colloidal particles

Electrocoagulation (EC) was investigated as a magnetic seeding method to be used prior to a high-gradient magnetic separation (HGMS) process. Experimental results showed that particulates with significant magnetic susceptibility were formed by EC with steel electrodes. Magnetite was specifically formed most readily in a sodium chloride solution, in the absence of other ions, but also in surrogate wastewater under controlled conditions. These results suggest that EC could be employed in a magnetic seeding process in which paramagnetic particles are formed and then removed through high-gradient magnetic filtration (HGMF). The effects of applied potential and current on the magnetic susceptibility and composition of particles formed by EC in a pure sodium chloride solution and in a surrogate wastewater solution were investigated by X-ray diffraction analysis, scanning electron microscopy (SEM), and magnetic susceptibility measurements. Results showed that pure magnetite particles of 100-nm diameter were formed in the sodium chloride solution. Various compounds were present in particles produced by the surrogate wastewater solution, indicating that the formation of magnetite particles was hindered by the presence of some cations and anions. Although these particles had a much lower magnetic susceptibility than magnetite particles, their magnetic susceptibility was relatively high and permitted good removal in HGMF. The removal of copper ions from both deionized water and surrogate wastewater by EC followed by HGMF was also investigated. Results obtained at pH 10 and 12 showed a higher copper ion removal from the deionized water solution than from the surrogate wastewater.

Phosphate removal by high-gradient magnetic filtration using permanent magnets

On the basis of rare-earth permanent magnets, a second prototype of a carousel magnetic filter has been constructed for a 'third-stage' phosphate elimination from municipal sewage. As compared to the first prototype presented on the MT-15, the filter throughput has been increased by more than 500% to about 3-4 m/sup 3//h with the dimensions and the magnet system used remaining the same. At an inlet concentration of 2 mg/L P, separation efficiencies of approximately 80% can be achieved by continuous operation at filtration rates of 100 m/h. The resulting outlet concentrations are below the limit values specified in Germany or Europe. Furthermore it is evident from cost calculations that the system represents a real alternative to the well-established solid-liquid separation methods for phosphate elimination, e.g, sand filters or microsieves.

Modelling of the buildup process of particles in pores of high-gradient magnetic filters using the Fokker-Planck equation

The stochastic model of the accumulation of particles in a filter matrix composed of magnetized ferromagnetic spheres is considered. The distribution function, which gives the time dependence of the saturation radius that is characterized by both the capturing and detachment events occurring in the capture region, is determined. Taking into account the motional properties of the particles in the capture region, the distribution is evaluated from the solution of the Fokker-Planck equation. The results obtained are compared with, and shown to be similar to, the results of the other methods and some experiments reported in the literature.

Filtration model of high gradient magnetic filters with granular matrix

Considering the flow regime of the fluid through the pores of a magnetic filter having a granular matrix composed of ferromagnetic spheres and the accumulation process of the captured particles, the filtration mechanism is investigated. The effect of the different parameters of the filtration system on the efficiency of the magnetic filter is identified. New mathematical expressions are obtained to explain some events which take place in the filtration mechanism and which have not been described completely in the literature so far. The efficiency of the magnetic filter is expressed in terms of the ratios of the magnetic and static pressures which can be measured or identified easily. The theoretical results are compared with the experimental data and it is concluded that they are in good agreement.

Theory of high-gradient magnetic filter performance

A unique general model for high-gradient magnetic filters is presented. The functional dependence of the filter performance on the system's physical and geometrical parameters is derived. The derived theoretical expression makes it possible to explain both of the two different, apparently opposite, experimental results reported in the literature. The new quality factor does not include the suspension viscosity, but instead depends on the suspension density, which leads to the application of the formula for a larger class of filtration media including liquids, gases, and vapors.

MAGNETIC-SEEDING FILTRATION1*

Magnetic-seeding filtration consists of two steps: heterogeneous particle flocculation of magnetic and nonmagnetic particles in a stirred tank and high-gradient magnetic filtration (HGMF). The effects of various parameters affecting magnetic-seeding filtration (HGMF). The effects of various parameters affecting magnetic seeding filtration are theoretically and experimentally investigated. A trajectory model that includes hydrodynamic resistance, van der Waals, and electrostatic forces is developed to calculate the flocculation frequency in a turbulent-shear regime. Fractal dimension is introduced to simulate the open structure of aggregates. A magnetic-filtration model that consists of trajectory analysis, a particle build-up model, a breakthrough model, and a bivariate population-balance model is developed to predict the breakthrough curve of magnetic-seeding filtration. A good agreement between modeling results and experimental data is obtained. The results show that the model developed in this study can be used to predict the performance of magnetic-seeding filtration without using empirical coefficients or fitting parameters. 35 refs., 7 figs., 1 tab.