High Gradient Magnetic Separation Process Research Articles

Effect of lime (CaOH+) on chalcopyrite-arsenopyrite separation in high gradient magnetic separation: Experiment and molecular simulation

During the flotation of chalcopyrite from arsenopyrite, the addition of lime (with CaOH+ as the active component) can affect the subsequent high-gradient magnetic separation (HGMS) performance. However, this issue has been overlooked in previous researches. The present study confirms this effect and elucidates its underlying mechanism. Findings demonstrate that CaOH+ could decrease the magnetic moment of Fe atoms in chalcopyrite, deteriorating its separation from arsenopyrite via HGMS method. For a high-arsenic copper ore assaying 0.63 % Cu and 0.78 % As with chalcopyrite and arsenopyrite as the dominant copper-bearing and arsenic-bearing minerals, the HGMS results has confirmed that increasing the lime dosage from 0 kg/t to 14 kg/t reduced the copper grade in the copper concentrate from 0.92 % to 0.61 % and decreased the copper recovery from 67.03 % to 53.95 %. However, the arsenic grade and recovery in the concentrate were improved from 0.35 % to 0.64 % and from 28.27 % to 42.19 %, respectively. The calculations using Density Functional Theory and Crystal-Field Theory revealed that the interaction between Fe ions in chalcopyrite and CaOH+ in lime leads to a considerable change in the single electron occupancy of the d orbitals, that is, it transitions from a high-spin state to a low-spin state; thus, the magnetic susceptibility of the chalcopyrite decreases, reducing the HGMS efficiency for separation of chalcopyrite from arsenopyrite. The findings of this study provide considerable theoretical insights and improved understanding for the effect of lime on the chalcopyrite-arsenopyrite separation efficiency in HGMS process.

Pulsation curves strengthen the high gradient magnetic separation process Ⅱ: Consideration of separation performance

The use of pulsating slurry has been found to be effective in overcoming matrix blockage and improving separation selectivity in high gradient magnetic separators (HGMS). The velocity of the pulsating slurry is regulated by a sinusoidal cycle function, which causes the downward velocity to be much greater than the upward velocity due to the superposition of the sinusoidal pulsation velocity and the feeding velocity. However, the unbalanced velocity configuration in the up-downward stroke limits separation efficiency. This paper investigates the use of asymmetrical pulsation curves in a lab-scale HGMS to balance the velocity configuration and consequently improve separation performance. Magnetic field strength, feed velocity, and pulsating frequency were varied in separate experiments to determine the effect of pulsation curves on separation performance. The asymmetrical pulsation curve with a faster upward stroke and slower downward stroke was found to achieve a TiO2 concentrate grade of 23.94 %, a recovery of 66.78 %, and a separation efficiency of 50.46 % for the separation of ilmenite. When the concentrate grade is slightly higher, this new curve shows an increase of 5.68 % in recovery and 5.05 % in separation efficiency compared to the conventional sinusoidal pulsation curve. This improvement is attributed to a simultaneous strengthening of the material loose-adsorption process by separately regulating the pulsating upward and downward strokes.

Development of a Single‐Use Device and an Associated Optical Measurement Method for Automated Magnetic Bioseparation

AbstractIn bioseparation, magnetic particles can be used for the adsorption of biomolecules. They can be selectively separated from multi‐component suspensions with high‐gradient magnetic separation (HGMS). A single‐use HGMS separation chamber has been developed to avoid cross‐contamination. As with fixed‐bed adsorption, breakthrough occurs after a certain time. Subsequently, the magnetic particles that are then still further fed, are lost together with the biomolecules bound to them. In order to stop the HGMS process before breakthrough, an associated optical measurement method was developed.

Pulsation curves strengthen the high gradient magnetic separation process: Experimental study and simulation explanation

The pulsating slurry high gradient magnetic separator (PHGMS) has been widely used for the separation of feebly magnetic materials. As the main competing force, pulsating slurry effectively overcomes matrix blockage and affects the buildup behavior of particles. At present, the used pulse shape in PHGMS constitutes a sinusoidal harmonic vertical motion in which the duration and intensity of the impulsion and suction strokes are similar. However, other pulsation profiles, such as, trapezoidal shape and saw-tooth shape pulses, can also be obtained depending on the stratification mechanism. There is little literature to focus on how pulse shape influences the performance of PHGMS. The change of curve could be a method worth exploring to improve the separation. In this paper, the asymmetry pulsating curves are obtained by switching the velocity of the step motor during one cycle. Then, the single-wire experiments, single-wire 2D numerical simulation and multi-wires experiments are presented to indicate the effect of different pulse shapes. In single-wire experiments, compared with the traditional sinusoidal harmonic curve, the asymmetry pulsating curves have a higher grade, finer particle buildup, but lower accumulation volume. The curves of the rapid downward stroke and slow upward stroke are better than the inverse movement curve in asymmetry pulsation. The results of separating the up and downstream accumulations on the magnetized wire and numerical simulation reveal that these effects can be attributed to the direction of net force and vortex strengthening. The trajectory simulation of multi-component obtains a similar result with single-wire experiments to confirm the superiority of rapid downward stroke and slow upward stroke in selectivity. However, in multi-wires experiments, due to the matrix blockage the curves of rapid upward stroke and slow upward stroke show the greater potential advantages in both grade and weight compared with other curves at condition of high feed velocity.

Theoretical description on size matching for magnetic element to independent particle in high gradient magnetic separation

Magnetic element is the basic component of matrix in high gradient magnetic separation (HGMS), and its configurative parameters such as size have marked effects on the capture efficiency of the matrix. Therefore, the geometric design of the element should be matched with the properties of the material to be separated, to optimize the HGMS performance. In this work, the capture of independent magnetic particles on a cylindrical element in pulsating HGMS process was theoretically described, and their size matching ratios (magnetic element to particle) under the maximum capture probability and critical capture conditions were specifically discussed. These theoretically calculated size ratios were much larger than that (2.69) in the literatures available, but generally consistent with those obtained from pulsating HGMS applications. The theoretical analysis were basically validated by the actual capture of ilmenite and hematite particles on cylindrical elements, using an experimental magnetic capture method. According to the new theoretical model, the size matching ratio is not fixed at the value of 2.69. It depends on the properties of the material to be separated such as volume magnetic susceptibility and the operating parameters of a HGMS process such as magnetic induction and flow velocity through the magnetic element. This theoretical description provides a new fundamental understanding in the size matching between magnetic element and particle, and would contribute to the solution of size matching issue in the real capture situation considering the interactions between magnetic particles, and therefore to the optimal design and operations of matrix in HGMS applications.

The choice of high gradient magnetic separation processes for removal of Fe2O3 carriers from quartz raw material

Abstract This review article surveys the subject of choice of high gradient magnetic separation processes for removal of Fe2O3 carriers from quartz raw material by electromagnetic separator with magnetic field intensity of 1.4 T.

Quantitative investigation on magnetic capture of single wires in pulsating HGMS

Pulsating high gradient magnetic separation (HGMS) achieves high separation efficiency to fine weakly magnetic minerals with a rod matrix. In practice, the matrix is made of numerous cylindrical wires, so that an insight into the magnetic capture of single wires to magnetic minerals would provide a crucial foundation for the analysis, design and choice of matrix. In the investigation, the magnetic capture of single wires to ilmenite minerals and its dependence on the key parameters of a pilot-scale pulsating HGMS separator, i.e., magnetic induction, pulsating frequency and feed velocity, is investigated using an innovatively experimental method. It is found that these parameters have significant effects on the magnetic capture of single wires; the mass weight of magnetic particles captured onto the wires increases with increase in magnetic induction, and it is opposite for pulsating frequency and feed velocity. The cylindrical wire captures more particles than that of rectangular one, due to its larger capture area, and it has a stronger adaptability to variations in the parameters. The single wire captures more magnetic particles but a greatly reduced stability to the parameters' variation, compared to the multi-wires. This experimental method provides a new perspective in the understanding of magnetic capture to magnetic particles in a HGMS process, contributing to the optimal design of matrix and to the improvement of HGMS performance.

In-situ observation of particles deposition process on a ferromagnetic filter during high-gradient magnetic separation process

Abstracts In-situ observations of particles deposition process on a ferromagnetic filter in high gradient magnetic separation were carried out under high magnetic fields to obtain information for the optimization of separation condition. The spike-like deposition structure was observed on the upper stream of the magnetic filter, different from the conventional deposition image obtained for paramagnetic particles. The length of the spike structure tends to be long with lower flow velocity and lower applied magnetic field. It was also observed that the chain structure or the bundle of such chaines were formed on the way to the filter under the condition of the low applied magnetic field and low flow rates. Results obtained here indicate that the effect of deposited particles on the spatial distribution of the magnetic field and the hydrodynamics, they are often ignored in the simulation so far, should be considered appropriately.

Effect and mechanism of a High Gradient Magnetic Separation (HGMS) and Ultraviolet (UV) composite process on the inactivation of microbes in ballast water

The patented technology of a High Gradient Magnetic Separation (HGMS)-Ultraviolet (UV) composite process was used to treat ballast water. Staphylococcus aureus (S. aureus) was selected as the reference bacteria. After treatment by the HGMS-UV process, the concentration of S. aureus on the log 10 scale was lower than 2 at different flow rates, S. aureus suffered the most serious damage, and K+ leakage of the bacteria was 1.73mg/L higher than separate 60min UV irradiation (1.17mg/L) and HGMS (0.12mg/L) processes. These results demonstrated that the HGMS-UV composite process was an effective approach to treat ballast water. Further, the HGMS process had synergistic action on the subsequent UV irradiation process and accelerated cell membrane damage. Meanwhile, the results of superoxide dismutase (SOD) activities of bacteria and DNA band analyses indicated that the inactivation mechanisms were different for HGMS and UV irradiation.

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.

Simulation of magnetic suspensions for HGMS using CFD, FEM and DEM modeling

Properties of magnetic suspensions depend on the fluid, the particles and the magnetic background field. The simulation is aimed at understanding the influence of magnetic properties in High Gradient Magnetic Separation processes. In HGMS magnetic particles are collected on magnetic wires for separation. External magnetic forces are calculated or simulated using the Finite Element Method and embedded first in a Computational Fluid Dynamics simulation. In the simulation, elliptic and rectangular wires aligned in field direction reach higher separation efficiencies than cylindrical wires. Magnetic forces from FEM with implemented dipole forces in a Discrete Element Method code show magnetically induced agglomeration and yield an acceptable agreement with experiments. Particle deposition on wires is investigated under the influence of different parameters. The porosity of the deposit is dependent on the magnetization of the wire and particles. A centrifugal force of 60g has an important influence.

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.

Calculated Reduction of the Residual Adsorbent Mass Requiring Long-Term Storage in Radioactive Waste Processing by Magnetic Separation

This paper describes the uptake of plutonium, 238Pu, by an adsorbent consisting of Brimac 216 natural carbon, a type of bone char. A strongly magnetic Brimac 216 fine powder produced by Lidzey has been shown to be an excellent adsorbent for many radionuclides. After the adsorption of the radionuclides has taken place, from solution onto the magnetic Brimac 216 powder, the powder, together with the adsorbed radionuclides, can be rapidly removed from suspension, as a concentrate, using high gradient magnetic separation (HGMS). A comparison is drawn between experimental results using the conventional column filter, with bone char as the adsorbent medium, and calculations for the HGMS process to treat 3.22 m3 of solution containing 8 mg·l-1 of 238Pu and to remove the 238Pu from the suspension to reduce the effluent to less than the maximum concentration limit (MCL) for 238Pu, which is 0.74 Bq·l-1; however, the minimum concentration value used here is less than the MCL and is 0.0444 Bq·l-1 (7.006 · 10-14 g·l-1 of 238Pu) and is denoted as the lower concentration level. Calculations indicate that HGMS is considerably faster than the column filtration method. This leads to a significant reduction in the time required to process the solution, even though the HGMS process is repeated a number of times. Also, the mass of adsorbent requiring long-term storage is much smaller for HGMS than for the column filtration method.

A realistic description of the process of high-gradient magnetic separation

An experimentally well-supported model, which realistically describes particle behaviour in HGMS, was developed more than a decade ago. The model assumed that HGMS is essentially a deep bed filter onto which an external magnetic field is imposed. In this present contribution, the model is revisited. It is shown that under suitable conditions the collision efficiency of particles with the matrix approaches unity, even in the absence of the magnetic traction force. It is further shown that the efficiency of capture is determined by the interplay of the static dipolar magnetic interaction and hydrodynamic shear stress. The threshold magnetic induction required for particles to be retained by the matrix is derived. Experimental data are used to demonstrate that there is a limited incentive to operate HGMS at a field higher than 2 T. Moreover, it is shown that undue emphasis on the magnetic field strength usually results in poor metallurgical performance. Excessively high capital and operating costs are an additional consequence of such an approach.

Feasibility and limitations of nanolevel high gradient magnetic separation

This work proposes a new separation concept denoted as nanolevel high gradient magnetic separation (HGMS) or magnetic adsorption. A magnetic heteroflocculation model describes the magnetic forces between two spherical particles with different sizes and magnetic properties, and reveals the feasibilities and limitations of nanolevel HGMS. The adsorbent particles, composed of antiferromagnetic magnetite, are modeled as large, immobile spheres on the order of 100–500 nm in radius. The adsorbate, paramagnetic colloidal Fe(OH)2 particles, are treated as freely diffusing small spheres on the order of 20–80 nm in radius. The model assumes that the magnetite particles are dispersed throughout a porous, nonmagnetic, solid matrix and that they are free of convective forces. The model also assumes that magnetic forces alone act on the Fe(OH)2 particles, opposed only by Brownian motion. When the magnetic force is attractive and overwhelms the randomizing Brownian force, adsorption occurs. The results from this model show the importance of the external field strength, the sizes of the adsorbent and adsorbate particles, and their magnetic properties in developing a practical nanolevel HGMS process.

Pulverized coal beneficiation by a fluidized high gradient magnetic separation process with slotted steel plates

New novel dry type high gradient magnetic separation devices comprising fluidizing-bed (FHGMS) with horizontal (type B) or vertical (type C) slotted steel plates in place of ferro-magnetic wires (normal wire type, type A) to trap magnetic particles in coal powder are developed for the purpose of coal beneficiation on a large scale. The separation performance of new devices is examined relative to powder size, gas velocity, amount of feed and so on. Ash reduction (AR) of type C is 22.3% with coal loss factor (CLF) of 6.7% indicating better separation performance compared with type A where AR is 19.7% with CLF of 6.6%. Ash reduction of type B is 31% which is more than that of type C, however, CLF of type B is also very high (18.5%). The difference (AR - CLF) of type B is surely smaller than that of types A or C, indicating the worst separation performance of type B among three types.

Characteristics of pressure drop across spongy nickel filter in magnetic separation process

The increase in pressure drop across the filter in high-gradient magnetic separation process has been examined experimentally. Spongy nickel with irregular-shaped skeleton was used as the magnetic filter and magnetite slurry was filtrated. Discussion of the pressure drop was carried out on the basis of particle deposit in the filter. For the sponge with 0.3 mm foam size, the pressure gradient increased proportionally with the local specific deposit. Empirical correlations for the characteristics of pressure drop were also obtained.

Pulverized coal beneficiation by dry type high gradient magnetic separation process

A novel dry type high gradient magnetic separation (HGMS) device comprising a fluidizing bed is studied for the purpose of the pulverized coal beneficiation. The separation performance of the device is examined related to powder size, gas velocity, amount of feed, processing time, wire size and repeated process. Chinese Coal in the size range of 44 and 297 μm in diameter with high magnetic susceptibility compared with other coals can be cleaned by magnetic effect. About 33% ash reduction at 86% coal recovery is observed at 1.5 minutes processing (3 passes).

Single wire model of high gradient magnetic separation processes I

A rate equation is being developed to model the buildup of single-sized, weakly magnetic particles on a single ferromagnetic cylindrical wire. The equation relates the rate of buildup on the wire to the fraction of the incoming particles that are captured and the portion of the particles that are carried away by the fluid stream. The theoretical predictions and experimental results generally agree well for a range of field values, flow rates, and particle concentrations. A more accurate model of the collection process will enable development of more accurate models for arrays and entire filters.