High Gradient Magnetic Separation Research Articles

Mechanical entrainment study by separately collecting particle deposit on matrix in high gradient magnetic separation

Mechanical entrainment of nonmagnetic particles is a leading issue deteriorating selectivity in high-gradient magnetic separation (HGMS). Previous researchers studied the high selectivity of downstream capture realized by increasing fluid velocity (despite the rapid loss of recovery). To enhance selectivity and extend the application fields of HGMS, a deep insight into mechanical entrainment in more realistic conditions of HGMS was essential. In this paper, captured particles from upstream and downstream side of a matrix were separately collected and analyzed with a novel experimental setup. Results showed that selectivity of downstream deposit was better than that of upstream deposit in all cases considered. Nonmagnetic particles were primarily trapped in upstream deposit due to higher chance of collision. Increasing fluid velocity could enhance selectivity in HGMS, but massive fine weakly magnetic particles would be lost in tailings. Gravity may play an important role in mechanical entrainment. Weakening upstream capture and enhancing downstream capture under relatively lower fluid velocity was meaningful and three potential technical solutions to improve selectivity were put forward.

Rotating flow characteristics in centrifugal high gradient magnetic separation and its effect on particle capture behavior

Centrifugal high gradient magnetic separation (CHGMS) concentrates weakly magnetic minerals at high selectivity, and the rotating flow in the separating area of the CHGMS separator significantly affects its separation performance. In this work, a simulation model based on finite element method was built up to simulate the rotating flow, and the effects of two most important operating parameters affecting the flow, i.e., matrix rotation speed and feed velocity, on the matrix capture behavior were analyzed through a pilot-scale CHGMS separator in concentrating a fine ilmenite ore. The COMSOL Multiphysics simulation of the rotating flow indicates that the slurry in the separating area forms into a rotating flow as a result of the rotation of matrix, and its flow trace length of unit volume slurry prolongs with increase in the matrix rotation speed and reduces with increase in the feed velocity, thereby affecting the collision probability of matrix to particles. It was found that the slurry velocities on the upstream and downstream of magnetic wire in the matrix are significantly higher than those on the right and left sides. There is a large radial velocity gradient in the separating area, which produces a fluid shearing stress to particles in the slurry, thus improves the loosing state of particles and the capture selectivity of matrix; this velocity gradient increases with increase in the matrix rotation speed and decreases with increase in the feed velocity. The capture experiments of matrix to ilmenite particles indicate that the increased matrix rotation speed has a more significant effect on the capture behavior than that of the feed velocity, and these results are basically consistent with those of simulations. This investigation provides an important reference for the optimum development and application of CHGMS technology.

Pulsating high-gradient magnetic separation of chalcopyrite and talc

The selective flotation of chalcopyrite from talc in practice is currently difficult and consumes a large amount of depressors, resulting in high production and environmental costs. The pulsating high-gradient magnetic separation (PHGMS) method has a strong potential for the effective separation of chalcopyrite and talc, based on their difference in magnetic susceptibility. In this work, the effects of magnetic induction, pulsating frequency and feed velocity of a pliot-scale PHGMS separator on the separation performance for pure chalcopyrite and talc minerals were investigated. The results indicate that the PHGMS achieves a selective separation of chalcopyrite from talc; and under the optimized conditions, a chalcopyrite concentrate of 30.22% Cu grade with 75.79% chalcopyrite recovery at talc content as low as 5.77% was produced from a chalcopyrite-talc mixture assaying 10.69% Cu and 66.67% talc. It was found that the chalcopyrite recovery for the ultra-fine particles fraction below 30 µm is lower than those of coarser fractions, as a result of the increased hydrodynamic drag over the magnetic force acting upon the ultra-fine particle. Entrainment may also occur between ultra-fine talc and chalcopyrite particles, which reduces the Cu grade for such ultra-fine particles in the copper concentrate. The PHGMS method may provide an environment-friendly and low-cost technology for the separation of chalcopyrite and talc.

β-Cyclodextrin functionalized magnetic nanoparticles for the removal of pharmaceutical residues in drinking water

Trace amounts of pharmaceuticals and personal care products (PPCPs) are found in our water systems, and they are known to have adverse effects on wildlife and human at the ng/L to μg/L range, below the detection limit of most water analytical instruments. Methacrylate acid (MAA)-ethyl acrylate (EA) colloidal scaffolds were prepared via emulsion polymerization and used as templates for the in-situ co-precipitation of Fe2+ to produce stable functional magnetic nanoparticles (MNPs) (<500 nm) decorated with β-cyclodextrin (β-CD) (FMNP). Emulsion polymerization with the controlled addition of monomer mixtures allowed for good size control, and silica coating was introduced to prevent the oxidation of FMNP. The superparamagnetic FMNP with high saturation magnetization (33 emu/g) could be readily separated from water using a high gradient magnetic separator (HGMS). Procaine hydrochloride (PrHy) was used as a model pharmaceutical residue to evaluate the performance of the FMNP, and 53.65 mg PrHy/g FMNP was absorbed using 600 ppm FMNP. A fast (30 min) adsorption kinetic follows the Pseudo-first-order kinetic model that described the physical adsorption through a 1 to 1 host–guest inclusion mechanism. And the adsorption behavior followed the Freundlich isotherm with a linear adsorption performance. The proposed system is scalable and adaptable to existing water treatment processes, and it can be used for the detection of low concentration pharmaceuticals via a pre-concentrating strategy.

Comparative effects of ferric hydroxide and (semi) conductive iron oxides on the anaerobic digestion of oxytetracycline-contaminated dairy manure

Additives, such as iron oxides, have been used in anaerobic digestion (AD) to promote direct interspecies electron transfer and to boost methane yield. However, the function of additives in the AD of antibiotic-contaminated organic wastes remained unclear. In this study, the effects of ferric hydroxide and (semi) conductive iron oxides, namely hematite and magnetite, on the AD of oxytetracycline (OTC)-contaminated dairy manure were investigated. Each iron oxide was assigned to a set of experiment where 0.25 g/L of OTC was added to 1 L batch digesters, while the concentration of iron oxide was varied from 0.08 to 0.34 g/L. Generally, magnetite was the most effective iron oxide to enhance methane yield in OTC-free dairy manure followed by ferric hydroxide and hematite. However, when the manure was contaminated with OTC, higher methane yield was observed in ferric hydroxide followed by hematite, while the lowest was with magnetite. In all digesters, the highest methane yield was observed with ferric hydroxide at 0.08 g/L, which was 1.43-fold of that with OTC and without iron oxides. The kinetic studies of methane yield demonstrated that the addition of iron oxides in the AD of OTC-contaminated dairy manure did not shorten the lag phase period despite the increase of methane yield. Thus, the increase of methane yield with ferric hydroxide was attributed to the possible formation of Fe-OTC complex, which attenuated the inhibition of OTC. A strategy to recover OTC residue in the AD was proposed using magnetite, a ferromagnetic particle, and high gradient magnetic separator.

Selectivity evaluation for high gradient magnetic separation performance based on static buildup model

Selectivity is an important indicator for the assessment of high gradient magnetic separation (HGMS) performance, but so far there were no theoretical methods available for such purpose. In this paper, the static buildup model (SBM) was improved and a modified SBM was established to solve this problem. Reported for the first time, the effect of both magnetic capture and mechanical entrainment were taken into consideration, and selectivity change during the whole accumulation process was intuitively demonstrated. The results implied that mechanical entrainment was weak in the earlier stage of accumulation but was quite serious in the later period, making selectivity decrease rapidly when particle accumulation was approaching saturation. Experimental results testified the model's ability of predicting a relatively accurate mass and grade of concentrate once characteristics of the feed were given, which will provide important guidance for HGMS research and deserves further investigation for refinement

Development and Application Characteristics of High Gradient Magnetic Separator

As one of the most effective techniques for fine particle processing, high gradient magnetic separation is mainly used in the separation and enrichment of fine and weak magnetic particles and other important industrial fields. High gradient magnetic separator is a new type of high intensity magnetic separator, which has strong ability to capture fine and weak magnetic particles, developed on the basis of ordinary high intensity magnetic separator. Based on the early periodic- high -gradient magnetic separators, the optimization development direction of high gradient magnetic separators and their application characteristics of various high gradient magnetic separators in these decades were summarized, and the future development directions of high gradient magnetic separator were presented.

Simulation of particle accumulation in high gradient magnetic separation based on static buildup model (SBM)

Static buildup model (SBM) is an analytical approach to predict upstream buildup profile of circular matrix in high-gradient magnetic separation (HGMS). But it was confined to single-wire system in idealized fluid and magnetic field, and was not applicable for more complicated or generalized systems. As better separation performance can be obtained by introducing composite force field or employing novel structural matrices in HGMS, it is necessary to develop models that are more adaptable for predicting particle buildup. In this paper, a simulation model based on SBM was developed to extend its application to complicated situation. The boundary of the buildup was updated by judging whether a particle released from locations near buildup surface would stay or not. And a characterized thickness within boundary layer was proposed to ensure that the released particles were subjected to forces of the same expression as that in SBM. The established model was proved to obtain close results with SBM when HGMS system was in idealized condition. Experimental results testified the model’s ability to predict saturated buildup profile of both circular and elliptic matrices in a realistic system. Since fluid and magnetic field information are processed by the simulation software, this model is also believed applicable for more complicated conditions such as multi-wire system and novel structure matrix system, which will be investigated in follow-up studies.

Rapid Extraction of High- and Low-Density Microplastics from Soil Using High-Gradient Magnetic Separation

Rapid Extraction of High- and Low-Density Microplastics from Soil Using High-Gradient Magnetic Separation

M R.N.A. Purifications Process: Affinity Chromato-Graphy, Magnetic Beads and Graphene Coated Large Scale Production and Toxicological Aspects

Aim of this work is to verify the state of the art related m R.N.A. purification process , the technology used as well as the materials employed. New methods vs classic methods: the use of affinity cromato-graphy or and high‐gradient magnetic separation (H.G.M.S.). In particular the use of magnetic beads since introduction of the graphene coated ones. Various producers provide many kind of magnetic beads with various grade of efficiency in separation. Becasue today there is a great debate around graphene derivates peresence (or not) in vials of m R.N.A. VACCINE it is relevant to better clarify the production process as well and the materials used.

FeOOH and nZVI combined with superconducting high gradient magnetic separation for the remediation of high-arsenic metallurgical wastewater

Metallurgical wastewater with high arsenic (As) concentration presents important challenges to human health and the environment because of its high toxicity and carcinogenicity. Iron (Fe)-based adsorbents can effectively detoxify low As-containing wastewater but are less helpful for high concentration of As and for solid–liquid separation. Herein, an advanced strategy is proposed to dispose high As wastewater using nano-zerovalent iron (nZVI) and ferric oxyhydroxide (FeOOH) combined with superconducting high gradient magnetic separation (HGMS) technology. The superconducting HGMS technology promoted the removal of As by nZVI and FeOOH via a magnetic flocculation reaction, while simultaneously separating reaction products adsorbed As from wastewater. Interestingly, nZVI could be corroded to release Fe(II) ions which then generated Fenton reaction under aerobic conditions, facilitating the oxidization of As(III)/Fe(II) to As(V)/Fe(III) ions. The Fe(II) and Fe(III) hydrolyzed in the form of hydroxy hydroxide and further generated the magnetic flocculates and coprecipitate. The results showed that 99.06% of As was successfully removed from wastewater with an initial As concentration of 5358 mg/L, at a dosage of 20 g/L, a magnetic field strength of 5 T, and a flow velocity of 500 mL/min. Compared with FeOOH, nZVI showed more favorable adaptability for lead smelting wastewater. Removal of As from wastewater by using nZVI combined with superconducting HGMS technology has a great potential to achieve industrial application for metallurgical heavy metal wastewater.

Modern trends of technological advancement in iron ore processing

The authors discuss evolution of technologies and procedures in iron ore processing. It is emphasized that an iron ore treatment approach is governed by the type and nature of dissemination of metallic and nonmetallic minerals. Iron ore is mostly processed using magnetic, magnetic&ndash;gravity or magnetic&ndash;flotation separation. High grade ore with the iron content of 60&ndash;63 % is utilized without dressing, immediately after crushing and size grading. Magnetic and flotation circuits are used in processing of the most rebellious and finely disseminated low-grade ore. The ore pretreatment technologies feature the trends of introduction of press&ndash;rollers, which reduces energy inputs by 10&ndash;30 % as compared with the semi autogenous grinding. The essential improvement of size grading efficiency is reached via inclusion of fine sifting in the grinding circuits. Due to persistently growing demand for high-quality concentrate, fine sifting is also included in the finishing processing of rough concentrates. One of the methods to produce &lsquo;super concentrates&rsquo; is the reverse cation flotation of rough iron concentrates using collectors composed of mono-, di- and ether amines, as well as their mixtures, including alcohols. The need to dress ROM hematite ore and to after-treat magnetic separation tailings of magnetite ore initiated engineering, manufacturing and commercial-scale introduction of high-gradient and highduty magnetic separators based on permanent rare earth magnets with the field density to 1.7 T. These machines have much smaller weight and consume much less energy than the high-gradient separators based on electromagnets. The promising method for hematite ore treatment is the reverse cation flotation. The use of the described processes, technologies and equipment allows production of concentrates with the iron content higher than 70 % and the silicon content less than 2 % at the iron recovery more than 90 %.

Insights into the effect of magnetic interactions on the magnetization process of matrices in high gradient magnetic separation

In-depth understanding and prediction of the magnetization process of matrices in high gradient magnetic separation are essential for matrix design and performance analysis. However, the existing research typically ignores the magnetic interactions between magnetized elements in the matrices. This article numerically reveals the role of the magnetic interactions on the magnetization process of these elements with different configurations, showing that both the gap distance between elements and the relative direction between the applied magnetic field and the matrix structure have a significant effect on the magnetization of elements in matrices. Meanwhile, it is pointed out that the effect of magnetic interactions limits the application of the existing methods for predicting magnetization state of matrices. To solve this problem, a convenient and versatile method is further proposed with considering magnetic interactions and is validated by numerical simulations, providing an effective tool to determine applicable magnetization models of matrices in different situations.

Innovative pre-concentration technology for recovering ultrafine ilmenite using superconducting high gradient magnetic separator

To achieve the utilization of the abandoned ultrafine ilmenite (−20 μm) produced in the titanium magnetite processing plant in Panzhihua, the superconducting high-gradient magnetic separation (SMS) technology was proposed in this study. After optimizing the conditions of magnetic intensity, feeding and pulsation, an SMS concentrate with TiO2 grade of 16.03% and TiO2 recovery of 66.39% was obtained through one roughing–one cleaning pre-concentration flowsheet. The specific magnetic force and magnetic force were calculated and analysed to illustrate the pre-concentration mechanism, and the results revealed that the combination of high magnetic field and strong pulsating resulted in the effective pre-concentration of the ultrafine ilmenite in the SMS process. In addition, the magnetic force analysis indicated that the high magnetic intensity and high magnetic gradient are the key factors of the SMS technology. Furthermore, the EDS-Mapping detection certified that the ultrafine ilmenite was concentrated from the gangue minerals using SMS technology.

High-Gradient Magnetic Separation of Compact Fluorescent Lamp Phosphors: Elucidation of the Removal Dynamics in a Rotary Permanent Magnet Separator

In an ongoing effort towards a more sustainable rare-earth element market, there is a high potential for an efficient recycling of rare-earth elements from end-of-life compact fluorescent lamps by physical separation of the individual phosphors. In this study, we investigate the separation of five fluorescent lamp particles by high-gradient magnetic separation in a rotary permanent magnet separator. We thoroughly characterize the phosphors by ICP-MS, laser diffraction analysis, gas displacement pycnometry, surface area analysis, SQUID-VSM, and Time-Resolved Laser-Induced Fluorescence Spectroscopy. We present a fast and reliable quantification method for mixtures of the investigated phosphors, based on a combination of Time-Resolved Laser-Induced Fluorescence Spectroscopy and parallel factor analysis. With this method, we were able to monitor each phosphors’ removal dynamics in the high-gradient magnetic separator and we estimate that the particles’ removal efficiencies are proportional to (d2·χ)1/3. Finally, we have found that the removed phosphors can readily be recovered easily from the separation cell by backwashing with an intermittent air–water flow. This work should contribute to a better understanding of the phosphors’ separability by high-gradient magnetic separation and can simultaneously be considered to be an important preparation for an upscalable separation process with (bio)functionalized superparamagnetic carriers.

SPIONs self-assembly and magnetic sedimentation in quadrupole magnets: Gaining insight into the separation mechanisms

Superparamagnetic iron oxide nanoparticles (SPIONs) are currently popular materials experiencing rapid development with potential application value, especially in biomedical and chemical engineering fields. Examples include wastewater management, bio-detection, biological imaging, targeted drug delivery and biosensing. While not exclusive, magnetically driven isolation methods are typically required to separate the desired entity from the media in specific applications and in their manufacture and/or quality control. However, due to the nano-size of SPIONs, their magnetic manipulation is affected by Brownian motion, adding considerable complexities. The two most common methods for SPION magnetic separation are high and low gradient magnetic separation (HGMS and LGMS, respectively). Nevertheless, the effect of specific magnetic energy fields on SPIONs, such as horizontal (perpendicular to gravity), high fields and gradients (higher than LGMS) on the horizontal magnetophoresis and vertical sedimentation of SPIONs has only recently been suggested as a way to separate very small particles (5 nm). In this work, we continue those studies on the magnetic separation of 5–30 nm SPIONs by applying fields and gradients perpendicular to gravity. The magnetic field was generated by permanent magnets arranged in quadrupolar configurations (QMS). Different conditions were studied, and multiple variables were evaluated, including the particle size, the initial SPIONs concentration, the temperature, the magnetic field gradient and the magnetic exposure time. Our experimental data show that particles are subjected to horizontal magnetic forces, to particle agglomeration due to dipole–dipole interactions, and to vertical sedimentation due to gravity. The particle size and the type of separator employed (i.e. different gradient and field distribution acting on the particle suspension) have significant effects on the phenomena involved in the separation, whereas the temperature and particle concentration affect the separation to a lesser extent. Finally, the separation process was observed to occur in less than 3 mins for our experimental conditions, which is encouraging considering the long operation time (up to days) necessary to separate particles of similar sizes in LGMS columns that also employ permanent magnets.

Magnetic Preconcentration and Process Mineralogical Study of the Kiviniemi Sc-Enriched Ferrodiorite

Scandium is classified as a critical raw material by the European Union. Its beneficiation from various primary and secondary sources is currently being studied under several research and development projects. Due to the geochemical characteristics of Sc, its enrichment to ore grades by geological processes is scarce. Potential new sources are investigated to respond to the expected increasing demand for this rare earth metal. The recently discovered Kiviniemi Sc deposit in Finland represents an igneous occurrence with estimated total resources of 13.4 Mt and an average Sc grade of 163 g/t. The deposit consists of relatively homogeneous ferrodioritic intrusive body with its main unit with ~2.5 ha surface extension. Scandium is mainly incorporated into the lattice of clinopyroxene and amphibole within the main unit. Composite samples from three drill cores from various parts of the main unit were concentrated with a combination of low-intensity and high-gradient magnetic separation. Depending on the feed characteristics, high-gradient magnetic separation reached recoveries between 87% and 92% with 230–310 ppm Sc while removing 35–49 mass percent of gangue minerals, mainly plagioclase and potassium feldspar. Our study provides information on the magnetic preconcentration conditions with process mineralogical details and produced concentrates for further testing according to the suggested processing scheme.

Understanding and prediction of magnetization state of elliptic cross-section matrices in high gradient magnetic separation

Theoretical prediction of magnetization state of matrices in high gradient magnetic separation is of importance to the separation performance analysis. However, the existing methods are limited to the cases where a magnetic field is parallel or perpendicular to one axis of magnetic elements in matrices. To solve this issue, in this work, we propose an easily understood method to construct the correlation between the magnetization of an elliptic cross-section element and the externally applied magnetic field. On this basis, we develop a simple relation to rapidly determine the demarcation for judging the magnetization sate of the element, which is suitable for the cases with an arbitrary magnetic field direction. Furthermore, we reveal the influence of the shape coefficient of the element on the prediction accuracy of its magnetization process. This work has important theoretical value for understanding the magnetization process of elliptic cross-section matrices under different magnetic fields.

Accurate calculation of major forces acting on magnetic particles in a high-gradient magnetic field: A 3D finite element analysis

Magnetic agglomeration of magnetic particles under the influence of magnetic field plays a vital role in enhancing the separation of fine magnetic mineral particles. In this study, the major forces acting on weakly magnetic particles and the ratio between forces in high-gradient magnetic separators (HGMS) are investigated. A 3D high-gradient magnetic field based on HGMS was simulated, and the major forces (magnetic force Fm, magnetic agglomeration force Fmm, and gravity G) acting on weakly magnetic particles were calculated in the form of Fm/Fmm, Fm/G by finite element method (FEM). The results show that the value of Fm/Fmm became lower as the increase of magnetic field intensity and the relative permeability of particles, higher as the increase of the magnetic field gradient, the particle size and the distance between particles. However, there was no correlation between the value of Fm/Fmm and the density of the magnetic particles. Furthermore, the value of Fm/G was inversely proportional to the density of the particles and directly proportional to the relative permeability of particles, the magnetic field intensity and magnetic field gradient. Meanwhile, Fm was at least 190 times greater than Fmm in any case and Fm was far bigger than G in most cases, indicating that the magnetic agglomeration is not significant in HGMS and gravity has little effect on high-gradient magnetic separation, and HGMS are destined to be a kind of high-efficiency magnetic separation equipment.

Recovery of Metals from Heat-Treated Printed Circuit Boards via an Enhanced Gravity Concentrator and High-Gradient Magnetic Separator.

The recovery and reuse of waste printed circuit boards (PCBs) has attracted more and more attention from global researchers, as recycling of waste PCB metals is of great significance to the rational utilization of metal material resources. This study puts forward a clean and economical method in which enhanced gravity separation and wet high-gradient magnetic separation were combined to recover waste PCBs with heat treatment at a temperature of 240 °C. The heat treatment could improve the metal liberation effect of the PCBs, and the thermal behavior was measured by thermogravimetric analysis (TGA). The pyrolysis of the non-metal fraction (NMF) began around 300 °C, and the glass transition temperature of epoxy resin was 135.17 °C. The enhanced gravity separation technique was used for the separation of metals and NMF under the compound force field. The metals grade of the gravity concentrates fraction (GRF) was 82.97% under the optimal conditions, and the metals recovery reached 90.55%. A wet high-gradient magnetic separator was applied to classify the GRF into magnetic (MA) and non-magnetic (NMA) fractions, which could achieve iron and copper enrichment. After the three stages combined process, the copper and iron grades of the NMA and MA fractions were 70.17% and 73.42%, and the recovery reached 74.02% and 78.11%, respectively.