Scrap Magnets Research Articles

Transforming Highly Corroded Scrap Magnets Into Coercive Powders

Transforming Highly Corroded Scrap Magnets Into Coercive Powders

A strategy for selective extraction of lanthanides based on self-assembly with MPyEDChDGA from nitric acid solution☆

The development of new and efficient extractants plays a key role in the separation and recovery of rare earth elements. In this paper, the extractant (N,N-methylpyridineethyl-N',N'-dicyclohexyl-3-oxadiglycolamide, MPyEDChDGA) with a new structure was synthesized, and the pyridine group was successfully grafted onto the 3-oxadiglycolamide structure. Using MPyEDChDGA for efficient enrichment of rare earth ions, the self-assembled solids were recovered by simple filtration without further back-extraction and final precipitation, achieving a one-step strategy for the recovery of rare earth ions. Several important parameters affecting the self-assembly extraction, including pH, diluent, temperature, and extractant concentration, were systematically evaluated using La(NO3)3, Tb(NO3)3, and Lu(NO3)3 as representatives. The self-assembled solids were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), 1H nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FT-IR), Raman, and X-ray photoelectron spectroscopy (XPS) analyses. The stoichiometry of the extraction species was characterized using the Job’s method and electrospray ionization mass spectrometry (ESI-MS). In addition, MPyEDChDGA was applied to the recovery of Sm in SmCoCu simulated liquid, and the results show that MPyEDChDGA has good selectivity of Sm from transition metals (Co, Cu). The separation factor of Sm/Co can reach 6281±117, which provides a new approach to recovering Sm from SmCoCu scrap magnets. This study presents an efficient and convenient new strategy for the recovery and separation of rare earth elements.

Vacuum processing temperature effect on highly coercive recycled NdFeB permanent magnets with Pr-based alloy addition

This study presents a modified method for recycling NdFeB scrap magnets, producing up to 100 kg of recycled sintered NdFeB magnets per batch. By adding a Pr-based alloy to N40H-grade NdFeB scrap and optimizing vacuum sintering and heat treatment conditions, we enhanced the magnetic properties and corrosion resistance of the recycled magnets. Various analyses, including BH Tracer measurements, FE-EPMA, accelerated corrosion tests, and C/N/O content analysis, evaluated differences in magnetic properties, microstructure, corrosion resistance, and impurity content. Optimal recycling involved vacuum sintering at 1085 °C, followed by heat treatments at 900 °C and 470 °C. Recycled magnets with PrCoGa alloy showed superior properties, such as an intrinsic coercivity (iHc) of 1414 kA/m, remanence (Br) of 1.290 T, and a maximum magnetic energy product ((BH)max) of 315.4 kJ/m, meeting N40H standards. Accelerated corrosion tests also indicated enhanced corrosion resistance in recycled magnets with Pr90Co8Ga2 alloy. This research offers a commercially viable approach for NdFeB magnet and rare earth element recycling.

An experimental investigation and predictive modeling using machine learning technique for reclamation of metal values from scrap NdFeB magnets

Neodymium-Iron-Boron (NdFeB) magnets are widely used in various industries due to their exceptional magnetic properties, such as high coercivity, remanence, and maximum energy product. These magnets consist of rare earth elements (REEs) viz., neodymium (Nd), praseodymium (Pr), and Dysprosium (Dy), along with other metals. With the ever increasing demand for REEs and the need to bridge the supply gap, it is crucial to develop alternative methods for their extraction. Recycling metal from scrap magnets is a promising approach to address the pressure on the supply chain and work towards sustainable development. The primary goal of this study is to generate a predictive model based on machine learning to determine the optimal conditions for metal recovery from scrap NdFeB magnets through water leaching after chloridizing roasting. Bench-scale leaching experiments were carried out to generate a dataset for statistical process optimization and machine learning analysis. The leaching kinetics of neodymium was also explored, and mixed-controlled shrinking core model was found to be most suitable, with an activation energy of 58.11 kJ/mol in the temperature range of 25– 95 °C. This study is the first to utilize a machine learning approach to analyze the potential process variables and their impact on metal recovery from calcined NdFeB magnet powder. A comparative analysis between experimental and machine learning approaches is presented to predict the optimal conditions for selective recovery of metal values from scrap NdFeB magnets. The maximum efficiency of extraction of metal ions was found to occur at a temperature of 95 °C, solid to liquid ratio of 125 g/l, and leaching duration of 60 min.

Magnetic and structural properties of multiple recycled and sustainable sintered Nd-Fe-B magnets

Scrap magnets from magnetic resonance tomography (MRT) devices with nominal composition of Nd28.04Dy0.80Tb0.44FebalB1.06Co1.65Al0.34Ga0.22Cu0.18 (wt. %) were recycled multiple times with the so-called magnet-to-magnet or functional recycling approach employing hydrogen decrepitation. Changes in different material properties like chemical composition, impurity content, particle size, magnetic properties, microstructure and degree of alignment were investigated in detail. The multiple processing and recycling of the material leads to a decrease in texture, orientation and the resulting magnetic properties of the recycled magnets, respectively. Meanwhile impurities and particle size of the material increase through several milling and sintering processes. Different amounts of Nd hydride were mixed with the recyclate to improve the properties. With 4 wt. % Nd hydride the density of the recycled magnets can be fully restored. It was shown that magnetic properties of the recycled magnets meet the specification of primary magnets even after several cycles. However, they outperform magnets produced from primary materials in terms of sustainability with lower ecological and social footprints. Furthermore, they can lower the production cost of products using permanent magnets by reducing the energy consumption and raw material costs.

Separation of Cobalt, Samarium, Iron, and Copper in the Leaching Solution of Scrap Magnets

With the growing awareness of protecting the urban environment and the increasing demand for strategic materials, recycling of SmCo magnets has become imperative. This paper provides a series of methods regarding the available hydrometallurgical technologies for recycling scrap magnets. This study aimed to recover samarium (Sm), cobalt (Co), copper (Cu), and iron (Fe) from acid leachate of SmCo scrap by using precipitation and ion exchange. IRC748 showed a good adsorption capacity for Fe and Cu. Elution tests were conducted using sulfuric acid at the concentration of 2N as eluents. Precipitation was performed first using a selective chemical precipitation method, and the Sm was first precipitated as a sodium samarium sulfate powder. Then, the samarium-deprived solution was placed in the beaker, and the addition of oxalic acid promoted cobalt oxalate precipitation. Furthermore, the leachate, which is rich in Cu and Fe, was mixed with oxalic acid to obtain the copper oxalate precipitation. This study successfully recovered SmCo magnets through ion exchange and precipitants.

Experimental evidence for the suitability of the hydrogen decomposition process for the recycling of Nd-Fe-B sintered magnets

An effective and complete processing route for the recycling of sintered Nd-Fe-B scrap magnets was proposed. Sintered Nd-Fe-B magnets were subjected to the Hydrogen Decrepitation (HD) process at various temperatures in the range of 50–300 °C, at two different pressures, 50 kPa and 200 kPa, followed by vacuum dehydrogenation in the range of 720–820 °C. The structure refinement efficiency and magnetic properties of the powders obtained were characterized. Low hydrogen pressure (50 kPa) was found to increase the magnetic properties at each temperature for all powder fractions. It was also shown that particle refinement occurs at low (50 °C, 100 °C) temperatures for low (50 kPa) pressure and higher temperatures (200 °C, 300 °C) for high pressure (200 kPa), respectively. High pressure also accelerates the initialization of the HD process at each temperature. No correlation was found between hydrogenation temperature and magnetic properties of the powders, except for the small increase in coercivity increase with growing temperature. The coarse fraction (400–500 µm) was found to have the highest magnetic properties for almost each HD process. The best magnetic properties Hci = 497 kA/m, Br = 1.1 T, and (BH)max = 121 kJ/m3 were obtained for hydrogenation at a temperature of 50 °C, pressure 50 kPa and dehydrogenation at 780 °C.

The extraction of NdFeB magnets from automotive scrap rotors using hydrogen

Scrap containing NdFeB is a valuable resource for the production of NdFeB magnets as the demand for these materials grows. One of the challenges is to recover the rare earths or the NdFeB alloy powder in a clean and cost effective manner so that it can be re-processed into new magnets rather than becoming lost to landfill. Work on using hydrogen to process scrap magnets (HPMS) has been shown to be successful when targeting hard disk drives. Currently, there is a lack of information on reliable methods to separate out NdFeB from other scrap sources such as automotive drives. In the near future, with increasing sales and electrification of cars, the automotive sector could be an important source for Dy containing magnets. In this paper, the hydrogen processing of scrap magnets has been demonstrated as an extraction method for NdFeB from automotive rotors for the first time, with the aim to examine the viability of this recycling process and learn lessons for design for recycling. Thus leading to the sustainable production of these components. Significant challenges were outlined when applying the hydrogen process to rotors with embedded magnets. After the extraction, further process steps may also be needed to separate epoxy coatings, as sieving could only reduce the carbon content to 1420 ppm, compared to 770 ppm in the base alloy. The gravimetric measurements also confirmed that Dy additions increase both the initiation and absorption time for hydrogen decrepitation. Hence, a higher hydrogen pressure will be required to speed up the process.

An innovative environmental process for the treatment of scrap Nd-Fe-B magnets

Strict environmental regulations as well as requirement of conservation of natural resources compelled the researchers to recycle the metal values from secondary resources. The scrap magnets found to be a potential alternative resource to extract rare earth metal, Nd. Present paper reports a novel process flow-sheet for the recycling of scrap Nd-Fe-B magnets to recover Nd as marketable salt and other valuable by-products. The Nd-Fe-B magnets were demagnetized, crushed and charged to atmospheric leaching resulting in ~99.99% recovery of REMs (Nd, Pr, Dy) and Fe using 1 M H2SO4 solution at room temperature for 90 min and pulp density 50 g/L. The obtained leach liquor was subjected to acid extraction procedure by mixing the liquor with 70% TEHA diluted in kerosene for 10 min, which requires five stages for complete extraction of acid from the liquor having O/A ratio 2:1. Ammonia solution was used to increase the pH of acid free leach liquor to 1.65 for the precipitation of Nd (with minor amount of Pr and Dy) and above that to precipitate Fe. Further, processing of these valuables make them industrially applicable. The leached residue was checked using Toxicity Characteristics Leachability Procedure (TCLP) test and found the remained metals within the permissible limit. This process offers a simple and efficient means to reduce the toxicological effect by recovering Nd from magnets of computer hard disks.

Selective Recovery of Rare Earth Elements from a Wide Range of E-Waste and Process Scalability of Membrane Solvent Extraction.

In this study, the scalability of the supported membrane solvent extraction (MSX) process for the recovery of rare earth elements (REEs) from scrap permanent magnets was demonstrated by processing larger quantities of different scrap magnet feedstocks with a membrane area of more than 1 m2. The MSX process was successfully employed to recover high-purity REEs in their oxide form (REOs) from a wide range of end-of-life magnet feedstocks including hard disk drives (HDDs), MRI, cell phone, bonded, swarf, and hybrid car magnets. REEs with the purity of more than 99.5 wt %, recovery of more than 95%, and an extraction rate of as high as 9.3 g/(h m2) were recovered from feed solutions containing REEs of up to 46 000 mg/L. It was found that the extraction rate strongly depends on the initial REE concentration in the feed solution and to some extent on the composition of the scrap magnet source. The results demonstrated that MSX is a scalable and versatile process for the recovery of REEs from a wide range of electronic wastes.

Particle size dependent sinterability and magnetic properties of recycled HDDR Nd–Fe–B powders consolidated with spark plasma sintering

The dependence of the magnetic properties on the particle size of recycled HDDR Nd–Fe–B powders was investigated, with the aim to assess the reprocessing potential of the end-of-life scrap magnets via spark plasma sintering (SPS). The as received recycled HDDR powder has coercivity (Hci) = 830 kA/m and particles in the range from 30 to 700 μm (average 220 μm). After burr milling, the average particle size is reduced to 120 μm and subsequently the Hci of fine (milled) powder was 595 kA/m. Spark plasma sintering was exploited to consolidate the nanograined HDDR powders and limit the abnormal grain coarsening. The optimal SPS-ing of coarse HDDR powder at 750 °C for 1 min produces fully dense magnets with Hci = 950 ± 100 kA/m which further increases to 1200 kA/m via thermal treatment at 750 °C for 15 min. The burr milled fine HDDR powder under similar SPS conditions and after thermal treatment results in Hci = 940 kA/m. The fine powder is further sieved down from 630 to less than 50 μm mesh size, to evaluate the possible reduction in Hci in relation to the particle size. The gain in oxygen content doubles for <50 μm sized particles as compared with coarser fractions (>200 μm). The XRD analysis for fractionated powder indicates an increase in Nd2O3 phase peaks in the finer (<100 μm) fractions. Similarly, the Hci reduces from 820 kA/m in the coarse particles (>200 μm) to 460 kA/m in the fine sized particles (<100 μm). SPS was done on each HDDR powder fraction under the optimal conditions to measure the variation in HCi and density. The Hci of SPS-ed coarse fraction (>200 μm) is higher than 930 kA/m and it falls abruptly to just 70 kA/m for the fine sized particles (<100 μm). The thermal treatment further improves the Hci to >1000 kA/m only up to 100 μm sized fractions with >90% sintered density. The full densification (>99%) is observed only in the coarse fractions. The loss of coercivity and lack of sinterability in the fine sized particles (<100 μm) are attributed to a very high oxygen content. This implies that during recycling, if good magnetic properties are to be maintained or even increase the HDDR powder particles can be sized down only up to ≥100 μm.

Neodymium recovery from scrap magnet using ammonium persulfate

This study proposes a novel leaching methodology to recover neodymium from scrap magnet using ammonium persulfate ((NH4)2S2O8) solutions. The NdFeB magnets from obsolete Hard-Disk-Drives were physically treated by thermal demagnetization (400 °C, 45 min) and mechanical crushing (< 420 μm). The chemical composition of the ground sample was Nd: 31.5 wt%, Fe: 64.8 wt%, Co: 1.9 wt%, Ni: 0.6 wt%. Diagrams of equilibrium phases (Eh vs. pH) were designed to determine the predominance of the formed species in the (NH4)2S2O8 system. Ammonium persulfate aqueous solutions were prepared to generate oxidative sulfate radicals. These radicals allowed to leach the ground samples of NdFeB magnets and recover of neodymium sulfate. The influence of (NH4)2S2O8 concentration (0.7–1.3 M), temperature (25–75 °C) and L/S ratio (25–50 mL/g) on NdFeB magnets leaching was investigated employing analysis of variance in a 23 full factorial experimental design. At the optimal conditions, quantities >98% of NdFeB magnets were leached after 15 min reaction time. Neodymium sulfate was selectively recovered as crystals, and evaluated by chemical and crystallographic analyses. The findings presented in this investigation suggest that neodymium could be recovered from scrap magnet using an eco-friendly leaching methodology assisted by ammonium persulfate.

The sintering mechanism of fully dense and highly coercive Nd-Fe-B magnets from the recycled HDDR powders reprocessed by spark plasma sintering

The goal of this study was to justify the reprocessing of recycled HDDR Nd-Fe-B powders with spark plasma sintering (SPS) and to investigate the dependence of the final magnetic properties on SPS and thermal treatment. The initial recycled HDDR powder of the composition Nd13.4Dy0.6Fe78.6B6.1Nb0.4Al0.7 with 4760 ppm O2 content, coercivity (HCi) = 830 kA/m, and large particle size distribution <50–600 μm, was treated using the SPS parameters as follows: T = 650–850 °C for 1–5 min and 50 MPa pressure. The post SPS thermal treatment was performed at 750 °C for 15 min in vacuum. The optimal SPS conditions at 750 °C for 1 min, yielded fully dense magnets with the coercivity HCi = 1060 kA/m, which was boosted to 1160 kA/m after the post-SPS thermal treatment. The grain growth was obvious in samples SPS-ed above 800 °C and subsequently, the HCi was reduced. The SPS reprocessing beyond 850 °C was found to be detrimental to the overall magnetic properties due to the formation of bimodal grain size distribution origination from the abnormal grain growth (700–2600 nm). The redistribution of Nd-rich grain boundary phase between the Nd2Fe14B matrix grains in thermally treated magnets and the relaxation of the internal stresses induced via SPS are the possible reasons for the HCi surpassing the HCi of the starting recycled HDDR powder. It was shown that the SPS consolidation technique is suitable for producing fully dense nanograined bulk Nd-Fe-B magnets, with coercivities even exceeding the initial HDDR-powder and is one of the most suitable routes for revitalizing the Nd-Fe-B scrap magnets.

Towards an Alloy Recycling of Nd–Fe–B Permanent Magnets in a Circular Economy

Rare earth permanent magnets are an integral part of many electrical and electronic devices as well as numerous other applications, including emerging technologies like wind power, electric vehicles, fully automized industrial machines, and robots. Due to their outstanding properties, magnets based on Nd–Fe–B alloys are often not substitutable by employing less critical material systems. Today, WEEE (Waste Electrical and Electronic Equipment) take-back systems for a variety of products containing Nd–Fe–B magnets are well established. They form an ideal basis for a systematic provision of scrap magnets that can be recycled. Hydrometallurgical approaches that aim at completely dissolving the material to regain elements or oxides are energy and time consuming. Thus, they are costly and come with a large environmental footprint. Recycled rare earth elements and oxides would have to compete with virgin materials from China and can hardly be processed in Europe, due to the lack of respective industries. This paper presents material-to-material recycling approaches, which would maintain the magnet alloys and use them directly for a new magnet production loop. The recycled magnets compete well with those made from primary materials, that is, in terms of magnetic properties as well as in terms of production costs. They excel by far rare earth permanent magnets made from primary materials regarding the environmental footprint. Regarding the shift towards a Green Economy, humanity will consume less fuels in combustion processes but rather exploit functional materials in renewable energy and mobility technologies in the future. This shift fundamentally depends on a circular economy of noble as well as less-noble technology metals.

Leaching kinetics study of neodymium from the scrap magnet using acetic acid

Abstract Leaching kinetics of neodymium was investigated from Nd–Fe–B scrap magnet using green solvent as CH3COOH. The Characterization study of the scarp magnet was performed by XRD and SEM–EDAX to ascertain the phase as Nd2Fe14B (31.05% Nd, 65.15% Fe and 0.66% B). Influence of the factors such as CH3COOH concentrations (0.05–0.8 M), agitation speed (200–1000 rpm), particle size (45–150 μm), temperature (308–353 K) and S/L ratio (1–5% (W/V)) affecting on leaching of Nd was investigated to obtain an optimum condition. Maximum yield (99.99%) of Nd along with definite extraction of Fe was resulted at the condition: Agitation speed: 800 rpm, S/L: 1% (W/V), temp. 353 K, 0.4 M CH3COOH and particle size: 106–150 μm). The key factors such as CH3COOH concentration and temperature appears to be critical on effective dissolution of both Nd and Fe from the scrap magnet phase. Leaching kinetic results showed best fit with the shrinking-sphere model ( 1 - 1 - X 1 / 3 = k ap t ) ensuring the overall leaching process is governed by surface chemical control mechanism. The activation energy determined from the experimental study was of +17.13 kJ/mol further more supports the proposed chemical control leaching process. Thermodynamics variables like ΔG0, ΔH0 values determined from the Arrhenius plot at varied temperature indicating the feasibility of the leaching reaction of endothermic type. Linear dependence of the plot of log kap on log 1/do and a first order dependence of kap with CH3COOH at 0.4 M was derived from the above proposed leaching model.

Commercial-scale recycling of NdFeB-type magnets with grain boundary modification yields products with ‘designer properties’ that exceed those of starting materials

NdFeB-type magnets dominate the market for high performance magnetic materials, yet production of ‘virgin’ magnets via mining is environmentally, financially and energetically costly. Hence, interest is growing in ‘magnet to magnet’ recycling schemes that offer the potential for cheaper, more environmentally-friendly solutions to the world’s growing appetite for rare-earth based magnetic materials. Unfortunately, previously described recycling processes only partially capitalise on this potential, because the methods described to date are limited to ‘laboratory scale’ or operate only under ideal conditions and result in products that fail to recapture the coercivity of the starting, scrap materials.Herein, we report a commercial scale process (120kg batches) that completely recovers the properties of the starting scrap magnets. Indeed, ‘grain boundary modification’, via careful addition of a proprietary mix of blended elements, produces magnets with ‘designer properties’ that can exceed those of the starting materials and can be closely tailored to meet a wide variety of end-user applications, including high-coercivity (>2000kA/m), sintered magnets suitable for motor applications.

Selective Extraction of Rare Earth Elements from Permanent Magnet Scraps with Membrane Solvent Extraction.

The rare earth elements (REEs) such as neodymium, praseodymium, and dysprosium were successfully recovered from commercial NdFeB magnets and industrial scrap magnets via membrane assisted solvent extraction (MSX). A hollow fiber membrane system was evaluated to extract REEs in a single step with the feed and strip solutions circulating continuously through the MSX system. The effects of several experimental variables on REE extraction such as flow rate, concentration of REEs in the feed solution, membrane configuration, and composition of acids were investigated with the MSX system. A multimembrane module configuration with REEs dissolved in aqueous nitric acid solutions showed high selectivity for REE extraction with no coextraction of non-REEs, whereas the use of aqueous hydrochloric acid solution resulted in coextraction of non-REEs due to the formation of chloroanions of non-REEs. The REE oxides were recovered from the strip solution through precipitation, drying, and annealing steps. The resulting REE oxides were characterized with XRD, SEM-EDX, and ICP-OES, demonstrating that the membrane assisted solvent extraction is capable of selectively recovering pure REEs from the industrial scrap magnets.

Anisotropic powder from sintered NdFeB magnets by the HDDR processing route

Sintered NdFeB-based scrap magnets were recovered and processed using the HD and HDDR routes. The effects of varying the HDDR processing temperature were investigated (over the range 835–930°C). The disproportion was carried out with a pressure ramp to a maximum of 1000mbar hydrogen pressure with a 1h hold time at each step and the optimum recombination conditions were set at 100mbar with a 20min hold time. Anisotropic NdFeB powder was produced in all cases with the best magnetic properties achieved at a processing temperature of 880°C, producing powder with a remanence of 1.10(±0.02)T and an intrinsic coercivity of 800 (±16)kAm−1 and giving a (BH)max of 129(±2.5)kJm−3.