REE Recovery Research Articles

Recovery of samarium and cobalt/iron oxide from SmCo magnets through acid baking and water leaching

AbstractRare earth elements (REEs) and cobalt (Co) are listed as critical raw materials because of their importance in global industrial production growth, high supply risk, and economic significance. The recovery of Co and REEs from secondary resources is therefore proposed as a key countermeasure to address this concern. In this study, a straightforward process that integrates acid baking and water leaching is proposed for the recovery of samarium (Sm) and Co from scrap SmCo magnets. Firstly, the chemical composition of SmCo magnets is revealed by ICP-OES and XRF. The Taguchi experimental design technique is employed to optimize nitric acid baking and water leaching. Based on the thermal decomposition behavior of Co, Fe, and Sm, the acid baking temperature is studied for the conversion of metal nitrates, excluding REEs nitrates, into metal oxides. The optimal conditions for acid baking and water leaching are identified, and a reactor for the pilot-scale acid baking process is proposed. The optimum parameters are tested with the proposed reactor.

The recent developments in EV batteries and REEs recovery processes from spent NiMH batteries

The recent developments in EV batteries and REEs recovery processes from spent NiMH batteries

Study of the kinetics and mechanisms of rare earth elements leaching from end-of-life NdFeB magnets through Hydro-Nd process

With the growing demand for REEs in numerous high-tech and energy transition-related applications, recycling these elements from secondary sources, mainly from end-of-life permanent magnets, has become crucial for responsible sourcing of raw materials from a circular economy. To date, numerous processes have been developed and optimized to allow this recovery to be sustainable from both an economic and environmental point of view. In this context, hydrometallurgy is one of the most promising avenues. Through an innovative hydrometallurgical process (Hydro-Nd), this research investigated the kinetics and mechanisms involved in leaching REEs from end-of-life permanent magnets. This process involves the use of citric acid in the leaching phase. Through systematic experimentation and analysis, the article elucidates key factors influencing leaching kinetics, providing insight into critical mechanisms of the process. In particular, ANOVA was used to study the influence of important factors (temperature, particle size, and agitation) on the recovery yields of the elements of interest. The shrinking core model studied the leaching mechanisms to identify a possible rate-determining step. Thanks to the results obtained, the Arrhenius parameters were estimated for the different heterogeneous reactions involved in the process, and the trend of the time constants versus the average diameter of the solid particles was identified. Also, the results showed that 100 % of Nd, Fe, Dy, B, and Pr from small PM particles (0–40 µm) in 4 h and more than 90 % of the mentioned metals from large particles (1000–1700 µm) within 5 h of leaching time were dissolved by citric acid solution. This research not only contributes to the development of an even more sustainable rare earth recovery process thanks to the optimization of several factors but also clarifies fundamental aspects of leaching kinetics and mechanisms, paving the way for future advances in the recovery of REEs from different sources.

Selectively recovering rare earth elements with carboxyl immobilized metal-organic framework from ammonium-rich wastewater

The material with high adsorption capacity and selectivity is essential for recovering rare earth elements (REES) from ammonium (NH4+-N)-rich wastewater. Although the emerging metal-organic framework (MOF) has gained intensive attention in REES recovery, there are scientific difficulties unsolved regarding restricted adsorption capacity and selectivity, hindering its extensive engineering applications. In this work, a diethylenetriamine pentaacetic (DTPA)-modified MOF material (MIL-101(Cr)-NH-DTPA) was prepared through an amidation reaction. The MIL-101(Cr)-NH-DTPA showed enhanced adsorption capacity for La(III) (69.78 mg g−1), Eu(III) (103.01 mg g−1) and Er(III) (83.41 mg g−1). The adsorption isotherm and physical chemistry of materials indicated that the adsorption of REEs with MIL-101(Cr)-NH-DTPA was achieved via complexation instead of electrostatic adsorption. Such complexation reaction was principally governed by -COOH instead of -NH2 or -NO2. Meanwhile, the resulting material remained in its superior activity even after five cycles. Such a constructed adsorbent also exhibited excellent selective adsorption activity for La(III), Eu(III), and Er(III), with removal efficiency reaching 70% in NH4+-N concentrations ranging from 100 to 1500 mg L−1. This work offers underlying guidelines for exploitation an adsorbent for REEs recovery from wastewater.

Solvent extraction of La, Nd, and Eu using a newly designed solutions spray system

This research covers a new continuous solvent extraction “solutions spray system” technique to extract lanthanum (La), neodymium (Nd), and europium (Eu) from chloride solution using DEHPA. This setup enhanced the extraction kinetics and mass transfer compared to the conventional mixer-settler by generating micro-sized droplets of the feed streams in the mixing chamber, causing speedy and better mass transfer, and the special design of the settling column boosted the separation process with improved quality products. Variables like pH, DEHPA concentration, ionic strength, and aqueous/organic phase ratio were studied to determine the performance of this setup. At the optimum values of these variables (2.0 pH, 0.303 M DEHPA, and 1.54 mol/L ionic strength), the percent extraction of La, Nd, and Eu was 95.03 %, 99.36 %, and 99.98 %, and the distribution ratio was 19.14, 155.25 and 4165 respectively, which showed the extraction in a single stage. Furthermore, the values of separation factors, SFEu/La = 6.69, SFEu/Nd = 5.33, and SFNd/La = 1.26 at 0.50 pH, showed the selectivity of these elements. Later on, McCabe Thiele diagrams were plotted for extraction and stripping sections to see the minimum number of theoretical stages for the complete recovery of REEs and their selective separation from each other.

Selective recovery of europium from real acid mine drainage using modified Cr-MIL and SBA15 adsorbents

The successful adoption and widespread implementation of innovative acid mine drainage treatment and resource recovery methods hinge on their capacity to demonstrate enhanced performance, economic viability, and environmental sustainability compared to conventional approaches. Here, an evaluation of the efficacy of chromium-based metal–organic frameworks and amine-grafted SBA15 materials in adsorbing europium (Eu) from actual mining wastewater was conducted. The adsorbents underwent comprehensive characterization and examination for their affinity for Eu. Cr-MIL-PMIDA and SBA15-NH-PMIDA had a highest Langmuir adsorption capacity of 69 mg/g and 86 mg/g, respectively, for an optimum level of pH 4.8. Preferential adsorption tests followed using real AMD collected at a disused mine in the north of Norway. A comparative study utilizing pH-adjusted real AMD revealed that Cr-MIL-PMIDA (88%) exhibited slightly higher selectivity towards Eu compared to SBA15-NH-PMIDA (81%) in real mining wastewater. While Cr-MIL-PMIDA displays excellent properties for the selective recovery of REEs, practical challenges related to production costs and potential susceptibility to chromium leaching make it less appealing for widespread applications. A cost–benefit analysis was then undertaken to quantify the advantages of employing SBA15-NH-PMIDA material. The study disclosed that 193.2 g of EuCl3 with 99% purity can be recovered by treating 1000 m3 of AMD.

Modern Rare Earth Imprinted Membranes for the Recovery of Rare Earth Metal Ions from Coal Fly Ash Extracts.

The need to identify secondary sources of REEs and their recovery has led to the search for new methods and materials. In this study, a novel type of ion-imprinted adsorption membranes based on modified chitosan was synthesized. Their application for the recovery of chosen REEs from synthetic coal fly ash extracts was analyzed. The examined membranes were analyzed in terms of adsorption kinetics, isotherms, selectivity, reuse, and their separation abilities. The experimental data obtained were analyzed with two applications, namely, REE 2.0 and REE_isotherm. It was found that the adsorption of Nd3+ and Y3+ ions in the obtained membranes took place according to the chemisorption mechanism and was significantly controlled by film diffusion. The binding sites on the adsorbent surface were uniformly distributed; the examined ions showed the features of regular monolayer adsorption; and the adsorbents showed a strong affinity to the REE ions. The high values of Kd (900-1472.8 mL/g) demonstrate their high efficiency in the recovery of REEs. After five subsequent adsorption-desorption processes, approximately 85% of the value of one cycle was reached. The synthesized membranes showed a high rejection of the matrix components (Na, Mg, Ca, Al, Fe, and Si) in the extracts of the coal fly ashes, and the retention ratio for these Nd and Y ions was 90.11% and 80.95%, respectively.

Sustainable recovery of rare earth elements from Ni-MH batteries: Flux-free thermal isolation and Subsequent hydrometallurgical refinement

This study details a sustainable approach for efficient recovery of highly pure rare earth elements oxides (REOs) from Ni-MH batteries. REOs (i.e., La, Ce, Sm, Nd, and Pr oxides) were thermally isolated from spent Ni-MH batteries into an oxide phase with the REO concentration of 67.4 wt%. Subsequently, separate leaching processes were conducted using sulfuric acid and hydrochloric acid solutions, and the results were compared in terms of efficiency and feasibility. Sodium REEs sulfate hydrate (NaRE(SO4)2.xH2O) was precipitated from the sulfuric acid leachate by adjusting the pH to 1.5 using sodium hydroxide, while the addition of oxalic acid to the hydrochloric acid leachate enabled the recovery of REEs as oxalate hydrate (RE2(C2O4)3.xH2O). The resulting sulfate salt was mixed with a sodium hydroxide solution, leading to the formation of REEs hydroxide. The REEs hydroxide and oxalate were calcined at 1000 °C, resulting in the production of REOs with a purity exceeding 99.7%. This research demonstrates the feasibility of developing an efficient, environmentally friendly, and sustainable approach for the recovery of highly pure REOs from Ni-MH batteries which potentially can minimize the environmental impact associated with the extraction of REOs from virgin sources, while addressing the challenge of effective recycling of end-of-life Ni-MH batteries.

The hydrometallurgical recovery of critical and valuable elements from WEEE shredding dust: Process effectiveness in a life cycle perspective

Waste electrical and electronic equipment (WEEE) recycling stands as a crucial opportunity to get critical resources while managing a waste stream in accordance with the circular economy principles. Recently, a two-step hydrometallurgical process has been successfully investigated to treat the dust originating from the mechanical processing of WEEE. The best operating conditions selected in this study were used to further investigate the recovery of precious metals and critical elements, achieving extraction yields of approximately 77.7 % and 53.1 %, respectively; base metals (i.e. aluminum, zinc, copper, ..) were also leached from dust up to 96 %. A life cycle approach was also applied to preliminary assess and compare the potential environmental impact of the proposed process with respect to the manufacturing process of the virgin material. The analysis focused on standard environmental indicators (i.e. global warming potential, acidification, …), human toxicity and eco-toxicty and a set of five different characterisation models for abiotic depletion of resources. Four scenarios, differing for allocation criteria (mass/economic) and the possible recovery of metals along with REEs, were compared. Among the recovered products, the greates potential benefits were found in the case of rare earth elements, in the scenario considering the complete recovery of base and precious metals and performing an economic allocation. Impacts on abiotic depletion and toxicity account for the highest benefits from maerial recovery. Nevertheless, the recovery of sulphuric acid would allow a further reduction also in other impacts, strengthening the potential competitiveness of REE recovery against the manufacturing of virgin materials.

The recovery of yttrium sulfate through antisolvent crystallization using alcohols

The rare earth elements are used extensively throughout modern technologies due to their unique electronic properties. However, current recovery methods of these elements from leaching solutions are not economically feasible, therefore ongoing research is being conducted to establish alternative processes. Antisolvent crystallization is one of the proposed techniques where antisolvents such as alcohols are used to recover inorganic salts from aqueous solutions. For this study, yttrium sulfate [Y2(SO4)3] was used as model compound to investigate the effect of different short primary alcohols, i.e., methanol, ethanol, and 1-propanol, as antisolvents on the solubility of the salt under isothermal conditions at 23 °C. This work also featured thermodynamic simulations done by using OLI Studio. Experimental values were compared to the simulated data. All the alcohols investigated in this study were ultimately able to reduce the solubility of Y2(SO4)3 by over 99%. Experimental evaluation showed that the concentration of alcohol needed on molar basis was similar ethanol and 1-propanol, followed by methanol. The solid phase recovered from the suspension was experimentally found to be Y2(SO4)3·8H2O for all the alcohols. Lastly, a theoretical case study was done comparing the simulated data with experimental data extracted from literature for the recovery of REEs, which included Y3+, from a NiMH battery leach solution using alcohol. The Y3+ concentration of 1.3 g/kg, observed in the leach solution, was used for the case study in which ethanol was shown to be the most effective antisolvent needing only 0.89 kg (1.13 L) to achieve the maximum plateau yield of 92% from the 1 kg aqueous feed solution. A possible kinetic limitation for the crystallization of Y2(SO4)3 using ethanol as antisolvent was also identified.

Effect of pretreatment methods on the selective leaching of rare earth elements from NdFeB permanent magnets using deep eutectic solvents

In this study, deep eutectic solvents (DESs) were employed as environmentally friendly alternatives of inorganic acid to selectively leach REEs from waste NdFeB magnets. Three DESs were tested, effective for light REE leaching, and preliminary experiments were conducted to study the selective leaching of REEs, using synthetic materials, Nd2O3, Fe, Fe3O4, and Fe2O3. The findings suggest that neodymium and iron should exist as Nd2O3 and Fe2O3, respectively, for selective leaching. To enhance the selective leaching of the NdFeB magnet, three pretreatment methods were applied: oxidative roasting, NaOH digestion, and NaOH digestion-oxidative roasting. During the oxidative roasting, NdFeO3 was formed, and it hindered REE leaching, achieving the highest REE leaching efficiency of 22.5% in the guanidine hydrochloride (GUC)-lactic acid (LA) DES. To counteract NdFeO3 formation, the NaOH digestion was introduced, yielding Nd(OH)3 and Fe3O4. These were then converted to Nd2O3 and Fe2O3 through oxidative roasting. With the NaOH-digested product, selective REE leaching was achieved solely with the ethylene glycol (EG)-maleic acid (MA) DES, while it was feasible in all three DESs with the NaOH digestion-oxidative roasting. The EG-MA DES displayed the highest selectivity, with a leaching efficiency of 97.3% Nd and 0.8% Fe. Additionally, the solvent could be reused at least twice, and the leaching efficiencies of 97% for Nd and 0.7% for Fe were maintained. This selective leaching technique benefits from using environmentally friendly solvents compared to the traditional inorganic acid leaching and demonstrates high REE selectivity and solvent reusability, suggesting a novel method for REE recovery via DESs.

Solvent extraction for high separation strategy of light and heavy rare earth elements from a sulfate-leached solution of low-grade monazite

A novel separation strategy for light REEs (Ce4+ and La3+) and heavy REEs (Y3+ and Eu3+) from a low-grade monazite ore leached solution in a sulfate medium was studied to achieve a higher selectivity of metal ions. A prior separation of higher valence Ce4+ was performed using 8.0 vol% Cyanex 923, 0.2 mol/L H2SO4 in the aqueous feed, an organic-to-aqueous (O/A) phase ratio of 1, and a temperature of 25 °C, yielding the separation factor β(Ce4+/REEs3+) = 9424. A reductive back-extraction of Ce2(SO4)3 was efficiently performed using a solution mixture of H2SO4 + H2O2 with concentrations ≥1.0 mol/L each. Further, Y3+ from Ce4+-depleted solution was selectively extracted using 2.0 vol% Cyanex 572 organic extractant and 0.2 mol/L H2SO4 in aqueous feed at an O/A ratio of 1, yielding a separation factor of 6438 at 25 °C. The subsequent extraction of Eu3+ over La3+ was carried out at 2.5 vol% D2EHPA, 0.05 mol/L H2SO4 in the aqueous feed, an O/A ratio of 1, and a temperature of 55 °C, yielding β(Eu3+/La3+) = 5787. Both Y3+ and Eu3+ from the individually loaded organics were stripped with an efficiency of ∼ 99.9% by contact with 2.0 mol/L (COOH)2 prepared in a 1.0 mol/L HCl solution. The remaining La3+ in the raffinate was directly precipitated by adding ≥0.01 mol/L (COOH)2 crystals at 90 °C. This article provides an efficient and highly selective recovery of REEs from a low-grade monazite leached solution with higher separation values β(Ce4+/REEs3+) = 9424 and β(Eu3+/La3+) = 5787.

The Ce3+ Metal Ion Adsorbent Based on Calcium Alginate Loaded Fe3O4 (Ca-Alg/Fe3O4)

Rare earth metal frequently utilized in technological advancements is cerium. The high utilization of cerium correlates with the depletion of primary REEs reserves and the accumulation of secondary materials that can enter aquatic environments. Recycling and recovery of REEs through methods such as solvent extraction, filtration, and adsorption are commonly employed. Adsorption is chosen due to the abundance of adsorbent materials in nature, simple fabrication, efficiency, and cost-effectiveness. Calcium alginate biosorbent loaded with magnetite (Ca-Alg/Fe3O4) has been used to adsorb (Ce3+)aq, with optimal conditions achieved at Ca-alginate:Fe3O4 ratio of 2:1 (w/w), 0.075 g, pH 4, a contact time of 210 minutes, and 250 ppm, [Ce3+]0. The adsorption process follows the Langmuir isotherm model with qmax at 50.505 mg/g. Hence, the Ca-Alg/Fe3O4 biosorbent shows potential in adsorbing (Ce3+)aq.

Iron, copper, and rare earth minerals beneficiation in an IOCG type deposit

ABSTRACT The sample of the Sineqan mine (Arak, Iran), containing 16.5% Fe, 0.13% Cu, 475 ppm Ce, 446 ppm La, and 134 ppm Nd, was characterised and processed to investigate the possibility of separating iron, copper, and REE minerals. Microscopic studies showed that the main minerals in the sample include magnetite, hematite, goethite, specularite, pyrite, and chalcopyrite, while the gangue minerals consist of quartz, clay minerals, and carbonate minerals. The results of heavy liquid studies using Bromoform showed that by reducing the particle size from 1180 to 300 micrometre, 76.6% of iron and 72.76% of copper went into the heavy section, while 77.9% of REEs entered the light section. The magnetic separation experiments revealed that higher magnetic field intensity increased the recovery of iron, copper, and REEs with no separation between them. In summary, the results indicate that REEs are primarily present in the light section due to their association with sphene silicate mineral, and gravity separation demonstrated superior performance in terms of both recovery and selectivity. The results of this research are significant for the processing of iron oxide-type deposits that contain copper and REEs.

Precipitation of Rare Earth Element from Indonesian Coal Fly Ash Using Sodium Sulfate

The rare earth element is a critical element in many industrial sectors. Due to unbalanced supply and demand, it is necessary to look for an alternative source. Coal ash is a waste product of power plant combustion. Previous research revealed that coal ash contained levels of rare earth elements. This research uses coal fly ash from the Paiton power plant. The objectives of this study were to determine the effect of the Na2SO4 concentration, stirring rate, and temperature on the recovery of REE concentrate. The experiment was conducted in four steps: (1) alkaline leaching, the process was carried out for 2 hours at 90°C with fly ash solid to 8 M NaOH solution ratio of 1:4 to break the aluminosilicate bonds. (2) Acid leaching of residue for 4 hours at 90°C in 3 M HCl. (3) Precipitation of residue to remove the impurities such as Fe using 1 M NaOH at pH 5. (4) Precipitation of filtrate from process (3) using Na2SO4 to produce REE concentrate precipitates. The best condition to obtain the highest REE residue is conducting recovery at the concentration of 20% Na2SO4, stirring rate of 500 rpm, and temperature of 50°C, with a yield of 88.72%.

Recovery of REE and TPE Radionuclides from Irradiated Targets by the Chromatographic Method Using Nonferrous Metal Ion Intercalators

Recovery of REE and TPE Radionuclides from Irradiated Targets by the Chromatographic Method Using Nonferrous Metal Ion Intercalators

Adsorption of rare earth elements onto diatomite M45: Experimental investigations and modeling with statistical physics theory

The separation of rare earth elements using diatomite M45 from aqueous solutions was studied. The experimental isotherms for the adsorption of trivalent lanthanum, cerium, and neodymium cations on this adsorbent were quantified under strongly acidic conditions (pH 2) at 298–328 K. The adsorption equilibria of these earth elements were analyzed using two statistical physics models (homogeneous and heterogeneous monolayer models). The results show that the adsorption of these ions implies a multi-ionic mechanism, which is exothermic. Si-containing functional groups are responsible for the adsorption of these rare-earth elements on the diatomite surface. A heterogeneous statistical physics model confirms that two Si-based functional groups participate in the separation of these cations. The calculated adsorption capacities at saturation follow the order: neodymium > cerium > lanthanum. Calculated interaction energies range from 28600 to 40100 J/mol, indicating physical adsorption on diatomite M45. This study demonstrates that diatomite M45 is a promising separation medium that can be used for the recovery of REEs dissolved in aqueous solutions via adsorption.

Recovery of critical metals from carbonatite-type mineral wastes: Geochemical modeling investigation of (bio)hydrometallurgical leaching of REEs

Abstract Rare earth elements (REEs) are typically found in low concentrations within natural rocks that make up mine tailings, such as carbonates in association with silicates within carbonatite igneous rocks, so it is of interest to develop (bio)hydrometallurgical ways to liberate them from the silicate matrix. This work investigated, through geochemical modeling, the extraction of europium and ytterbium carbonates from rocks containing one of four silicates (chrysotile, forsterite, montmorillonite, and phlogopite) via chemical (mineral acid) or biological (organic acid) leaching. The results indicated conditions that led to either congruent or incongruent dissolution of the mineral phases and the formation of transient mineral phases. Chemical leaching models suggest that REE carbonates are recoverable in one-step leaching from forsterite and chrysotile rocks, while they are recoverable in a secondary leaching step from montmorillonite and phlogopite rocks. Gibbsite as a transient phase is shown to complicate REE recovery, potentially requiring reactive extraction. REEs have the potential to be recovered from silicate rocks via chemoorganotrophic bioleaching, but the process configuration would differ depending on the predominant minerals that make up the rock, and the type of REE present in it.

Combined Physicochemical and Energy Methods to Improve the Recovery of Rare Earth Elements from Eudialyte Concentrate

The parameters for efficient nitric acid leaching were experimentally determined, which ensured the recoveries of Zr and REEs from eudialyte concentrate up to 87.0%–91.7% and 76.0%–81.1%, respectively. The possibility was shown of intensifying the leaching process through preliminary energy treatments to ensure the intensive breakdown of mineral complexes and grains; as a result, the recovery of Zr and REEs increased by more than 10%. A process was developed for the selective recovery of up to 91.5% of zirconium and up to 71.2% of REEs in the form of carbonate compounds from the pregnant solution of nitric acid leaching by chemical precipitation as well as up to 81.1% REEs and up to 91.7% zirconium on hypercrosslinked polystyrene sorbents.

Recovery of rare earth elements from coal samples from the Sohagpur coalfield, Madhya Pradesh, India

ABSTRACT REEs play a pivotal role in the manufacturing of numerous industrial, defense, consumer, and aviation-related gadgets. As many primary sources of REEs are either exhausted or depleted, coal can be a good secondary source of REEs in the near future. The traditional thermochemical processes to extract REEs are expensive and detrimental to the environment, and thus exploration of more environment friendly and sustainable recovery methods are of the utmost necessity at the present time. In this study, we present in-depth investigation of REEs extraction from the coal samples from the Sohagpur coalfield, Madhya Pradesh. We conducted multiple experiments mainly focusing on rotational movement with the help of a laboratory shaker, magnetic stirrer with hot plate, and a flocculator jar test apparatus in the presence of acidic solutions. Our study highlights that the flocculator jar test apparatus exhibits the maximum recovery of REEs (Ce- 95%, Nd- 83%, La- 82%, Eu- 82%, Pr- 76%, Sm- 74%, Gd- 69%, and Tb- 69%) from coal in the presence of 2 M HNO3. This technique of REEs recovery from coal is easy to use, effective, has little environmental impact, and can be applied on an industrial scale with only minor adjustments to the machinery.