The thermodynamics and kinetics of ethanol antisolvent crystallization of rare earths from sulfate solutions has been explored, with a view towards separating the rare earths as part of a NdFeB magnet recycling process. The solubility of single and binary metal (Nd, Pr, Fe) phases in aqueous ethanol solutions has been determined. The impact of Fe and Pr on the crystallization of Nd is evaluated, the oxidation kinetics of Fe(II) to Fe(III) quantified, and the influence of Fe oxidation state on the thermodynamics and kinetics of crystallization investigated. Oxidation to Fe(III) is slow, with a half life of approx. 600 h. For pure Nd, the solubility of the obtained, stable sulphate octahydrate decreases exponentially with increased molar organic:aqueous (O/A) ratio, and is well described by the OLI model until O/A=0.2. Pr crystallizes as an isostructural octahydrate with similar solubility. Fe(II) precipitates as a mixed solid phase, with a solubility approximately 40 times higher than the rare earths at O/A=0.2. Fe(III) solutions exhibit liquid–liquid phase separation without precipitation at all evaluated concentrations. Nd and Pr coprecipitate together in proportion to their relative concentrations, with Pr precipitating at concentrations well below its pure component solubility. Fe(II) does not precipitate with Nd at O/A≤0.2 even at high concentration, with significant precipitation as separate particles at higher O/A for all concentrations. The crystallization kinetics and the morphology of the Nd phase is affected by the Fe oxidation state. The work highlights the potential of antisolvent crystallization for selective and efficient separation of REE from Fe.

Rare earth elements (REEs) are important for permanent magnets used in for example wind turbines and motors. There is an imbalance in supply and demand of this commodity and the REE have been identified as critical raw materials by the European Union. This study focuses on recovery of REEs from sulfuric acid solutions using antisolvent crystallization in recycling of magnet waste. Ethanol is used as an antisolvent to crystallize Nd2(SO4)3∙8H2O and (Nd/Dy)2(SO4)3∙8H2O. The impact of the presence of Fe in ferrous and ferric states, and of different seeding strategies, on the quality of the crystal product in terms of purity, crystal size, morphology and agglomeration has been investigated. Higher purity (above 99%) is obtained for seeded experiments and the purity is higher for higher seed loading and lower antisolvent dosing rate. Furthermore, Fe(III) has a higher tendency to be incorporated into the pure Nd phase compared to the Nd phase containing 10% of Dy, while Fe(II) is not detected in any of the phases. By balancing the addition of antisolvent and seed loading the optimum conditions in terms of high purity and productivity can be found. The results provide insights to improve the recovery of REEs as a pure concentrate.

The large scale deployment of Si PV panels presents significant end-of-life challenges due to their limited lifespan. Effective recycling strategies are crucial to reduce the environmental impact and recovering valuable metals. This study presents a simple yet highly efficient two-stage chemical process to preserve Si purity by sequential extraction of Al and Ag from discarded Si solar cells. In the first stage, Al was dissolved with sodium hydroxide (NaOH) and then precipitated by adjusting the pH with sulfuric acid (H2SO4). In the second stage, the Ag was extracted with nitric acid (HNO3), precipitated with sodium chloride (NaCl), and then reduced to metallic Ag with a glucose. Under optimized conditions, the recovery efficiency for Al and Ag was over 99 %, while the resulting Si substrate reached a purity of >99.9 %. ICP-OES, XRF, XRD, and SEM-EDS confirmed the recovered materials' high selectivity and negligible impurities, highlighting their potential for high-value industrial applications.

This volume presents papers from a symposium on extraction of rare metals from primary and secondary materials and residues as well as rare extraction processing techniques used in metal production. The collection covers the extraction of less common or minor metals including elements such as antimony, bismuth, barium, beryllium, boron, calcium, chromium, gallium, germanium, hafnium, indium, manganese, molybdenum, platinum group metals, rare earth metals, rhenium, scandium, selenium, sodium, strontium, tantalum, tellurium, and tungsten. It also includes rare metals of low-tonnage sales compared to high-tonnage metals (iron, copper, nickel, lead, tin, zinc, or light metals such as aluminum, magnesium, or titanium and electronic metalloid silicon). Rare metal processing covers biometallurgy, hydrometallurgy, and electrometallurgy while novel high-temperature processes such as microwave heating, solar-thermal reaction synthesis, and cold crucible synthesis of rare metals are also addressed. Also included in this collection is the design of extraction equipment used in these processes from suppliers as well as laboratory and pilot plant studies.

Manganese is a crucial metal for various industrial applications, particularly in the production of batteries. For example, NMC, one of the most commonly used cathode materials in lithium-ion batteries (LIBs), contains manganese (Ju et al. in Chem Eng J 466:143218, 2023 [1]). Therefore, there have been notable efforts to recycle batteries to recover valuable metals like manganese, minimize waste, and reduce the environmental impact of batteries (Li in Sep Purif Technol 306:122559, 2023 [2]). Eutectic freeze crystallizationEutectic freeze crystallization (EFC) is a technique employed to recover metal salts from aqueous solutions. EFC can provide significant benefits over traditional methods such as evaporative crystallization, including lower energy consumption and decreased operational corrosion (Randall et al. in Desalination 266(1–3):256–262, 2011 [3]). This study investigates the recovery of manganese as manganese sulfate heptahydrate from diluted sulfuric acid solutionsAcid solutions using EFC. Additionally, at increased temperatures, manganese sulfate heptahydrate crystals produced by EFC transform into a pentahydrate and subsequently into a monohydrate. The experimentally observed transition temperatures were compared with those estimated using the OLI Stream Analyzer software.

Hollow fibre renewal liquid membranes (HFRLMs) are susceptible to third-phase formation during rare earth element (REE) extraction using D2EHPA (bis(2-ethylhexyl phosphoric acid)), potentially leading to membrane fouling and decreased mass transfer efficiency. This study investigated the effects of various parameters, such as the composition of the aqueous feed and organic phases, on the third-phase formation and limiting organic concentration (LOC) of REE(III) in D2EHPA. Higher concentrations of REEs and a higher pH in the feed phase correlated with decreased mass transfer, while yttrium showed a greater propensity to induce third-phase formation compared to other REEs. Conditions favouring the use of linear aliphatic diluents, low extractant concentrations (5–10 v/v% D2EHPA) and the absence of modifiers also contributed to third-phase formation. The addition of tri-n-butyl phosphate (TBP) mitigated third-phase formation without evidence of synergy with D2EHPA. These findings provide key insights into formulating extraction systems that prevent third-phase formation in HFRLM processes.

Deep eutectic solvents (DESs) have garnered attention in Li-ion battery (LIB) recycling due to their declared eco-friendly attributes and adjustable metal dissolution selectivity, offering a promising avenue for recycling processes. However, DESs currently lack competitiveness compared to mineral acids, commonly used in industrial-scale LIB recycling. Current research primarily focuses on optimizing DES formulation and experimental conditions to maximize metal dissolution yields in standalone leaching experiments. While achieving yields comparable to traditional leaching systems is important, extensive DES reuse is vital for overall recycling feasibility. To achieve this, evaluating the metal dissolution mechanism can assist in estimating DES consumption rates and assessing process makeup stream costs. The selection of appropriate metal recovery and DES regeneration strategies is essential to enable subsequent reuse over multiple cycles. Finally, decomposition of DES components should be avoided throughout the designed recycling process, as by-products can impact leaching efficiency and compromise the safety and environmental friendliness of DES. In this review, these aspects are emphasized with the aim of directing research efforts away from simply pursuing the maximization of metal dissolution efficiency, towards a broader view focusing on the application of DES beyond the laboratory scale.

Alumina extraction via the Bayer process produces an inorganic species laden liquor containing aluminium and valuable trace elements (REEs, V, Ga) promoting liquor impurity but with valorisation potential. Vanadium has applications for multiple industries, but current primary extraction techniques generate voluminous, highly saline ammonium wastewater. This investigation explores synthetic high purity vanadium crystallization in a temperature-controlled jacketed batch reactor. Acetone was the antisolvent for treating the synthetic feed solutions. This crystallization route may serve as an alternative to the crystallization and calcination steps in the conventional production of high purity vanadium salts. Supersaturation is generated through the addition of acetone, and is controlled by varying precipitant concentration, addition rate, agitation rate, and seeding. Vanadium salt composition, yield, purity, and particle morphology was analysed using XRD, ICP-OES, and SEM-EDS. Elevated supersaturation led to rapid vanadium crystallization with high yield but low purity. The yield, purity, and product characteristics of the crystals for different final organic to aqueous (O/A) ratio, at constant addition rate of antisolvent at room temperature has been investigated. A batch time and precipitant concentration dependent effect was observed. The best product quality, in terms of size and crystal habit (dominated by hexagonal laths), was attained at a batch time of 2 h and O/A ratio of 0.75 using more dilute acetone (80% acetone (v/v)). The results from the higher O/A ratio of 0.75 indicated a faster attainment of desirable yields (≥97%) but also brought an early onset of acicular crystal formation along with more impurity incorporation into the solid phase, although this was less pronounced in cases where dilute acetone was used.

Alumina extraction via the Bayer process produces an inorganic species laden liquor containing aluminium and valuable trace elements (REEs, V, Ga) promoting liquor impurity but with valorisation potential. Vanadium has applications for multiple industries, but current primary extraction techniques generate voluminous, highly saline ammonium wastewater. This investigation explores synthetic high purity vanadium crystallization in a temperature-controlled jacketed batch reactor. Acetone was the antisolvent for treating the synthetic feed solutions. This crystallization route may serve as an alternative to the crystallization and calcination steps in the conventional production of high purity vanadium salts. Supersaturation is generated through the addition of acetone, and is controlled by varying precipitant concentration, addition rate, agitation rate, and seeding. Vanadium salt composition, yield, purity, and particle morphology was analysed using XRD, ICP-OES, and SEM-EDS. Elevated supersaturation led to rapid vanadium crystallization with high yield but low purity. The yield, purity, and product characteristics of the crystals for different final organic to aqueous (O/A) ratio, at constant addition rate of antisolvent at room temperature has been investigated. A batch time and precipitant concentration dependent effect was observed. The best product quality, in terms of size and crystal habit (dominated by hexagonal laths), was attained at a batch time of 2 h and O/A ratio of 0.75 using more dilute acetone (80% acetone (v/v)). The results from the higher O/A ratio of 0.75 indicated a faster attainment of desirable yields (≥97%) but also brought an early onset of acicular crystal formation along with more impurity incorporation into the solid phase, although this was less pronounced in cases where dilute acetone was used.