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.

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.

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.

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.

It has proven effective to recover metal compounds from aqueous mixtures by use of antisolvents; organic compounds that induce selective precipitation. A challenge with antisolvents is that they are both costly to produce and recover on an industrial scale. In recycling of lithium-ion batteries and recovering critical metals, we find that electrodialysis can be a competitive method for purifying and recycling antisolvents. In this study we investigate the use of electrodialysis to separate salt and water from a ternary solution of water, KCl and ethanol. A coupled non-equilibrium electrochemical model is developed to understand how such systems may be operated, designed, and which characteristics that are required for the ion exchange membranes. We demonstrate how the water transference coefficients of the membranes should be tuned in the process optimisation and why membrane property design is crucial to the success of this concept. Residual mixtures from antisolvent precipitation, with ethanol (EtOH) solvent weight fractions around 0.6-0.7, can be demineralised and the EtOH fraction increased by 0.1-0.2 at an energy requirement of 60-200 kWh mEtOH−3 by use of electrodialysis. In an example application of the concept, aqueous KCl is precipitated by recycled ethanol in a cyclic process, requiring 0.161 kWh molKCl−1. This example case considers complete ethanol rejection by the membranes and abundant water co-transport, characterised by the transference coefficients: tw=15 and ta=0 for water and EtOH respectively. The findings pave the way for new applications with aqueous mixtures of critical metals.

This paper reports the solid-liquid phase equilibria of the CoSO4-H2O and CoSO4-H2SO4-H2O systems at low temperatures. Binary and ternary phase diagrams, including the stable solid phases CoSO4·6H2O and CoSO4·7H2O were established using experimental data and thermodynamic modeling applying the mixed-solvent electrolyte (MSE) model. The results showed that the addition of H2SO4 shifts the eutectic temperature and concentration to lower values for cobalt sulfate and ice crystallization. The trends obtained from the experimental data and the modeling are consistent for the binary CoSO4-H2O system with good agreement, but the ternary CoSO4-H2SO4-H2O system shows some deviations. In general, the MSE model is shown to be reliable for inferring and establishing the phase diagram of the low-temperature system. The phase diagrams are helpful for designing the pathways of cooling crystallization and eutectic freeze crystallization and assessing the performance of the low-temperature crystallization process in the production of CoSO4 hydrates. In addition, some practical examples of cooling crystallization and eutectic freeze crystallization of CoSO4 solutions are provided.

Bauxite oresBauxite ore used in aluminium oxide production via the Bayer process contain trace elements (REEs, V, Li, Sc, Ga) currently not valorised. VanadiumVanadium and GalliumGallium dissolve during the Bayer process forming impurities in the Bayer liquorBayer liquor (sodium aluminate solution). VanadiumVanadium application ranges from steel to aircraft industries, and extraction involves ammonium treatment of strip liquor for vanadiumVanadium salt (AMV, V2O5) precipitation. Current crystallizationCrystallization techniques have drawbacks of generating voluminous, highly saline wastewater. This study investigated the use of antisolventAntisolvent (acetone) crystallizationCrystallization with synthetic solutions as an alternative to the crystallizationCrystallization and calcination step in the conventional production of high purityPurityvanadiumVanadium salts. The yieldYield, purityPurity, and product characteristics of the crystals for different final organic to aqueous (O/A) ratio at constant addition rate of antisolventAntisolvent at room temperature have been investigated. A batch time-dependent effect was observed with the best product quality, in terms of size and crystal habit (dominated by hexagonal laths), being attained when tb ≤ 2 h at an O/A ratio of 0.5. The early onset of acicular crystal formation and higher yieldsYield (≥ 97%), along with higher impurity incorporation into the solid phase, was observed at an O/A ratio of 0.75, and this was attributed to higher levels of supersaturationSupersaturation.