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.

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.

Despite being of paramount importance for developing the biorefinery concept and being a highly versatile building block to synthesize a plethora of biobased molecules, experimental data on the solubility of sorbitol in pure organic solvents and heat capacity data are scarce. This work reports the solubility of the stable γ polymorph of sorbitol in eleven organic solvents of polar protic and polar aprotic nature within the range of temperature 298–338 K using a gravimetric method. No solution-mediated polymorphic transformation was detected during equilibration as confirmed by PXRD. Moreover, the solid sorbitol is characterized by TGA, DSC, FTIR, SEM and optical microscopy. Molar fraction solubility data has been modelled using empirical, semiempirical and mechanistic-based rigorous thermodynamic analysis approaches, providing thus expressions of practical usefulness to interpolate and extrapolate solubility data. In addition to the melting point and melting enthalpy, the heat capacity dependence upon temperature is determined experimentally for the pure solid, the pure liquid and the supercooled melt. Such data is used to estimate the sorbitol activity coefficients in the studied solvents at different temperatures, revealing strongly positive deviations with respect to ideality, i.e. weaker solute–solvent interactions than solute–solute. The rank of solubility obtained shows: (i) that sorbitol is soluble in all the studied solvents, yet to different extent, (ii) a higher solubility for proton donor solvents, which increases upon branching and decreases with increasing molecular size, and (iii) polar aprotic solvents can exploit the benefits from H-bonding but these languish with increasing size of the alkyl groups attached to the carbonyl group. Finally, molecular dynamics simulations are used to compute solvation free energies, which are ultimately correlated to the rank of solubility observed and underline H-bonding as the most prominent interaction governing solubility. A comprehensive discussion on the H-bonding relevance from Hansen solubility parameters as a function of the studied polar solvents protic/aprotic nature, and the size related role of non-polar moieties in solvents molecules is provided, contributing to enhance our knowledge on the solid–liquid equilibria governing interactions of polysaccharide-organic solvents systems.

Hypothesis: It is hypothesised in this work that mesoscale clusters will be present in both undersaturated and supersaturated solutions of organic pharmaceutical molecules. These clusters, being loose aggregates, could be sensitive to shear forces experienced during filtration. Thus, comparing the behaviour of these clusters alongside nanoparticles during filtration—an important sample treatment parameter during crystallization—will elucidate qualitative differences from solid, crystalline nanoparticles of similar size. Experiments: The impact of filtration with different pore sizes and membranes on (i) mesoscale clusters of flufenamic acid (FFA) ethanol solutions and (ii) aqueous FFA nanosuspensions was studied with dynamic light scattering and nanoparticle tracking analysis. Findings: FFA solutions, ranging from undersaturated to supersaturated, were found to form mesoscale clusters, where the cluster size and number concentration were independent of solute concentration. Under filtration stress, irrespective of pore size and membrane used, the mesoscale cluster peak disappeared from the size distribution with no detectable change in concentration. In contrast, similarly sized FFA nanoparticles were removed by filtration, causing a significant change in solute concentration and size distribution. Mesoscale clusters of FFA in ethanol constitute only a tiny fraction of the total solute concentration and possess poor light scattering properties, lower mass density than solid particles of similar size, and no clear phase boundary.

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.

In this study L-(+)-tartaric acid was used to extract metals from either pure cathode material (NMC111) or black mass from spent lithium-ion batteries. The leaching efficiencies of Li, Co, Ni, and Mn from NMC111 are > 87% at 70 °C, with an initial solid to liquid ratio of 17, and > 72.4±1.0% from black mass under corresponding conditions. The metals tend to form mixed phases in antisolvent crystallization and seeding has a minimal effect on the final solid composition. Impurities influence both crystal nucleation and growth. By controlling the antisolvent addition rate crystal growth can be promoted. The theoretical dielectric constant of the solution is shown to correlate excellently to the recovery efficiency across different antisolvents, where a value <52 results in over 95% total transition metal recovery efficiency. The correlation can be a powerful tool for quantitative prediction of optimal solvent composition for effective antisolvent crystallization.

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.

Rare earth elements (REE) are recognized as critical raw materials because of their crucial role in vital components of numerous green and high-tech applications. In the present study, antisolvent crystallization of REE sulfate hydrates of industrial interest (Nd (III), Pr (III), and Dy (III)) from sulfuric acid solutions by the addition of ethanol has been studied. Crystallization of REEs in the presence of Fe (II) and Fe (III) as major impurities along with Al (III), Cu (II), Co (II), and B (III) as trace elements is investigated. The incorporation of impurities and its effect on the growing REE phase is examined. The effect of controlled supersaturation generation rate on the product quality (e.g. purity) and crystal phase is investigated. The solid phases are characterized using optical microscopy, SEM-EDX, powder-XRD, and ICP-OES. The findings can offer significant insights to understand and optimize the recovery of REEs from leach liquor in the recycling of magnet waste.

Precipitation and crystallization have long been common components of hydrometallurgical processes involving rare earth elements (REEs), for purposes of concentration, separation, and recovery. In this chapter, different possible crystallization-based techniques for separation of REEs as solid compounds from solution are reviewed. Some of the techniques are well-established, while others are promising alternatives of lower technological maturity. Fundamental theory common to all methods of crystallization of ionic compounds is covered, solubility data of different rare earth salts are presented, and important aspects of the underlying chemistry behind rare earth crystallization are highlighted, in order to rationalize the behavior of the different REEs and to give a deeper understanding of the phenomena at hand. The chapter supplies information helpful in the design of a suitable and efficient crystallization-based REE-separation process.