Li-ion battery materials have been widely studied over the past decades. The metal salts that serve as starting materials for cathode and production, including Li₂CO₃, NiSO₄, CoSO₄ and MnSO₄, are mainly produced using hydrometallurgical processes. In hydrometallurgy, aqueous precipitation and crystallization are important unit operations. Precipitation is mainly used in the processes of impurity removal, separation and preliminary production, while controlled crystallization can be very important to produce a pure product that separates well from the liquid solution. Precipitation and crystallization are often considered in the development of sustainable technologies, and there is still room for applying novel techniques. This review focuses on precipitation and crystallization applied to the production of metal salts for Li-ion battery materials. A number of novel and promising precipitation and crystallization methods, including eutectic freeze crystallization, antisolvent crystallization, and homogeneous precipitation are discussed. Finally, the application of precipitation and crystallization techniques in hydrometallurgical recycling processes for Li-ion batteries are reviewed.

Eudialyte is a promising mineral for rare earth elements (REE) extraction due to its good solubility in acid, low radioactive, and relatively high content of REE. In this paper, a two stage hydrometallurgical treatment of eudialyte concentrate was studied: dry digestion with hydrochloric acid and leaching with water. The hydrochloric acid for dry digestion to eudialyte concentrate ratio, mass of water for leaching to mass of eudialyte concentrate ratio, leaching temperature and leaching time as the predictor variables, and the total rare earth elements (TREE) extraction efficiency as the response were considered. After experimental work in laboratory conditions, according to design of experiment theory (DoE), the modeling process was performed using Multiple Linear Regression (MLR), Stepwise Regression (SWR), and Artificial Neural Network (ANN). The ANN model of REE extraction was adopted. Additional tests showed that values predicted by the neural network model were in very good agreement with the experimental results. Finally, the experiments were performed on a scaled up system under optimal conditions that were predicted by the adopted ANN model. Results at the scale-up plant confirmed the results that were obtained in the laboratory.

H₂SO₄ was ensured to be the best candidate for Zr leaching from the eudialyte. The resulting sulfuric leach solution consisted of Zr(IV), Nb(V), Hf(IV), Al(III), and Fe(III). It was found that ordinary metal hydroxide precipitation was not feasible for obtaining a relatively pure product due to the co-precipitation of Al(III) and Fe(III). In this reported study, a basic zirconium sulfate precipitation method was investigated to recover Zr from a sulfuric acid leach solution of a eudialyte residue after rare earth elements extraction. Nb precipitated preferentially by adjusting the pH of the solution to around 1.0. After partial removal of SO₄²⁻ by adding 120 g of CaCl₂ per 1L solution, a basic zirconium sulfate precipitate was obtained by adjusting the pH to ~1.6 and maintaining the solution at 75 °C for 60 min. Under the optimum conditions, the loss of Zr during the SO₄²⁻ removal step was only 0.11%, and the yield in the basic zirconium sulfate precipitation step was 96.18%. The precipitate contained 33.77% Zr and 0.59% Hf with low concentrations of Fe and Al. It was found that a high-quality product of ZrO₂ could be obtained from the basic sulfate precipitate.

Acid mine drainage (AMD), red mud (RM) and coal fly ash (CFA) are potential high environmental pollution problems due to their acidity, toxic metals and sulphate contents. Treatment of acidic mine water requires the generation of enough alkalinity to neutralize the excess acidity. Therefore, red mud types from Germany and Greece were chosen for the neutralization of AMD from South Africa, where this problem is notorious. Because of the high alkalinity, German red mud is the most promising precipitation agent achieving the highest pH-values. CFA is less efficient for a neutralization and precipitation process. An increase in temperature increases the adsorption kinetics. The maximum pH-value of 6.0 can be reached by the addition of 100 g German red mud at 20 °C to AMD-water with an initial pH value of 1.9. German red mud removes 99% of the aluminium as aluminium hydroxide at pH 5.0. The rare earth elements (yttrium and cerium) are adsorbed by Greek red mud with an efficiency of 50% and 80% at 60 °C in 5 min, respectively.

In the traditional vanadium precipitation process, the use of ammonium salts can produce serious pollution problems from the ammonia waste-water and the ammonia gas generated during the processing. In this reported study, an eco-friendly technology was investigated to prepare vanadium oxides from a typical vanadium (IV) strip liquor, obtained after the hydrometallurgical treatment of a vanadium-bearing shale. Thermodynamic analysis demonstrated that VO(OH)₂ could be prepared as a precursor over a suitable solution pH range. Experimental results showed that by adjusting the pH to around 5.6, at room temperature, 98.6% of the vanadium in the strip liquor was formed into hydroxide, in 5 min. After obtaining the VO(OH)₂, it was washed with dilute acid to minimize the level of impurities. VO₂ and V₂O₅ were then produced by reacting the VO(OH)₂ with air or argon, in a tube furnace. The XRD analyses of the products showed that VO₂ had been produced in air and V₂O₅ had been produced in argon. The purity of the VO₂ was 98.82% after calcining for 2 h at 550 °C, in argon flow, at a rate of 50 mL/min. It was found that the purity of the V₂O₅ was 98.70%, using the same reaction conditions in air. Compared to the traditional precipitation method that uses ammonium salt, followed by calcination, this proposed method is eco-friendly and employs less quantities of reagents and energy, and two types of products can be produced. Consequently, this process could promote the sustainable development of the vanadium chemical industry.