Hydrometallurgical recycling processes for spent Li-ion batteries (LIBs) often produce pregnant leach solutions (PLS) that contain metals like Co, Ni, Mn, Li, Al, etc. Although significant research has focused on the recovery of the most valuable materials (e.g., Co, Ni, Li), the reclamation of Mn from PLS is often neglected. In this study, recovery of Mn via a multi-step process based on solvent extraction with di-2-ethylhexyl phosphoric acid, scrubbing, stripping and oxidative Mn precipitation has been undertaken. The results demonstrate that more than 99% of Mn can be successfully recovered as a high-purity MnO₂ product (purity > 99.5%) with almost no loss of Co, Ni and Li. In addition, the behavior of other metal elements present in the PLS were also studied in detail. Overall, this study investigates the fundamentals of Mn recovery from the complicated PLS of LIBs waste and outlines industrial process feasibility based on known unit process steps.

In this study, the electrodeposition-redox replacement (EDRR) method was studied for the recovery of minor concentrations of silver from dilute solutions. The parameter optimization was carried out with synthetic solutions similar to silver oxide button battery recycling effluents, consisting of sulfuric acid and concentrated base metal (10 g·L⁻¹ H₂SO₄, 60 g/L Zn²⁺) with a minor amount of silver (100 ppm) and a varying amount of Fe³⁺ ions. Results of these experiments were analyzed both electrochemically and by use of SEM-EDS. The role of dissolved Fe³⁺ ions was studied by varying the concentration from 0 to 1000 ppm and the results showed that although the presence of Fe ions decreased silver recovery efficiency, final product purity was found to increase slightly. The EDRR process was also found to be more effective for Ag recovery and has less energy consumption when Fe³⁺ concentrations are relatively low (≤ 100 ppm) when compared with conventional direct current electrowinning. In the final stage, silver was successfully recovered via EDRR, using the optimized conditions, from a real pregnant leaching solution (PLS) obtained from the leaching of silver oxide batteries.

This study outlines a novel and sustainable electrodeposition–redox replacement (EDRR) method to produce Cu/Zn alloys using a simulated hydrometallurgical Zn solution containing 200 ppm Cu, 65 g/L Zn, and 10 g/L H₂SO₄. The results indicate that by tailoring the EDRR parameters, like deposition time, replacement time, and agitation conditions, Cu/Zn alloys with controllable properties including chemical composition, microstructures, colorations, and crystalline phases can be readily obtained. Scanning electron microscopy (SEM) analysis shows that coherent Cu/Zn films grow from separate nanoscale particles produced during the initial EDRR cycles. Furthermore, the corrosion performance of the prepared Cu/Zn films is tunable by changing the crystalline phases through the variation of operating conditions. For example, deposits containing Zn-rich phases (CuZn₅, Cu₅Zn₈) obtained with short redox replacement times without agitation resulted in relatively poor corrosion resistance. In contrast, Cu-rich phases (Cu_0.75Zn_0.25, Cu_0.85Zn_0.15) with enhanced corrosion performance were achieved with prolonged redox replacement times and/or the application of magnetic stirring. Unlike traditional electrodeposition, the EDRR method does not involve any complexing agents and the currently underutilized hydrometallurgical solutions were used as potential raw materials. Overall, the study suggests the EDRR method as a promising approach to achieve sustainable manufacturing of Cu/Zn alloys and an improved circular economy of metals.

Ag/Zn and Ag particles have been successfully produced from electrolytes simulating zinc process solutions containing a high zinc concentration (65 g/L) and a negligible silver concentration (0.5–50 ppm) using a facile and sustainable electrodeposition-redox replacement (EDRR) method. Results show that the particle size and chemical composition of the deposited Ag/Zn and Ag particles can be readily controlled by varying the operating parameters such as replacement time and agitation. Electrochemical quartz crystal microbalance (EQCM) studies supported with SEM-EDS and TEM results indicate that the EDRR process consists of three regions: (I) zinc pulse deposition; (II) redox replacement between the Ag⁺ ions and the deposited Zn, formation of a Zn/Ag alloy structure, and competing Zn oxidation by H⁺ ions; and (III) further replacement between Ag⁺ ions and Zn (alloy) formed in the previous stage and possible silver reduction by hydrogen. The Zn (alloy) has a higher reduction potential which hinders the competing H⁺ reduction and sequentially improves the utilization efficiency of the sacrificial metal (Zn). Furthermore, by using the EDRR method, Ag/Zn particles could be successfully obtained from solutions with an extremely low Ag concentration of 0.5 ppm. The promising results demonstrate the feasibility of producing Ag-based functional materials utilizing trace amounts of Ag from zinc process solutions.

Zinc electrowinning is an energy-intensive step of hydrometallurgical zinc production in which ohmic drop contributes the second highest overpotential in the process. As the ohmic drop is a result of electrolyte conductivity, three conductivity models (Aalto-I, Aalto-II and Aalto-III) were formulated in this study based on the synthetic industrial electrolyte conditions of Zn (50–70 g/dm³), H₂SO₄ (150–200 g/dm³), Mn (0–8 g/dm³), Mg (0–4 g/dm³), and temperature, T (30–40 °C). These studies indicate that electrolyte conductivity increases with temperature and H₂SO₄ concentration, whereas metal ions have negative effects on conductivity. In addition, the interaction effects of temperature and the concentrations of metal ions on solution conductivity were tested by comparing the performance of the linear model (Aalto-I) and interrelated models (Aalto-II and Aalto-III) to determine their significance in the electrowinning process. Statistical analysis shows that Aalto-I has the highest accuracy of all the models developed and investigated in this study. From the industrial validation, Aalto-I also demonstrates a high level of correlation in comparison to the other models presented in this study. Further comparison of model Aalto-I with the existing published models from previous studies shows that model Aalto-I substantially improves the accuracy of the zinc conductivity empirical model.