Introduction
The separation of manganese (Mn) with different oxidation states after leaching in sulfuric acid media is a largely overlooked topic in battery recycling. Manganese plays a crucial role in NMC (Nickel-Manganese-Cobalt) cathodes, but its speciation after leaching significantly affects its recovery efficiency. Manganese typically is present in NMC-622 blackmass in a +4 oxidation state, and being reduced to Mn2+ during the leaching process with sulfuric acid and hydrogen peroxide. Depending on the leaching conditions, Mn can exist in different oxidation states such as Mn²⁺and Mn3⁺, influencing its solubility, precipitation behavior, and extractability. This variation directly impacts the solvent extraction (SX), where different oxidation states require different reagents and process conditions. This study investigates the impact of leaching conditions, oxidation-reduction potential (Eh), and reagent selection on Mn speciation. To further investigate this phenomenon, upscaling experiments were conducted using mixer-settler units (MEAB MSU 2.5) to validate separation strategies under continuous operation. Understanding the role of Mn oxidation states is essential for optimizing Mn recovery and ensuring the efficiency of hydrometallurgical battery recycling processes.
Methodology
Batch equilibrium experiments were conducted to evaluate the extraction performance of D2EHPA (Di(2-ethylhexyl)phosphoric acid) for manganese separation. The influence of pH, temperature, and diluent selection was systematically studied to determine their impact on metal loading and extraction efficiency. Analytical techniques such as ICP-OES were used to quantify metal concentrations, while phase disengagement time measurements were performed to assess separation behavior. To validate process scalability, mixer-settler units (MEAB MSU 2.5) were utilized for continuous operation, ensuring that the findings from batch experiments could be effectively translated into pilot-scale applications.
Results and Discussion
The extraction of manganese using D2EHPA demonstrated high efficiency, with concentrations reduced from 3.5 g/L to 8.2 mg/L, achieving more than 99.5% extraction in pilot-scale operations. The influence of key process parameters, including pH, temperature, phase disengagement, and diluent selection, was systematically evaluated to optimize extraction performance. The results confirmed that controlled process conditions are critical for maximizing manganese recovery while ensuring efficient phase separation. Additionally, the transition from batch equilibrium experiments to continuous pilot-scale operation in mixer-settler units (MEAB MSU 2.5) validated the scalability and robustness of the extraction process.
Conclusion
This study demonstrated the efficient extraction of manganese using D2EHPA, achieving >99.5% removal in pilot-scale operations. The influence of pH, temperature, diluent selection, and phase separation was systematically analyzed, confirming the scalability and robustness of the process. Continuous operation in mixer-settler units (MEAB MSU 2.5) validated the feasibility of manganese recovery for industrial applications.