Oral Presentation International Solvent Extraction Conference 2025

The Role of Scrubbing Circuits in the Recovery and Purification of Manganese From Lithium-ion Battery Leachates by Solvent Extraction (122578)

Niklas Jantunen 1 , Mikko Kohvakka 1 , Sami Virolainen 1
  1. LUT University, Lappeenranta, SOUTHERN KARELIA, Finland

High-purity manganese sulfate is an important chemical for the lithium-ion battery (LIB) industry. For example, lithium–nickel–manganese–cobalt oxide (NMC), and lithium–manganese–oxide (NMO) cathodes contain significant amounts of manganese in their structures. It is now trivial that LIBs are widely applied for energy storage, and their consumption is increasing. Once the batteries reach the end of their lifespan, they must be recycled to maintain sustainability and to meet the regulated recycling targets within the European Union (The European Parliament and the council of European Union, 2023).

Recycling of the end-of-life LIBs involves several mechanical and thermal treatments before liberation and recovery of the valuable metals by hydrometallurgical processing. The hydrometallurgical leaching step is most often performed using H2SO4 and H2O2, and it yields an acidic multi-metal sulfate solution (LIB leachate), from which the individual metals can be recovered. NMC cathode leachates contain mainly lithium, cobalt, nickel, and manganese. However, copper, aluminium, and iron are also found in the leachates because the current collectors and the casing are not completely removed by the preceding mechanical treatments. Other elements, for example, magnesium and zinc, can be found from the leachates (Vieceli et al., 2023), possibly because of structural doping and coating of the cathodes (Weng et al., 2013; Zhao et al., 2015).

Although there seems to be no official consensus on the maximum impurity levels in “battery grade” manganese sulfate, it is known that salts with minimal impurity content are preferred in the co-precipitation synthesis of new precursor cathode active materials (PCAMs). High-purity manganese sulfate monohydrate (HPMSM) supplied by Vibrantz Minerals SRL (Belgium) contains a minimum of 31.5 % manganese, less than 5 ppm copper, iron, cobalt, or nickel, and less than 10 ppm aluminium (Vibrantz Minerals SRL, 2024).

Any method for direct and selective recovery of manganese sulfate from LIB leachates, at higher than 99.9 % cationic purity, is currently unknown. Several researchers (Feather et al., 1999; Hoh et al., 1984; Locati et al., 2024; Peng et al., 2020; Sole et al., 2022; Vieceli et al., 2021, 2023) have studied the solvent extraction (SX) of manganese with bis-(2-ethylhexyl) hydrogen phosphate (D2EHPA). However, the most common acidic organophosphorus extractants (D2EHPA, bis(2,4,4-trimethylpentyl) phosphinic acid, and 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate) have higher affinity for iron and aluminium than for manganese (Sole, 2018). Copper and cobalt are also co-extracted within the pH range suitable for manganese extraction. Sole et al. (2022) and Vieceli et al. (2023) have suggested that co-extracted cobalt in manganese-bearing D2EHPA extracts can be removed by scrubbing. Nevertheless, copper and manganese remaining in the raffinate would also interfere with the subsequent cobalt–nickel separation. Therefore, copper, aluminium, and iron should preferably be completely removed from the LIB leachate before extracting manganese. Additionally, manganese should be completely extracted at very high cationic purity. Otherwise, purities of the metal sulfate products (MnSO4, CoSO4, and NiSO4) are compromised.

Losses of lithium, manganese, cobalt, and nickel are undesirable when iron and aluminium are removed from the LIB leachate. In this work, SX was evaluated for the removal of iron and aluminium, because findings of a previous study (Jantunen et al., 2021) suggested that co-extracted manganese can be selectively stripped from D2EHPA and CYANEX 272 extracts that contain iron. Therefore, this research focused on 1) controlling the co-extraction of manganese during the extraction of iron and aluminium, and 2) controlling the co-extraction of cobalt during the extraction of manganese. Loaded D2EHPA with minimum of 99.9 % cationic purity of manganese was obtained by scrubbing an extract containing 300 mg/L cobalt and 30 mg/L nickel.

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