Hydrometallurgical processing of Li-ion batteries

Hydrometallurgical processing of Li-ion batteries is based on the leaching of active material (cathode and anodes – black mass) with preferable mineral acids, followed by metal separation using solvent extraction, ion exchange and precipitation (Figure 1) after mechanical processing. Sometimes thermal pre-treatment (pyrolysis) is applied as well.

After pre-treatments, leaching is applied as next step in the hydrometallurgy process. This step is considered to be the most significant one when it comes to valuable metals recovery as its purpose is to convert the metals present in the cathode material procured in the pre-treatment process into ionic solution. The leaching media is, most often mineral acids (H₂SO₄, HCl and HNO₃), alkali and organic acids. Studies show that inorganic acids are highly effective for the recovery of Co and Li (99%) in the leaching procedure when applied in optimal conditions. Graphite is not recovered and stays in a solid residue after filtration of the leachate.

As leaching solution has complicated composition, the separation step is necessary to accomplish recovery of the valuable metals (Li, Co, Ni, Mn, Cu, Al, Fe). The most common separation methods are solvent extraction, chemical precipitation, electrochemical deposition. Due to leaching solutions complex composition, it is complicated to recover all the valuable components from the leachate by applying only one separation method. The separation procedure is usually a combination of two or more of the mentioned methods [12]. Figure 1 shows a flowchart of generalized hydrometallurgical process. Precipitation is most common for removal of Fe, Al and Cu. Solvent extraction is usually applied to separate Mn/Co/Ni. If copper concentration in the leachate is high, solvent extraction is applied for its recovery. Lithium is recovered in the end via precipitation with sodium carbonate.

Figure 1: Principle of hydrometallurgical treatment of Li-ion batteries with thermal pre-treatment included.

Currently a hydrometallurgical processing is mostly used in China (Brunp, Soundon New Energy, GEM, Huayou Cobalt, Ganpower, etc) and South Korea, where majority of the batteries are produced nowadays and thus the infrastructure is well developed for the production waste and obsolete batteries.

In Europe, hydrometallurgical processes are used in Sweden, where the battery producer Northvolt, integrate a hydrometallurgical recycling process in the loop to secure the raw materials supply chain and to decrease the environmental impact of battery production (Figure 2). Hydrometallurgical processing is also used in companies such Eramet (France) and Fortum (Finland), etc.

At Northvolt, the principle is that the initial collection and handling of batteries followed by processing of batteries up to the point of recovering aluminum, copper, steel, plastics, electronics and electrolyte. Once these materials are set aside for processing by third-parties, or in the case of aluminum, by Hydro, the remaining material is a black mass. Its treatment which will be undertaken by Northvolt in Sweden. Initial black mass volumes will be directed to Northvolt’s pilot recycling plant at Northvolt Labs in Västerås (official website of Northvolt). The full-scale recycling plant will have initial capacity to process 8,500 tonnes of black mass per year, roughly equivalent to the material required for 4 GWh of new battery cells.

Figure 2: Northvolt’s approach in Li-ion batteries recycling.

At Fortum, the lithium-ion batteries are first disassembled and treated during a mechanical process at Fortum’s plant in Ikaalinen, Finland. The battery’s black mass, containing critical metals, is collected and then taken to hydrometallurgical processing at Fortum’s plant in Harjavalta, Finland. Recycling technology is able to achieve a recovery rate up to 95% of the scarce metals in battery’s black mass. The hydrometallurgical recycling process involves a chemical precipitation methodology (official website of Frotum).

Recupyl (France) process had an annual LiB recycling capacity of 110 tons. The main Li products recovered from this process were Li₂CO₃ and Li₃PO₄. The recovery method used by Recupyl was a precipitation with CO₂. There is no efficiency or purity data for this process, but it is known that their recovery products were meant to be used for cathode production.

Figure 3: Simplified flowchart of Recupyl’s process

There are several companies which apply a combined approach. Nickelhütte Aue GmbH (Germany) or Umicore (Belgium) use a hydrometallurgical treatment after smelting of the batteries to recover metals from the alloy (matté).

Figure 4: Simplified flowsheet of Nickelhütte Aue GmbH (Brückner et al., 2020).

Nickelhütte Aue GmbH operates a comparatively small hydrometallurgical plant and produces approximately 3900t Ni per year and smaller amounts of Co and Cu. Matte processing starts with comminution followed by pressure oxidation leaching at 6 to 8 bar. Afterwards, impurities are removed prior to solvent extraction. For example, Fe is precipitated as goethite (FeOOH) by using H₂O₂ as an oxidizing agent and basic nickel carbonate for pH adjustment. Leaching and precipitation residues are recirculated into the smelter. Co, Cu, and Ni are separated and purified by several solvent extraction circuits. Depending on the process configuration, cobalt sulfate, nickel sulfate, nickel carbonate, nickel chloride, and copper sulfate are produced (Brückner et al., 2020).

The main advantage of hydrometallurgy is the possibility to produce new battery precursors from the waste with the sufficient purity. Despite the large demand for the chemical reagents, hydrometallurgy allows the use of many solvents for several years and re-utilization of several by-products within the same technology, thus minimizing the overall secondary waste generation (Armand et al., 2020). With future battery legislation and demands for higher material recovery rates, hydrometallurgy is one of the most promising approaches to meet the requirements but also to create a path to circular economy in the battery market.

References

Armand, M., Axmann, P., Bresser, D., Copley, M., Edström, K., Ekberg, C., Guyomard, D., Lestriez, B., Novák, P., Petranikova, M., Porcher, W., Trabesinger, S., Wohlfahrt-Mehrens, M., Zhang, H., 2020. Lithium-ion batteries – Current state of the art and anticipated developments. Journal of Power Sources 479, 228708.