5.2 Hydrometallurgy

Hydrometallurgy is a chemical separation technology used to extract and purify valuable metals from black mass. Various proprietary and innovative processing options are currently being developed and implemented. The process typically consists of the following main steps: 

• Metal dissolution in acid (leaching): The black mass is dissolved in an acid solution using sulfuric acid (H₂SO₄) or hydrochloric acid (HCl), often combined with oxidizing agents such as hydrogen peroxide (H₂O₂). This step dissolves the metals into the solution, while some impurities—such as graphite or plastics—remain undissolved as solid residue. 
• Precipitation, impurity removal, and separation: Metals are selectively extracted by adjusting the pH (precipitation) or by using organic solvents (solvent extraction). Impurities like iron (Fe), aluminum (Al), and copper (Cu) are removed through precipitation and filtration. Cobalt (Co) and nickel (Ni) can be separated using solvent extraction. Alternatively, a mixed hydroxide precipitate (MHP) can be produced without separating the nickel and cobalt. Lithium is typically recovered in a later step. 
• Crystallization: This is a controlled precipitation of dissolved metals by adjusting temperature. Water is evaporated, and the solution is concentrated—sometimes with the addition of other chemicals. As the solution becomes supersaturated, metal ions begin forming solid crystals. As evaporation continues, additional ions attach to the seed crystals, causing them to grow. The solid crystals are then separated from the liquid by filtration. To produce battery-grade materials, the crystals must be dried and possibly milled to achieve the required particle size.