Abstract
The global transition to electric vehicles (EVs) has prompted significant research into the sustainable and efficient production of battery-grade materials. Nickel (Ni) is a crucial element in rechargeable batteries, primarily for its vital role in cathode materials, especially in Nickel Manganese Cobalt (NMC) and Nickel Cobalt Aluminum (NCA) batteries. Nickel is generally extracted from natural sources, such as laterite ores (which contain 1-2% nickel by mass), using either hydrometallurgy (involving acid-intensive processing) or pyrometallurgy (entailing high temperature, energy intensive processing). Hydrometallurgical extraction yields an intermediate product known as mixed-hydroxide precipitate (MHP), which may contain up to 50% nickel by mass on a dry basis; however, more processing is necessary to achieve high-purity nickel. This research addresses a sustainable and selective extraction technique for nickel from mixed hydroxide precipitates derived from laterite ores and used battery materials (black mass). The process relies on a vapometallurgical approach that involves two main steps. First, the nickel hydroxides in the MHP are reduced to metallic nickel using hydrogen at temperatures between 400°C and 600°C. Then, this metallic nickel is selectively extracted through carbonylation, carried out at 100–120°C and pressures between 10 and 30 bar. During carbonylation, nickel reacts with carbon monoxide (CO) to form a volatile compound nickel tetracarbonyl (Ni(CO)₄), which allows nickel to be transported in the vapor phase. Reduction and subsequent carbonylation experiments were conducted in a high-pressure thermogravimetric analyzer (HPTGA), enabling real-time monitoring of mass changes associated with the operations. Characterization techniques were utilized to quantify nickel extraction, evaluate morphological changes from fresh samples to reaction residues, and confirm the synthesis of Ni(CO)₄. Main findings revealed that nickel extraction via carbonylation is highly dependent on the structural properties of the precursor, requiring increased surface areas, suitable pore sizes, and diminished cobalt concentration to enable the movement of carbon monoxide and nickel tetracarbonyl. Nickel extraction efficiencies above 95% were achieved, indicating highly effective carbonylation under the optimized conditions.