Dry Extraction of Nickel from Mixed-Hydroxide Precipitates via Reduction and Carbonylation

Abstract

The global transition towards electric vehicles (EVs) has prompted significant research into the sustainable and efficient production of battery-grade materials. Among the critical components of rechargeable batteries, nickel (Ni) is of particular importance due to its central role in cathode materials, specifically for Nickel Manganese Cobalt (NMC) and Nickel Cobalt Aluminum (NCA) batteries. Ni is conventionally extracted from primary sources such as laterite ores (containing 2-3% Ni by mass) through hydrometallurgy (with acid-intensive processing) or pyrometallurgy (with high-temperature, energy-intensive processing). Hydrometallurgical extraction produces an intermediate product called mixed-hydroxide precipitate (MHP), which can contain up to 50% Ni by mass on a dry basis, but still requires further processing to obtain high-purity nickel. This study explores an alternative, sustainable and selective extraction pathway for nickel from MHPs derived from laterite ores and spent battery materials (black mass). The explored vapour metallurgical approach is a two-step, dry process: 1) hydrogen reduction of nickel hydroxides with the MHP to metallic nickel at temperatures between 400°C to 500°C, and 2) selective nickel extraction via carbonylation and conditions of 100°C to 120°C and 150 psig to 450 psig. The carbonylation of metallic Ni using carbon monoxide (CO) produces a volatile molecule called nickel tetracarbonyl (Ni(CO)4), which selectively extracts Ni into the vapour phase. Rigorous safety protocols were employed in this research study to handle the toxic nature of the produced Ni(CO)4 molecules, including CO detectors to identify leaks, and an in-situ decomposition furnace downstream of the reactor to thermally decompose the carbonyls. Reduction and subsequent carbonylation experiments were conducted in a pressurized thermogravimetric analyzer (PTGA), allowing for real-time monitoring of mass changes associated with the reactions. Characterization techniques, including Fourier Transform Infrared (FTIR) spectroscopy, inductively coupled plasma–optical emission spectroscopy (ICP-OES), and Brunauer-Emmett-Teller (BET) analysis, were used to quantify Ni extraction, evaluate morphological changes from fresh samples to reaction residue, and confirm the formation of Ni(CO)4. Significant results demonstrated that the Ni extraction via carbonylation is strongly dependent on the precursor’s structural properties, specifically requiring high surface areas, adequate pore sizes, and minimal cobalt content to enhance transport of CO and Ni(CO)4. Optimal reduction conditions were identified at 450°C, producing residues with a balanced surface area and average pore size, favourable for the carbonylation reaction. Increased carbonylation pressure, at 450 psig, improved Ni extraction efficiency to 95% for a black mass-based MHP.