Corrosion Challenges in Hydrometallurgical Recovery of Cobalt and Nickel: A Review of Materials and Coating Solutions for Sustainable Critical Mineral Processing

The mineral industry is key to the development of modern industry, as it supports technologies ranging from advanced manufacturing to the aerospace sector, as well as electronics, the defense sector, and clean energy technologies. A sustainable supply of minerals such as cobalt and nickel is dependent on the recovery of these critical metals from hydrometallurgical processes. Increasing worldwide demand, alongside diminishing grades of primary ores, has heightened dependence on hydrometallurgical methods particularly high-pressure acid leaching (HPAL) and solvent extraction for the recovery of metals from lower-grade ores and mine tailings; however, owing to the aggressive operating conditions, these processes are subject to significant corrosion problems. These procedures use strong sulfate- or chloride-based solutions at high temperatures and oxidizing conditions, which are extremely corrosive to the steel and alloy equipment found in autoclaves, reactors, pipelines, and mixers. As a result, corrosion phenomena such as pitting, stress corrosion cracking, and erosion-corrosion pose significant technical and economic issues, including increased downtime, high replacement prices, and product contamination hazards. Addressing these difficulties necessitates a mix of sophisticated material selection, protective coatings, and process optimization, making corrosion control an important enabler for long-term cobalt and nickel production. This paper critically evaluates current methods, identifies gaps, and proposes sustainable corrosion control based on developments in corrosion mechanisms, process conditions, and protective materials.