Circular hydrometallurgy for energy-transition metals

CIRMET will lead to a new approach to hydrometallurgy, called “circular hydrometallurgy”, with a focus on the design of energy-efficient flowsheets or unit processes that consume a minimum amount of reagents and produce virtually no waste. CIRMET has the ambitious goal to replace the traditional, linear hydrometallurgical flowsheets for extraction and refining of the “energy-transition” metals cobalt and nickel into a next-generation, circular flowsheet, which (1) consumes no chemicals other than (green) hydrogen, water and carbon dioxide (taking advantage of the unique chemical properties of carbon dioxide); (2) uses the acid for the leaching process as a “catalyst” that is continually regenerated rather than consumed; (3) reduces the net consumption of acids and bases to virtually zero through ingenious manipulations of chemical equilibria via solvent extraction; and (4) comprises a virtually zero discharge of solid and liquid waste streams. As such, CIRMET can drastically reduce the environmental footprint of hydrometallurgical processes. To enable such circular flowsheets, a new theoretical chemical thermodynamic framework for multiphase electrolyte equilibria involving two immiscible liquids and innovative unit operations for sustainable metal and sulphur recovery are developed. Hydrometallurgical processes are approached from a molecular level. Liquid-liquid equilibria are modelled by Gibbs-energy-minimisation (GEM) methods, rather than by solving law-of-mass action (LMA) equations. The proof of concept of circular flowsheets is demonstrated for metal recovery from real, complex (rather than synthetic), impurity-bearing input streams: nickel laterites, cobalt-nickel sulphide ores, mixed hydroxide precipitate (MHP), and mixed sulphide precipitate (MSP). Only by combining these three mutually supporting spheres of innovation – (1) the “thermodynamic framework”, (2) the “unit process level” and (3) the “general flowsheet” sphere – can CIRMET be successful.