Elemental metals for environmental remediation: lessons from hydrometallurgy

Abstract

In the mining industry, the separation of economically valuable metals from gangue materials is a well established process. As part of this field, hydrometallurgy uses chemical fluids (leachates) of acidic or basic pH to dissolve the target metal(s) for subsequent concentration, purification and recovery. The type and concentration of the leach solution is typically controlled to allow selective dissolution of the target metal(s), and other parameters such as oxidation potential, temperature and the presence of complexing/chelating agents. In the remediation industry the use of elemental metals (M0) for the removal of aqueous contaminant species is also a well established process. Removal is achieved by the oxidative corrosion of the M0 and associated pH and/or redox potential change. Whilst the two processes are directly opposed and mutually exclusive they both stem from the same theoretical background: metal dissolution/precipitation reactions. In the mining industry, with each prospective ore deposit physically and chemically unique, a robust series of tests are performed at each mine site to determine optimal hydrometallurgical fluid composition and treatment conditions (e.g. fluid temperature, flow rate) for target metal dissolution/yield. In comparison, within the remediation industry not all such variables are typically considered. In the present communication a comparison of the processes adopted in both industries are presented. The consequent need for a more robust empirical framework within the remediation industry is outlined.