Ion flotation - its potential for hydrometallurgical operations

Ion flotation is a separation technology for recovering and removing metal ions from dilute aqueous solutions. In this process, an ionic collector is utilized to transport non-surface active colligend ions of the opposite charge from a bulk solution to the solution-vapor interface. If a sufficiently large solution-vapor interfacial area can be provided by sparging gas through the solution, the colligend can be concentrated and removed along with the collector in a foam phase. Ion flotation has a long history for laboratory-scale metal separations, and has been tested at the pilot scale for recovering gold from leach solutions. Although ion flotation has not yet been adopted in commercial hydrometallurgical operations, the process has many attractive features that are promising for treating dilute solutions and effluents. Here, the fundamental characteristics of ion flotation are reviewed in the context of their implications for commercial applications. These characteristics include the kinetics of metal ion removal, the ability to separate target ions selectively from mixed solutions, the ability to manipulate selectivity, the ability to recover metal values from the foam product and a comparison of the performance of ion flotation with widely adopted separation methods such as solvent extraction, ion exchange and precipitation. It is evident from consideration of the kinetics of ion flotation that the equipment traditionally used for ion flotation is far from optimized, and that significant improvements in throughput could be achieved with redesigned equipment. (C) 2003 Elsevier B.V. All rights reserved.