Targeted Resource Recovery from Mine Waters by Selective Ion Exchange

Waste stockpiles generated as a result of mining cause long-term damage to the environment and can continue to act as a source of pollution for decades beyond mine closure. Current treatment options tend to focus predominantly on Fe removal and may not properly target other trace metal species that may also be present, e.g. Ni, Mn, Co, Cu; metals with an intrinsic recovery value. As such, this thesis explores the potential application of ion exchange resins to selectively recover metals from mine waters, with the hope that by viewing the wastes as a resource rather than a problem, an incentive is provided to deal with this globally significant pollution source.
A range of commercially available ion exchange resins of different chemical functionality were screened for their selective metal recovery performance under a range of pH and [SO42-] conditions. Of the most suitable resins, fixed-bed breakthrough modelling was used to describe their extractive abilities under dynamic operation, and to define optimum operating conditions. Of particular note, a resin was identified which was capable of truly selective Cu recovery from the complex waste stream. The extent to which metals could be recovered from resins after extraction was determined through elution studies, and the composition of eluents was tailored to maximise the concentration of solutions recovered. For one of the resins, a two-stage elution process was proposed for the selective recovery of Co and Ni as two separate, concentrated product streams; a highly desirable separation given the high value of each metal. The reusability of each resin was determined through cyclic adsorption and desorption studies to assess process sustainability, and where appropriate, resin degradation mechanisms were explored. Finally, a bench-scale system was operated to explore the potential of a coupled-column system design for continuous treatment and resource recovery.