Cementation for metal removal in zinc electrowinning circuits

Step changes in technology, including adoption of new process configurations and chemistry, require modelling and experimental work for establishing process feasibility and process optimisation. In this work the results of such modelling and experimentation as applied to purification via zinc dust cementation of a zinc-bearing leachate are presented. The novelty of the process, developed by Intec Ltd, lies in the use of a mixed halide leachant over the traditional sulphide leach. The process has the advantages of operation at low temperatures and atmospheric pressure, and regeneration and recycle of leachant. Thermodynamic modelling results demonstrated that feasible removal of major and trace metals via cementation is possible down to levels suitable for electrowinning. A challenge in this respect is accounting for the competing evolution of hydrogen. Experimental work provided guidance in identifying the optimal quantity and method of zinc dust addition required to achieve removal, and will be used to guide the development of a suitable operational strategy for the plant. Comment is offered on opportunities for selective recovery of valuable metal species.