The University of Cape Town (UCT) has completed sample preparation for leach and characterisation testwork as part of a concept study into developing a mini-scale simple and energy efficient process to recover pure zinc from polymetallic ore concentrates.

The university sourced a suitable zinc concentrate sample from mining company Vedanta’s Black Mountain operation, in the Northern Cape, to conduct the testwork.

Vedanta, as well as steel sheet galvaniser Duferco Steel Processing, based in Saldanha Bay, serve as sponsors of the testwork.

UCT Department of Chemical Engineering's Professor Jochen Petersen says a comprehensive review of current industry practice for zinc refining will soon be submitted to scientific journal Minerals Processing and Extractive Metallurgy Review.

Next, the study will focus on extracting data from the leach experiments to inform the operating conditions and likely efficiencies of an ammonia-based leaching process.

UCT plans to develop a basic process flowsheet, as well as a baseline prefeasibility cost evaluation for operating the process at a 40 000 t/y zinc production facility.

“The outcomes will enable the decision whether to develop the envisaged process further towards industrialisation and what aspects of the process may require further technology development,” Petersen states.

He explains that, while using an ammonia medium for base metal processing has been well established, it has yet to be applied to zinc refining.

The low-voltage, direct current electrowinning required presents the possibility of linking the process directly to using electricity generated by solar power. What is more, the production of green hydrogen by electrolysis can also be used to produce the oxygen required in the leach process, Petersen notes.

“This is an exciting project that takes a whole new look at zinc refining in the light of the need to use low power processes and work clean and green,” says zinc promotion organisation International Zinc Association Africa executive director Simon Norton.

He highlights that the funding sponsors are keen to see the development of local capability to produce high-grade refined zinc, while simultaneously supporting fundamental chemical engineering research.