Direct leaching of PGM ores and concentrates

Jacques Eksteen

Last month's Precious Metals '15 conference got off to a fine start with a keynote lecture, given by Jacques Eksteen of Curtin University, Australia, who reviewed recent innovations in the processing of difficult and low grade gold ores, and we look forward to seeing this paper published in the special issue of Minerals Engineering.

Jacques and his co-workers at Curtin University have another excellent paper on precious metals processing, this time platinum group metals (PGMs), in Volume 78, the latest issue of Minerals Engineering. PGMs, often with associated gold, have very few occurrences where they are present in an ore deposit at economically extractable levels. They are classified as both precious and critical metals due to their scarcity and their wide industrial use. With deteriorating socio-political environments in most primary PGM producing countries, PGM deposits that are smaller but in less risky jurisdictions have to be evaluated. However, the lower PGM grades, increased mineralogical complexity of the ores, capital intensity and strict environmental regulations in other international jurisdictions, limit the implementation of conventional metallurgical processing options, particularly smelter-based operations. The conventional smelter-based process options are justifiable for high grade, low chromite, large resource and long life-of-mine operations.

In the present paper, Eksteen and his co-authors review some of the most recent literature on the predominantly hydrometallurgical approaches to PGM extraction. A number of metallurgical processes that generate either a PGM rich leachate or a residue containing metal values, and the various methods in use for their recoveries from pregnant rich solutions are reviewed. Sixteen process flowsheet variants combining conventional and proprietary unit process technologies are provided, and their process chemistries and key technical operating parameters are compared. Where appropriate, the key thermodynamic and kinetic factors are given and compared.