Direct leach approaches to Platinum Group Metal (PGM) ores and concentrates: A review C.N. Mpinga, J.J. Eksteen ⇑ , C. Aldrich, L. Dyer Department of Mining Engineering and Metallurgical Engineering, Western Australian School of Mines, Curtin University, GPO Box U1987, Perth 6845, Western Australia, Australia article info Article history: Received 8 December 2014 Revised 8 April 2015 Accepted 10 April 2015 Available online 16 May 2015 Keywords: Low-grade deposits Refractory materials Platinum group metals Platinum and palladium recovery Leaching abstract Platinum Group Metals (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, we review some of the most recent literature on the predominantly hydrometal- lurgical 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. Ó 2015 Elsevier Ltd. All rights reserved. Contents 1. Introduction .......................................................................................................... 94 2. Remote PGM deposits in friendly jurisdictions: A Western Australian example .................................................... 94 3. Existing technologies in the extractive metallurgy of low-grade refractory precious metals .......................................... 96 3.1. Precious metal rich solution processes ............................................................................... 96 3.1.1. Chloride-based atmospheric leach process: Intec Copper process................................................... 96 3.1.2. Sulfate-based pressure leach process: Platsol Ò process ........................................................... 97 3.2. Precious metal rich residue processes ................................................................................ 98 3.2.1. Cyanide-based atmospheric leaching ......................................................................... 98 3.2.2. Cyanide-based pressure leaching: Two-stage selective pressure leach process ........................................ 99 3.2.3. Chloride-based processes .................................................................................. 100 3.2.4. Sulfate-based leach processes .............................................................................. 101 3.2.5. Galvanically-assisted chalcopyrite leach process: Galvanox™..................................................... 105 3.3. Summary ...................................................................................................... 106 4. Use of unconventional lixiviants ......................................................................................... 106 4.1. Alkaline glycine leach processes.................................................................................... 106 4.2. Halide system (bromide, chloride and iodide) leach processes ........................................................... 106 4.2.1. Iodide leach processes of precious metals .................................................................... 107 4.2.2. Chloride leach processes of precious metals ................................................................... 107 http://dx.doi.org/10.1016/j.mineng.2015.04.015 0892-6875/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: jacques.eksteen@curtin.edu.au (J.J. Eksteen). Minerals Engineering 78 (2015) 93–113 Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng