SGS MINERALS SERVICES TECHNICAL PAPER 2002-03 2002 A REVIEW OF THE BENEFICIATION AND EXTRACTIVE METALLURGY OF THE PLATINUM GROUP ELEMENTS, HIGHLIGHTING RECENT PROCESS INNOVATIONS STEVE COLE, C. JOE FERRON –– SGS INTRODUCTION The six platinum-group elements (PGE): ruthenium, rhodium, palladium, osmium, iridium and platinum, together with gold and silver, are considered to be “precious” metals. The recent spike in platinum and palladium prices coupled with the projected increase in demand for the metals has fuelled a spate of exploration and new projects in the PGE sector. Historically, primary producers of PGE metals have controlled the flow of information relating to the mining and processing of these ores into the public domain. Very little published information relating to individual operations and processes is available in comparison to the available literature relating to other metals. The purpose of this paper is to provide authors have tried to briefly describe regarded platinum as an unwanted a general overview of the issues commercial operations, as well as impurity in the silver that they were relating to the processing of PGE ores. recent developments. In attempting to mining (Wagner, 1929). Each topic discussed could easily be summarize a large body of work, much In the early 1900’s, the only significant the topic of a paper or book and so, in detail has been sacrificed. It is hoped uses for PGE’s were for laboratory many cases, only the surface of the that the information provided will be ware, as catalysts in the manufacturing topic will be scratched. An attempt has sufficient to highlight some important process of sulphuric and nitric acids and therefore been made to provide as many issues relating to the recovery of PGE in jewellery. The supply of this metal references as possible. The intent of and to point the reader in the direction of was primarily from placer deposits in the the authors is to review and compare more detailed information, should this be Russian Urals, southwestern Alaska and metallurgical processes from a technical required. gold placers in California and from co- point of view, without reference to the production of PGE metal from Sudbury size of the operation. If one wants to TERMINOLOGY basin ores. keep things in perspective, one should not forget that in 2000, two countries, The terms PGE (Platinum Group In 1920, Hans Merensky discovered namely South Africa and Russia, Elements) and PGM (Platinum Group the PGE reef bearing his name in the produced more than 90% of the world’s Minerals) are often used interchangeably, Bushveld Igneous Complex in South Pt, Pd and Rh supply (Appendix 1). and incorrectly, in the processing and Africa. For many years, this reef has metallurgical literature. The terminology been the primary source for the majority The paper is comprised of three main is confused further by PGM being of the PGE used worldwide. sections. The first section briefly referred to as platinum group metals In the 1960’s, improvements in analytical describes the various PGE ore types and (which is strictly correct) but often leads techniques for determining trace the mineralogical factors that affect the to the abbreviation of PGM, which refers amounts of PGE were developed. This recovery of the PGE’s. to the mineral and not the metal. The led to a better understanding of the abbreviation, PM, should be avoided as geochemistry of PGE occurrences and The second section deals with the this includes silver, and silver is not often hence an interest in looking for PGE beneficiation of the PGE ores, describing associated with platinum group metals deposits in areas previously unexplored the present status and discussing the (Cabri, 1981a). for PGE, such as the Stillwater area. new trends. HISTORY Finally, the third section covers the extractive metallurgy of the PGE’s Naturally occurring platinum and (smelting and base metal refinery), platinum-rich alloys have been known again starting with reviewing the to mankind for hundreds of years. The existing operations and ending with Spaniards named the native metal a presentation of some of the new “platina” or little silver, when they trends and technologies in that area, first encountered it in Colombia. They and finally the PGE refining section, the SGS MINERALS SERVICES TECHNICAL BULLETIN 2002-03 2 During the 1970’s the United States classification presented in this paper from being fairly minor to being government introduced legislation uses a combination of PGE content the “deciding factor” on project mandating a reduction in the level of and mode of geological occurrence to economics. pollutants emitted from automobile group ore types. Figure 1 depicts the • Miscellaneous ores - These are ores exhausts. Catalytic converters containing “family tree” of PGE ores as defined in which PGE values have been platinum, palladium and rhodium (in by this classification. It should be noted noted but not recovered due to low varied combinations) were accepted by that this classification system has been concentrations or recovered as a the automobile industry as a technology largely adopted from the classification by-product with little or no economic that would enable them to comply with presented in CIM Special Volume 23 advantage for the primary producer. the new legislation. During the 1980’s (Cabri, 1981a). The information presented Typically, little is known about the and 1990’s, the demand for platinum was in this section was largely assembled distribution and recovery of the PGE growing every year in response to new from Chapters 10 (Naldrett, 1981) and 11 is these ores. An example of this type requirements for catalysts in general (Cabri, 1981b) of that volume. of ore is that PGE is recovered from (not only for the automobile industry), copper refining in the United States. demands from the electronic industry, In this classification PGE ores are divided However, PGE content and recovery and an increase in the amount of into three primary classes: is rarely determined for any of the platinum used in the jewellery industry. • PGE dominant - Those ores exploited concentrates feeding the smelting Since the mid-1970’s, the UG2 reef, primarily for their PGE content with process. PGE values in the primary ore in the Bushveld Igneous Complex, other metals such at Cu, Ni and Co contribute no financial value. has been increasingly exploited for its being produced as co-products. The PGE content. Until recently, the mining economic values of the co-products A key point to note is that regardless of companies exploiting this reef were the are, in general, minor in comparison to the mode of formation, a detailed study same mining companies exploiting the the PGE values. of ore mineralogy is essential when Merensky reef, some 15 to 330 meters • Ni-Cu dominant ores - Those ores considering the metallurgical response of above the UG2 reef. exploited primarily for the Ni and Cu a PGE ore since mineralogical variations content. The PGE are produced as a within a particular mineralized horizon In 1986, the Stillwater project heralded co-product. The economic importance (or reef) can be as significant as variation the first major primary PGE project in of the PGE in these ores can vary between ore types. Cases in point are North America. The Lac des Iles mine (owned by North American Palladium Ltd.) followed the Stillwater success story in 1993. There are currently a PGE Ores number of exploration projects targeting primary and secondary PGE deposits in North America (see, for example, in this volume: Farrow and Lightfoot; Barrie et Ni-Cu Dominant Miscellaneous PGE Dominant PGE Dominant Ores Ores al.; Peek et al.) Throughout the history of development Porphyry Copper Merensky Type Class I Ni-Cu Ore of primary PGE deposits, Canada has Ores supplied PGE metals as a by-product of nickel and copper mining, primarily from the Sudbury and Thompson regions. Inco Chromite Type Class II Ni-Cu Ore Copper- Molybdenum Ores started production of PGE in 1908 when it opened a refinery in the U.K. to refine ores from the Sudbury basin (Johnson Placer Type Class III Ni-Cu Ore Carbonatite Ores Matthey, 2001). SECTION I: CLASSIFICATION Dunite Pipes Class IV Ni-Cu Ore Black Shales OF PGE ORES AND MINERALOGICAL FACTORS RELATING TO RECOVERY Hydrothermal and Other Ni-Cu Ores Supergene Cu Ores There are various methods (mineralogical, sulphur content, chromite content, grade of PGE, etc.) used to classify ore types, each Ni Laterites with merits and disadvantages. The Figure 1. Classification of PGE Ores SGS MINERALS SERVICES TECHNICAL BULLETIN 2002-03 3 the variations noted in the Merensky reef with most operations choosing a grind Great Dyke on both a regional and mine site scale. size (P80) between 75 and 150 μm. The The most recent publication on the Great (Cawthorn et al., this volume). presence of talc in some areas can cause PGE deposits is that of Oberthur (this significant process difficulties. volume). The BHP-owned mine, Hartley PGE DOMINANT ORES Platinum, was exploiting this ore body Merensky Type The Stillwater Complex and failed because of mining problems These deposits occur in very large • The production from the Stillwater relating to grade dilution (no marker for bodies of basaltic magma, which complex originates from the J-M the reef such as the thin chromite layers intruded into stable continental rocks. (Johns-Manville) reef. Unlike the associated with the Merensky reef). In general, the Merensky type deposits Merensky reef where Pt is the primary The average head grades for this reef are layered with disseminated sulphides. PGE, Pd is the most significant PGE are approximately 4 g/t PGE with about The total sulphide content is fairly low; present in the Stillwater complex. 55% of the PGE content present as Pt.