Characterizing and recovering the platinum group minerals––a review
Introduction
The six platinum group elements (PGEs); ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt), together with gold and silver have been considered to be “precious” metals. Platinum was first discovered in the 16th century in the Choco district of Columbia (McDonald, 1960). Palladium, rhodium, osmium and iridium were all discovered in 1803, some 300 years after platinum. The last platinum group element discovered was ruthenium.
All six of the platinum group metals are silvery white lustrous metals, although osmium has a bluish tinge. They are all sufficiently ductile and malleable to be drawn into wire, rolled into sheet or formed by spinning and stamping. These six elements can be classified into two groups compared to the specific gravity of gold. These elements in the group lighter than gold are ruthenium, rhodium, and palladium, with specific gravities around 12.0–12.4. Those elements in the group heavier than gold are osmium, iridium, and platinum with the specific gravity in the range of 21–22.5. The elements of the later group also have a higher atomic number of 76, 77, and 78 respectively.
Valuable for their resistance to corrosion and oxidation, high melting points, electrical conductivity, and catalytic activity, these elements have wide industrial applications. The major uses are found in the chemical, electrical, electronic, glass, and automotive industries. However, the application of platinum group elements in the automotive industry is fairly recent, resulting from emission-control legislation in the USA. The exhaust gases are passed over a catalyst that contains Pt, Pd and Rh in the ratio 67:26:7, which converts the hydrocarbons, carbon monoxide, and nitrous oxide to harmless emissions. The approximate quantity of platinum group metals per automobile is 2.4 g. With the emission control legislation widely passed and Kyoto protocol accepted in more countries, the demand for PGEs will significantly increase. In the glass industry, the high melting points of the PGEs and their resistance to the abrasive nature of molten glass are utilized for producing high-quality optical glasses. Due to their rarity, platinum and palladium are widely used as jewellery in the world. In the chemical industry, PGEs are used extensively as catalysts, as well as in chemical and in laboratory equipment such as crucibles, forceps, combustion vessels and filters. Palladium is predominant in the electro-mechanical industry, relying on its resistance to corrosion for its application in connectors, sensors, and relays. On the medical side, platinum has found application in the prophylactic and therapeutic aspects of both human and veterinary science. The PGEs can also be used as coating materials on computer disks and the polished samples for scanning electron microscopy (SEM).
Major PGEs' reserves and production are in South African, with Russia taking the second place and Canada the third. South Africa production centers on the Bushveld Complex, the platinum group minerals bearing ores being primarily mined for the recovery of these metals. Canada's PGEs are by-products of nickel–copper mining, primarily from Falconbridge's and Inco's deposits in the Sudbury area.
Historically, little information relating to the mining and processing of the PGM ore can be obtained due to the combined geographic and academic isolation of the world's primary PGE producers. Further, the PGEs industry's strict corporate-secrecy policies blocked the research cooperation with academic research group. This veil of secrecy is now slowly lifting. Recently, the stronger demand for PGEs (Johnson Matthey, 2002), the economic and strategic importance of PGEs is fuelling the exploration and development efforts in the precious metals mining sector. More geologists began looking for PGEs for the first time in their careers (Freeman, 2003), more PGMs companies are now willing to put more effort and cooperate with academic groups on the research of improving the recovery of PGMs.
Much work has been done on the flotation recovery of PGMs from primary ores (Cole and Ferron, 2002). Recently, more concerted efforts are made to study the mineralogy of PGEs and use gravity or flash flotation to improve PGE recoveries in the process of nickel–copper dominant ores. This is strongly desirable for Canada's ore types because virtually all PGEs are produced as by-products of nickel–copper dominant ores. Due to mineralogical studies playing an important role in optimizing and improving the PGEs recovery in the nickel–copper ores. This paper will review the methods for characterizing and recovering PGEs in various ore types in the world.
Section snippets
Classification of PGEs ores
Various methods (such as the mineralogical data, chromite content, grade of PGEs, and sulphur content, etc.) are used to classify PGEs ores. A combination of PGEs content and mode of geological occurrence to classify ore types has been adopted from the classification presented in CIM Special Volume 23: Platinum Group Elements––Mineralogy, Geology, Recovery (Edited by Louis Cabri) (Cole and Ferron, 2002). The information presented in this section was largely assembled from Chapters 10 and 11 of
Platinum-group minerals
Unlike gold and major base metals, which form a fairly small number of minerals, there are 109 PGM species recognized by the International Mineralogical Association (IMA), ranging from sulphides (i.e. braggite, (Pt,Pd)S) to tellurides (i.e. maslovite, PtBiTe), antimonides (i.e. sudburyite, PdSb) to arsenides (i.e. sperrylite, PtAs2), and alloys (i.e. ferroplatinum alloy) to native species (i.e. native Pt nuggets). Table 1 lists some of the PGMs extracted from Cabri's two books: “Platinum-Group
Applied/process mineralogy and sampling preparation techniques using pre-concentration of the PGMs
Petruk (2000) defined applied mineralogy as the application of mineralogical information to understand and solve problems encountered during processing of ores and concentrates. It involves characterizing minerals and interpreting the data with respect to mineral processing. When processing problems are due to the mineralogical characteristics of the ore and/or process products, mineralogical data should be generated to solve this problem.
Henley (1983) reviewed process mineralogy as an
Instruments for characterizing PGMs in applied/process mineralogy studies
There are a wide variety of instruments used for applied/process mineralogy: The optical microscope is used to identify many minerals, to observe mineral textures, and to determine mineral quantities by point counting. X-ray diffractometer (XRD) is used to identify many minerals with a high degree of certainty, and to qualitatively determine mineral contents in powdered materials. The development of the microprobe (MP) was a giant progress in applied mineralogy. Not only can it determine the
Relationship between mineralogy and the recovery of platinum-group elements from ores
Different platinum-group element deposits or ores should be treated with different recovery methods according to their mineralogical features and other factors. The following briefly discusses several different ores: those amenable to gravity separation, those amenable to flotation, and those where platinum-group elements are by-products of base metal sulphides. Most of these following information are from the special volume of “Platinum-Group Elements: Mineralogy, Geology, Recovery” edited by
Intensive mineralogy research and development
The strong correlation between the mineralogy and plant performance discussed above drives the mining industry put more efforts to the applied/process mineralogy studies. Freeman (2003) advocated that mineralogical identification should be conducted early and often, during exploration. Such effort would lead to a maximum benefit of a project. For example, early determination of whether the PGMs were sulphides or alloys and whether there is a presence or absence of bismuth, tin, tellurium or
Conclusions
In this review, documented information about the classification of PGEs ores, the techniques of sample preparation for mineralogy study was examined. It was found that for different ore types the preconcentration methods differ. As do the mineralogical features. Although the preconcentration method is complicated in some cases, it is very effective for the mineralogical analysis.
Mineralogical analysis is very important to choose the flowsheet for recovering the PGMs. It is also critical to
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2022, Advanced Powder TechnologyCitation Excerpt :The Platinum group of elements (PGE) such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) is of strategic importance and have enormous interest from explorers across the world due to their scarcity, high economic value and growing demand in various applications [1,2].