In recent years there has been a worldwide trend showing the increased demand of gold, silver and platinum group metals (PGM) for electronic devices and jewelry usage. The result of the increasing demand has been a steady rise in the price of metals and an increase in the price differential between PGM and the old standard, gold. The platinum group of metals comprises platinum, palladium, rhodium, iridium, osmium, and ruthenium, of which platinum is the most important. Of these metals, osmium is generally alloyed with iridium. The platinum group metals occur chiefly as natural alloys of various proportions and to a much lesser extent as sulfides and arsenides. All of these metals are rare and expensive. They possess individual properties that make them uniquely attractive for certain uses in highly developed technology and for use in jewelry and for decorative purposes.
Platinum and palladium are the most abundant and most widely used of the group; the other four metals are mainly used as alloy modifiers with platinum or palladium. The high melting points, corrosion resistance, and catalytic properties of these metals have many industrial applications. There has been minor past production of the platinum group metals from California and Alaska, and the main production of PGM was as a by-product in the refining of copper. There some locations around the world where the presence of gold and PGM is important and the metallurgy is complex. PGM production has received a major boost with Stillwater, Anglo Platinum, Impala platinum and Lonmin.
One additional source of PGM will be low-grade projects where expertise in treatment of low grade precious metals is important. Tailing dumps, open cast and slag deposits are examples of these projects. Try to recover gold and PGM is not simple and several alternatives routes has been studies. It is well known that cyanide is almost the universal leaching agent employed to dissolve gold from its ores, but it has not been employed to dissolve PGM, even though these elements are known to form stable complexes with cyanide. Some studies were performed in South Africa, but they were not totally optimized in order to study the effect of leaching conditions on the level of recovery of platinum. Basically, PGM are an important group of elements and are present in a wide variety of minerals and their reactions respect to a special leaching agent such cyanide could be different and the optimum leaching conditions needed for the recovery of PGM from different ores is a little different and the metallurgist must find out the appropriate process to recover gold, silver and PGM.
Traditional processing of PGM ores involves flotation, concentration, matte smelting, leaching and refining steps. Nowadays, mining companies want to reduce costs, avoid contamination and improve recoveries. The solution is not simple, but there are interesting alternatives.