MINING AND PROCESSING OF PGMs

The establishment of a platinum group metal (PGM) mine – from the discovery of a deposit to commissioning and operating – can take a number of years. Once an operation has been developed and constructed, the production of these precious metals involves a number of complex processes, including extraction, crushing and milling, flotation and drying, and finally, smelting and refining. It may take up to six months from the extraction of ore to the refining phase. A volume of approximately 4.5 tonnes of ore needs to be processed to produce a single gram of platinum; however, this ratio varies depending on the type of ore and geological deposition.

The key stages of PGM mining

Exploration drilling

Exploration drilling is drilling carried out in search of new mineral deposits on extensions of known ore deposits, or at the location of a discovery, with the aim of evaluating the site for sufficient mineable ore reserves to justify commercial exploitation.

Mine development and construction

Mine development is the second phase of the mining process. This involves preparing the site for ore extraction. The mine is then constructed in preparation for mining.

Opencast and underground mining

Although there is some open-pit mining, most platinum mining takes place underground and extraction is therefore a labour-intensive process. Miners bore holes with hand-held pneumatic devices and then blast with explosives to obtain the ore.

Ore transportation

In the case of underground mining, the ore is transported to the surface for processing.

Crushing and milling

The ore is then crushed and milled to obtain smaller rock particles thus exposing the PGM minerals.

Flotation and drying

These particles are mixed with water and special reagents, before air is passed through the liquid in a 'froth flotation' process. The PGM-rich particles float to the surface and are removed as a soapy-looking froth. In order to extract the maximum PGMs, the flotation concentrate is taken through a second milling and flotation process. The concentrate is then dried.

Smelting and refining

After drying, the flotation concentrate is smelted in an electric furnace at over 1,500ºC during which a matte containing the valuable metal is separated from the waste. This matte is then periodically tapped before air is blown through it in converters to remove iron and sulphur from it, increasing its PGM content.

As the matte still contains other metals at this point - nickel, copper and cobalt - it is refined through standard electrolytic techniques to separate these metals and obtain a PGM concentrate. The last and most intricate part of the platinum production process involves combining solvent extraction, distillation and ion-exchange techniques to separate and purify the PGMs from gold and small amounts of silver. The soluble metals, which dissolve in hydrochloric acid and chlorine gas, are obtained: first gold and then palladium and platinum. The insoluble PGMs are the last to be extracted.

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