Low-cost leaching could help recover low-grade platinum

Most processes of platinum group metals (PGMs) extraction are only applicable to places containing considerably large amounts of PGM deposits, such as South Africa and Russia. These two areas are world's biggest primary producers of PGMs.

However, the local energy shortages and socio-political issues in these jurisdictions are deteriorating, signaling the time to source materials elsewhere. But this still poses a problem for miners, as there are no practical ways of processing lower grades of PGMs using conventional smelter-based operations.

"There's an opportunity to grow the market for platinum metals significantly," said Jacques Eksteen, Chair of Extractive Metallurgy at Curtin University . "[But] none of these deposits is large enough to support the capital costs of building a smelter."

For instance, Australia's largest PGM deposits, such as Munni in Pilbara, Panton in the Kimberley, and Fitfield in Central New South Wales, have all been too small to justify traditional metallurgical processing options. Even in Russia, it is impractical to use smelter-based methods for the 16.9 tons of platinum and 18 tons of palladium byproducts by nickel miner Amur Minerals (London AIM: AMC) , as the logistical costs could be too much.

But thanks to ongoing research at the Western Australia School of Mines in collaboration with Stellenbosch University in South Africa, there may soon be a cheaper alternative for conventional smelting processes: heap leaching.

"We found we could recover economic levels of platinum metal using heap leaching, then we were able to recover it from solution," Eksteen said in a report by Science Network Western Australia.

The two-stage leaching process involves biological leaching, which selectively removes copper and nickel often found in PGM deposits, followed by cyanide leaching to extract the remaining metals. Once leached, the metals are absorbed from solution onto activated carbon. The metals are then washed with solvent from the carbon in a concentrated form, and then released one by one.

While this development sounds promising especially for places that contain low grade PGMs, the research still has a long way to go before it can be implemented. For one, PGMs include platinum, palladium, iridium, osmium, ruthenium, and rhodium, so separating them is no easy feat. The task of removing nickel, copper, and even chromium from PGMs can be challenging as well.

"PGMs tend to form a complex range of minerals. We're talking about 30 to 40 different minerals, and they each have different resistance to leaching, making it hard to find a unique solution for all deposits," Eksteen noted. For now, they are developing reagents for improved recoveries, higher selectivity, and lower environmental impact.

Considered as both precious and critical metals, PGMs are used widely in electronics, laboratory equipment, catalytic converters, hydrogen fuel cells, and even jewellery. According to FX Empire , prices of platinum and other precious metals rallied last week as they became attractive as safe havens against the currency devaluations of the People's Bank of China. Platinum posted a 3.16 percent gain, supported by budding optimism that this year's price slide will encourage higher demand from jewellers and carmakers, especially in Europe, which accounts for 25 percent of global use of the white metal.

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