Giant leap in copper leaching technology

The top ore layer of an open pit copper mine is easily processed using heap leach in tandem with solvent extraction and electrowinning to produce copper cathodes. The copper mineral most predominate in mines is however chalcopyrite (CuFeS₂), a refractory sulfide mineral that is found deeper in the mine. Consequently, mining companies struggle to maintain copper production during the transition from oxide ore to sulfide ore as open pit mines reach the later stages of development. Mining companies also struggle to recover the copper from very low-grade concentrates and from concentrates contaminated with arsenic.

FLSmidth recently filed patents for a new hydrometallurgy process called the FLSmidth^® Rapid Oxidative Leach that can economically remove the passivation layer of primary sulfides and thereby allow the extraction of copper. The technology operates at atmospheric pressure and temperature around 80 °C, making it possible to leach directly at the mine and hence provide a seamless transition from oxide ore to sulfide concentrates.

While existing atmospheric leach processes leach a maximum of 95 % copper in 20-60 hours, the FLSmidth^® Rapid Oxidative Leach process can leach more than 98 % of copper from concentrates containing as low as 8 % copper in less than 6 hours; a faster and much simpler process. And that, as Head of Group R&D, Jens Almdal, points out is a giant leap in productivity improvements: “For a copper mine with remaining low quality copper deposits producing around 200 000 tons of copper per year, our 3 % output increase would mean an extra US$ 40 million per year with a copper price around US$ 6600 per ton. That is indeed a significant contribution to profitability in an industry that normally chases 0.1-0.2 % increase in copper recovery by design modifications of flotation machinery,” Jens Almdal states.

For copper producers, the new technology could mean a renewed business case for remaining deposits: several existing mines have lost the ability to make copper concentrates suitable for smelting. The FLSmidth^® Rapid Oxidative Leach technology makes it possible to recover more copper from low grade concentrate. Also, there are mineral deposits yet to be developed that are unsuitable for smelting but with the new technology would be suitable for leaching.

The new technology also makes it possible to develop mineral deposits containing arsenic for recovery of copper, gold and silver, while complying with stringent environmental air and land pollution regulations. As the new technology operates at atmospheric pressure, a concentrate can be treated at the mine location, with complete control over the arsenic-bearing residues generated after leaching. This makes it possible to avoid the potential of arsenic contamination of sea, air and land while en route from mine to smelter.

“A lot of existing mines have piles of copper concentrate with more than 0.5 % arsenic concentrations which is too high for smelting. Our technology can be used to process these piles of high arsenic concentrate or even make it possible to develop new mineral deposits high in arsenic,” explains Manfred Schaffer, President, Minerals division. FLSmidth has patents pending for the new technology and a cooperation initiated with two customers with the technology expected to be implemented in large scale in 2017.

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