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Thinking outside the box for the customer

A world leader in minerals and metals processing, Outokumpu Technology recently commercialised a new type of leaching reactor: the OKTOP™ VFF. The latest member of the OKTOP™ family, this has been developed for particle diffusion zone limited oxidative leaching.

How to make money mining copper ore when the cost of extracting it using existing methods can sometimes exceed the price you can sell it for?

Rodrigo Grau (left) and Jussi Vaarno played a key role in developing the new OKTOP™ VFF atmospheric leaching reactor. The patented technology behind the innovation joins the over 400 patent families and 2,000 individual patents held by Outokumpu Technology.

Not an easy question for anyone in the minerals business, not least of all for Cobre Las Cruces S.A., a subsidiary of Inmet Mining Corporation, which wanted to open up a major deposit of copper ore near Seville in southern Spain that was one of the highest-grade copper formations yet to be mined anywhere.

The problem was that there simply was no technology available off the shelf that would enable Cobre Las Cruces to recover the ore, which has an average copper content of 6.2%, profitably.

That is when Outokumpu Technology came into the picture.

Making it all possible

Working at their state-of-the-art Research Centre in Pori in Finland, the company's R&D experts created an innovative process to extend existing hydrometallurgical copper production technology and make the mine a reality.

The new atmospheric leaching process – including the new type of leaching reactor, the OKTOP™ VFF, that lies at its heart – was tested down to the smallest detail in a laboratory-scale plant built at Pori by Outokumpu Technology. This proved beyond doubt that the technology would offer high yields, low operating costs, and flexibility, as well as operate within tough environmental limits. And enable the mine to extract over 90% of the copper in the formation at industry-leading low costs.

The new OKTOP™ VFF reactor offers outstanding process performance and a very attractive cost profile.

Outokumpu Technology will deliver process know-how and key equipment for grinding, thickening, and leaching, an Outokumpu VSF™ solvent extraction system, a tank farm, and an electrowinning plant, together with supervisory services from installation to commissioning.

Work is moving ahead well on the project, and the mine is expected to be up and running in early 2008, when it will begin producing 72,000 tonnes of LME Grade A copper cathodes annually until 2022.

Bypassing the need for merchant smelters/refiners in this way will allow the facility to sell most of its output directly to manufacturers, and eliminate the mine's exposure to volatilities in the concentrate market.

Vertical Fast Flow

OKTOP™ VFF technology offers a number of benefits. Chief among these is the ability to leach larger particles than has been possible previously. This gives significant cost savings in terms of feed grinding and residue filtration. Enhanced leaching recovery also means that the payback times on investments are much shorter. Overall investment costs are also lower, compared to autoclave leaching.

The technology achieves this thanks to a patent-pending configuration with outstanding process performance: delivering high reaction rates, despite demanding leaching kinetics; an excellent oxygen/reaction gas utilisation rate; and heavy-duty suspension properties.

A high level of sludge circulation is maintained between the two impellers in the reactor, creating a strong downdraft of bubbles into the reaction zone, enhanced gas dissolution, and a good updraft of solids for overflow offtake. Using a higher-rated lower impeller results in a minimal diffusion zone and effective abrasion of passivation layers. A unique sub-vortex shedding structure ensures good gas entrainment and circulation.

Recognising the realities of the sites where these units will be installed, the impellers and the overall installation have been designed to be both robust and capable of smooth and reliable operations in even very challenging conditions.

> Kari Knuutila
(Published in High Technology Finland )