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MEI Online: Pyrometallurgy: Latest News: May 20th 2008


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:: Mintek, Braemore Achieve Important Milestones in Conroast Technology Development

Mintek and Braemore Resources plc are planning to double the throughput of the ConRoast smelter at Mintek, following seven months of successful continuous operation.

Since October 2007, the DC arc furnace at Mintek has treated high-chromium material containing platinum group metals (PGMs) sourced by Braemore at rates of more than 1 000 tons per month, producing a total of more than 600 tons of alloy containing PGMs. PGM recoveries have consistently exceeded 99 per cent, even when smelting selected lower-grade revert tailings. Throughout the operation, the sulphur dioxide (SO2) emissions have been negligible, averaging less than three parts per million (ppm) - well below the regulated limit.

"After two years into the ConRoast technology development programme, considerable progress has been made, and we are very happy with the results", said Tom Curr, manager of Mintek's Pyrometallurgy Division. "Mintek and Braemore have developed an excellent working relationship, and the contractual milestones have all been achieved to date. The DC arc technology has proved to be extremely robust and reliable, and preparations are well advanced for upgrading the installation to a nominal power of about 3 MW, which will increase its capacity to 2 000 tons per month. This is scheduled to take place in the third quarter of 2008."

The ConRoast technology is able to recover platinum-group metals (PGMs) from concentrates and other materials that contain high levels of chromium and low sulphur, which are metallurgically challenging for conventional "six-in-line" smelters. Most of the development-stage PGM projects in South Africa would produce concentrates with higher chromium and/or nickel contents. Moreover, the established smelters are running at, or close to, capacity. Braemore, in conjunction with TWP Consulting, is finalising a feasibility study for a new 10 MW ConRoast smelting facility on the western limb of the Bushveld Complex to treat concentrates from emerging and established PGM producers. Commissioning is planned for 2010, and this could be followed by a larger facility (about 40 MW) incorporating a base metal refinery.

Various unit process options in the ConRoast flowsheet have been extensively tested in Mintek's facilities, as well as those of leading global specialist engineering companies, with very satisfactory results. This includes:

  • The dead-roasting step has been tested by major fluidised-bed vendors in pilot plants in North America and Europe;
  • Water atomisation of the alloy from the DC arc furnace has been conducted by the leading supplier of atomisation technology in the UK; and,
  • Small scale roasting and smelting tests on a range of PGM concentrates have been completed, and converting tests of the product alloy started at small scale. This work has also provided samples for subsequent leaching tests on the alloys, as part of the overall ConRoast development programme.

The technology options for the full ConRoast process are being evaluated by a team from Braemore, Mintek, and TWP Consulting. The findings will form the basis for an engineering feasibility study being compiled by TWP, which will provide the definitive design and costing of the second-stage commercial unit, with a capacity of 360 000 tons of PGM concentrate per annum.




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