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MEI Online: Pyrometallurgy: Latest News: August 23rd 2005


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:: Milestone for Thermal Magnesium Process

The latest magnesium smelting campaign, carried out in November 2004, to demonstrate Mintek's DC arc-based thermal magnesium process was an 'outstanding success', according to Dr Roger Paul, General Manager: Technology.

During the eight-day run, about 30 t of feed materials were smelted in the DC furnace, which was operated at power levels up to 8OO kW. and the magnesium was extracted as vapour for delivery to the condenser. Fifteen taps of liquid magnesium, totalling 3500 kg of magnesium metal, were carried out from the condenser during online operation. The crude magnesium was of a consistently better quality than that produced by conventional thermal processes, particularly with regard to calcium.

The campaign was conducted with a new condenser designed to prevent the build-up of dross that limited previous runs to about 20 hours of continuous operation. The modified condenser performed extremely well, achieving continuous production with a condenser efficiency of 85 percent.

This campaign demonstrates, for the first lime, the feasibility of a continuous atmospheric process for thermal magnesium production.

The robustness of the process was shown by the ability of the condenser to withstand a furnace shutdown - for example to clear a blocked feed port or to add an electrode section - and immediately re-start magnesium production and tapping. It was demonstrated that the magnesium plant can be maintained online, without dismantling and cleaning of condenser components, as practiced in industry.

The results of the campaign are being used to prepare an updated cost analysis of the process. R&D work on the Mintek pilot-plan) scale has been completed successfully. Technically, the MTMP process is now ready for scaling up to a demonstration - and further to an industrial size operation.

Mintek, in partnership with Anglo American and Eskom Enterprises, has been developing the Mintek Thermal Magnesium Process (MTMP) for almost five years. The project, which is partially funded by the Department of Science and Technology, is aimed at obtaining design data for a possible magnesium production facility in South Africa.

The MTMP uses DC arc smelting technology, a field in which Mintek is a world leader, to produce magnesium vapour from calcined dolomite at atmospheric pressure, instead of under a vacuum as is used in conventional thermal magnesium production. The vapour is then condensed to liquid magnesium in a novel condenser arrangement. The advantages include the ability to operate the furnace and condenser continuously, without the necessity to stop the process and break the vacuum in order to tap the magnesium metal from the condenser and the slag from the furnace. This results in higher productivity and lower operating costs.

Two main routes to magnesium production arc currently employed, i.e. fused salt electrolysis of magnesium chloride, and thermal reduction of magnesium oxide in calcined dolomite. A MTMP plant should achieve production costs comparable with those of an electrolytic process, while retaining the low capital costs associated with thermal plants.

Mintek and its partners are evaluating the commercial possibilities of the new process and would welcome other participants in a demonstration-scale plant.




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