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In 1992, five companies (Unimétal of the Usinor Group as the leader, EDF, Union minière, BRGM and RVX) combined their resources to develop a hydrometallurgy process using sodium to recover all the elements contained in the dust from electric steel mills.

The process itself consists of three stages:
- Leaching the dust from electric steel mills in 300 g/l of sodium solution, producing, on the one hand, a solution rich in zinc and on the other hand, an insoluble residue rich in iron for recycling in an electric furnace.
- Purification of the sodium solution by carburising the zinc powder, allowing the heavy metals (lead, cadmium) to be concentrated in a solid residue to be exploited by the lead industry.
- Electrolysis of the purified solution allowing the zinc to be extracted in powder form.

The salts, also extracted and concentrated, can be used as thawing salts.

The operation, over a period of 18 months, of a pilot plant with a capacity of 100 kg of dust per hour has solved all the technological problems, enabled the total investment amount required for the construction of an industrial unit to be calculated and has produced a zinc powder of excellent quality.

Additional information

Authors: ROCCHIA L, UNIMÉTAL, Amnéville (FR)
Bibliographic Reference: EUR 20289 FR (2002), pp.52. Euro: 8.50
Availability: EUR-OP reference: KI-NA-20289-FR-S Available from EUR-OP sales agents. URL:
ISBN: ISBN: 92-894-3468-6
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