The 2012 Southern Africa Stainless Steel Development Association Project Award for Engineering has been awarded to the Veolia Water Solutions & Technologies South Africa subcontractor, Metso ND Engineering, for work completed on the Ammonium sulphate plant at the Ambatovy nickel cobalt refinery in Madagascar.

Veolia commissioned Metso ND Engineering to pre-manufacture three large crystalliser structures, along with a series of ancillary tanks and equipment, in modular form for shipment from Durban to the mine’s processing site, Toamasina, for final assembly. The project marks the first time in South Africa that a crystallisation plant of this size has been constructed off-site to enable reduced costs and shorter construction periods.

The structures, 10 m x 10 m and 17 m high in size, are designed to withstand 280 km/h hurricane winds, as well as mild earthquakes caused by nearby fault lines. Metso used 316 ℓ stainless steel, and carefully coordinated the three shipments to coincide with Veolia’s ground-up assembly approach.

Veolia has since successfully handed over a completely functional ammonium sulphate extraction plant to the Ambatovy mine, capable of drying up to 26   per hour for sale as a fertiliser to agricultural markets.

The largest crystallisation project designed in South Africa

Because the ammonium sulphate is found in a slurry solution (already stripped of nickel and cobalt by the mine’s main refinement processes), engineers agreed that crystallisation would be the best extraction technology: Crystallisation facilitates large scale evaporation, effectively drying the ammonium sulphate into a waterless and manageable product.

Veolia designed the zero liquid discharge (ZLD) recovery plant, manufactured system components, and project-managed suppliers from around the world, including Metso, to deliver the plant to suit the refinery start-up schedule.

Maximising value

The ammonium sulphate extraction plant will boost Ambatovy’s profitability while utilising available resources to the maximum. This flagship project will set the trend in the African mining industry to make the most of available mineral assets using viable ZLD and extraction technology.

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