Industrial Preparation and Processing

Sherritt ammonia pressure leaching. This hydrometallurgical process was first implemented in 1954 by Sherritt Gordon Mines in Fort Saskatchewan, Alberta, Canada. In this process, the finely ground nickel sulfide concentrates obtained after flotation or the metal matte are reacted at 80 to 95°C in a high-pressure autoclave under 850 kPa with an oxygenated ammonia or ammonia-ammonium sulfate liquor. Ammonia dissolves nickel and, to a lesser extent, cobalt, zinc, and copper by forming soluble ammonia complex cations as follows  

After removing iron as iron hydroxide and precipitating copper as copper sulfide, nickel is recovered from the leach liquor by reduction with pure hydrogen at 200 C under a high pressure of 3 MPa  

The remaining liquor contains all the cobalt that is recovered by precipitating it as cobalt sulfide with hydrogen sulfide. Finally, the remaining spent solution consists of ammonium sulfate, which is sold as fertilizer. 

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