Authors: D. van den Berg, P. Mare and G. Nel, Norilsk Nickel
SAIMM Hydrometallurgy Conference 2009, Feb. 24-26, 2009
Abstract
The TATI Base Metal Refinery (BMR) was designed to be a hydrometallurgical processing plant employing Norilsk Nickel Process Technology’s Activox® leaching technology, solvent extraction and electrowinning to annually extract and recover 25 kt of LME grade nickel, 22 kt of LME grade copper and 640 tonnes of cobalt as a carbonate. The BMR requires acid neutralisation in the Cobalt and Nickel Solvent Extraction (SX) circuits where pH control is crucial for selective extraction of the base metal sulphides from the pregnant leach liquors. The choice of neutralising reagent and treatment of the resultant neutralisation product impact the overall plant design.
This work discusses the criteria used to select Ammonia as the neutralising reagent for the BMR design, as well as the development of an ammonia recovery circuit.
The ammonia forms a soluble ammonium sulphate neutralisation product which reports to the SX raffinate stream. The BMR ammonia recovery circuit uses vibrating mills to contact the ammonium sulphate with calcium oxide (fine quicklime). The ammonium sulphate is converted to CaSO4 (fine gypsum precipitate) and aqueous ammonia. A series of seeded reaction tanks are used to further encourage the gypsum precipitation and crystal growth. Aqueous ammonia is then stripped from the slurry in steam stripping column, and condensed to a 10% solution for re-use. The barren gypsum slurry reports to the tailings dam, where supernatant solution is recovered for use as process water.
Anhydrous ammonia is used as top up to account for losses due to the ammonia recovery circuit.
