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An electrochemical study of reactions of nickel matte in acid media

Ho, Elizabeth M. (1998) An electrochemical study of reactions of nickel matte in acid media. PhD thesis, Murdoch University.

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Nickel matte is a nickel sulfide concentrate produced by smelting. It consists mainly of two components: a nickel-copper alloy and heazlewoodite (Ni3S2); but also contains varying amounts of djurleite, Cu1.96S. There are several hydrometallurgical routes for processing nickel matte. The most recent of these involves an oxidative leach in acid chloride or sulfate solution. Nickel is subsequently recovered fiom the leach solution by electrowinning or by hydrogen reduction. In the work described in this thesis, various aspects of the acid leaching of nickel matte are investigated using mostly electrochemical methods.

The first section concerns the use of copper(II) as an oxidant for the alloy component of nickel matte. In this cementation reaction, nickel goes into solution while copper is deposited on the dissolving metal swf8ce. The same reaction is important in removing traces of copper present in the nickel solution. Here nickel powder is added to the process liquor. A survey of the literature pertaining to the cementation of copper by nickel shows that there is considerable dispute as to the conditions under which cementation takes place. Evans' diagrams for the cementation reaction were constructed by superimposing the polarisation curves for the oxidation of nickel and the reduction of copper. It was found that cementation occurred provided that the two polarisation curves intersected in the region of active nickel dissolution. Outside this region, a copper deposit could not be seen.

The second part of the thesis presents some investigations into the electrochemistry of nickel sulfides and nickel matte, and compares both chloride and sulfate media. Oxidation and dissolution rates of nickel matte powders using copper(I1) as an oxidant were also carried out. Dissolution was chemically controlled and so the rate was very dependent upon temperature and solution potential. Displacement of copper(II) from solution to form copper sulfide was also found to be important.

In addition to the above studies, which relate directly to the oxidative leaching of nickel matte, an investigation of the oxidation of HzS to sulfur in acidic solution was carried out. Sulfer deposition was found to be strongly dependent on substrate and pH. Under some conditions, two types of sulfur were deposited, with the more crystalline sulfer being reduced at the more negative potential.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Mathematical and Physical Sciences
Supervisor(s): Ritchie, Ian and Muir, David
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