A large-scale pilot plant, smelting test, to demonstrate the process was carried out by Mintek at their premises in Johannesburg, South Africa during March 2005. A 450 tonne sample of ore was delivered to Mintek in December 2004. This sample was sourced from three different areas in the deposit, namely Shevchenko, Blizhny and Tarasov with the respective nickel head grades 1.41%, 1.15% and 0.87% on a dry ore basis. It was decided to smelt each ore separately to demonstrate the process over the widest possible range of likely feed compositions and to gather the maximum information for the commercial plant design, including the technical criteria for optimum ore blending. The objectives for the test were: firstly to demonstrate the suitability of these ores for the DC arc furnace process, and secondly, to gather detailed data for the commercial furnace design. The DC arc furnace was set-up in a twin-cathode configuration to replicate the proposed commercial furnace and incorporated an advanced design of water–cooled copper panels in the furnace sidewall to withstand the aggressive nature of ferronickel slags towards refractories.

 

The results from the smelting campaign demonstrated that each of the three ores could be successfully smelted in a twin-cathode DC arc furnace. Specifically, 90% nickel recovery was achieved for each ore. The alloy quality was within acceptable limits for standard refining methods to meet market specifications for carbon, silicon, sulphur and phosphorus. The alloy nickel to cobalt ratio was very similar to Ni/Co ratio in the various ores fed (ranging from 8 to 30), as expected thermodynamically. Therefore the Ni/Co ratio can in principle be controlled via blending of the ore types. Excellent data for furnace design was captured and a process model was developed to calculate the furnace specific energy requirements. The model was validated by the experimental results and was used to optimise the blend of ores, operating temperature, flux and coal addition in the subsequent design study to finalise the furnace design parameters and smelting mass and energy balance.