Phase chemical composition of slag from a direct nickel flash furnace and associated slag cleaning furnace

During the recovery of base metals from the Bushveld Igneous Complex ores, South Africa, a two-stage process is used to ensure complete recovery of nickel from the ore. A nickel flash smelting furnace is initially used to obtain the valuable metal but the loss of nickel in the slag amounts to about 4 % and thus an electric slag-cleaning furnace has to be subsequently used to reduce the loss of the valuable metal to less than 0.5 % nickel oxide in the slag. The Fe2 + /Fe3 + ratio and mineralogy in the two different furnaces differ and can be used as a tool to determine the efficiency of the nickel recovered in the two-stage process. By means of XRD, SEM/EDS and Mossbauer spectroscopy the Fe2 + /Fe3 + ratio and the amount of magnetite was determined in each furnace, which was then used as an indicator of the effectiveness of the whole process.