Phase chemical composition of slag from a direct nickel flash furnace and associated slag cleaning furnace
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Phase chemical composition of slag from a direct nickel flash furnace and associated slag cleaning furnace F. B. Waanders · J. Nell
Published online: 14 November 2012 © Springer Science+Business Media Dordrecht 2012
Abstract 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 slagcleaning 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 Mössbauer 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. Keywords Slag · Nickel smelting · Magnetite
1 Introduction Most of South Africa’s nickel is produced as a by-product of platinum mining activities on the Bushveld Igneous Complex. South Africa is about the tenth largest producer of nickel in the world with a production of about 42,000 metric tonnes in 2011 [1]. Slag generated in the direct nickel flash smelting process (DON process) contains approximately 4 % dissolved nickel oxide and has a relatively high ratio of Fe2+ /Fe3+ because of the oxidizing conditions applied during smelting [2]. To recover
F. B. Waanders (B) School of Chemical and Minerals Engineering, North-West University, Potchefstroom, 2530, South Africa e-mail: [email protected] J. Nell Hatch, Private bag X20, Gallo Manor, Johannesburg, 2052, South Africa e-mail: [email protected]
102 Table 1 Phase-chemical composition (wt%) of the slag samples determined by powder XRD
F.B. Waanders, J. Nell
Sample
Flash furnace 3 5 7
8
Electric furnace 1 2 3
6
Olivine Magnetite Fayalite
84 16 0
85 15 0
96 4 0
98 2 0
55 23 23
89 11 0
99 1 0
97 3 0
the nickel oxide from the slag it is transferred to an electric slag-cleaning furnace where NiO is reduced from the slag with a suitable reductant such as coke. Slag from the slag-cleaning furnace contains less than 0.5 % NiO and has a much lower ratio of Fe2+ /Fe3+ [2]. Because of the relatively high ratio of Fe2+ /Fe3+ in the flash furnace slag it crystallizes a significant amount of magnetite during cooling. Slag from the electric slag cleaning furnace, on the other hand, hardly crystallizes any magnetite during cooling. The Fe2+ /Fe3+ ratio and the amount of magnetite, determined with the aid of XRD, SEM and Mössbauer spectroscopy, occurring in the two different furnaces was used as an indicator of the effectiveness of the nickel recovery process.
2 Experimental 2.1 Samples and analytical methods Water-quenched samples of slag from the DON flash furnace and associated electric sl
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