A study of the chlorination reactions of the nickel segregation process

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Copyright: Seaborn, Colin James
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Abstract
The chlorination of Fe203 and Fe304 has been investigated in a fluidised bed in the range 850- 950°C in order to elucidate the role of iron in the segregation process for nickeliferous laterites. The kinetics of Fe203 chlorination in the range using 20% HCl - 80% N2 gas mixtures is consistent with a single- stage starvation control model, whereas Fe304 exhibits a two- stage reaction mechanism. Oxygen potential measurements using a CSZ probe located above the bed and X-ray powder results confirm the proposed reaction scheme. When a serpentitic nickeliferous laterite (1.03% Ni - 11.7% Fe) was chlorinated at 900°C with a 2o% HCl - 80% N2 gas mixture it was found that the oxidic iron in the ore was extracted in a similar manner to the synthetic iron oxides. Al so, it was found that the nickel extraction from the ore paralleled that of the iron and the tests indicated that for the major part of the extraction, the solid nickel species were in equilibrium with the gas phase. The results obtained from the chlorination of Fe203 and Fe304 with 2o% HCl - 5% CO - 75% N2 at 900°C indicated that a starvation control model should again be applicable, but, no completely satisfactory model was devised. However, when Fe3o4 was chlorinated in more reducing conditions with 20% HCl - 10% CO - 70% N2 or 10% HCl - 1o% CO - 80% N2 at 90cPC it was found that the rates of iron extraction were consistent with those predicted by a starvation control model. This model assumed equilibrium between Fe3O4/FexO and the gas phase. On extension of these tests to the nickel laterite or e it was found that the iron oxides in the ore reacted in an analogous manner to the synthetic oxides. However, these free iron oxides quickly disappeared from the ore not only due to the rapid rates of chlorination but the interaction between iron species and the silicate minerals also. Hence , initially there was an increase in the iron content of the silicate minerals, but, after all of the iron oxides had been removed the iron in the silicate minerals reacted with the gases. Although increasing the CO content of the reacting gas mixture resulted in a significantly greater rate of iron extraction, there was only a slight effect on the nickel chlorination. This can be explained by applying to the ore a model similar to that developed for the pure iron oxides. CO when added to the reacting gas mixture appeared to lower the ultimate recoveries of both nickel and iron. This apparent effect is not well understood but could be associated with solid state changes in the ore. It has been found that the models devised for chlorination of the iron oxides and ore can be used to explain the fluidised bed results of Webb (40) and Brittan and Liebenberg (7). Furthermore, it was shown by thermodynamic calculations based on the results of Brittan and Liebenberg (7) that the stability of the iron deposited by reduction of the fluidised bed effluent gas could be explained by considering equilibrium of simple gaseous species.
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Author(s)
Seaborn, Colin James
Supervisor(s)
Young, David
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Publication Year
1976
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Thesis
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PhD Doctorate
UNSW Faculty
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