Reactions of lime with aluminate-containing solutions
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In the Bayer process for refining alumina, lime (either quicklime or slaked lime) is added to the process liquor to precipitate calcium carbonate and restore alkalinity to the solution. Lime also precipitates calcium aluminate in an unwanted side reaction which consumes both lime and aluminate. The work described in this paper was undertaken to elucidate the mechanism of this precipitation reaction about which little is known. The kinetics of the reaction between quicklime powder and aluminate in solution were studied as a function of stirring, reaction temperature, lime charge and sodium hydroxide concentration. It was concluded that the reaction was diffusion controlled, at least in the early stages. The second part of this study was directed towards assessing the effect of the calcium aluminate deposit on the lime slaking reaction. The kinetics of this reaction were investigated as a function of aluminate concentration, stirring, temperature and lime charge. The kinetic measurements were complemented by X-ray diffraction and scanning electron microscopy. It was found that the calcium aluminate deposit progressively shuts down the lime slaking reaction. If the aluminate concentration in solution is high enough, the lime particles are encapsulated by calcium aluminate and dissolution ceases.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||Parker Cooperative Research Centre for Integrated Hydrometallurgy Solutions
School of Mathematical and Physical Sciences
|Copyright:||© 1997 Published by Elsevier B.V.|
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