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GIBBSITE NUCLEATION AT SODIUM OXALATE SURFACES

Reyhani, M.M., Dwyer, A., Parkinson, G.M., Rosenberg, S.P., Healy, S.J., Armstrong, L., Soirat, A. and Rowe S.

Sodium oxalate is one of the most important impurities in an alumina refinery, due to its limited solubility in Bayer Process liquor streams. If allowed to build to a critical supersaturation, sodium oxalate will coprecipitate with gibbsite in Bayer precipitator circuits. The occurrence of this in the first stages of gibbsite precipitation can lead to gibbsite fines "showers" and hence to excessively fine alumina. This has variously been ascribed to oxalate interfering with gibbsite agglomeration, or to enhanced gibbsite nucleation. Despite the serious and costly impact that oxalate can have on the particle size distribution of gibbsite, little work appears to have been published which examines this relationship.

In this study, the nucleation of gibbsite at oxalate surfaces is examined in both plant and synthetic liquors. Scanning and transmission electron microscopy (SEM and TEM) of these structures has revealed interesting characteristics of these crystal intergrowths. The relationship between this interaction and gibbsite particle size characteristics in Bayer precipitation circuits is also discussed.