PRECIPITATION OF GIBBSITE: DEVELOPMENT OF A NEW RATE EQUATION
Cornell, R.M., Pannett, D.S., Sullivan, N.S., Clarke, P.C. and Bailey, C.M.
The equation used by Alcoa (derived from the King equation) to describe gibbsite precipitation in Bayer liquors is applicable only over a narrow range of conditions. Outside of this range the rate "constant" is strongly dependent on Total Caustic (TC) and temperature.
A new rate equation that applies over a far wider range of TC (100-300 g/L) and temperature has now been developed using synthetic liquor. This equation is based on supersaturation ratio instead of supersaturation difference. The kinetics experiments were carried out with a carefully prepared, nonagglomerating seed with smooth, well grown, low index faces. Use of this material ensured that the surface area of the seed remained constant during the experiment.
Before the main kinetics experiments could proceed, considerable background work into the various factors influencing the precipitation induction time had to be carried out. Both the results of this work and the new rate equation itself, are presented in this paper.