EXTRACTION KINETICS OF WEIPA MONOHYDRATE BAUXITE
Pei, B., Taylor, D. and Thomas, D.
Weipa bauxite is mainly present in pisolitic (pea-like) form and is typically ground to liberate alumina prior to high-temperature digestion. Digestion residence time is kept relatively short to minimise quartz attack.
Laboratory tests were undertaken to study the digestion kinetics. Tests using monodispersed bauxite size fractions at 10 minutes residence time showed effectively complete extraction for particles up to 850 μm diameter. Above this size, alumina extraction begins to fall away.
A simple shrinking-core extraction model was found to give an excellent fit to the experimental data. The shrinkage rate correlated strongly with the bauxite boehmite content. The model was extended to cover broader particle size distributions, which then predicted that the bauxite needs to be significantly finer than 850 μm to ensure complete extraction. Laboratory tests and plant operating data validate these predictions.