Ilievski, D., Whittington, B., Austin, P., Schibeci, M. and Bedell D.
The literature suggests that hydrate properties are a significant determinant of the alumina properties that, in turn, determine alumina quality. It can be postulated that those hydrate properties affecting alumina quality include hydrate voidage and other hydrate structural features, such as the relative orientation between adjacent gibbsite crystallites and the location and nature of the cement binding the agglomerate.
This paper outlines techniques that have been developed or adapted to allow for the quantification of hydrate voidage (Floc Density Analyser), determination of relative changes in gibbsite crystal orientation (Raman spectroscopy and electron backscattered diffraction) and location of the cement binding agglomerated gibbsite particles (Raman spectroscopy, charge contrast and orientation contrast imaging). Existing techniques for quantification of hydrate external morphology or examination of hydrate internal structure (charge contrast imaging) are also discussed.
These techniques were used to:
(1) help establish if a particular product gibbsite particle was a single crystal or a six-fold twin.
(2) locate an “interface” region between gibbsite crystallites and show that this region was made up of crystalline gibbsite.
This suite of techniques provide the means to explore the links between alumina quality and the properties of the precursor hydrates formed under different precipitation conditions, as is being done in the AMIRA P575A “Gibbsite and Alumina Quality” project.