Gallium in precipitated gibbsite is a future product quality concern for alumina producers in Western Australia.
This work was undertaken to establish the mechanism of gallium incorporation into gibbsite, and to develop a model to determine the level of gallium uptake from synthetic Bayer liquors.
It has been shown that -
- Isomorphous substitution is the most likely mechanism of incorporation, although there was a surprisingly low upper limit to the level of incorporation that could be achieved (~2 mole%).
- At levels of gallium in the liquor of <1800 ppm, the concentration of gallium in precipitated gibbsite is dependent on the concentration of gallium in the liquor, and virtually independent of other precipitation parameters.
The relationship of gallium in the precipitated gibbsite to the level in the liquor is given by
(Ga/Al)ppt x 106 = K x GaL (ppm Ga2O3 in liquor)
where for our system K=0.266.