Evaluation of Bayer process gibbsite reactivity in magnesium aluminate spinel formation

Stoichiometric magnesium aluminate spinel was synthesized by solid-state reaction of calcined magnesia with tabular alumina, calcined alumina and industrial gibbsite at 1100, 1300 and 1500 °C for 2 h. The pellets made from both types of alumina and magnesia expanded after the heat treatment, whereas pellets made from industrial gibbsite and magnesia contracted. It was found that shrinkage could be produced by phase transformations in gibbsite and magnesia densification process in unreacted magnesia during the sintering. The X-ray diffraction patterns indicated a minor reactivity for industrial gibbsite in comparison with the calcined alumina and tabular alumina at all firing temperatures.