Morphological study of Bayer process desilication product and its application to laboratory and plant digests

Abstract

Desilication product (DSP) formed in the Bayer process is difficult to study using electron microscopy because it is masked by iron oxide particles. Differences in the rate of DSP formation under plant and laboratory conditions, which may be due to particle size and hence surface area, are difficult to resolve. Iron oxides were successfully removed from bauxite refining residue (red mud) without destroying the DSP, enabling the morphology of the DSP to be studied with scanning and transmission electron microscopes. The procedure makes it possible to compare the morphology of DSP formed under plant conditions and using pure components in the laboratory. The DSP formed under plant conditions and removed with the residue has typically a wood-ball-like structure with diameter of around 2 μm. The structure is formed rapidly (within minutes) under plant conditions. Similarities with DSP formed under certain laboratory conditions were observed. The procedure provides a means of confirming the validity of laboratory studies under appropriate conditions for simulating DSP formation under plant operating conditions.