The Bayer process is the principal method for refining bauxite into aluminium oxide (alumina), which is used to make aluminium metal. During the production of alumina via the Bayer process, aluminium hydroxide (gibbsite) is crystallised from solution. A common problem encountered during this process is the generation of finely sized gibbsite particles through secondary nucleation (when new particles form on the surface of existing particles). These fine particles are undesirable because they are difficult to separate and classify, and can cause dusting issues at aluminium smelters. Drs Weng Fu and James Vaughan from The University of Queensland, together with Dr Alistair Gillespie from Rio Tinto, have recently identified a new approach for removing the gibbsite fines from the aluminium production process.
The researchers used a synthetic solution, sodium oxalate, to mimic the effects of the highly alkaline Bayer liquor used during the industrial production of alumina. With technical support from ANFF-Q Professional Officer Dr Elena Taran, the team used atomic force microscopy (AFM) at ANFF-Q to observe the gibbsite interacting with sodium oxalate during the crystallisation process and discovered that the fine gibbsite nuclei could be completely encapsulated in the faster growing sodium oxalate crystal. This discovery provides new insight into modelling and controlling the Bayer process, an old technology with high economic value to the Australian resources industry. The research team is currently considering ways that this approach to eliminating gibbsite fines could be practically implemented in the alumina production industry.