Crystallization of sodalite particles under Bayer-type conditions

The formation of desilication products (DSPs) is an important process in the pre-desilication step of the Bayer process, helping to limit the potential for unwanted scale on the heat exchangers by limiting the amount of silicate in the Bayer liquor. These solids generally have a crystalline sodalite structure, however, the fundamentals of crystallization are still to be fully understood. We show in this work that the DSP formed is initially amorphous when solution silicate is used. When kaolinite solids are present DSP is initially heterogeneously nucleated on the kaolinite but there is also a secondary nucleation event that occurs. DSP, or sodalite, initially heterogenously nucleates on dissolving kaolin under Bayer type conditions. [Display omitted] •Soluble silicate results in the formation of initially amorphous phase DSP.•The amorphous phase is kinetically controlled.•High aluminate concentrations stabilise aluminosilicate in solution.•DSP starts through heterogenous nucleation when kaolinite is present.•Overall, DSP forms via a secondary nucleation mechanism when kaolinite is present.