A comparison toward the effects of Ti- and Si-containing minerals on goethite transformation in Bayer digestion from goethitic bauxite

Goethitic bauxite is a widely used raw materials in the alumina industry. Clarifying the effect of Ti- and Si-containing minerals on goethite transformation in the Bayer digestion process is an essential prerequisite for efficiently utilizing the Fe- and Al-containing minerals in goethitic bauxite. In this work, the interactions between anatase or kaolinite with goethite under various Bayer digestion process were investigated using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscope, scanning electron microscope. The results show that anatase and kaolinite hindered the transformation of goethite. Anatase caused more significant effects by producing a dense sodium titanate layer on the goethite surface after reacting with sodium aluminate solution. While for the case of kaolinite, a loose desilication product adhered to the goethite surface due to the reaction of kaolinite with sodium aluminate solution. Adding the reductants (hydrazine hydrate) could eliminate the retard effect by inducing the transformation of goethite to magnetite, in which titanium is embedded in the magnetite lattice to form Ti-containing magnetite. In contrast, the weakening of the interaction between magnetite and DSP further reduced the influence of kaolinite. As a validation, a reductive Bayer method achieved the transformation of goethite in goethitic bauxite with a 98.87% relative alumina digestion rate. The obtained red mud with a 72.99wt% Fe₂O₃ content could be further utilized in the steel industry. This work provided a clear understanding of the transformative effects of Ti- and Si-containing minerals to iron minerals transformation and helped with the comprehensive use of iron and aluminum in goethitic bauxite by the reductive Bayer method.