Bauxite Residue Sinter Phase Transformations

In the Bayer Process, between 2-35% aluminium (as wt. Al₂O₃%) is lost with bauxite residue (BR).  This is primarily due to the inefficient dissolution of aluminium-bearing minerals during caustic leaching or from the formation of desilication product (DSP) that also constrains the recycling of caustic soda from the circuit. If these lost alumina and caustic can be recovered from BR, numerous potential processing options become available which could lead to zero-waste BR valorisation.

Whilst the pyrometallurgical routes (lime soda and lime-soda sintering) have been extensively discussed in the literature for recovering alumina and sodium from BR, understanding of the mineralogical phase formation during sintering and the relationship to the thermodynamic driving forces are poorly reported .This paper presents the investigation of sintering tests conducted on two separate residues with different characteristics; Greek BR and Australian Br, and mineral phases present both before and after sintering for two distinctly different BRs. These mineral phases were characterised and quantified using XRD and XDB software. The Factsage thermodynamic software package was used to analyse reaction equilibria with potential sintering chemical reaction pathways being described.