Interactions of iron and titanium-bearing minerals under high-temperature Bayer digestion conditions

Abstract Clarifying the interactions among iron and titanium-bearing minerals in the treatment of diasporic bauxite with Bayer liquor at elevated temperature is crucial to understanding reductive Bayer digestion, in which the inhibition of sodium titanate on diaspore digestion is eliminated by the use of non-lime additive. In this work, we carried out a thermodynamic analysis, which predicted that ilmenite (FeTiO 3 ), ulvite (Fe 2 TiO 4 ), and sodium iron titanium oxide (NaFeTiO 4 ) will result from the interactions among iron and titanium bearing minerals in Bayer digestion, whereas pseudobrookite (Fe 2 TiO 5 ) cannot be generated. In addition, the perovskite (CaTiO 3 ) is more stable than the produced Ti-Fe compounds, thus, the Ti-Fe compounds could be converted into this perovskite by the addition of extra lime. In order to confirm the thermodynamic analysis results, we then carried out both typical and reductive Bayer digestion experiments. Unlike the dense sodium titanate layer formed on the other minerals present in typical Bayer digestion, the fibrous porous sodium iron titanium oxide layer produced in reductive Bayer digestion allows the passage of the alkaline solution through the precipitated layer to the mineral particles beneath, and thus ensures the efficient digestion of the diaspore. The reaction of HFeO 2 − and titanium-bearing mineral to form Ti-Fe compounds occurs prior to the reaction of HFeO 2 − and hematite to form magnetite, meanwhile some of the insoluble Ti-Fe compounds have low iron content, therefore only a small amount of iron powder is needed to eliminate the inhibition. These results are important for the efficient digestion of diasporic bauxite through the addition of iron powder, which avoids the loss of alumina through the hydro-garnet produced by adding excess lime.