The Dependence of Ilmenite’s Dissolution Rate in Hydrochloric Acid on the Fe(III)/Fe(II) Ratio, with Fe K-Edge XANES Pre-Edge Peak Analysis

The complete dissolution of the Ti and Fe content of ilmenite is a necessary first step for the production of TiO2 directly from ilmenite. Hydrochloric acid is one of the possible solubilizing agents. However, the ability to dissolve ilmenite in hydrochloric acid depends on the nature of the source material. Here, we consider the effect that the oxidation state of Fe in the ilmenite has on the dissolution rate. Three placer ilmenite fractions from New Zealand and India were dissolved in concentrated hydrochloric acid in a stirred vessel. The dissolution rate constants for Fe and Ti for each fraction based on a shrinking sphere model were compared with the Fe(III)/Fe(II) ratio. Pre-edge Fe K-edge XANES as a measure of Fe(III)/Fe(II) has been shown to extend to ilmenite, which has a complex pre-edge region due to the involvement of Ti electronic levels. It was found that there is a relationship between the oxidation state of Fe and the dissolution rate, with a higher Fe(II) content resulting in more rapid dissolution. A higher Fe(II) content reflects a younger, less weathered material, closer to the “standard” stoichiometry of ilmenite. These data and the presented correlation may support the design of industrial processes to digest ilmenite in hydrochloric acid from varying feedstocks.