Spectroscopic characterisation of weak interactions in acidic titanyl sulfate–iron(ii) sulfate solutions

Abstract

The titanyl equilibria in strongly acidic solutions related to the hydrometallurgical production of titania have been investigated in the presence of inorganic ions (ClO₄⁻, NO₃⁻, Cl⁻, SO₄²⁻, Fe²⁺ and Fe³⁺) using spectroscopic (UV–Vis and EPR) methods. UV–Vis experiments showed no interaction or ion pairing effect in the acidic titanyl nitrate and titanyl perchlorate samples indicating that they would be suitable background electrolytes for further thermodynamic measurements. The stoichiometry of the titanyl chloride complex was determined as TiOCl₂⁰ and its stability constant was calculated (log β₂ = 1.12 ± 0.03). The interaction between titanyl and sulfate ions was quantified by determining the stoichiometry (1:1) and stability (log β₁ = 1.64 ± 0.06) of the titanyl sulfate species. Weak sulfate complexes were also detected with the ferric (log β₁ = 2.00 ± 0.10; log β₂ = 2.49 ± 0.08) and ferrous (log β₁ = 1.52 ± 0.06) ions under strongly acidic conditions. A double sulfato complex FeTiO(SO₄)₃²⁻ with relatively high stability (log β = 7.13 ± 0.07) was found in solutions containing titanyl, ferrous and sulfate ions in sulfuric acid medium. In addition, an EPR signal was assigned to the FeTiO(SO₄)₃²⁻ species. This double sulfato complex was found to be the major metal-containing species in the system similar to that used in the leaching process of ilmenite during the industrial production of titania.