Determination of aluminium, titanium and iron oxides in wet-processed phosphoric acid by extraction spectrophotometry

Abstract

A spectrophotometric method for Fe₂O₃, Al₂O₃ and TiO₂ determination in wet-processed phosphoric acid (with up to a 0.5% fluoride content) based on two successive extractions is suggested. First, Ti and Fe are simultaneously separated by chloroform extraction of their TiO²⁺–H₂O₂–Ox and Fe³⁺–Ox complexes (Ox = 8-hydroxyquinoline) at pH 3–4; then Al is extracted as Al³⁺–Ox from the same solution at pH 5. Fe₂O₃ and Al₂O₃ contents are independently calculated from their oxyquinolate complex absorptions measured at wavelengths of 580 and 390 nm, respectively. The Ti content is found by difference from the second organic phase absorption at 425 nm and iron absorption, calculated at the same wavelength. The accuracy of the spectrophotometric results was corroborated by model solution experiments (introduced – found) and gravimetrically. The results show good reproducibility (relative standard deviation 1–5%) and the analysis is rapid and allows the determination of each oxide separately.