Production of α-Ti(HPO4)2·H2O, TiP2O7 and (TiO)2P2O7 from ilmenite by KOH roasting, H3PO4 leaching and calcination

Alpha titanium bis(hydrogenphosphate) monohydrate, α-Ti(HPO₄)₂·H₂O, (α-TiP) is a precursor material utilized to obtain a broad range of important compounds having a great deal of applications ranging from ion-exchange chromatography, chemical catalysis to energy storage materials. The novel synthetic procedure developed in this study shows a higher conversion of titanium in ilmenite to α-TiP with a good purity. For the synthesis of TiPs, the direct use of natural ilmenite ore with commonly available chemicals such as KOH, H₃PO₄, HCl, and H₂C₂O₄ highlights the significance of the present investigation. A mixture of ilmenite and KOH with a molar ratio of 1:4 was roasted at 800${}^{°}C$ for 4 h to concentrate all the titanium to potassium titanate and iron to iron oxide. A reaction between potassium titanate and iron oxide with 85% (w/w) H₃PO₄ acid results in a leachate rich in iron in the form of soluble iron phosphates and a white precipitate identified as α-TiP. Calcination of α-TiP at 800${}^{°}C$ produces titanium pyrophosphate, TiP₂O₇. Residual iron that co-precipitated with α-TiP was further removed by multiple washing steps with complexing acids; H₃PO₄ or concentrated HCl. Washing with oxalic acid (H₂C₂O₄) produces a precipitate upon calcination identified as titanyl pyrophosphate, (TiO)₂P₂O₇. Flowcharts were developed and the chemical identities and the purity of the prepared α-Ti(HPO₄)₂·H₂O and (TiO)₂P₂O₇ were tested with X-ray diffraction, X-ray fluorescence, thermogravimetric, and Raman spectroscopic techniques.