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.