Nonhazardous Process for Extracting Pure Titanium Dioxide Nanorods from Geogenic Ilmenite.

The current rate of industrial production of titanium dioxide, from natural ilmenite, is around 6500 kT per annum. The two main processes used, namely, sulfate and chloride processes, require concentrated corrosive acids and drastic conditions, such as 1000 °C, in open processes, thus contributing to considerable costs and environmental pollution. To reduce the cost and impact to the environment, a closed process involving a rotatory autoclaving followed by refluxing and stationary solvothermal treatment of ilmenite, below 170 °C, was developed. The as-synthesized product is 100% pure titanium dioxide in its amorphous state (24% crystallinity), which has nanorods arranged in a flowerlike morphology. This can be converted to over 99% pure anatase phase with 90% crystallinity and 100% pure rutile phase nanorods with 98% crystallinity by calcining at 350 and 650 °C, respectively. The direct band gaps of the three materials are 3. 40, 3.60, and 3.15 eV, respectively.