Mechanical activation of natural titanite and its influence on the mineral decomposition

Abstract

Processes induced by mechanical activation of the natural titanite CaTiSiO 5 using a laboratory agate mechanical mortar and a planetary mill AGO-3 have been studied. Titanite consumes substantial amounts of atmospheric carbon dioxide during prolonged dry grinding in air. Carbonisation of titanite occurs alongside with its amorphyzation. According to FT-IR spectroscopic data CO 2 is present in the ground sample in the form of distorted CO 3 2− groups resulting in the characteristic double band in the 1500–1430 cm −1 region. Previously similar processes were revealed for Ca and Mg containing silicate gangue minerals such as enstatite MgSiO 3, diopside CaMgSi 2O 6, åkermanite Ca 2MgSi 2O 7, and wollastonite CaSiO 3. The CO 2 content in the ground titanite reached 4.0 and 7.0 wt.% after grinding in the laboratory agate mechanical mortar for 36 and 108 h, respectively. The amount of carbon dioxide consumed due to grinding increases with increasing CaO content in the chemical formula of minerals and correlates with Gibbs free energies of reactions of the crystalline minerals with CO 2. The following sequence concerning carbon dioxide sorption ability was revealed: enstatite<diopside<titanite<åkermanite<wollastonite. Preliminary mechanical activation results in considerable rise of titanite reactivity with respect to 5–20% nitric acid. According to the results obtained the release of Ti and Ca increases with increasing extent of mechanically induced crystal structure disordering and amorphyzation. In contrast to other titanium containing minerals such as leucoxene, ilmenite, rutile, anatase preliminary mechanical activation of titanite in planetary mill for 30 min allows to reach practically complete leaching of Ti with diluted nitric acid at room temperature.