The Effect of Different Outer Cations on the Stability of Fluorotitanium Complex

Abstract

Fluoride-rich fluid is believed to be able to activate and migrate Ti and other high field-strength elements to the greatest extent. The stability of F-rich titanium complexes can ensure their migration in the fluid, but is inseparable from the physical and chemical properties of the fluid, such as concentration, temperature and pH value—important factors affecting the stability of the complexes. In this study, the influence of the outer cationic complex fluid on the stability of the fluorine titanium complex was studied. Studies were based on different kinds of fluorine titanium complex (K2TiF6, Na2TiF6, (NH4)2TiF6 and H2TiF6) in 100 MPa pressure. Under the condition of 200~500 °C temperature, we found that as the temperature rises, the hydrolysis of F-rich titanium complexes is violent. We compared the stability of four F-titanium complexes with different outer cations according to the hydrolysis rate and the cumulative hydrolysis equilibrium constant. We compared the F-titanium complexes with alkali metal as the outer cations that are more stable, such as K2TiF6 and Na2TiF6. However, the F-rich titanium complex in an acidic fluid is relatively unstable, which is not conducive to the migration of Ti elements. Due to the water–rock reactions that occur in hydrothermal fluid migration, mixing and alteration, once in the hydrothermal system, the fluid composition, pH value and temperature change. Thus, the F-titanium complex becomes extremely unstable, leading to the precipitation of titanium from the hydrothermal fluid and the growth of Ti-rich minerals.