TITANIUM COMPLEXATION IN HYDROTHERMAL SYSTEMS

Abstract

The solubility of rutile in aqueous solutions of HCl, HF,H2 SO4,NaOH, and NaF was determined at 500°C, 1000 bar, and hydrogen fugacity from 8 × 10-12 to 10.3 bar (Mn3O4/Mn2O3 and Ni/NiO buffers, dissolution of an Al batch weight). The experimentally determined solubility values were used to calculate the constants of the following equilibria at 500°C and 1 kbar pressure: TiO2 (rutile) + H2O + HCl0 = Ti(OH)3 (pK = 4.89); TiO2 (rutile) + 2HCl0 = Ti(OH)2 (pK = 4.69), TiO2 (rutile) + 2HS + H + = Ti(OH)2 S (pK = 1.98), TiO2 (rutile) + 2HS + 2H + = Ti(SO4 + 2H2O (pK = 1.50), TiO2 (rutile) + 2H2 O + OH = Ti(OH)5- (pK = 3.17), TiO2 (rutile) + 2H2 O + 2OH = Ti(OH)62- (pK = 1.46), TiO2 (rutile) + 2H2 O + F = Ti(OH)3F0 + OH- (pK = 5.86), TiO2 (rutile) + 2HF0 = Ti(OH)2 (pK = 2.99), and TiO2 (rutile) + 2H2 O + F Ti(OH)4F-(pK = 3.69). Based on the results obtained on the composition of volcanic emanations whose Ti concentrations were determined, we evaluated the constants of the equilibria TiO2 (rutile) + H2O + HCl0 Ti(OH)3Cl0 (pK = 2.74) and TiO2 (rutile) + HS + H+ = Ti(OH)2S (pK = 3.40) at 25°C. The electrostatic model of electrolye ionization was used to calculate the ionization constants and the Gibbs free energy values for the following Ti species in aqueous fluids at the parameters of postmagmatic processes: Ti(OH)3+, Ti(OH)40, Ti(OH)5-, Ti(OH)62-, Ti(OH)3F0, Ti(OH)2, Ti(OH)4F-, Ti(OH)3Cl0, Ti(OH)2, Ti(OH)2S, and Ti(SO4)20. As follows from our data on Ti complexation with Cl, F, and SO4, fluids the most favorable for migration are aqueous acid F-rich solutions with Ti concentrations of no higher than a few fractions of a milligram per kilogram of water. © Pleiades Publishing, Inc. 2006.