2020 年 61 巻 1 号 p. 150-155
Leaching and hydrolysis of Ti from washed Na2TiO3 were studied. Synthetic rutile was mixed with NaOH at a weight ratio of 1:1.13 and salt-roasted at 773 K for 4 hours to synthesize Na2TiO3. This was washed with distilled water to obtain a leached sample. Acid leaching was carried out at 303, 323, 333, 343, 353, 363, and 373 K for 4 hours using 5 M hydrochloric acid. From 303 to 343 K, the leaching efficiency of Ti increased with an increase in time, with 96% Ti leached at 343 K. From 353 to 373 K, Ti was preferentially leached with time and precipitated by hydrolysis, and the leaching efficiency decreased. The leaching and hydrolysis of Ti were investigated using reaction equations and thermodynamic data corresponding to each leaching temperature. The kinetics of the leaching reaction were studied using kinetic equation for the chemical-reaction-controlled step, applying a shrinking core model of the heterogeneous reaction. The activation energies, derived from the Arrhenius plot, was 38.9 kJ/mol for the chemical-reaction-controlled plot, indicating that the chemical reaction was the rate-determining step. The hydrolysis reaction was dominant at temperatures above 353 K, and the residue after the reaction consisted mostly of TiO2.
