Effect of pH of Ti(SO₄)₂ Solution on Properties of Hydrous Ti(IV) Oxide Precipitated from the Solution

Abstract

Hydrous Ti(IV) oxides were prepared, at room temperature, by adding aqueous ammonia to concentrated or diluted Ti (SO₄)₂ solutions until pH of the solutions were raised to 3.0, 4.5, 6.0 and 8.0, respectively. Chemical, thermal, IR absorption spectrum and X-ray diffraction analyses were made of these hydrous oxides. Their specific surface areas and adsorption capacities of (UO₂(CO₂)₂)^4- ions in alkaline solutions were also measured. The results obtained can be summarized as follows:
1) The crystallinity of the hydrous Ti (IV) oxide decreased linearly with increasing pH of the mother solution the crystallinity of the hydrous oxide prepared at pH 8.0 was about one fifth of that of the hydrous oxide prepared at pH 3.0 (Fig.6).
2) The specific surface area of the hydrous oxide increased linearly and markedly with increasing pH of the mother solution (Fig.7). The adsorption capacity of the oxides showed a remarkable increase with increasing pH of the mother solution (Fig.8). The oxides with maximum adsorption capacity were prepared from the solution of pH6.0 for the concentrated Ti(IV) solution, and from the solution of pH4.5 for the diluted Ti(IV) solution.
3)The chemical composition of the hydrous oxide was greatly dependent on the concentration of Ti(SO₄)₂ in the mother so1ution (Table 1 and Table 2). The result revealed that the chemical composition had close relation ship to the hydrolytic mechanism in Ti(SO₄)₂ solution.
4)The dependencies of the crystallinity and the adsorption capacity etc. on pH of the mother solution were explained in terms of the hydrolytic mechanism, the growth and aggregation model of hydrous Ti(IV) oxide polymers, and the constitutional formulas of the hydrous oxides after heated at 50°C (Fig.12, 13 and Table 3).