Precipitation · and Hydrolysis of Thorium(IV) in Aqueous Solution:
Thorium Nitrate - Potassium Hydroxide. I. Determination of Solubility Constants of Th(OH)4
The precipitation and h ydrolysis 0f thorium (IV) in aqueous
solutions of thorium nitrate - potassium hydroxide was investigated
at 20oc with a tyndallometel\u27.\u27 a nd a pH-meter. A three-dimensional
precipitation diagram for a wide r ange of concentrations
of both precipitating components was constructed. The concentration
region of thorium hydroxide, the fast precipitation, the
formation of sols and of stable clear solutions were observed.
The decreased precipitation of thorium h ydroxide at pH
between 9 - 10.4 is considered to be the effect of the carbonate ions
present. By a very simple graphical tyndallometric method the
solubility products of thorium hydroxide were directly determined
as:
log K so = - 45.7; log Ks2 = - 24.3
and the cumulative hydrolytic constant */3 2 = 1.029 X 10-1 was
calculated. The predominant hydrolytic species of thorium-ion in
aqueous solution in equilibrium with the solid phase of Th(OH) 4
were estimated. The predominant species is the free ion Th4+ for pH
3.4 and [Th(OH)22+]n for the pH between 3.5 and 4.L At values lower
pH 4.1 ionic species of thorium are formed with more than two
OH- ions per one thorium ion
