Equilibrium Ultrafiltration of Hydrolyzed Thorium (IV) Solutions

The polymeric species formed on the hydrolysis of Th(IV) from solubility experiments of $ThO_2$ in 0.1M $NaClO_4$ and $Th(OH)_4\;in\;0.5M\;NaClO_4$ were removed by ultrafiltration using 1 nm ultrafilters. The resultant equilibrium concentrations of mono-hydroxy Th(IV) species in solutions between pH 1.5 to 13 were measured by the NAA method. From these data solubility product of thorium dioxide and the stability constants of mono-hydroxy Th(Ⅳ) were determined. The values obtained were log $K_{sp}\;-\;50.76\;{\pm}\;0.08, log\;{\beta}_{1,1}\;12.42\;{\pm}\;0.02,\;log\;{\beta}_{1,2}\;22.46\;{\pm}\;0.15, log\;{\beta}_{1,3}\;34.36\;{\pm}\;0.07,\;log\;{\beta}_{1,4}\;42.58\;{\pm}\;0.08$, which are in good agreement with the values given in the literature. In addition, several dimeric species, $Th_2(OH)_2\;^{6+},\;Th_2(OH)_3\;^{5+} and\;Th_2(OH)_4\;^{4+}$ have been identified.