Homogeneous hydrolysis of thorium by thermal decomposition of urea

Thorium was precipitated homogeneously from a thorium nitrate solution by the thermal decomposition products of urea. The kinetics of the hydrolysis were studied at 90 and 100 degrees C by pH measurement during the initial 5 h and the precipitation efficiencies of thorium and radium were measured over a 24 h period. Precipitation of the radium daughters was closely followed with the aim of co-precipitation of radium with thorium. The CO2 formed during urea decomposition dissolved in the solution, forming CO32- during the experiment upon reaching a sufficiently high pH level (>7). This allowed radium to co-precipitate partially, thus reducing the activity of the filtrate. After filtration or centrifugation, the precipitate is composed of nanocrystalline thorium dioxide (crystallite size similar to 10 nm), with weakly bound H2O and CO2.