Hydrolysis and colloid formation of thorium in water and consequences for its migration behaviour - comparison with uranium

The different behaviour of Th and U in aqueous solutions is discussed. Hydrolysis, colloid formation and retention of Th are studied by paper chromatography and by filtration and ultrafiltration as function of pH and time. The behaviour of Th in three natural groundwaters is investigated as function of time by filtration and ultrafiltration and by means of a scanning electron microscope with microprobe. Autoradiography is also applied. - Evidence for the formation of colloids of Th is presented. In groundwaters silicic acid serves as carrier. After filtration and ultrafiltration new fine (colloid) and coarse particles are formed carrying Th. The percentage of Th in the coarse particle fractions increases with the concentration of Th and with salinity of the groundwater. (orig.)