Coprecipitation of macro amounts of uranium and thorium in the UO22+-Th4+-NO3--CO32-(OH-)-H2O system and study of the solid phases

Using chemical analysis, IR spectroscopy, DTA, and TGA the authors studied the solid phases formed upon coprecipitation of uranium (VL) and thorium from carbonate-containing and alkali solutions. They have established that the solid phases of the studied system have variable chemical composition depending on the coprecipitation conditions, and contain certain amounts of water and carbonate ions. Practically complete coprecipitation of uranium and thorium is observed at pH = 8.0 from alkali solution. In systems with sodium carbonate, the highest relative coprecipitation of uranium with thorium is characteristic of the system with final pH value pH = 5.0. At pH = 8.0 in carbonate medium, thorium coprecipitates with uranium to a lesser degree than for other pH values. The degree of coprecipitation correlates with the content of water and carbonate ions in the precipitates: the higher the atom-to-molecule ratio of uranium to H2O and CO2, the lower is the degree of precipitation