Coprecipitation of Rare Earth Iodates with Thorium Iodate Precipitated from Homogeneous Solution

The separation of thorium from rare earths by precipitation of thorium iodate from homogeneous solution is evaluated. The extent of coprecipitation is given when thorium is precipitated in the presence of the rare earths lanthanum, praseodymium, promethium, and europium, and the related elements, yttrium and scandium. The extent of coprecipitation is determined by the use of radioactive tracers of these elements. The distribution of rare earths with thorium follows the logarithmic or heterogeneous distribution law. It is concluded that trivalent rare earths coprecipitate with thorium iodate by a type oi isomorphous replacement wiyhin the thorium iodate lattice. A correlation is given between ionic radii and extent of coprecipitation. (auth)