Fractional precipitation of rare earth iodates using complexation and hydrolysis of dimethyl sulfate

Abstract

A new procedure has been developed to separate the trivalent rare earths. The rare earth cations are complexed with one of the following chelating agents; DTPA (diethylenetriaminepenta-acetic acid), DCTA (1,2-diaminocyclohexane-N,N,N′,N′-tetra-acetic acid) or EDTA (ethylenediaminetetra-acetic acid). The pH is adjusted to about 3·5, and iodate is then added without causing a precipitate. About 1 ml of dimethyl sulfate is added and the resulting solution is agitated at room temperature for several hours. As the dimethyl sulfate slowly hydrolyses, the hydrogen ion concentration gradually increases. Hydrogen ions compete for the chelating agents, which results in a gradual increase in the free rare earth cations. Each chelate formed between each rare earth cation and each chelating agent has a different formation constant. The rare earth cation with the lowest formation constant is selectively released from its chelate as the hydrogen ion concentration is increased. The selectively released rare earth cation then precipitates as the iodate. Coprecipitation of adjacent rare earth cations is significantly decreased. Considerably improved separations have been achieved.