At present, in rare earth production, double salt precipitation is widely used for separation of rare and non-rare earth elements, and separation of quaternary cerium and trivalent rare earth elements. Rare earth double sulphates are commonly treated by hydroxide, but the filtration is difficult because the rare earth hydroxide obtained during the hydroxide conversion is an amorphous precipitate. In contrast, if RE double sulphates are converted into carbonates, filtration and dissolution by acids become easier because RE carbonates are crystalline precipitates.
Ri Sun Chol, a researcher at the Faculty of Chemistry, conducted a study to convert rare earth double sulphates obtained from monazite sulphate leachates to rare earth carbonates using sodium carbonate.
Aiming to improve the conversion of rare earths and to effectively separate U and Th from RE carbonates, he investigated the influence of reaction parameters using Taguchi-Grey Relation Analysis (Taguchi-GRA), determined the optimum conditions and studied the separation of U and Th.
When reaction temperature is 80℃, reaction time 2h, additive amount of sodium carbonate 1.5 times the theoretical amount, the ratio of solid to liquid 2:1 and stirring speed 200r/min, the RE carbonate conversion was 97.1% and the U and thorium removal 80.8% and 0.3%, respectively.
For more information, please refer to his paper “Study on the Carbonate Conversion of Rare Earth Double Sulfates” in “Proceedings of KUTIC-2025”.