Synergistic extraction and separation of thorium from rare earths in chloride media using mixture of Cextrant 230 and Cyanex 923

Abstract

In order to lower the usage of expensive Cyanex 923 and increase the extraction capacity of the system of Cextrant 230, the synergistic extraction of thorium from chloride media by a mixture of Cextrant 230 and Cyanex 923 was investigated. The maximum synergistic enhancement coefficient (R) of 1.53 is obtained at 1:1 molar ratio of Cextrant 230/ Cyanex 923. The synergistic extracted species of Th4+ is determined as ThCl4·2Cextrant 230·Cyanex 923. The synergistic extraction of Th4+ is an entropy-driven exothermic process. The loading capacity of 0.60 mol/L mixed extractant for thorium is about 17.10 g/L (calculated as ThO2), and the loaded thorium in the organic phase can be effectively stripped by distilled water. For comparison, rare earth cations are barely extracted under the similar conditions, suggesting that the mixtures can be applied to separate thorium from rare earths. A cascade extraction process was developed based on the synergistic extraction system to separate thorium from the hydrochloric acid leaching of bastnaesite. The content of thorium in the leaching solution decreases obviously from 19.90 mg/L to 1.4 μg/L by 3 stages of extraction, which is superior to sole Cextrant 230 or Cyanex 923. The introduction of Cextrant 230 into the extraction system not only lowers the usage of Cyanex 923 but also enhances the selective extraction of thorium at low acidity, implying that the synergistic extraction system can selectively extract thorium more efficiently and economically than the sole systems.