Separation of Cs+ from Rb+ and Cs+ co-existing solution by Cs3Bi2I9 precipitation to produce CsI

Cesium and rubidium are highly-priced rare alkaline elements that are quite difficult to separate from each other. In this paper, Cs+ was successfully separated from co-existing solutions of Cs+, Rb+ and K+ in the form of Cs3Bi2I9 precipitation. The effects of various factors (pH value, Bi3+/Cs+ molar ratio, reaction time, and decomposition temperature) on the separation ratio of Cs+ were explored. The results showed that the maximum recovery of Cs+ was 98.55% from the solution with a Cs/Rb ratio of 1.28. The content of Rb+ in Cs3Bi2I9 was 0.189%, indicating that the method can effectively separate rubidium and cesium from each other. The separation factor of cesium-rubidium was 85. By subsequent vacuum thermal decomposition, Cs3Bi2I9 was directly converted to CsI and BiI3. The purity of CsI was greater than 99.00%, and BiI3 was recycled back to produce Cs3Bi2I9. This process has the advantages of low cost, short process, environment-friendly, and simple operation.