Phase Transformation of Metal Hexacyanoferrates Containing Rubidium–Cesium to Separate Rubidium and Cesium from Each Other

Abstract Rb + and Cs + lack independent ore resources in nature, and they often coexist with K + and Na + . Hexacyanoferrates containing Rb + and Cs + are often calcinated and leaching to release Rb + and Cs + into solution to separate from co‐existing Na + and K + . In this study, co‐precipitate containing Rb + and Cs + , RbCs‐CuZnHCF, is treated by phase‐ transformation method using (NH 4 ) 2 S as phase‐transformation agent to achieve the separation of Rb + and Cs + from each other. The kinetics and thermodynamics of the phase‐transformation are studied. The results indicated that solid RbCs‐CuZnHCF is transformed to Rb + and [Fe(CN) 6 ] 4‐ by the aid of S 2‐ , while Cs‐CuZnHCF maintains its original solid state. The removal efficiency of Rb + is 64.22%, while the loss of Cs + is 0.86% under the optimal conditions (T = 60℃, S 2 ‐ /(Cu 2+ +Zn 2+ ) = 0.6, pH = 3‐7, t = 60 min), and the separation coefficient of Rb‐Cs was up to 207.89. Thermodynamics analysis reveals that the reaction is endothermic. Kinetic analysis reveals a low activation energy (17.99 kJ/mol) and pre‐exponential factor of 10.18 L/ (mol·s), indicative of a diffusion‐controlled process. By this method, the high‐priced hexacyanoferrates can be re‐used as co‐precipitant agent to separate Rb + and Cs + from co‐existing Na + and K + .