An ammonium-free process for sustainably extracting Rb and Cs from salt lake brine by potassium phosphotungstate

With the surging demand for rubidium and cesium, rubidium and cesium extraction resources have gradually expanded from ores to brines to ensure the security of supply of key metals. However, traditional adsorbents of heteropoly salts inevitably suffer from environmental pollution risks, unsustainability, and cumbersome process flows. In this study, potassium phosphotungstate is employed as an ammonium-free adsorbent for sustainably extracting Rb and Cs from salt lake brine. K 3 PW 12 O 40 shows high adsorption capacity (37.71 mg/g for Rb and 60.42 mg/g for Cs) and fast adsorption kinetics (adsorption equilibrium within only 2 min). The adsorbent also exhibits excellent selectivity, with the separation coefficients of Rb/K up to 167.95 and those of Cs/K up to 759.07. It also maintains chemical stability within a broad pH range of 2–10. The desorption efficiency of rubidium and cesium is up to 99.8 % and 85.6 % respectively. After five desorption-adsorption cycles, the adsorption capacity of Rb and Cs remains at 99.8 % and 86.7 % of the initial adsorption capacity. The adsorbent selectively adsorbs Rb + and Cs + from the practical brine even in the presence of a large number of co-existing ions. The Rb and Cs adsorption mechanism for K 3 PW 12 O 40 was primarily ionic exchange with K. The adsorption process provides excellent performance and environmental advantages based on the salt lake industrial cluster. Efficient adsorption performance of Rb and Cs was achieved without the emission of ammonia nitrogen pollutants and the use of ammonium salt chemicals. This study offers a sustainable alternative for extracting Rb and Cs from salt lake brine.