**Wei-Sheng Chen, Cheng-Han Lee \*, Yi-Fan Chung, Ko-Wei Tien, Yen-Jung Chen and Yu-An Chen**

Department of Resources Engineering, National Cheng Kung University, No.1, DaxueRoad, Tainan City 70101, Taiwan; kenchen@mail.ncku.edu.tw (W.-S.C.); eddie21039@gmail.com (Y.-F.C.);

n46071172@gs.ncku.edu.tw (K.-W.T.); qaz5932201@gmail.com (Y.-J.C.); evan860102@gmail.com (Y.-A.C.)

**\*** Correspondence: happy980074@gmail.com; Tel.: +886-6-2757575 (ext. 62828)

Received: 23 April 2020; Accepted: 6 May 2020; Published: 8 May 2020

**Abstract:** 50 billion cubic meters of brine every year creates ecological hazards to the environment. In order to reuse brine efficiently, rubidium and cesium were recovered in this experiment. On the other hand, the main impurities which were needed to be eliminated in brine were lithium, sodium, potassium, calcium, and magnesium. In the procedure, seawater was distilled and evaporated first to turn into simulated brine. Perchloric acid was then added into simulated brine to precipitate potassium perchlorate which could reduce the influence of potassium in the extraction procedure. After that, t-BAMBP and ammonia were separately used as extractant and stripping agent in the extraction and stripping procedures to get rubidium hydroxide solutions and cesium hydroxide solutions. Subsequently, they reacted with ammonium carbonate to get rubidium carbonate and cesium carbonate. In a nutshell, this study shows the optimal parameters of pH value to precipitate potassium perchlorate. Besides, pH value in the system, the concentration of t-BAMBP and ammonia, organic phase/aqueous phase ratio (O/A ratio), reaction time, and reaction temperature in solvent extraction step were investigated to get high purities of rubidium carbonate and cesium carbonate.

**Keywords:** solvent extraction; t-BAMBP; rubidium; cesium; brine; chemical precipitation; recovery
