Solvent extraction of rubidium from a sulfate solution with high concentrations of rubidium and potassium using 4-tert-butyl-2-(α-methylbenzyl)-phenol

Rubidium is a critical mineral due to its important role in the rubidium atomic clock in global positioning systems. In our previous study, lithium, rubidium, cesium were extracted simultaneously from lepidolite by a sulfuric acid baking process; a sulfate solution with 10.26 g/L-Rb+ and 40.74 g/L-K+ was obtained after recovery of lithium and cesium. As the continuity of this research, solvent extraction was used to separate rubidium from the above solution with high concentrations of Rb+ and K+ in this study. An organic phase with 1 mol/L 4-tert-butyl-2-(alpha-methylbenzyl)-phenol was introduced to extract the rubidium. The Rb+ extraction efficiency reached 97.02%, with 17.28% K+ co-extracted after a four-stage countercurrent extraction. The rubidium-loaded organic phase was then scrubbed with water, and the scrubbing efficiency of the potassium was 96.17%, with 7.25% of rubidium lost. After potassium scrubbing, a potassium-depleted organic phase with 3.2 g/L-Rb+ and 0.093 g/L-K+ was obtained. Almost all the rubidium could be stripped from the organic phase using 0.1 mol/L sulfuric acid. A rubidium sulfate product with a purity of 98.17 wt.% was obtained by evaporation and crystallization of the stripping solution. Finally, an integrated process for recovery of lithium, cesium, and rubidium from lepidolite was proposed. (c) 2020 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.