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-(α-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.