Separation and recovery of cesium sulfate from the leach solution obtained in the sulfuric acid baking process of lepidolite concentrate

Abstract

Lepidolite is an important mineral resource of lithium, rubidium and cesium. Lithium, rubidium and cesium were extracted simultaneously from a lepidolite concentrate by sulfuric acid baking and water leaching. A crystallization-roasting-dissolution-solvent extraction process was developed to recover cesium from the leach solution in this study. During crystallization, leach solution was cooled from 85 °C to 35 °C firstly to precipitate most parts of Rb+ with 98.65% and Cs+ with 94.59% in the form of RbAl(SO4)2·xH2O and RbAl(SO4)2·xH2O, respectively. The mixed alums were then roasted at 900 °C to decompose them into Cs2SO4, Rb2SO4, K2SO4 and Al2O3. Next, a mixed sulfates solution with 12.51 g/L Rb+ and 2.4 g/L Cs+ was obtained by water dissolution of the roasted alums. Cesium was then separated from the solution by solvent extraction, scrubbing and stripping. A Cs-loaded organic phase with 4.66 g/L Cs+ and 3.05 g/L Rb+ was obtained after a four-stage countercurrent extraction. Around 99.20% of Cs+ and 10.44% of Rb+ were extracted by using 4-tert-butyl-2-(α-methylbenzyl) phenol (t-BAMBP). After scrubbing and stripping of the Cs-loaded organic phase by diluted H2SO4, a cesium sulfate solution of 16.6 g/L Cs+ was obtained. A cesium sulfate product with a purity of 98.47 wt% was then recovered by evaporation and crystallization of the stripping solution