Energy-efficient and simultaneous extraction of lithium, rubidium and cesium from lepidolite concentrate via sulfuric acid baking and water leaching

Lepidolite is a valuable mineral resources of lithium, rubidium and cesium. However, most researches only focused on the lithium extraction without recovery of rubidium and cesium, and most of these processes involved energy-intensive high-temperature roasting and/or mechanical activation. In this study, simultaneous extractions of lithium, rubidium and cesium from a lepidolite concentrate were conducted through a low-temperature sulfuric acid baking and water leaching route. The influence of the extraction process parameters were systematically investigated. An optimized baking and leaching condition was determined as follows: H2SO4 concentration 85 wt%, baking temperature 200 °C, acid-to-concentrate mass ratio 1.7:1, baking time 4 h, 88% concentrate particles <74 μm, and water leaching temperature 85 °C. Under the optimal condition, the maximum extractions of Li, Rb and Cs reached 97.1%, 96.0% and 95.1%, respectively. Besides, the chemical formula of the lepidolite mineral in the concentrate was determined as KLi1.6Al2.2Si3.2O10FOH via AMICS characterization. During the baking process, the lepidolite reacted with hot sulfuric acid to generate water-soluble but acid-insoluble sulfates, KAl(SO4)2, Al(SO4)OH·5H2O and Li2SO4, while the rubidium and cesium might be converted to RbAl(SO4)2 and CsAl(SO4)2 existing in the form of isomorphism in KAl(SO4)2.