Research on the migration of rubidium and mineral phase changes during sulfuric acid leaching of biotite

Acid leaching has been widely employed for the extraction of rubidium (Rb) and lithium (Li) from mica owing to operational simplicity, reduced energy consumption, and enhanced efficiency. However, previous investigations have primarily focused on Li leaching behavior and mechanisms, with limited attention paid to understanding the lattice occupancy of Rb in mica and its influence on the leaching mechanisms. This study examined the effects of various factors on the leaching efficiency and behavior of Rb in sulfuric acid leaching of biotite. The mechanisms of Rb transfer were elucidated through density functional theory (DFT) calculations. Under optimized conditions, Rb leaching efficiency reached 93.8 %. The DFT analyses demonstrated that Rb substitution occurred at potassium sites within biotite (K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂) layers, with preferential occupation of the six-membered tetrahedral ring centroids. During sulfuric acid leaching of biotite, H⁺ initially penetrates the (001) crystal surface through ion exchange with Rb⁺ and K⁺. It then corrodes the aluminum oxide tetrahedron, resulting in the release of Al³⁺. Ultimately, the octahedral layer undergoes structural disintegration through H⁺ induced cleavage of FeO bonds, releasing Fe²⁺ species. These findings offer valuable insights and lay the foundation for developing next-generation acid leaching techniques for extracting Rb from Rb-bearing mica.