Lithium Carbonate Conversion to Lithium Hydroxide Using Calcium Hydroxide: Equilibrium is Governed by Vaterite Formation

The conversion of lithium carbonate (Li₂CO₃) with calcium hydroxide (Ca(OH)₂) is a cornerstone industrial process for synthesizing lithium hydroxide (LiOH), a critical precursor for high-performance cathodes in advanced lithium-ion batteries. Achieving a high Li₂CO₃-to-LiOH yield is crucial for efficient industrial processing. However, despite its industrial relevance, the influence of concentration and equilibrium conditions on this conversion reaction remains insufficiently explored. To address this gap, we investigated the conversion reaction by varying the Li₂CO₃ concentration and the Ca(OH)₂:Li₂CO₃ molar ratio. Near-complete conversion yields occur below the maximum concentration threshold of 1.6 mol L^-1 LiOH, while yields diminish above this limit. Sequential reaction experiments confirm that the system adheres to Le Chatelier's principle, and reverse reactions initiated from LiOH and CaCO₃ demonstrate true equilibrium behavior. Furthermore, backward reactions involving distinct CaCO₃ polymorphs reveal different equilibrium states. Notably, the presence of vaterite alongside calcite significantly affects the equilibrium concentration of LiOH, underscoring the role of solid-phase composition in governing reaction thermodynamics. These findings provide a deeper understanding of the causticization mechanism and offer actionable insights for optimizing LiOH production in industrial settings.