Mechanisms of Lithium Enrichment and Metallogenesis in a Simulated Montmorillonite-Fluid System

Due to strong industrial demand for Li, Li-bearing montmorillonite (Li-Mt) deposits are a focus for exploration, but the Li enrichment mechanisms in such deposits are unclear. In this study, adsorption experiments and mineralogical analyses were used to investigate the water-rock reactions at different Li concentrations, temperatures, durations, and pH conditions, in order to reveal the Li enrichment mechanisms in F- and Cl-rich systems. Our results suggest that water-rock reactions are different in the two halogen systems. The reaction in the LiCl-Mt system involves deprotonation, whereas dehydroxylation occurs in a LiF-Mt system. Lithium is adsorbed or exchanges with interlayer cations in Mt. Adsorption forms a monolayer that is consistent with the Langmuir model in a LiCl system. Lithium is adsorbed in multi-layers in Mt in a LiF system. For a given Li concentration, the adsorption capacity of the LiF-Mt system is 2.8 times greater than that of the LiCl-Mt system. The pH has a weaker effect in the LiCl-Mt system than in the LiF-Mt system. Furthermore, Li adsorption is hindered at very high or low pH in a LiF system. The chemical shift of Li is -0.2 ppm (±0.1 ppm) in a nuclear magnetic resonance (NMR), which indicates that Li occurs as inner-sphere complexes in the pseudo-hexagonal cavity in Mt. Based on a CaCl₂ leaching experiment, >50% (up to 97.94%) of the Li can be easily exchanged out of the Mt. The residual Li in the inner-sphere is the key to metallogenesis of Li-Mt deposits. Therefore, the grade of ion adsorption-type Li deposits is determined by the exchangeable Li.