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

Abstract

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 CaCl 2 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.

Effects of the Hydroxy-Regulated Li-Montmorillonite Atomic Interface Arrangement on Li Cycle of Marine Sedimentation and pH

“…The experiment controlled for variables, and the differences in Li enrichment were directly related to differences in halogens, indicating that the halogen species induce Li to different degrees of adsorption. There was more Li enrichment in the Mt in the F-rich system than the Cl-rich system . The changes of the reactions occur as the Li–Na replacement, so the results show that the cation exchange effect of Mt is stronger in the F-rich system.…”

“…In summary, halogen species may be an important factor that affect the global Li cycle. The atomic arrangement of Li in both halogen systems indicates that Li enters the pseudohexagonal cavity of Mt with hexa-coordinate, which is more like an octahedral occupation than its surface and interlayers. , …”