Occurrence State of Lithium in Clay Minerals Based on Element-Complexation Mechanisms

Lithium (Li) is a cornerstone of green technology in reducing carbon emissions. However, conventional Li mining faces potential supply chain disruptions by 2030, underscoring the urgency of exploring clay-type Li deposits with poorly understood occurrence states and extraction mechanisms. This study investigates a drill core from central Yunnan to elucidate the modes of Li occurrence and the genetic mechanisms. The claystone is primarily composed of cookeite, diaspore, and anatase, exhibiting a world-class Li grade of up to 1.94 wt % in whole rock. The occurrence state of Li is constrained by using X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analyses. Fitted XPS Li 1s peaks in samples AN 1.62 and AN 1.58 at 57.0, 56.3, 55.9, and 55.4 eV and 57.2, 56.6, 56.0, and 55.3 eV, respectively, suggest Li occurrence on surfaces, within pseudohexagonal cavities, and in the lattice, forming LiCl, Li₂O, LiF, and LiOH species. The ⁷Li NMR chemical shift at -0.7 ppm indicates that Li predominantly resides in the lattice, while the asymmetry and positive skew of the peaks suggest the coexistence of surficial and structural Li. The genetic mechanisms of these Lis likely involve isomorphic substitution within tetrahedral Al-Si and octahedral Fe/Mg-Al sites. The presence of Al/Mg/Fe-F complexes and F-Li species further suggests the structural Li incorporation. Li exhibits coupled enrichment with Al, Mg, and Fe in cookeite but is decoupled from Al in the diaspore. TOF-SIMS three-dimensional (3D) reconstruction reveals that Li is predominantly concentrated in the O₂ sheets of cookeite's TO₁T-O₂-TO₁T structure. Stepwise leaching experiments further constrain Li occurrence, demonstrating that most Li is hosted within the lattice. Calcination at 400 °C promotes Li incorporation into the lattice, while subsequent treatment at 600 °C-200 °C (H₂SO₄) or 200 °C (concentrated H₂SO₄) effectively mobilizes Li, particularly in sample AN 1.58, achieving nearly complete extraction.