Thermally Assisted Sulfuric Acid Leaching of Clay-Type Lithium Ores: Protonation-Induced Al–O Bond Cleavage and Sulfate Complexation for Enhanced Li Extraction

The green exploitation of clay-type lithium deposits in Yunnan represents a strategically critical supplement to alleviating lithium supply-demand imbalances. A combined flotation-magnetic pretreatment removed a significant amount of lithium-barren high-iron gangue minerals (hematite and garnet) prior to leaching. The optimized two-stage sulfuric acid leaching process comprises primary leaching with 30 wt % H₂SO₄ at 126 °C (solid-liquid ratio 1:5 g/mL, 1.5 h), followed by secondary water leaching (1:8 g/mL, 0.5 h). This approach achieved 87.89% Li leaching efficiency with 72.80% residue yield. Mineralogical mapping, Time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS) analyses revealed that H⁺ protonation partially disrupts Al-O octahedra via bond polarization, liberating Al³⁺/Li⁺, which form soluble sulfate complexes (Al₂(SO₄)₃, Li₂SO₄), suppressing hydrolysis. Molecular dynamics (MD) simulations verified enhanced H₃O⁺-Li⁺ ion exchange and accelerated diffusion kinetics at elevated temperatures (399 K), with Li⁺ diffusivity increasing by 228% versus 298 K. Compared to roasting methods, this approach eliminates energy-intensive pretreatment while maintaining high Al dissolution (72.70%) and minimal Si release (5.97%). Moreover, the integrated flotation-magnetic pretreatment significantly reduced acid consumption in subsequent leaching. The leaching temperature (126 °C) is substantially lower than that required by most direct leaching processes. The protonation-complexation mechanism provides a sustainable pathway for clay-type lithium extraction.