Study on the Extraction of Lithium from Lepidolite Ore by Composite Sulfate Roasting and First-Principle Computation

The composite sulfate roasting method is a highly effective technique for the extraction of lithium from lepidolite ore; however, the atomic-level mechanism underlying the roasting reaction remains inadequately understood. This study employs a combination of experimental methodologies and density functional theory (DFT) calculations to elucidate the roasting mechanism. Lepidolite ore was subjected to roasting with a mixture of sodium sulfate (Na₂SO₄) and calcium sulfate (CaSO₄) as roasting agents. A comprehensive investigation was conducted to evaluate the influence of various roasting process conditions on the lithium-leaching rate, which facilitated the identification of optimal roasting parameters. Characterization of both the lepidolite ore and the resultant calcine was performed utilizing X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS). The stability, electronic structure, and bonding characteristics of the crystal structures KLi₂AlSi₄O₁₂F₂ (Le), KLiNaAlSi₄O₁₂F₂ (Le–Na), and KLiCaAlSi₄O₁₂F₂ (Le–Ca) were analyzed using Materials Studio software. The results from both experimental investigations and DFT calculations suggest that the Si–O and Al–O bonds in lepidolite interact with Na₂SO₄ and CaSO₄, leading to bond cleavage and recombination. This process ultimately produces roasted products predominantly composed of anorthite and albite at elevated temperatures. Furthermore, the Li–O bond reacts with Na₂SO₄ and CaSO₄ to generate a soluble lithium-containing salt.