Amidst the surge of Li demand, technology development for Li extraction from diverse Li resources has gained considerable interest. Montebrasite, a significant lithium ore, is distinguished by its high Li content. Despite its potential, research into its processing technologies are scarce, leading to its limited and slow industrial adoption. On this basis, a novel process combining aluminum sulfate roasting and water leaching was proposed in this study to achieve its clean and efficient utilization. Firstly, thermal behaviors of montebrasite were investigated through various characterizations. It was observed that montebrasite underwent obvious decomposition above 700 °C, and began to melt after 800 °C. The mineral phases transformed into Li3PO4, AlPO4 and Al2O3 after decomposition. Thermodynamic calculation indicated that when Al2(SO4)3 was used as roasting agent, Li+ can be entirely substituted by Al3+ to form soluble Li2SO4, while Al3+ combined with PO43− to form insoluble AlPO4, enabling selective and efficient Li extraction. The experimental results demonstrated a high agreement with thermodynamic analysis. Under the optimal conditions (roasting: 760 ℃, 1.0 h, 29.4 % Al2(SO4)3), 94.1 % Li was extracted selectively, while only 0.04 % Al and 0.3 % P entered into solution. The leach residue, primarily composed of AlPO4, SiO2, mullite and Al2O3, can be recycled for further utilization. This process offers distinct advantages over traditional salt roasting methods, including reduced reagent usage and elimination of solid waste discharge. It presents an efficient, cost-effective and environmentally benign pathway for the utilization of montebrasite.