The flotation separation of cassiterite and dravite was realized using lead complexes of benzohydroxamic acid (Pb-BHA) as a collector and sodium fluosilicate (SF) as a depressant. Zeta potential tests confirmed that SF enabled the selective depression of dravite. The results of Fourier transform infrared (FTIR) spectroscopy analysis demonstrated that hydroxyl-containing groups in the hydrolysis products of SF selectively chemisorbed on the surface of dravite. X-ray photoelectron spectroscopy (XPS) analysis results further demonstrated the strong chemisorption of SF hydrolysis products (F-containing groups and hydroxyl-containing groups) on dravite (Mg sites). Consequently, the adsorption of Pb-BHA on dravite was selectively prevented. Based on the results, a selective depression model of SF on cassiterite and dravite was proposed.