Abstract: The influence and mechanism of citric acid to the flotation of cassiterite were investigated by flotation tests, contact angle measurements, zeta potential determination and solution chemistry calculations.The results of flotation experiments revealed that the recovery of cassiterite was above 80% in the pH value range of 7-9 with 200 mg/L salicylhydroxamic acid as the collector.In the range of pH> 4, citric acid showed significant inhibiting effect in the flotation of cassiterite.When pH=7.0 and 50 mg/L citric acid was added, the recovery of cassiterite was just 25.3%.Contact angle measurements demonstrated that the contact angle of the pure cassiterite surfaces was 33°.After the addition of salicylhydroxamic acid, the contact angle was increased to 120°, and citric acid reduced the contact angle to 44°.Zeta potential determination and solution chemistry calculations suggested that both salicylhydroxamic acid and citric acid chemisorbed on cassiterite surfaces.The adsorption of citric acid made the cassiterite surfaces more hydrophilic and decreased the adsorption amount of salicylhydroxamic acid on cassiteritesurfaces, which resulted in that cassiterite was depressed in the flotation process.