Abstract: The influence of oxalic acid on the floatation of cassiterite under the styrene phosphonic acid （SPA） collector system was investigated by flotation tests. Solution chemistry calculations， Zeta potential determination and infrared spectroscopy were used to explore its mechanism. The results of flotation experiments revealed that the recovery of cassiterite was above 79.37% in the pH value range of 2~10， with 80 mg/L SPA as the collector. After 4 mg/L of oxalic acid was added， the inhibitory effect of oxalic acid on cassiterite increased with increasing pH， and cassiterite could not be effectively recovered when the pH value was above 10. Based on the flotation behavior of cassiterite， fluorite and calcite， a new idea of reverse-flotation was proposed. Solution chemical calculation， Zeta potential measurement and infrared spectrum analysis demonstrated that both oxalic acid and SPA could chemically adsorb on the surface of cassiterite. Oxalic acid formed a stable tin oxalate complex on the surface of cassiterite， the adsorption of the two kinds reagents was affected by each other's existence. The inhibition mechanism is explained as the adsorption of oxalic acid on the surface of cassiterite increases its hydrophilicity and occupies active sites. This article provides a reference for the mechanism of the influence of inhibitors on cassiterite flotation behavior. 

Key words: Cassiterite, Styrene phosphonic acid, Oxalic acid, Flotation, Inhibition