Abstract: In order to further understand the influence of PO₄^3- ions on the removal of silicon from collophane by reverse flotation of amine collectors, the flotation behavior of pure quartz in the presence of PO₄^3- is examined. Combined with zeta potential analysis and Φ-pH diagram of PO₄^3- ions, the inhibition mechanism of PO₄^3- is analyzed. The results show that PO₄^3- ions have a significant inhibitory effect on the flotation of quartz by oleamine, and the inhibitory effect at pH=4~5 is significantly greater than that at pH=8~10; H₂PO₄^- ions are the primary species at pH=4~5 and HPO₄^2- at pH=8~10. The inhibition effect could be attributed to the adsorption of H₂PO₄^- and HPO₄^2- ions hydrolyzed from PO₄^3- ions on the positive region of the quartz surface, which makes the quartz surface hydrophilic.