To effectively solve the problems of poor selectivity and only being suitable for separation in weakly alkaline environment of traditional cationic collectors used in reverse flotation desilication of phosphate, a novel high-efficiency cationic collector SDTQ suitable for separation in weakly acidic environment was developed. Flotation tests were carried out on a siliceous-magnesian phosphate from Guizhou Province using this collector. The results show that when pH=6 and the SDTQ dosage is 25 mg/L, the recovery of pure quartz mineral is close to 100%, while fluorapatite exhibits no obvious floatability. In the flotation of artificial mixed ore, good separation effect of fluorapatite and quartz is achieved at pH=6 with an SDTQ dosage of 100 mg/L. On this basis, using the magnesium-depleted phosphate concentrate pulp at pH=6 as the research object, the collector dosage condition test was carried out. The optimal SDTQ dosage is determined to be 1.1 kg/t. Under this collector dosage, open-circuit tests were carried out. The separation indexes of P₂O₅ grade 35.38%, P₂O₅ recovery 85.41% and acid-insoluble content 5.53% in phosphate concentrate are obtained. Finally, through the closed-circuit process of one roughing, one cleaning and one scavenging, favorable separation indexes are obtained, with P₂O₅ grade of 35.49%, P₂O₅ recovery of 90.31% and acid-insoluble content of 9.81% in phosphate concentrate. Compared with dodecylamine, SDTQ increases the P₂O₅ grade of phosphate concentrate by 2.05 percentage points and the recovery by 10.02 percentage points. The measurement results of Zeta potential and contact angle show that SDTQ is selectively adsorbed on the quartz surface through electrostatic interaction, and the enhanced hydrophobicity difference between quartz and fluorapatite is the key mechanism to achieve efficient desilication in phosphate reverse flotation. The test results of atomic force microscopy and Fourier transform infrared spectroscopy show that SDTQ collector acts on the quartz surface in the form of physical adsorption through the synergistic effect of quaternary ammonium cationic groups and long-chain alkyl groups. SDTQ collector can improve the grade of phosphate, reduce reagent cost, and has both economic and environmental advantages.