By studying the various metal ions released from the grinding process, and conducting the flotation test of monazite and symbiotic ore, using zeta potential measurements and FTIR infrared spectrum analysis methods, the influence of metal ions on the surface of monazite and the mechanism of action are obtained. The results showed that the main metal ions in the flotation environment of monazite are Ca²⁺, Ba²⁺, and Fe³⁺. When the pulp pH value was 8, Ca²⁺, Fe³⁺, and Ba²⁺ concentration was 3×10^-4 mol/dm³, 3×10^-5 mol/dm³, and was 2×10^-4 mol/dm³ respectively, and OHA collector dosage was 5×10^-4 mol/dm³, while the flotation recoveries of monazite, calcite. And fluorite was above 95 %, 40.43 %, and below 45.32 %, and the recovery rate of barite and bastnaesite in the presence of Ca²⁺ and Fe³⁺ is below 54.32 % and 38.68 %, respectively and the effective separation of monazite and symbiotic ore was obtained. The zeta potential measurements showed that when only metal ions are added to monazite, monazite (IEP) shifts to the right, and the negative charge on the surface of monazite decreases, which may be due to the positive charge of metal ions adsorbed on the surface of monazite, increasing the positive charge on the surface of monazite. When Ca²⁺, Ba²⁺, Fe³⁺, and OHA were added to the monazite pulp, the IEP of monazite moved to the left, and the negative charge of monazite shifted to the positive direction as a whole, indicating that Ca²⁺, Ba²⁺, and Fe³⁺ were adsorbed on the surface of monazite and increase the positive charge on the surface of monazite. When the pH value was 7 ~ 10, the surface of monazite was the same as that before and after the action of the agent, and both were negatively charged. At this time, OHA can still adsorb on the calcite, that was, the chemical affinity overcomes the same electric repulsion and adsorbs, so that the potential of the monazite after the action is reduced, which is chemical adsorption. The FTIR showed that when the metal ions Ca²⁺, Ba²⁺, and Fe³⁺ are added to activate the surface of monazite, the peak area of the organic functional group-CH2−CH3 at 3000-2800 cm−1 was enhanced, and a new peak appears at 1382 cm⁻¹. The reason is that the N-O-H functional group of OHA collector was adsorbed on the surface of monazite, and a red shift (44 cm⁻¹) occurs, and a new peak appears at 1454 cm⁻¹. The reason is that the C-N functional group of OHA collector is adsorbed on the surface of monazite. The lone electron pair of the nitrogen atom of the amide group in the OHA forms chelates with Ca²⁺, Ba²⁺, and Fe³⁺ atoms, which further increases the adsorption amount of OHA. This showed that the adsorption of monazite surface by metal ions provides active sites for the adsorption of OHA collectors. These phenomena indicate that the adsorption capacity of OHA on the surface of monazite activated by Ca²⁺, Ba²⁺, and Fe³⁺ is enhanced and a stable five-membered ring metal chelate is formed. Combined with flotation results and zeta potential data, infrared spectroscopy analysis, the adsorption capacity of Ca²⁺, Ba²⁺, and Fe³⁺ activated monazite surface: Fe³⁺>Ca²⁺>Ba²⁺.