Study on regulation mechanism and optimization of pulp properties in rare earth flotation with sodium silicate system

To address the engineering problem where the depressing performance of sodium silicate is attenuated with prolonged stirring time during rare earth flotation——leading to low concentrate grade——and to clarify the internal relationship among the action time of sodium silicate, slurry environment, and flotation indexes, the high-intensity magnetic concentrate of rare earth-bearing polymetallic ore is used as the experimental material in this study. The influence of stirring time following the addition of sodium silicate on rare earth flotation indexes is systematically investigated. The evolution mechanisms of ion concentration, pH value, and hydrogen bonding network of water molecules in the slurry are revealed via ICP-OES, pH value measurement, infrared spectroscopy, and Raman spectroscopy. The results indicate that the flotation concentrate yield is significantly increased with the extension of sodium silicate stirring time, while the concentrate grade decreases continuously, and the depression selectivity of sodium silicate is notably reduced. The dissolution of silicate and Fe-Al-bearing minerals is significantly promoted by sodium silicate in the slurry. As stirring time increases, the concentrations of SiO₂, Fe³⁺, and Al³⁺ in the slurry increase continuously, and the slurry pH value decreases gradually. The surface electrical properties of minerals can be altered, and the active sites for the interaction between minerals and collectors can be increased by Fe³⁺ and Al³⁺, which is the core reason for the increased concentrate yield, with the decrease of pH value also playing an auxiliary role. The increase in Fe³⁺ and Al³⁺ concentrations is attributed to the complexation between silicate and metal ions, rather than the effect of a high pH value environment. Fe³⁺ and Al³⁺ can be precipitated into hydroxides by the addition of alkaline regulators （e.g., NaOH and Na₂CO₃） to the slurry, and the concentrate grade is significantly improved under the premise of basically stable rare earth recovery. A better regulation effect is exhibited by NaOH than by Na₂CO₃ at the same dosage. It is confirmed by spectral analysis that the hydrogen bonding network of water molecules in the slurry filtrate is altered by the combination of sodium silicate and alkaline agents, the proportion of polymeric water is increased, and the proportion of strong hydrogen bonds is reduced, so that the depression effect on gangue minerals is enhanced. The time-dependent attenuation mechanism of sodium silicate is clarified in this study, and an optimized strategy for cooperative regulation with alkaline regulators is proposed. Theoretical support and engineering reference for the precise regulation and efficient separation of the rare earth flotation process are provided by this strategy.