Non-Hydrolyzable Alkali Metal Electrolytes as Novel Coagulants for Enhanced Flotation Recovery of Fine Smithsonite

Efficient froth flotation of fine smithsonite from slime-containing zinc oxide ores remains challenging due to low particle–bubble collision efficiency and strong surface hydration. Conventional agglomeration methods suffer from high reagent costs, non-selective agglomeration, or reduced surface hydrophobicity. Herein, non-hydrolyzable alkali metal salts, exemplified by NaCl, were introduced as novel and efficient coagulants to enhance the flotation of fine smithsonite, and the underlying mechanisms were systematically elucidated. In the sodium oleate flotation system, alkali metal ions promoted the formation and agglomeration of oleate micelles. Meanwhile, they significantly facilitated collector adsorption onto the smithsonite surface and improved the hydrophobicity of the mineral particles. At high ionic strengths, compression of the electrical double layer reduced the Zeta potential and interparticle electrostatic repulsion. These synergistic mechanisms promoted the growth and stability of hydrophobic aggregates, increasing their collision and attachment efficiency with bubbles. By employing non-hydrolyzable salts, the loss of surface hydrophobicity typically induced by conventional hydrolyzable coagulants was avoided. Validation tests on an industrial zinc oxide ore confirmed the feasibility of this approach, offering a promising pathway to mitigate zinc resource losses and associated environmental hazards.