Surface modification of serpentine using phosphate and its implication for the selective flotation separation of pyrite from serpentine

During the flotation of sulfide minerals in the presence of serpentine, fine serpentine particles tend to coat the surfaces of sulfide minerals, severely deteriorating their flotation performance. To address this issue, sodium phosphate was used as a surface modifier for serpentine in this study to eliminate its detrimental effect on the flotation of sulfide minerals. Micro-flotation results indicated that under flotation conditions with pH = 8, the presence of natural serpentine in the slurry significantly reduced the recovery of pyrite. However, surface modification of serpentine with phosphate effectively eliminated its adverse effect, allowing the pyrite recovery in the mixed mineral system to nearly return to the level observed for pure pyrite. The underlying mechanism of this modification effect was elucidated through theoretical simulations and characterization techniques, revealing that phosphate readily interacted with surface-exposed Mg 2+ sites on serpentine, leading to a change of the surface charge from positive to negative. As a result, the serpentine and pyrite particles in the mixed slurry acquired similar surface charges, promoting a well-dispersed system and significantly enhancing the pyrite flotation recovery. This study highlights the potential use of phosphate for reducing the magnesium content in sulfide concentrates and provides a feasible strategy for the flotation separation of sulfide minerals from serpentine.