Facet-dependent adsorption of dissolved metal ions on serpentine: new insights for hetero-aggregation between serpentine and pyrite

Serpentine is easily activated by metal ions and floats upward into the concentrate in the flotation separation of copper-nickel sulfide ores, resulting in increased MgO content, which seriously affects the downstream smelting process. However, the specific adsorption mechanisms of metal ions on serpentine surfaces remain unclear, resulting in a challenge in the modulation of serpentine flotation behavior. In this work, the effect of inevitable divalent metal ions (e.g., Mg(Ⅱ), Ca(Ⅱ), and Cu(Ⅱ)) on serpentine floatability was systematically investigated. Flotation results showed that serpentine without treatment with divalent metal ions has weak floatability, whereas the introduction of divalent metal ions increased serpentine flotation recovery by ∼10 % after Ca or Mg treatment and ∼15 % after Cu species treatment. Spectroscopic and surface topography imaging analysis revealed imaging revealed that Mg(Ⅱ) exhibited weak adsorption, primarily in the outer sphere, on the Mg-OH plane; whereas Ca(Ⅱ) tends to adsorb onto the edge planes. Notably, Cu(Ⅱ) demonstrated the strongest adsorption ability, binding with O − residue on the Mg-OH plane and edge planes via Cu–O bonds. Density functional theory calculations also revealed an increasing order of collector adsorption affinity: Cu(Ⅱ) > Ca(Ⅱ) > Mg(Ⅱ). Therefore, serpentine after Cu treatment can provide more sites for the adsorption of collectors, enhancing its floatability of serpentine. This study provides molecular interaction mechanisms of inevitable ion adsorptions on serpentine surfaces, which can offer theoretical guidance for chemical additives design and surface reaction control in minerals separation processes.