Modeling interactions between ethyl xanthate and Cu/Fe ions using DFT/B3LYP approach

• Different valences and spin states significantly influence the interaction of copper and iron ions with ethyl xanthate.
• High-spin Fe–EX complex with spin-V is the most stable.
• Stronger interaction exists between copper (II) and xanthate ion compared with copper (I).

The geometric and electronic structure properties of complexes of copper (Cu) and iron (Fe) ions with various valences and spin states with ethyl xanthate (EX) were calculated by the density functional theory (DFT/B3LYP). Analyses on the geometric parameters, interaction energies, natural bond orbital (NBO), and frontier molecular orbital reveal that there are two main structures in the metal–ethyl xanthate complexes, whose structure of metal atom with two sulfur atoms was more stable. Different spin status significantly influences the interaction of Fe ions with EX as well as the geometric structure of its complex. The most spin state for Fe2 + was spin-V, while it was spin-IV for Fe3 +. The binding energy of Fe3 + and EX is larger than that of Fe2 + and EX. Similarly, the binding energy of Cu2 + and EX is larger than that of Cu+ and EX. The covalent interaction between EX ion and Cu+ is relatively weak, whereas the ionic bond interaction is relatively strong. The solution effect hasn't been taken into account, but important information related to multi-spin states has been gained. The theoretical calculations in the present work may help explain the flotation mechanism and flotability difference of iron-bearing and copper-bearing minerals.