Study on the Selective Inhibition of FeSO4-NaH2PO4 in Sphalerite–Pyrite Flotation Separation

Sphalerite–pyrite separation has always been one of the key issues of concern in the field of mineral flotation. To achieve selective flotation separation of sphalerite and pyrite, a novel flotation system, FeSO4+NaH2PO4-CuSO4-SIBX, was adopted. This study validated the novel separation system using mineral flotation experiments. The changes in the hydrophobicity and surface charge of the minerals were evaluated using experiments such as contact angle, zeta potential, and agglomeration. Finally, the mechanism of sphalerite–pyrite separation was revealed through XPS and solution chemistry analysis. The results showed that sphalerite and pyrite were effectively separated by flotation. In the novel flotation system, the synergistic effect of FeSO4 and NaH2PO4 shifted the surface potential of pyrite positively, and subsequent treatment with CuSO4 and SIBX did not significantly alter its hydrophobicity. However, sphalerite, after treatment with FeSO4+NaH2PO4-CuSO4-SIBX, exhibited significantly enhanced hydrophobicity and marked mineral particle agglomeration. Further research revealed that within the pH range of 6.0–8.0, hydrophilic components formed by Fe2+ and H2PO4− (e.g., Fe(H2PO4)+ and Fe3(PO4)2·8H2O) selectively adsorbed onto the pyrite surface, enhancing its hydrophilicity. Meanwhile, sphalerite was activated by the substitution reaction of Cu2+ with ZnS, forming a hydrophobic layer on its surface with SIBX in the slurry.