Surface Pretreatment with Luteolin to Achieve the Effective Flotation Separation of Sphalerite from Pyrite in a CuSO4-Xanthate System

The flotation separation of sphalerite (ZnS) and pyrite (FeS2) in a copper sulfate (CuSO4)–butyl xanthate (BX) system is challenging because the indiscriminate activation of Cu2+ gives them similar floatability. To this end, the suitability of a novel depressant, luteolin (LUT), on the flotation separation of ZnS from FeS2 in this system was studied. Micro-flotation tests and contact angle measurement results showed that ZnS could be selectively separated from FeS2 using LUT as a depressant. At pH 7.0 ± 0.1, a flotation concentrate with a recovery of 93.90% ZnS and 2.84% FeS2 was obtained after adding LUT in artificial mixed minerals tests. Adsorption differences and characteristics results showed that the affinity of LUT to FeS2 was considerably higher than that of ZnS, which effectively hindered the subsequent adsorption of xanthate on FeS2 but had a relatively weak effect on ZnS. Thus, a large floatability difference between ZnS and FeS2 was achieved. Further analyses revealed that the adsorption behavior of LUT on FeS2 occurred mainly through the interaction between 4–5 sites and Fe(II) at the solid/liquid interface. These findings shed light for the first time on the suitability of LUT for the successful flotation separation of ZnS from FeS2, which has important guiding significance for the development of a lime-free depressant of FeS2.