Correlation of surface oxidation with xanthate adsorption and pyrite flotation

Various studies have emphasized the importance of surface oxidation of sulfide minerals with regard to xanthate adsorption and their flotation response. However, the correlation between pyrite surface oxidation, xanthate adsorption and its flotation response has not been clearly established. The complexity lies in various intermediate sulfur oxidation products in different solution conditions. Thus, investigation of sulfur oxidation behavior is the key to understand pyrite oxidation. Ion chromatography (IC) and high performance liquid chromatography (HPLC) results showed an increase in the total amounts of occurring sulfur species with increasing slurry pH. Meanwhile, the ratio of S⁰/sulfur oxyanions was to become lower; X-ray Photoelectron Spectroscopy (XPS) identified the oxidized pyrite surface was rich in SO₄²⁻ and FeOOH. Both the contact angle results and single mineral flotation data indicated that the more pyrite surface oxidized, the lower hydrophobicity and floatability were. Time-of-flight secondary ion mass spectroscopy (Tof-SIMS) was adopted to analyse xanthate adsorption on the surface of pyrite under conditions of either sufficient oxidation or on freshly polished surface which is assumed little oxidation. A significantly lower intensities of C₄H₉O and C₄H₉OCSS was found on the intensely oxidized pyrite surface, indicating xanthate adsorption had strong selectivity on FeS₂ rather than FeOOH. The experimental results were further confirmed by theoretical calculation. The self-consistent charge density functional tight binding (SCC-DFTB) calculations indicated that the distances between the xanthate S atoms and surface Fe atoms of FeOOH were larger than the atomic radius of SFe. Essentially, the different electron configurations of their Fe atoms led to the selective adsorption of xanthate on FeOOH and FeS₂ surfaces in terms of the coordination chemistry theory. This work provides valuable implications for understanding the correlation of surface oxidation, xanthate adsorption and its floatation behavior to mediate pyrite flotation.