Synergistic effect of ultrasonication on the depression of galena via the Fe(II)-activated persulfate process

The S₂O₈²⁻/Fe²⁺ system can be used to depress PbS, where the activation of S₂O₈²⁻ leads to the generation of SO₄•⁻ radicals that oxidize PbS. However, a high S₂O₈²⁻/Fe²⁺ dosage is needed for PbS depression (0.15 mol/L). In this study, ultrasonication was employed to improve the depression ability of S₂O₈²⁻/Fe²⁺. The flotation and contact angle results implied that 120-kHz ultrasonication enhanced the depression ability of S₂O₈²⁻/Fe²⁺ for PbS, resulting in a decrease in the S₂O₈²⁻/Fe²⁺ dosage. Ultrasonication induced hot spots (5000 K) in the PbS slurry and on the PbS surface. These hot spots may cause the thermal activation of S₂O₈²⁻ to generate SO₄•⁻ radicals, facilitating the oxidation of PbS. Thus, the ultrasound-assisted treatment increased the oxidation level of PbS. The XPS study revealed that ultrasonication favored the oxidation of S²⁻ on the PbS surface to SO₄²⁻, such that the surface was covered with PbSO₄ and the hydrophobicity of PbS was lowered. However, ultrasonication did not considerably increase the oxidation state of the CuFeS₂ surface; thus, CuFeS₂ could still be floated and separated from PbS. This study provides a novel strategy for separating PbS–CuFeS₂ mixtures.