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

The S 2 O 8 2− /Fe 2+ system can be used to depress PbS, where the activation of S 2 O 8 2− leads to the generation of SO 4 • − radicals that oxidize PbS. However, a high S 2 O 8 2− /Fe 2+ dosage is needed for PbS depression (0.15 mol/L). In this study, ultrasonication was employed to improve the depression ability of S 2 O 8 2− /Fe 2+ . The flotation and contact angle results implied that 120-kHz ultrasonication enhanced the depression ability of S 2 O 8 2− /Fe 2+ for PbS, resulting in a decrease in the S 2 O 8 2− /Fe 2+ 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 S 2 O 8 2− to generate SO 4 • − 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 S 2− on the PbS surface to SO 4 2− , such that the surface was covered with PbSO 4 and the hydrophobicity of PbS was lowered. However, ultrasonication did not considerably increase the oxidation state of the CuFeS 2 surface; thus, CuFeS 2 could still be floated and separated from PbS. This study provides a novel strategy for separating PbS–CuFeS 2 mixtures.