Sulfidization mechanism in the flotation of cerussite: A heterogeneous solid-liquid reaction that yields PbCO3/PbS core-shell particles

Abstract

Sulfidizationfollowed byxanthateflotation is an extensively used method for recovering the lead oxide minerals. However, there is a debate about the sulfidization mechanism of cerussite. In this work, the sulfidization mechanism was investigated using optical microscopy (OM), scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), atomic force microscopy (AFM), X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The OM, SEM-EDS and AFM results indicated that many microspheres grew on the cerussite particle surfaces to form a high-density sulfidization product layer after sulfidization, which changed the color, optic character, electrical conductivity and surface morphology of cerussite particles. The XRD results for the sulfidized cerussite samples showed that the sulfidization product layer was too thin to be detected. By the selective solvent action of acetic acid, the sulfidization product was extractedfrom the sulfidized cerussite particles. The XRD pattern interpreted that the sulfidization product were galena (PbS) phase, which provided the strongest proof for the generation of PbS on the cerussite surfaces. Moreover, the crystallite size of PbS calculated by the Scherer formula was in nanoscale. The EPMA analysis showed that the oxygen element was localized in the interior section, whereas the sulphur element was occurred in the outer surfaces of the particle. The aforementioned results demonstrated that after cerussite sulfidization, the mineral particles have a lead carbonate (PbCO3) core and a lead sulfide (PbS) shell. These findings also demonstrated that the sulfidization reaction is a heterogeneous reaction of solid phase (cerussite particles) with an aqueous solution (sodium sulfide solution) in which the solid reaction product adheres to the cerussite surface. From another point of view, the sulfidization process is a crystallization process including the heterogeneous nucleation and growth of PbS.