Recovery of ZnO from lead-zinc flotation tailings by hydrometallurgical processes: XRD, SEM, and AFM studies

Abstract

The hydrometallurgical route of zinc hydroxide and synthesis of nanocrystalline ZnO is a particularly attractive method to recover oxidized lead and zinc from lead-zinc flotation tailings. In Turkey, lead-zinc complex/mixed ores along with high iron content are not suitable for conventional mineral processing methods and need hydrometallurgical treatments. Therefore, the control of iron during zinc processes is really important. In this study, hydrometallurgical process route for zinc recovery from Pb-Zn flotation tailings was investigated by considering the effects of H2SO4 concentration, leaching and roasting temperatures on the zinc dissolution considering the Eh-pH variations. The iron and zinc products were also individually examined by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) images in order to compare before and after leaching, precipitation and roasting steps. 83.1% Zn and 91.6% Cd leaching efficiencies were obtained from Pb-Zn flotation tailing particles with the size range of 50-110 nm from AFM image cross-sections, while lead and iron were not dissolved. Elemental sulfur started to form and produce a layer around the particles or a partially agglomerated particle in the size of 170 nm during the sulphuric acid leaching. However, majority of the particles was determined to be less than 20 microns, and AFM images showed that the size reduction between the leached and unleached particles was over 50%. Selective precipitations of iron and zinc in the form of hydroxide were performed in high recovery efficiencies of 90.1% and 99%, respectively. After the heat treatment, nanocrystalline zincite clusters of 96.6% purity were produced in the ZnO mineral form and nearly 13 nm in size. Zinc can be successfully recovered and a flotation tailings ore can be a good candidate for the production of high technology needs of nanocrystalline ZnO nanoparticles.