Growth of covellite crystal onto azurite surface during sulfurization and its response to flotation behavior

In this work, the growth of copper sulfide crystal onto azurite surfaces during sulfurization and its response to flotation are investigated. Filed emission scanning electron microscopy-energy dispersive X-ray spectroscopy (FESEM) and X-ray diffraction (XRD) studies confirmed that the sulfurization of azurite is not limited to the mineral surface, but rather penetrates into the bulk to form covellite crystal (syn-CuS), creating favorable conditions for the stable adsorption of xanthate and greatly promoting the azurite flotation. Additionally, as demonstrated by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS) analyses, a redox reaction occurred during this process, and Cu(II) onto the mineral surface was reduced to Cu(I). Correspondingly, reduced S2- was oxidized to (S-2)(2-), (S-n)(2-), and even to deeper oxidation state S-0, (SxOy)(n-) and SO42-. Excess sodium sulfide strengthens copper sulfide to form onto the azurite surface, and provides enough raw material for crystal copper sulfide to grow, resulting in the formation of "flake-like" covellite with a better crystallinity. However, the floatability of azurite decreased dramatically under this condition, because the generated massive colloidal copper sulfide in flotation pulp deteriorates the flotation environment, resulting in a decreased effective adsorption of collector onto azurite surfaces. (C) 2021 Published by Elsevier B.V. on behalf of China University of Mining & Technology.