Fig. 5: Proposed mechanism for acid-free and selective leaching.
From: An acid-free process to prepare battery grade nickel and cobalt sulfates from complex resources
a N2 adsorption-desorption isotherms of the leaching residue. b High resolution transmission electron microscope (HRTEM) image of the leaching residue of non-activated Ni sulfide concentrate (NSC). Energy dispersive spectroscopy (EDS) line scanning and surface scanning of the cross-sections of the leaching residues of (c, e) nonactivated and (d, f) 240 min activated NSC. g Schematic diagram of the proposed acid-free and selective leaching mechanism. The non-activated NSC surface formed a dense hematite layer hindering oxygen diffusion, whereas 240 min activated NSC developed porous amorphous iron oxides. Oxygen permeated through these pores to access undercoordinated sulfur sites within particles, enabling in situ acid generation via sulfur oxidation. Source data are provided as a Source Data file.
