Assessment of minerals and iron-bearing phases present in hydrometallurgical residues from a nickel sulfide concentrate and availability of residue associated metals

Hydrometallurgical facilities refining nickel sulfide ores produce waste residues in the form of sludges which contain concentrations of metals as well as iron and sulfur-bearing minerals and phases. The geochemical and mineralogical character of hydrometallurgical residues is important for the management of this type of industrial waste. Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) analysis indicate that the minerals produced in the process are principally gypsum and the iron oxides, hematite and magnetite, iron hydroxides and residual sulfur and sulfides in the form of FeS, chalcopyrite, pyrrhotite and pentlandite. The iron oxide particles in the leach residue exhibit an atypical framboidal structure that is relevant to its metal leaching properties. The mineralogy and microstructure of mini plant residue is compared to that of the demonstration plant residue through the SEM and XRD. Sequential extractions are used to determine the association between different phases/minerals and select metals in each residue.