Abstract
Hydrometallurgical facilities produce large quantities of waste residues in the form of sludges which contain concentrations of metals as well as sulfur bearing minerals in crystalline and amorphous form. 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, and residual sulfur and sulfides in the form of FeS₂, 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 ore metals are associated with different minerals in each of the residues as determined through sequential extractions. The effect of aging and mixing of waste on solid residue and residue liquor is evaluated through the mineralogical and elemental analysis of residues.  Finally, the composition and microstructure of mini plant residue is compared to that of the demonstration plant residue.