Using Quantitative Mineralogy for Tailoring the Metal Extraction and Potential Recovery from Copper Slags

Abstract

Waste metallurgical slags have shown the potential to serve as a source of critical raw materials. In this study, we examined the extraction of Cu and Zn from a fine-grained copper slag from the Tsumeb smelter (Namibia). A combination of chemical analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and automated mineralogy (autoSEM) was used to determine its elemental and mineralogical composition. Silicate glass was determined as being the most abundant phase (over 90 area %) and the dominant host phase for the target elements (58-70% of the total Cu, over 90% of the total Zn). Based on these results, the reprocessing of the slag by sulfide flotation and subsequent pyrometallurgical treatment would be inefficient. For the extraction of Cu and Zn, a hydrometallurgical approach using acid leaching was proposed. Extraction tests to simulate agitation leaching were carried out by leaching the original fine-grained material in H<inf>2</inf>SO<inf>4</inf> (20, 50, and 100 g/l) at liquid/solid (L/S) ratios of 5, 10, and 20 kg/l and ambient temperature for 1 and 6 h. The extraction efficiencies increased with the increasing acid concentrations, L/S ratios, and leaching time, reaching up to 70% for Cu and 94% for Zn. High extraction efficiencies of As were reached (up to 91%), possibly lowering the environmental hazards posed by the original material.