Vanadium in slags from smelting of African Pb-Zn vanadate ores: Mineralogy, extractability and potential recovery

Abstract

Slags originating from the metallurgical processing of Pb-Zn vanadate ores at Berg Aukas (Namibia) and Kabwe (Zambia) contain interestingly high concentrations of V (3750–6140 mg/kg) and can be considered potential sources of this metal. We focused on the mineralogical determination of the major V-bearing phases in these slags using a combination of mineralogical methods (XRD, SEM/EDS, EPMA) and found that V is mainly bound in clinopyroxene (Berg Aukas) and glass/vanadates (Kabwe). The abiotic extraction tests, simulating a hydrometallurgical recovery via agitation leaching, were carried out in 0.5 mol/l sulfuric acid (25 °C and 70 °C, pulp density of 1%) to determine the release of V (and other metals: Pb, Zn) from these slags. The leaching of the metals attained a steady state after 24 h and was systematically higher for the high-temperature trials. There was an incomplete dissolution of V-bearing clinopyroxene from the Berg Aukas slags, as opposed to the much higher extractabilities of V (>80%) observed for the Kabwe slags. Compared to the relatively high Zn extractabilities (>72%), lower yields were observed for Pb due to massive formation of secondary Pb sulfate (anglesite) as confirmed by the PHREEQC-3 calculations and the mineralogical investigation of the slag residues. Due to the high expenses related to the mechanical sample treatment and chemical extraction and low prices of V and Zn, the recovery of these metals from the studied slags is currently non-economical. However, the Kabwe slags have a much higher potential for secondary metal recovery in the future, because they are relatively fine-grained and the extraction could potentially be carried out on the as-is materials without expensive comminution processes (crushing/milling).