Geochemistry and Mineralogy of Cobalt in Mine Wastes: Examples from Cobalt, Canada and Cornwall, England

Gabriel Ziwa ^1,2,3 Richard Crane ^2,3 Karen A. Hudson-Edwards ^2,3*

• ¹ Copperbelt University, Kitwe, Copperbelt, Zambia
• ² Environment & Sustainability Institute, University of Exeter, Penryn, England, United Kingdom
• ³ Camborne School of Mines, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, England, United Kingdom

Mine wastes can pose environmental and human health risks, especially when they contain high concentrations of potentially toxic metal(loid)s. In this study, the geochemistry and mineralogy of Co in mine wastes from Cobalt (Canada) and Cornwall (UK) were characterised to assess potential Co and other metal(loid) mobility in the aquatic environment. Cobalt concentrations in Nipissing high-and low-grade tailings at Cobalt were high (up to 5630 mg kg -1 and 1230 mg kg -1 , respectively), and were several orders of magnitude higher than those at Poldice, Wheal Unity, and Dolcoath in Cornwall (average 40 mg kg -1 , 76 mg kg -1 , and 59 mg kg -1 , respectively). Community Bureau of Reference (BCR)-sequential extraction analysis suggested that Co was equally mobile within the samples from Cobalt and Cornwall, with averages of 46% extracted in the exchangeable fraction. Erythrite was the most important secondary Co-bearing mineral that occurred widely in the Nipissing tailings. Other Cobearing secondary minerals included arseniosiderite, scorodite, and Fe oxyhydroxides. Primary Cobearing minerals identified included cobaltite and safflorite-skutterudite, and Co was also taken up in primary arsenopyrite, loellingite, pyrite and chalcopyrite. At the sites in Cornwall, however, Cobearing primary and secondary minerals were not identified. Instead, Co was observed as a trace component in primary arsenopyrite, pyrite, and chalcopyrite and in secondary scorodite and Fe-Mn oxyhydroxides. Despite these mineralogical and other geological and processing differences, Co showed consistently high potential for mobilization from the wastes. Further research is required to determine if Co shows similar behaviour in mine wastes globally. Commented [DGZ1]: LeBoutillier, N.G.