Résumé - Abstract
Mine tailings represent a promising secondary source of strategic and critical metals (SCM) like Co and Ni as they contain some amounts of valuable metals and are already excavated and finely ground. The recovery of Co and Ni from mine tailings might be of interest to allow a stable and secure supply by diversifying sources (while supporting the development of a circular economy through the recycling of tailings (economical benefit). Increasing of demands and monopolies of foreign countries of world production, encouraged countries to find economically reliable sources which contains those metals. In addition, the recovery of SCM in mine tailings would limit their impact on the environment during long-term storage by reducing the metal and metalloid loads inside (environmental benefit). The former Cobalt Mining Camp in Ontario, Canada appears to be a promising location for the recovery of Co and Ni still present in mine tailings. Indeed, several old mine sites around Cobalt City, were mined for Ag at the beginning of the 20th century, generating several million tons of mine waste. In this area, mine waste contain interesting Co and Ni contents (up to 3.5 wt% Co and 2.2 wt% Ni) for valorization, in addition to present some environmental issues related to the As contamination of nearby rivers and lakes. Hydrometallurgical reprocessing of these tailings, based on the use of chemical reagents to solubilize the elements of interest, might be promising to recover SCM. Indeed, preliminary leaching tests were conduced on three different mine tailings (sites A, B and C) from Cobalt Mining Camp to solubilize Co and Ni. More than 85% of both Co and Ni were solubilized from tailings from site A after only 30 min using H2SO4 (0.25 N) at room temperature. Lower efficiencies (36-62%) were observed for sites B and C, which can be partially explained by the higher amounts of acid-consuming minerals present in the gangue.
The aim of this research project is to compare the performance of two pre-treatment routes to pre-concentrate Co- and Ni-bearing minerals from these three different mine tailings prior to chemical leaching to reduce operating costs related to the use of reagents. Pre-concentration processes pathways include : (i) physico-chemical enrichment processes (gravity and/or magnetic separation, flotation) and (ii) the use of hyperaccumulating plants (agromining). A metallurgical process including mineralurgical separation to pre-concentrate minerals of interest combined with a chemical leaching to extract metals of interest (Co and Ni) present in the preconcentrated mine waste will be developed and optimized. The performances of an agromine system, which consist of using hyperaccumulating species to extract Co and Ni from tailings, followed by their recovery from incineration ash of aerial parts of plants by chemical leaching will be evaluated. Then, the geochemical behaviour of new solid and liquid releases generated by the different processes will be evaluated. A comparative study of the efficiency of the two pathways (metallurgical and agromine) will be done to determine the most suitable reprocessing process pathway for the recovery of Co and Ni in mine tailings.