Extraction of cobalt from historic sulphide tailings using bioleaching

Mineralogical and geochemical characterisation of sulphide minerals in historic tailings can assist in determining whether there are economic and environmental benefits of reprocessing such materials using modern metallurgical practices. At the Old Tailings Dam (OTD), Savage River, Western Tasmania, 38 million tonnes of pyritic tailings were deposited (1967 to 1982), and have since been generating acid and metalliferous drainage (AMD). Long term management options considered for this site have included the establishment of either a water, hard engineered or vegetation cover. However, due to geotechnical challenges posed and the lack of success demonstrated by previous pilot studies, these strategies have not been implemented. A detailed mineral chemistry indicated elevated cobalt in pyrite (up to 3 wt. %), however, as this is refractory, recovery via biohydrometallurgical processing was tested.

Bulk tailings samples (n= 4) were collected across the OTD from up to between 0.5 to 1.5 m depth specifically targeting three sulphide-bearing facies (C - E), across four physical zones (1 to 4; defined by hydrological regime and grain size). A bulk composite of these materials was subjected to bacterial oxidation using BIOX® bacteria to determine if Co could effectively be leached under standard operating conditions. Our adaption test work shows that the BIOX® bacteria were well adapted to the lean OTD feed material after 10 days with 93% cobalt recovery. This indicates that reprocessing of these deleterious materials may be a viable option for managing this historic site as part of a larger tailings desulphurisation management strategy.