At the Old Tailings Dam (OTD), Savage River, western Tasmania, 38 Mt of pyritic tailings were deposited (1967 to 1982) and have since been generating acid and metalliferous drainage (AMD). Mineral chemistry analysis confirmed high concentrations of refractory cobalt in pyrite (up to 3 wt %). This research sought to determine, through a series of bench scale tests, if Co could be liberated using biohydrometallurgical techniques. Four bulk tailings samples were collected across the OTD, from up to 1.5 m depth, targeting three sulfide-bearing facies. The study was conducted in four stages: (1) bacterial adaption using BIOX® bacteria; (2) biooxidation optimisation with pH, temperature and Fe medium parameters tested; (3) flotation test work to produce a sulfide concentrate followed by biooxidation; and (4) Fe and Co precipitation tests. The BIOX® culture adapted to the bulk composite (containing 7 wt % pyrite) in ~10 days, with biooxidation occurring most efficiently at pH 1.5–1.6 and 40 °C whilst the Fe medium concentration was identified as a less-controlling parameter. Flotation produced a 71% pyrite concentrate with total oxidation occurring after 14 days of biooxidation with 99% of Co leached. At pH 3, Co was effectively separated from Fe; however, Ni and Cu were also present in the pregnant liquor solution and therefore required refining before production of cobalt hydroxide, the intermediate saleable product.

This study showed that adopting a geometallurgical approach to tailings characterisation can identify if mine waste has commodity potential and how best to extract it, therefore unlocking the potential for unconventional rehabilitation of AMD-affected sites. The results have assisted the Tasmanian Government and Grange Resources in deciding on the future management of this site.

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 and the lack of success demonstrated by previous pilot studies, these strategies have not been implemented. A detailed mineral chemistry study indicated elevated cobalt in pyrite (up to 3 wt. %), however, as this is refractory, recovery via biohydrometallurgical processing was tested in this project, commissioned by the Tasmanian State Government and Grange Resources (through the Savage River Rehabilitation Program).

Bulk tailings samples were collected across the OTD targeting three sulfide-bearing facies. 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. This research focussed on producing a sulfide concentrate and optimising the recommended procedure for undertaking BIOX® experiments, with pH, temperature and iron concentration in the nutrient medium varied. Cobalt recovery was high (> 80 %) suggesting reprocessing of these tailings might be a viable option for managing this historic waste as part of an integrated tailings management strategy.