Abstract
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 study 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 sulphide-bearing facies. The study was conducted in four stages: (1) bacterial adaption using BIOX® bacteria; (2) biooxidation optimization with pH, temperature and Fe medium parameters tested; (3) flotation test work to produce a sulphide 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 shows 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.
Highlights
The mining industry produces approximately 14 billion tonnes of mine tailings per annum [1].These tailings are the remaining fine grained (1–600 μm) ground-up material left after the ore has been extracted from the mined material [2,3]
This study shows that adopting a geometallurgical approach to tailings characterisation can identify if mine waste has commodity potential and how best to extract it unlocking the potential for unconventional rehabilitation of AMD affected sites
The tailings mineralogy is dominated by hornblende and chlorite, with 7 wt % pyrite measured in the bulk composite indicating that, as a bacterial feed, this material is relatively lean as typically, sulphide concentrate materials used in bacterial oxidation experiments contain higher quantities, e.g., 70 wt % pyrite [32]
Summary
The mining industry produces approximately 14 billion tonnes of mine tailings per annum [1] These tailings are the remaining fine grained (1–600 μm) ground-up material left after the ore has been extracted from the mined material [2,3]. Tailings are typically discharged to purpose-built storage facilities and commonly are covered with either an engineered, vegetation or water cover [1,5,6,7]. As implied by their designation as waste, they have low economic value and can pose significant geoenvironmental risks if, for example, they contain sulphide minerals, e.g., pyrite or pyrrhotite [8]. Under surficial conditions, these sulphides are susceptible to oxidation producing acid and metalliferous drainage (AMD) characterised by metal-laden acid-sulphate waters)
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