Indirect oxidative bioleaching of a polymetallic black schist sulfide ore

- Metals were extracted from a polymetallic sulfide by indirect bioleaching.
- An acidic ferric iron lixiviant was generated using a laboratory-scale bioreactor.
- Microorganisms present in lixiviant solutions on mineral leachates were identified.

Biomining of base and precious metal-containing sulfidic ores and concentrates is an important global biotechnology. Currently, mineral bio-processing is carried out in dumps, heaps and stirred tanks located on the land surface. An alternative approach, “deep in situ biomining”, would solubilise target metals from fractured ore bodies buried deep (>1 km) underground, using a microbially-generated acidic, ferric iron-rich lixiviant. Pregnant leach solutions (PLS) generated are pumped to the land surface where metals are extracted and recovered, ferric iron regenerated in a bioreactor and the oxidised lixiviant re-injected underground. To examine the feasibility of using an indirect bioleaching approach to extract metals from an ore body, a laboratory test was carried out using a polymetallic sulfidic black schist ore (from Talvivaara, Finland) in a non-aerated column reactor, maintained at 30 °C at atmospheric pressure. Following an initial acid leaching phase (using 100 mM sulfuric acid) the ore was subjected to ferric iron-catalyzed oxidative dissolution using a lixiviant generated in a laboratory-scale ferric iron-generating bioreactor (FIGB). During the 16 week time course of the experiment, 93% of manganese, 88% of cobalt, 79% of nickel, 75% of iron, 75% of zinc and 55% of copper present in the ore was extracted. The planktonic microbial populations in the FIGB and those in the PLS were similar, and dominated by Leptospirillum ferriphilum, iron-oxidising Acidithiobacillus spp. and the archaeon Ferroplasma acidophilum.