Bioleaching cobalt from sulphide ores | COG3 Consortium

Recently, members of the Acidophile Research Team at Bangor University carried out some bioleaching experiments which aimed to leach cobalt from the Captain sulfide ore (from New Brunswick, Canada). Sarah Smith, a geomicrobiologist at Bangor University and one of the collaborators in the COG3 project reports.

a) Mixed bacterial cultures used to inoculate the bioreactor experiments. b) A bioreactor before the addition of the culture and the ore. c) Adding the culture to the bioreactor experiment. d) The bioreactor at the end of the bioleaching experiment carried out at 45°C.”

The aim was to compare the bioleaching rates of metals (primarily cobalt) from the ore at two different temperatures. To do this, two different mixed cultures were grown up (one containing bacteria that are happy at about 30°C, and another with bugs that prefer slightly higher temperatures). The cultures were then added to the bioreactors, along with the ore, and the bugs were left to work their magic!
The bioreactor control systems maintained the required conditions throughout the experiment, keeping the pH and temperature stable, and making sure that the experiments were stirred at a constant speed.

Following bioleaching, the ore material changed colour from dark grey of unreacted material to yellow-green. This change of colour is a quick visual indication for oxidation of pyrite, the mineral host of cobalt in the ore sample, which hopefully released the cobalt into solution.

bioleached ore
Change in colour of the ore material following bioleaching experiment.

To check how much cobalt had been leached during the experiments (which lasted for about 30 days), we analysed the leach solutions using a technique of atomic absorption spectroscopy (AAS). We also dried the residue, which will be analysed in the future to check the percentage of cobalt and other metals of interest that are still left in the ore.

Measuring metal concentrations
Sarah Smith measuring metal concentrations in the leach solutions using AAS

The next step is to characterize the bacterial communities that remained at the end of the experiments, to see which bacteria were largely responsible for leaching the metals from this particular ore.