Effects of ore mineralogy on the microbial leaching of low grade complex sulphide ores

The effect of ore mineralogy on the microbial leaching of low grade complex sulphide ores was investigated by utilizing mineralogical data on the variations in mineral and phase distribution within particle sizes of − 53, 53, 75 and 106 μm of a Nigerian ore consisting of siderite, sphalerite, galena and quartz, with traces of pyrite and chalcopyrite. Bioleaching was conducted using mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans in mechanically stirred glass reactors. The highest bioleaching recoveries were obtained at a particle size of 75 μm, while particle sizes of 106 μm gave the least recoveries. Mineral phases and morphologies of the bulk ore and the leached residues respectfully examined with XRD and SEM analysis showed differences both in phase and morphological changes, with the 75 μm having the highest transformation and attack. Higher silica contents which reduced acidity, iron mobility and oxidation led to lower recoveries at particle sizes of 53 and − 53 μm.