Early stage adsorption behaviour of Acidithiobacillus ferrooxidans on minerals I: An experimental approach

Bacterial adsorption is a prerequisite to bioleaching, but a detailed understanding of the adsorption behavior of bacteria to mineral substrates is still lacking. The adsorption behavior of Acidithiobacillus ferrooxidans (A. ferrooxidans) to high purity model minerals chalcopyrite, pyrite, bornite, mixed ore, quartz and poly-L-Lysine-modified quartz, was investigated. The effect of solution pH and medium type on the adsorption behavior of A. ferrooxidans to minerals was also investigated. The initial bacterial adsorption rate at mineral surfaces and the equilibrium adsorption capacity were quantified to elucidate the dominant factors dictating bacteria-mineral adsorption affinity and adsorption capacity, respectively. Our results show that the initial adsorption rate of A. ferrooxidans is enhanced for hydrophilic substrates, suggesting that the bacteria-mineral affinity is dictated by the wetting behavior of the substrates. Compelling experimental evidence suggests that electrostatic interaction does not control the affinity of A. ferrooxidans to minerals. The maximum equilibrium adsorption capacity is enhanced in the growth environment most suitable for A. ferrooxidans and in the presence of sulfide minerals. We propose that the number of accessible binding sites is dictated by the chemosensory system of A. ferrooxidans which regulates the chemotaxis response to initiate the bacteria-mineral contact and extracellular polymeric substance production that mediates the attachment.