Interfacial phenomena affecting the adhesion of Thiobacillus ferrooxidans to sulphide mineral surface

Abstract

The electrokinetic and hydrophobic properties of the autotrophic bacteria Thiobacillus ferrooxidans as well as selected minerals have been studied by microelectrophoresis, contact angle and hexadecane/aqueous phase partition measurements. Adhesion measurements were conducted on sized fractions of quartz, pyrite, chalcopyrite and other copper sulphides in order to establish the relationships between cell surface properties and cell adhesion to specific mineral surfaces. It was found that the bacteria had an isoelectric point at pH 3.0 and that they were slightly hydrophobic, showing a water contact angle of 20–24 and extraction recoveries into hexadecane in the range 14–22 wt.% Adhesion mechanisms involved in the interaction between Thiobacillus ferrooxidans and mineral surfaces as a function of the electrokinetic and hydrophobic properties of bacteria and minerals are illustrated. Calculated free energies of bacterial adhesion to quartz, chalcopyrite and pyrite indicated that adhesion appears to occur at the secondary minimum according to the Derjaguin—Landau—Verwey—Overbeek theory.