Investigation of the attachment of Thiobacillus ferrooxidans to mineral sulfides using scanning electron microscopy analysis

Thiobacillus ferrooxidans is a facultatively aerobic bacteria which catalys es the oxidation of inorganic substrates; in particular mineral sulfides. The mechanism(s) for the oxidation of mineral sulfides is not completely un derstood. The direct oxidation mechanism involves the attachment of bacteri a to the mineral surface. Scanning Electron Microscopy (SEM) was used to in vestigate the surface erosion of three mineral sulfide samples by the attac hment of Thiobacillus ferrooxidans (DSM 583). The mineral samples; Pyrite, a chalcopyrite concentrate (termed Chalconc) and a sample containing arseno pyrite and loellingite (FeAs2) (termed Arsenoconc) were all mounted in resi n blocks and following the addition of T.ferrooxidans the particles exhibit ed varying degrees of surface erosion. Erosion patterns on the surface of m inerals from the chalconc and arsenoconc samples appeared to follow the cry stallographic structure of the mineral species. However, no apparent erosio n patterns were observed on the pyrite sample. In addition, elemental sulfu r was found deposited on the surfaces of each mineral sample. Chalopyrite i n the Chalconc sample exhibited preferential erosion compared with the pyri te and indicated the electrochemical nobility of pyrite. In addition, durin g the oxidation of the Arsenoconc sample, loellingite was seen to be have b een significantly more oxidised than the arsenopyrite. The observations from the SEM suggested a greater involvement of the indire ct oxidation mechanism which utilises the oxidant ferric iron than direct b acterial attachment. (C) 2000 Elsevier Science Ltd. All rights reserved.