Bacterial pyrite oxidation III. Adsorption of Thiobacillus ferrooxidans cells on solid surfaces and its effect on iron release from pyrite.

Abstract

The cells of 'Thiobacillus ferrooxidans were rapidly adsorbed on the solid surfaces of an agitated flask containing 1 % pulp density of pyrite particles. More than ca. 99 % of the inoculated cells were adsorbed. However, considerably fewer cells were adsorbed on pyrite particles than on the glass wall of the flask. Scanning electron microscope observation revealed that T. ferrooxidans cells were adsorbed aggregatively on restricted areas of the pyrite particles. The surfaces of the pyrite particles were characteristically eroded to show etched polyhedral pits, but without prominent cell adsorption of the extensively eroded surfaces during markedly enhanced leaching. When T. ferrooxidans cells were adsorbed on the solid surfaces, the iron-oxidizing activity of the bacteria was strongly inhibited, resulting in a failure to enhance pyrite oxidation. Adsorbed cells did not proliferate on the solid surfaces. When the adsorbed cells were released into an aqueous phase by the addition of the surface active agent Tween 20, the bacterial iron-oxidizing activity inhibited by adsorption was recovered and, as a result, pyrite oxidation was markedly promoted. Significant enhancement of pyrite oxidation by T, ferrooxidans was ascribed to the development and iron-oxidizing activity of the freely dispersed cells in an aqueous phase. The function of the surface active agent is to prevent tenacious adsorption of the bacterial cells to solid surfaces and organic substances examined, such as protein, nucleic acid, yeast extract, peptone, and cell free extracts, operate in the same way as the surface active agent. The enhancement of the bacterial pyrite oxidation by the intact cells of Thiobacillus thiooxidans is thought to be attributable to the organic substances excreted from T. thiooxidans cells and/or to the exchange adsorption of cells of both thiobacilli. The present results indicate that bacterial concentration 63

Rate of Pyrite Bioleaching by Thiobacillus ferrooxidans : Results of an Interlaboratory Comparison

“…However, rates of pyrite oxidation by T. ferrooxidans reported in the literature are difficult to compare, making difficult the evaluation of different bacterial strains and leaching processes. In some recent reports, rates of pyrite bioleaching by T. ferrooxidans range from 2.5 to 30 mg/liter (4,5,6,11,12,18,19). This variability in leaching rates might be due to physiological differences among strains of T. ferrooxidans, but it could also be due to variables associated with conducting and measuring bioleaching rates.…”

Rate Equations and Kinetic Parameters of the Reactions Involved in Pyrite Oxidation by Thiobacillus ferrooxidans

“…T. ferrooxidans and T. thiooxidans cells are known to adsorb on solid surfaces even when they are killed by heat (19). The heat-killed T. thiooxidans cells virtually stopped the Fe2+ release from pyrite ( Fig.…”

Morphological, physiological, and chemotaxonomical characteristics of iron- and sulfur-oxidizing bacteria isolated from acid mine drainage waters.

“…Strains Fe l and Fe2 belong to T. ferrooxidans. Fe l has often been used in our studies (25)(26)(27). However, strains Fel and Fe2 are different in their ability to oxidize sulfur and thiosulfate.…”

“…We studied the ecological aspects of acidophilic chemolithotrophic iron-and sulfur-oxidizing bacteria at the abandoned Matsuo sulfur and iron sulfide (pyrite) mine areas (21,22,24) and the leaching of pyrite ores by the bacteria (25)(26)(27). We found that iron-and sulfur-oxidizing bacteria were ubiquitously distributed in both acid mine waters and pyrite ores, and were responsible for the rapid oxidation of iron and sulfur and the degradation of the ores.…”