| dc.description.abstract | The role of bacteria in the leaching of mineral sulphides is discussed with respect to Thiobacillus ferrooxidans. Column leaching studies were carried out on Malanjkhand lean?grade chalcopyrite ore samples using Thiobacillus ferrooxidans as leaching bacteria isolated from Malanjkhand mine waters, with an aim to optimise various process parameters such as particle size, addition of 9K nutrients, and the influence of gangue minerals.
Since leaching occurs by both direct and indirect mechanisms, ferric sulphate leaching was carried out to understand the significance of the indirect mechanism, while thermal leaching was carried out with an aim to study the leaching kinetics at higher temperatures. Some shake?flask leaching studies were also carried out on the above ore samples using adapted strains to have a comprehensive understanding of the role of adapted strains in leaching.
Further, attachment of Thiobacillus ferrooxidans to pyrite mineral was studied in detail to establish the probable mechanisms of bacterial attachment to various sulphides and its importance in leaching. Some cursory tests were performed on bacterial attachment to quartz mineral, both in the presence and absence of pyrite mineral, to understand the selectivity of attachment. Mineral samples were also observed under a SEM to understand the characteristic chemical and biological changes occurring at the mineral surfaces and to reveal any bacterial attachment.
The role of centrifugation and soniration on bacterial dislodgement was also studied. The effect of applied potential on bacterial attachment was examined. Results of column leaching experiments indicate that higher leaching rates are obtained with smaller particles. Higher copper dissolution was obtained from a quartz?based chalcopyrite ore sample than from a granite?based chalcopyrite ore sample. Also, the effect of 9K nutrients on leaching was not significant. Higher leaching rates were obtained at higher temperatures, while the leaching efficiency decreased with an increase in the volume of the packed ore bed. Ferric sulphate leaching results indicate the importance of ferric iron in the oxidation of mineral sulphides.
The amount of copper leached from quartz?based chalcopyrite ore sample in shake?flask leaching studies was found to be higher in the presence of adapted strains compared to that obtained with an unadapted strain. The copper dissolution was highest in the presence of a strain previously adapted to chalcopyrite mineral, followed by that obtained with a pyrite?adapted strain, and then an unadapted strain. An increase in metal dissolution was also observed with an increase in inoculum concentrations.
Bacterial attachment studies clearly indicated that parameters such as particle size, time, and static or dynamic conditions affected bacterial attachment. Increased bacterial attachment to minerals was observed with smaller particles. A minimum lag period to initiate bacterial attachment was observed. A continuous increase and decrease in bacterial growth was observed under agitation conditions, while a gradual increase was observed in the growth of bacteria both in the liquid and on the solid substrate under stationary conditions.
Scanning electron microscopic studies revealed bacterial attachment to mineral surfaces and also severe corrosion in the form of fissures and cracks. | |
