Effect of particle size on the kinetics of microbiological leaching of chalcopyrite

An experimental investigation was undertaken to study the microbiological leaching of chalcopyrite by Thiobacillus ferrooxidans. Leach tests were conducted on a small scale using shake flasks. Tests were done which showed that the optimal time for transfer of inocula was between 6 and 8 days. Attempts were made to clarify the complex media-mineral-bacteria interactions that occur in the bioleaching process relating bacterial growth with the changes in media composition as a result of the activities of the bacteria at the mineral surface. In so doing it was observed that a significant amount of copper was leached during the stationary phase of bacterial growth. A sedimentation technique was used to separate the chalcopyrite into various size fractions which were then used to determine bacterial leaching rates in separate experiments. The particle size ranges had average diameters of 1.07, 1.78, 2.52, 3.56, 5.48 and 7.41 μm. The method used to measure particle size was based on the direct comparison of the particles with the scale of an eyepiece micrometer using a microscope. Measurements of particle size distribution made during the course of leaching showed that as the leach proceeded, particle size decreased and the particle size distribution moved in the direction of more particles in the smaller size ranges. An attempt was made to apply Levenspiel's shrinking core model to the data obtained for leaching of the various sized particles. Agreement was reasonable but not perfect between the predicted and measured values of % copper extraction. Better agreement was observed at lower leaching times. Electron micrographs are presented which illustrate the attack of the chalcopyrite particles by the organisms. They also show the effects of jarosite precipitation.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat