The kinetics of the bioleaching of ZnS concentrate by Thiobacillus ferrooxidans was studied in a well-mixed batch reactor. Experimental studies were made at 30 degrees C and pH 2.2 on adsorption of the bacteria to the mineral, ferric iron leaching, and bacterial leaching. The adsorption rate of the bacteria was fairly rapid in comparison with the bioleaching rate, indicating that the bacterial adsorption is at equilibrium during the leaching process. The adsorption equilibrium data were correlated by the Langmuir isotherm, which is a useful means for predicting the number of bacteria adsorbed on the mineral surface. The rate of chemical leaching varied with the concentration of ferric iron, and the first-order reaction rate constant was determined. Bioleaching in an iron-containing medium was found to take place by both direct bacterial attack on the sulfide mineral and indirect attack via ferric iron. In this case, the ferric iron was formed from the reaction product (ferrous iron) through the biological oxidation reaction. To develop rate expressions for the kinetics of bacterial growth and zinc leaching, the two bacterial actions were considered. The key parameters appearing in the rate equations, the growth yield and specific growth rate of adsorbed bacteria, were evaluated by curve fitting using the experimental data. This kinetic model allowed us to predict the liquid-phase concentrations of the leached zinc and free cells during the batch bioleaching process.

To establish an optimization methodology for the emulsification process in microchannels, we have investigated the relationship between the channel geometry of micromixers and the size of the formed droplets. We focus the channel geometry of orifice including the sudden contraction and expansion of the flow. The experimental results indicate that the channel geometry is effective in producing fine droplets, and that the mean droplet diameter is predicted on the basis of the pressure drop due to convection and the energy dissipation rate in the mixer chamber irrespective of the orifice geometry. In the orifice-shaped micromixer, the kinetic energy given to a fluid by contraction is dissipated within the order of milliseconds by the formation of a jet flow of the order of several hundreds of micrometers; we have named this jet-micro-jet.‖ On the basis of this mechanism, the energy dissipation rate in a micro-jet, ε jet , is quantified. The mean droplet diameter is proportional to ε jet −0.4 irrespective of the channel geometry of the mixer. Using this formulation, we have integrated the geometric parameters of the orifice and the physical properties of the fluids into the expression of ε jet to establish an optimization methodology of the droplet formation in the orifice-shaped micromixer.

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Correlation betu,een the green (FAM) and red (TMRA) fiuorescence intensities wil] reveal an infiuence of the discreteness on the molecular computing reactions. [1]