Kinetics of uranium bioleaching in stirred and column reactors

A fundamental study on the kinetics of uranium mineral bioleahing using Acidithiobacillus ferrooxidans has been carried out in stirred reactor (SR) and column reactor (CR). The four factors affecting uranium dissolution kinetic including aeration rate, pH, initial Fe2+ concentration and temperature were selected to be optimized in SR. The aeration rate of 100 l/h pH of 1.8, initial Fe2+ concentration of 4 g/l and temperature of 35 °C were determined as optimal conditions. To understand ferric and ferrous ions changes by biooxidation, chemical leaching at constant potential were conducted. Results showed that the electrochemical reaction controlled the overall uranium dissolution. By the progress of bioleaching, three stages of bioleaching were observed. The rate controlling is anodic uranium mineral decomposition in the first and second stages while in the third stage cathodic ferric reduction is rate controlling. By using SEM, EDX, XRD and BET analysis, the formation of K-jarosite layer over the residue particles confirmed and the increasing of porosity in the particles surface proved that diffusion of ions from layer was not limiting in uranium bioleaching. The modified kinetic model during bioleaching in SR was presented and developed in CR. Comparing the results, the semi-empirical model data are in good agreement with the experimental data for both uranium leaching and bioleaching in SR and CR.