Kinetics of uranium bioleaching in stirred and column reactors

• Published in: Minerals engineering 2017-09, Vol.111, p.36-46
• Main Authors: Zare Tavakoli, H., Abdollahy, M., Ahmadi, S.J., Khodadadi Darban, A.
• Format: Article
• Language: English
• Subjects: Acidithiobacillus ferrooxidans; Column reactor; Kinetics; Stirred reactor; Uranium bioleaching
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/j.mineng.2017.06.003

•The optimized conditions of uranium bioleaching were evaluated in stirred and column reactors.•The uranium bioleaching process had three stages based on changing Fe3+/Fe2+ ratios by time.•The modified kinetic model during uranium bioleaching in two type reactors was presented.•In spite of formation the coating layer, the uranium biodissolution was not limited by diffusion of ions through the layers. 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 4g/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.