Continuous leaching of uranium from an Indian ore: Residence time scale up and heat effects

• Carbonate leaching of pitchblende and pyrite from a lean uranium ore is studied.
• Residence time distribution model is used for scaling batch to continuous leaching.
• Rise in temperature of the slurry due to pyrite reaction is predicted.
• Max limit of pyrite content in the ore to run commercial reactor safely forecasted
• Predicted recoveries and temperatures in a pilot reactor agree with those measured.

Commercial level operation of uranium leaching from the ores is carried out as a continuous process because of techno-economical benefits. Batch kinetic data of uranium leaching from a lean ore, is scaled to multiple continuous stirred tank reactors using the Residence Time Distribution (RTD) model. A graphical approach reported earlier was improved for better predictions of the observed experimental results. Batch data was obtained from a laboratory scale reactor. The scaling is used to predict the temperature rise in a continuous reactor, which happens mostly due to conversion of pyrites present in the ore. The scaling obtained with the modified model is compared with measurements of uranium conversions and reactor temperatures in a pilot scale continuous reactor having three stirred tanks in series. A good comparison is obtained for several different operating conditions of the pilot and commercial scale reactors. Hence, RTD is a good tool for scale-up and design of commercial scale leaching of uranium from lean ores.