Bench Scale Leading Studies on Uranium Mill Tailings

Abstract

<p>Uranium-bearing ore is crushed and leached to extract uranium in an ore processing plant. However, the decay products of uranium are discarded as wastes or tailings from the plant. One such decay product is Ra²²⁶, which is quite toxic and mobile. It remains dispersed with the tailings and spreads into air and potable waters from the tailing areas due to natural forces and decay to gaseous Rn²²².</p> <p>In this work, bench scale leaching of the uranium mill tailings was done with a view to extract Ra²²⁶ into the liquid phase. A gamma counting technique for determination of Ra²²⁶ concentrations in solid and liquid samples was also developed. Details of sample preparation, ingrowth, and calibration are discussed. For extraction of radium, several extractants such as water and solutions of CaCl₂, EDTA, DTPA and HNO₃ were used. Effects of solid to liquid ratio and time of contact on the extraction of Ra²²⁶ were studied for these extractants. In some cases, effects of temperature, concentration of extractant and multiple cross current contacting were also studied. The results of various leaching experiments are interpreted.</p> <p>The main results show that equilibrium distribution of radium between the extractants and tailings was attained rapidly. In all experiments, a fraction of radium was "unextractable", i.e., all operating lines had an intercept when extrapolated to zero solid to liquid ratio. In general, the operating lines had a relatively small slope indicating that high solid to liquid ratio could be used without significantly degrading extraction.</p>