The reducing-complexing treatment for the leaching of radium from uranium mill tailings

The removal of radium from acid-leach uranium mill tailings has been difficult due to its strong retention as mixed sulfates and in adsorbed forms. In this work, the leaching action of a complexing agent (reducing the free radium cation concentration in solution) is combined with that of a reducing agent. Thus high valency metal hydroxides and basic salts (notably Fe3+) which tend to retain radium are converted to the lower valency from which is much more soluble in the complexing agent. The reducing agent employed is sodium hydrosulfite, in combination with various organic complexing agents; the preferred complexing agent is EDTA. Over 90% of the radium in uranium leach tailings from Elliot Lake can be removed in 1 h contact at room temperature with a solution 0.04 M in hydrosulfite and EDTA, with 1.0 M potassium chloride added as a surface charge depressant. The gradual addition of solids to liquid permits the use of low liquid/solid ratios, and a treatment scheme for the process is proposed.