Radium in uranium mill tailings - Some observations on retention and removal

The various mechanisms by which radium can be retained by uranium mill tailings are discussed. These include coprecipitation (solid solutions), adsorption on silica and hydroxides, ion exchange in clay minerals, and retention in pores. Previous work on radium removal from mill tailings and on radioactive disequilibrium in uranium deposits is critically reviewed in relation to these mechanisms. Fresh data are presented, indicating the roles of charge-depressant ions and of organic complexing agents in radium removal. The addition of reducing agent has been found effective in the presence of complexing agents because it can convert some low-solubility metal hydroxides to their more soluble, lower valency form, thereby eliminating radium adsorption sites. A radium level of 30 pCi/g in the tailings is concluded to be environmentally safe for surface disposal of tailings.