ABSTRACT
Under sponsorship of the Nuclear Regulatory Commission’s Uranium Research and Recovery Program, Pacific Northwest Laboratory (PNL) has investigated the use of various neutralizing reagents and techniques to attenuate the movement of contaminants associated with acidic uranium mill tailings. The objective of this study was to identify those contaminants which are not effectively attenuated by common neutralization methods and to develop alternative control measures. Of those contaminants associated with uranium mill tailings which were identified as not being effectively immobilized by tailings neutralization, radium imposes an important environmental concern in terms of potential groundwater contamination.
Control or attenuation of radium is of special concern primarily due to its radiological health implications. For that reason, the Environmental Protection Agency (EPA) has implemented strict guidelines governing the maximum allowable concentration in drinking waters. Current EPA guidelines call for total radium activities not to exceed 5 pCi/L. Due to the high activity of soluble radium in the acidic uranium mill tailings environment (several hundred to several thousand pCi/L), specific ion removal procedures 500were investigated for use in attenuating radium in order to prevent future groundwater contamination. Results of these investigations led to the development of a tailings additive comprised of a mixture of hydrated lime and barium chloride, which, when added to acidic tailings, can reduce the amount of leachable radium escaping a designated tailings impoundment.
In laboratory verification tests, this radium specific tailings treatment reduced the effluent solution activity of radium by three orders of magnitude, from >3500 pCi/L to 1.7 pCi/L, in comparison with untreated acidic tailings.
