Bench- and pilot-scale studies relating to the removal of uranium from uranium-contaminated soils using carbonate and citrate lixiviants

Development of the nuclear industry has resulted in soil becoming contaminated with uranium from a variety of sources. To avoid the disposal of these soils in conventional low-level radwaste burial sites, a technology is needed to extract/leach and concentrate uranium in soil into small volumes of an acceptable waste form and returning the soil to its original place. Two lixiviants, carbonate and citrate, were evaluated as to their ability to extract uranium from soil in a soil washing engineering process. The objective was to use a washing/extracting process to selectively remove the uranium from soil without seriously degrading the soil's physicochemical characteristics or generating a secondary waste form that is difficult to manage and/or dispose. Both carbonate and citric acid lixiviants were observed to be effective extractants to remove uranium from the soils tested. Carbonate, because of the its ability to be recycled and its tendency to be more selective for uranium, is preferred for most soils. A major obstacle for using citric acid as well as mineral-based acids is their generation of waste streams from which it is difficult to remove uranium and manage (and dispose of any residual waste water sludges) in an environmentally acceptable manner. The removal of uranium was examined for three soils sampled from two US Department of Energy sites. Two soils were from the facility formerly called the Feed Materials Production Center at Fernald, Ohio and the other soil was from the Oak Ridge Tennessee Y-12 Plant. In the bench-scale studies, general relationships, such as the effect of carbonate and citrate concentrations, pH, the presence of oxidants, such as KMnO4, temperature, and extraction time were investigated. The best pilot-scale treatment consisted of three successive extractions with 0.25 M carbonate-bicarbonate (in presence of KMnO4 as an oxidant) at 40 degrees C followed with two water rinses. (C) 1999 Published by Elsevier Science B.V. All rights reserved.