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 contamina ted with uranium from a variety of sources. To avoid the disposal of these soils in conventional low-level radwaste burial sites, a technology is need ed to extract/leach and concentrate uranium in soil into small volumes of a n acceptable waste form and returning the soil to its original place. Two l ixiviants, carbonate and citrate, were evaluated as to their ability to ext ract 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 characteri stics or generating a secondary waste form that is difficult to manage and/ or dispose. Both carbonate and citric acid lixiviants were observed to be e ffective extractants to remove uranium from the soils tested. Carbonate, be cause of the its ability to be recycled and its tendency to be more selecti ve for uranium, is preferred for most soils. A major obstacle for using cit ric acid as well as mineral-based acids is their generation of waste stream s from which it is difficult to remove uranium and manage (and dispose of a ny residual waste water sludges) in an environmentally acceptable manner. T he removal of uranium was examined for three soils sampled from two US Depa rtment of Energy sites. Two soils were from the facility formerly called th e 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, genera l 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 s uccessive extractions with 0.25 M carbonate-bicarbonate (in presence of KMn O4 as an oxidant) at 40 degrees C followed with two water rinses. (C) 1999 Published by Elsevier Science B.V. All rights reserved.