THE EFFECT OF ACIDIFICATION AND CHELATING-AGENTS ON THE SOLUBILIZATION OF URANIUM FROM CONTAMINATED SOIL

The role of acidification and chelating agents in the solubilization o f uranium (U) from contaminated soil was examined in a series of exper iments. Soil acidification and the addition of chelating agents were t he two methods compared initially, The results indicated that the addi tion of citric acid solubilized more U than acidification or the other amendments tested. This increase in U solubility was, however, transi tory, A subsequent experiment indicated that citrate concentration had a more dramatic effect on U solubility than did acidification. The gr eatest soluble U concentration during this experiment (775 mg kg(-1) s oil, or -85% of the total U) was observed after 24 h in the presence o f 20 millimoles citrate kg(-1) soil at pH 5,The persistence of U solub ility over the 96-h experimental period was primarily a function of pl l and citrate degradation. In a separate experiment, in which citric a cid rather than citrate was added to contaminated soil, the soluble U concentrations observed were generally lower than those observed in th e presence of citrate, Citric acid decreased soil pit to values less t han or equal to 3.6, and solubilized higher concentrations of Al and F e than observed in the presence of citrate. Since the maximum solubili zation of U was observed at pii 5, the implication of these results is that a combined approach, using both soil acidification and citric ac id addition, may be necessary to maximize the phytoextraction of U fro m soils with a pH > 6.0.