Denitration of simulated high-level liquid waste by formic acid

In this study, the denitration tests of the raffinate aqueous solution from the TBP solvent extraction part by formic acid were carried out to know the behavior of the minor actinides and the occurable troubles on the interface between the processes. The solution was heated up to 90 degrees C under refluxing for 5.5 hrs after the addition of formic acid. The initial concentration ratio of formic acid to nitric acid in the solution ranged from 1.5 to 2.0 by increments of 0.25. As a result, the denitration reaction occurred much more drastically, comparing with the experiments using the simulated solution. This was considered to be due to the presence of some amount of dissolved organic components from the TBP solvent extraction part and some complex organic compounds of some metals. It was found that the optimum condition was the 1.5 molar ratio of [HCOOH]/[HNO3] and 2.5 hrs denitration. At this condition, the acidity of the denitrated solution could be reduced to 0.44 M, which provided a favorable condition for the following steps of the partitioning process. Zirconium and molybdenum could be removed over 99% and 95%, respectively. Also, minor actinide elements as americium and neptunium were not precipitated.