Photochemical decomposition of oxalate precipitates in nitric acid medium

This work has been performed as a part of the partitioning of minor actinid es. Minor actinides can be recovered from high-level wastes as oxalate prec ipitates, but they tend to be co-precipitated together with lanthanide oxal ates. This requires another partitioning step for mutual separation of acti nide and lanthanide groups. Accordingly, the objective of this study was to decompose and dissolve oxalate precipitates into a dilute nitric acid solu tion by using a photochemical reaction. In order to do this, oxalic acid an d neodymium oxalate precipitate were used in this study. Neodymium oxalate was chosen as a stand-in element representing americium, curium and lanthan ides. As a result, decomposition characteristics of oxalic acid were first investigated and then on the basis of these results, the decomposition of n eodymium oxalate precipitates was evaluated. From results using oxalic acid , the oxalate decomposition appeared to take place due to the reaction betw een the oxalate ion and hydroxyl radical generated from the nitric acid by photo-radiation. And the oxalate decomposition rate was measured in the exp eriments for various nitric acid contents when a mercury lamp (lambda=254 n m) was used as a light source. The maximum decomposition rate was obtained when the nitric acid concentration was around 0.5 M, while the decompositio n rate was reduced with an increase in the nitric acid concentration at mor e than 0.5 M. The photo-decomposition rate of neodymium oxalate precipitate s was found to be 0.0034 M/h at the condition of 0.5 M HNO3.