Waste denitration-oxalate precipitation

To prevent during the denitration step the formation of precipitates on which Pu and Am were partially and irreversibly adsorbed, denitration and oxalate precipitation were carried out in a single step by addition of the waste solution to the formic and oxalic acid mixture, the latter acid acting as a metal complexant during the denitration step. By experimental tests performed on simulated HAW according to this modified process scheme, separation yields of about 99.5% for Pu and 99.8% for Am were measured. A further reduction of the actinide content was reached by flowing the clarified HAW solution through a Dowex 50 resin column. The oxalate precipitation experiments on fully active HAW solutions have practically been completed. The results obtained from five runs (Table IV) confirmed the previous results obtained on simulated solutions. 

Precipitation Processes. Plutonium peroxide precipitation is used at Rocky Flats to convert the purified plutonium nitrate solution to a solid (14) the plutonium peroxide is then calcined to Pu02 and sent to the reduction step. The chemistry of the plutonium peroxide precipitation process is being studied, as well as alternative precipitation processes such as oxalate, carbonate, fluoride, and thermal denitration. The latter method shows the most promise for cost and waste reduction. 

The OXAL process. The flow-sheet of the Oxal process is shown in Fig. 3. The denitration is carried out by slow addition of the waste solution to the boiling mixture of formic and oxalic acid. The presence of the oxalic acid during the denitration prevents the polymerisation and precipitation of hydrolysable ions such as Zr and Mo ions, and assures the precipitation of the RE and actinide oxalates from homogeneous solutions in a we 11-crystallized form. After clarification, the supernatant is sent to vitrification and the oxalates are dissolved and destroyed by nitric acid so that a final solution (3M HN03) is obtained. 

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