Formic acid denitrations

After the laboratory demonstrations, plant scale demonstrations of formic acid denitration and of precipitation operations were performed in both canyon and MPPF equipment with nonradio-active chemicals. These demonstration runs confirmed the operating limits which had been established during the laboratory experiments. 

Americium is separated from iron, chromium, nickel, and other impurities by oxalate precipitation. The Am feed solution for precipitation in the MPPF after formic acid denitration and volume reduction was approximately 2 g Am/L, 14 g Cr/L, 1.2 g Fe/L, and 0.8 g Ni/L in 1M HNO3. Further concentration of the feed solution to >2 g Am/L necessitated evaporation at <85°C because of the potential corrosion of the stainless steel... 

Figure 5. Formic acid denitration of 2411 Am solutions containing gross quantities...

Full-scale simulations of the formic acid denitration and the precipitation of rare earths (simulating americium) were carried out in plant equipment before processing the actual stream containing the Am. 

Three simulated tests were run using only nitric and formic acids. In each case, the reaction began promptly and proceeded smoothly. After the second test, the denitrated material was evaporated and additional nitric acid added to simulate the tandem semi-batch operation to be used with actual process solution. At the end of formic acid feed for Test 3, the material was refluxed for 2 hours and evaporated to 2500 L to simulate the final canyon product batch. A final formic acid denitration reduced the acidity of the simulated concentrate to <1M HNO3. 

Formic Acid Denitrations. Simulated solutions were subjected to laboratory formic acid denitrations (Figures 2 and 3). The most usable free acid concentration for the simulated solutions was obtained when a formic acid to free acid ratio of about 1.6 to 1.9 was used. This ratio yielded a final free acidity of about 0.6 to 0.8M. As a result of Al3+ hydrolysis, it was possible to drive the A1-Am-Cm solution to about pH 10. However, acid concentrations less than 0.2M had to be avoided to prevent hydrolysis and precipitation of the actinides. 

Figure 2. Formic acid denitration of simulated Am-Cm-NaNOs feed solution...

Flowsheets. Generalized flowsheets for the separation procedures are given in Figures 8 and 9. The flowsheets provide for acid adjustment by formic acid denitration followed by dilution and precipitation in batches with precipitated slurry accumulated in the tank. After washing of the precipitated slurry to remove the contaminating cations, the product is dissolved by adjusting the acid concentration to <8M and heating the solution. Product is then stored until the MPPF is available to process the material. 

Formic Acid Denitrations. As a result of the denitrator tank volume limitations, approximately 65% of the Na-Am-Cm-N03 solution was transferred to the denitration tank, evaporated by 50%, and partially denitrated with formic acid. Then the remainder of the Na-Am-Cm-N03 solution was transferred into the tank, evaporated to 2500 L, and the complete solution denitrated to 0.9M HNO3. 

In its final version (18-20), see Fig. 2, the process started with a conditioning of the HLW by formic acid denitration, with the goal (a) to reduce... 

In 1976 he was appointed to Associate Professor for Technical Chemistry at the University Hannover. His research group experimentally investigated the interrelation of adsorption, transfer processes and chemical reaction in bubble columns by means of various model reactions a) the formation of tertiary-butanol from isobutene in the presence of sulphuric acid as a catalyst b) the absorption and interphase mass transfer of CO2 in the presence and absence of the enzyme carboanhydrase c) chlorination of toluene d) Fischer-Tropsch synthesis. Based on these data, the processes were mathematically modelled Fluid dynamic properties in Fischer-Tropsch Slurry Reactors were evaluated and mass transfer limitation of the process was proved. In addition, the solubiHties of oxygen and CO2 in various aqueous solutions and those of chlorine in benzene and toluene were determined. Within the framework of development of a process for reconditioning of nuclear fuel wastes the kinetics of the denitration of efQuents with formic acid was investigated. 

Hercules Method D90-3e (Ref 17, pll). Nitroglycerin by Periodic Acid Oxidation. NG and some other nitrate nitrogen esters which may be present in expl oils can be quantitatively denitrated to their, respective alcohols by action of methanol and coned HCl. On oxidizing the residue of polyhydric alcohols with periodic acid, H5I06, the secondary carbon and alcohol group in glycerin are oxidized to formic acid,... 

Nitrated Chitin or Chi tin Nitrate, [C6H702-(0N02)2.NH.C0.CH3] n mw (293.19)n, N l4.33%(found 7.5% nitrate N) wh fibrous flakes, ignites ca 163° burns vigorously thermally stable by Abel Test insol in most solvs partially sol in formic acid(from which it is repptd by w) sol in coned H2S04 or HCl(from which it is not repptd by w) various org solvs such as benz, tetralin, aniline, nitrobenz, phenol, pyridine furfural cause it to swell it is completely denitrated by NaSH in 3 hrs at 16°(Ref 3)... 

As described in Figure 3.7, TRU separation is performed by implementing the DIDPA process on pretreated PUREX raffinates. A front-end denitration step by formic acid is thus required to reduce the nitric acid concentration of the feed down to 0.5 M to allow the TRU elements to be extracted by the cation exchanger di-fvo-dccyl-phosphoric acid (DIDPA). This preliminary step, however, induces the precipitation of Mo and Zr (and thus the potential carrying of Pu), which requires filtration steps. The TRU and Ln(III) elements are coextracted by a solvent composed of the dimerized DIDPA and TBP, dissolved at 0.5 and 0.1 M, respectively, in n-dodecane. The An(III) + Ln(III) fraction is back-extracted into a concentrated 4 M nitric acid solution, whereas Np and Pu are selectively stripped by oxalic acid. 

Di-iso-decylphosphoric Acid The DIDPA Process An(III) and Ln(III) can be partitioned using the DIDPA solvent (DIDPA and TBP, respectively dissolved at 0.5 and 0.1 M in n-dodecane) in a two-step process approach. First coextracted and costripped in a 4 M nitric acid solution in a first DIDPA cycle (see Section 3.3.1.1.4), the An(III) + Ln(III) fraction is partitioned in a second cycle after denitration of the An(III) + Ln(III) product by formic acid to reduce the nitric acid concentration to at least 0.5 M. In this second DIDPA cycle, An(III) and Ln(III) are first coextracted by the DIDPA solvent, and the An(III) are selectively stripped by DTPA (0.05-0.1 M) in a solution buffered at pH 3 with lactic acid (1 M). The triva-lent lanthanides are further stripped with a 4 M nitric acid solution (134). 

To handle the volume of solution (about 30,000 L) necessary in the plant operation, a semi-batch denitration was necessary. Slow evaporation during product accumulation reduced the volume to <12,000 L, but increased the nitric acid concentration to about 11M. Experiments indicated that for a semi-batch denitration mode, a projected nitric acid concentration of 2M was an excellent stopping point, because no residual formic acid remains through the reflux and evaporation steps. Additional high nitric acid solution can then be added to the evaporated-denitrated solution without auto-initiation of a formic acid-nitric acid reaction. After all the Am-bearing solution had been transferred to the denitration evaporator and denitrated to <2M, the solution could be evaporated to 2500 L and denitrated to a residual free-acid concentration of 0.5 to 0.8M. In actual practice, the final 2500 L of solution was denitrated to 0.25M HNO3. 

After the evaporation, approximately 36% of the Am solution was moved to a denitration evaporator. After dilution from 11M to 8M HNO3, the acidity of the solution was reduced by reaction with formic acid to an estimated 3M HNO3. After refluxing to assure total destruction of the formic acid, the denitrated solution was concentrated in the evaporator to about 55% of its original volume. A second transfer of Am solution from storage to the denitrated solution was made. 

As a result of the high concentration of nitrate (from sodium and aluminum nitrate) the reaction rate was controlled by the formic acid addition rate until the free acid concentration was reduced to about 0.5M. For semi-batch denitrations it appears that a nitric acid concentration of 1 to 2M at the end of each individual denitration is an excellent stopping point. Using 1 to 2M HNO3 as a projected stopping point assured that there will be no residual formic acid at the end of the reflux and evaporation... 

These tests indicate that to obtain high yields from precipitation, the aluminum concentration of the slurry must be <0.2M (Figure 5). This can best be obtained by denitrating the Am-Cm-Al solution concentrate with formic acid (Figure 3) to about 0.5M HNO3. Then, dilution to an aluminum concentration of <0.5M would yield a feed suitable for oxalate precipitation. 

In early studies, di-(2-ethylhexyl) phosphoric acid (DEHPA) had been chosen as the extractant (22). DEHPA extracts americium from the solutions of low acid concentrations such as 0.1 M, while a small percentage of americium is carried with the precipitate formed by denitration of the HLW with formic acid for acidity adjustment. At the end of the denitration, the pH of solution has to be kept lower than 0.5 to avoid the loss of americium more than 0.1 % due to coprecipitation with zirconium, molybdenum and tellurium. 

TABLE II Behaviour of Pu during denitration of unconcentrated HAW solutions by formic acid... 

The principal actinides separation step is performed at low acidity, at pH of about 2. Denitration of HAW is therefore a crucial operation step on which little information is available. The operational margin is rather restricted. A too high pH would leak to heavy precipitate formation with actinides adsorbed on them. Only a batch-wise operation mode can satisfy the chemical and operational requirements and furthermore the utilisation of boiling formic acid raises material corrosion problems. 

Fig.2 shows the flow sheet of the HAW processing. The use of the waste solution directly for separation leads to the dissipation of avery large part of the electric energy for the electrolytic transport of the hydrogen and nitrate ions. The concentration of the nitric acid is therefore reduced to about 0.05 M through denitration by means of formic acid. To prevent the hydrolysis and the precipitation of some components, particularly Pu, acetic acid is added as complexing agent to the solution before denitration. The elements Nb,... 

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. 

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. 

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