Waste denitration

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. 

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. 

After the cotton has been removed from the nitration tank (Fig. 135) the composition of the acid in the tank is adjusted so that in quantity and strength of it remains unchanged throughout. The waste acid from the centrifuge is low in nitric acid. The regeneration of this spent acid by addition of oleum and fresh nitric acid is uneconomic. Spent acid is denitrated. 

Tetraphenylborate (TPB) was used at Savannah River to recover cesium from alkaline solutions, but attempts to treat HLW tanks with TPB resulted in the production of benzene (a TPB decomposition product) at levels that did not permit the safe operation of the process.8 Crown ethers and dicarbollides were proposed as extractants to remove cesium from acidic HAW, but these compounds are not selective enough to allow cesium to be removed from solutions containing large amounts of nitric acid or sodium nitrate.9 Dicarbollides were used in Russia at industrial scale to recover cesium from HAW, but the removal of cesium was only possible after partial denitration of the liquid waste.10... 

In the TNT manufg industry, the acid recovery house is equipped to operate a separate process called "denitration or "acid recovery . During the mono-nitration process, the monomix acid becomes progressively weaker in HNOa and richer in water, so that the mono-waste acid resulting after nitration is complete contains only 4% of actual HNOa. The mono-waste acid also contains such a high percentage of water that it cannot be fortified economically as can the bi-and tri-spent acids. It is necessary, therefore, for economic reasons to recover H2S04 HNOa by distillation... 

Diethyleneglycol dinitrate, like nitroglycerine, is prepared by nitrating diethylene glycol with mixed acid in batches or continuously. The diglycol is produced by synthesis. Since the waste acid is unstable, special formulations of mixed acid must be employed, and the mixed acid must be denitrated at the end of the nitration stage. 

Weisweiler, W. Environmentally friendly denitrification catalysts based on iron/manganese oxide/sulfate for use in simultaneous denitration and desulphurization of waste gases in a circulating fluidized bed, DECHEMA Monogr., 118 (Katalyse), pp. 81-103 (1989). 

We have seen how smoother nitrations are obtained in the laboratory by using a 10 per cent excess of nitric acid. In plant processes, a much smaller excess is used and even this is recovered completely by separating the waste acid into its components, sulfuric and nitric acids. This is done with steam in denitrating towers. 

Kondo, Y and Kuboto, M., Precipitation Behavior of Platinum Group Metals from Simulated High Level Liquid Waste in Sequential Denitration Process, J. Nucl. Sci. Technol., 29(2), (1992), ppl40-l48. 

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. 

The actinides as trace components will not take any penulty on the already tested waste management procedures (denitration, calcination, vitrification), provided that Np and Pu can be retained in the aqueous waste stream. Without changes of the THOREX flow-sheet, the 1st feed solution contains Np(V) and Pu(lV). Consequently, Np ends up in the waste stream, while Pu following the heavy metal, can be withdrawn with the aqueous phase of the 2nd coextraction step with reducing agents and thus combined with Np (hatched arrow) for the further waste treatment. 

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,... 

Thomson, and Rintoul process. Evers (D.R. Patent, 182,216) has described a new process for denitrating waste acid, in which a mixture of air and steam at a high temperature enters the denitrating tower at one or more points. 

Bray, L. A. Denitration of Purex Waste with Sugar, Report HW-76973 Rev., Apr. 1963. 

According to the present design, the liquid waste is transferred from a process storage vessel by air lift or steam jet to the denitrator. The denitration is performed batchwise with one batch of 720 liter waste per day. Then formaldehyde solution (37 w/o) is metered into the waste. It will destroy the nitric acid and much of the nitrates. The effect of the denitration step has not yet proven in detail. A final decision as to whether the additional effort is justified is still pending. 

The denitrated and concentrated waste is transferred to a mbdng vessel where 140 g... 

---