Denitration of Reprocessing Concentrate by Means of HCOOH

Summary

A batch process has been developed to destroy nitric acid present in waste solutions from reprocessing plants by formic acid. The main reaction products N₂O and CO₂ may be released into the atmosphere.

The process was subjected to testing on lab scale involving simulated and real medium-level waste concentrate, on semitechnical scale involving 50 1, and on pilot scale involving 200 1 batch volumes of simulated medium-level waste solutions. In the denitration runs between 81 and 99 % of the nitric acid could be destroyed. The final nitric acid concentration ranged from 0.2 to 0.02 mol/l. The aerosole drag-out with the reaction gases lies between 1 and 5 ppm related to the reaction vessel contents.

The amount of formic acid dragged out ranges from 0.2 to 0.3 %.The formic acid dragged out can be conveniently separated in quantitative terms in a scrubbing column.

Corrosion tests performed on material specimens and on the reaction vessel itself have shown that Incoloy 825 is a suitable construction material for the denitration vessel.

The explosion limits and pressures of formic acid vapour/water vapour/air mixtures were determined. The presence of an explosive mixture can be excluded downstream of the condenser.

A restart of the reaction after extended periods of interruption in metering which are necessary, e.g., in case of technical disturbances, was tested on the pilot facility under various conditions and does not cause problems. The associated induction period can be calculated in advance with sufficient accuracy using a mathematical approach developed from laboratory scale experiments. If the solution is cooled down immediately when metering is interrupted, the reaction restarts already during reheating, even before starting to meter the feed solution.