Concentration And Denitration Of Simulated High-level Liquid Waste By Formic Acid For The Connection Of PUREX Process With TRPO Process

TRPO is a promising process for the treatment of high-level liquid waste?HLLW?.The raffinate of PUREX process with a concentration of nitric acid up to 3 mol/L should be pretreated to fit the requirement of TRPO process for HNO₃ concentration of the feed solution?0.9-1.2 mol/L?.The concentration and denitration is a promising pretreatment process.The acidity of HLLW is reduced by denitration,while the volume of the waste liquid is controlled by concentration.In combination,the concentration and denitration of HLLW is speculated to be able to realize the effective connection of PUREX process with TRPO process.In this thesis,we present a study on the denitration of simulated HLLW by formic acid to investigate the best condition of concentration and denitration to lower both the volume and the concentration of nitric acid of the simulated HLLW associated with the connection of PUREX process with TRPO process.The experiments of concentration and denitration include three parts,that is,denitration of simulated HLLW without concentration,denitration with some common anions,and simultanious concentration and denitration.The composition of simulated HLLW after denitration are detected,including acidity,concentration of metal ions,nitrate and formate.Precipitation is observed in all our experiments,and the precipitates are characterized by various methods.Finally,the simulated HLLW after concentration and denitration are extracted by 30%TRPO in kerosene,to verify the extraction behavior,especially the formation of third phase.The results show that:?1?The optimal molar ratio of formic acid to nitric acid is 1.0 for denitration of simulated HLLW,and the denitration time is at least 4 h.Under this condition,the acidity of the simulated HLLW can be reduced to 0.86 mol/L,which meets the requirement of TRPO process for the acid concentration of the feed solution.?2?The incorporation of a small amount of common anions,such as F^-?Cl^-?NO₂^-and SO₄^2-,has no effect on the denitration process.?3?The sequence of concentration and denitration has no effect on concentration and denitration of simulated HLLW.The deposition rate of Zr,Mo,Sn and Te increases with the increase of concentration multiple.?4?After the acidity of simulated HLLW is reduced to 1mol/L,third phase is observed in the extraction with 30% TRPO in kerosene,even it is not concentrated.This problem is resolved by increasing the initial ratio of molybdenum to zirconium to above 2.0 in simulated HLLW.