Elimination of the Interfacial Crud in the Extraction of Simulated High-Level Liquid Waste After Denitration in the TRPO Process

Denitration is a proven technique that can reduce the nitric acid concentration of high-level liquid waste (HLLW) to meet the aqueous acidity requirement of the TRPO (TriAlkyl Phosphine Oxide) process. However, interfacial crud is generated in the TRPO extraction of the HLLW after denitration. In this work, the interfacial crud was characterized by Fourier-transform infrared spectroscopy and dynamic light scattering. The extraction distribution ratio of zirconium by 30% TRPO in kerosene decreases dramatically after the simulated HLLW is denitrated, and we proposed that the presence of zirconium in the simulated HLLW after denitration is responsible for the generation of interfacial crud. Using ammonium molybdate as a precipitant, the concentration of zirconium in the simulated HLLW was successfully reduced without essentially changing the concentration of other metal ions. The effects of reaction time, temperature, and amount of ammonium molybdate added on the zirconium removal process were investigated and the precipitates formed in the removal of zirconium were characterized by scanning electron microscope, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Finally, after reducing the concentration of zirconium in the simulated HLLW to below 10 mg/L by using ammonium molybdate, the extraction experiment was performed again and no interfacial crud was observed.