Precipitation formation of zirconium-dibutyl phosphate complex in Purex process.

Dibutyl phosphate (DBP) was added to 30% TBP-70% dodecane solvent (DBP concentration, 30–1,150mg/l). These samples were used to investigate distribution behavior of Zr from a 3 M nitric acid solution (Zr concentration, 60–4,000 mg/l). The experimental results show that the Zr distribution depended mainly on the total DBP/Zr mole ratio. Below DBP/Zr=2, the Zr distribution to the organic phase became larger as the DBP/Zr mole ratio increased. Above DBP/Zr=2, the Zr distribution factor was saturated. Moreover, colloidal precipitation at the interface between organic and aqueous phases was observed above DBP/Zr=2. Then in order to characterize the precipitation, 3 M nitric acid solution containing Zr ion was directly reacted with DBP and the obtained products were analyzed by 13C, 31P and 14N NMR spectroscopy. The measured NMR spectra indicated that the products were polymers having four kinds of bonding structures. One was a hydrogen bonded structure and the others were Zr bridged structures with two to four DBP molecules coordinated per Zr atom. The Zr bridged structure with four DBP molecules was thought to make the biggest contribution to precipitate formation.