TBP extraction of lanthanides from molten calcium nitrate hydrate

Extraction equilibrium of lanthanides between tri-butyl phosphate solution and molten calcium nitrate hydrate, which is generally called a hydrate melt, was studied radiochemically, The dependence of the extractions on the water content of the melt was studied at 70 degreesC in the range of R from 3 to 12.6 for Ca(NO3)(2) . RH2O. From the observed distribution ratios, variation of the activity coefficients of lanthanide nitrates in hydrate melts was analyzed as a function of water content. It was found that, in a concentration region of R greater than about 5.7, the increase of the activity coefficients with decreasing R shows a different tendency compared with the more water-abundant region, This is discussed in conjunction with the characteristics of the hydrate melt, as well as with the difference of the ionic size of lanthanide cations.