Hydrazoic acid distribution coefficients in Purex processing

Mixtures of hydroxylamine nitrate and hydrazine are being considered for the reductive stripping of plutonium during Purex processing. The hydrazine functions as a holding reductant for plutonium(III) by destroying nitrous acid via the fast reaction N2H4 + HNO2 → HN3 + 2H2O which leads to the stoichiometric formation of hydrazoic acid. We have measured the distribution coefficients for hydrazoic acid between nitric acid solutions and tributylphosphate-dodecane solutions. Values in the range of 1 to 10 were obtained under typical Purex process conditions. This indicates that most of the hydrazoic acid will be present in the organic phase leaving the plutonium stripping contactors. The distribution coefficients can be expressed as log(E O/A) = n log[Free TBP] + log K' where K' is 7.0, 10.0, 5.1 and 4.7, respectively, at 25, 35, 45 and 550C; and the corresponding values of n are 1.11, 1.27, 0.97 and 1.20