Effects of metal ion impurities on PuO2 dissolution in nitric--hydrofluoric acid solution

The effects of Cu2+, Hg2+, Zn2+, La3+, Ce3+, Al3+, Pu4+, Th4+, and Zr4+ metal ion impurities on PuO2 dissolution in 8.0M HNO3--0.1M HF solution at 1000C have been investigated. Results based on 1.0 h of dissolution time show that such metal ions as Al3+, Pu4+, Th4+, and Zr4+, which form strong fluoride complexes, greatly decrease the dissolution rate, whereas such metal ions as Cu2+, Hg2+, Zn2+, La3+, and Ce3+, which form relatively weak fluoride complexes, have little or no effect. Fluoride ion activities in the dissolvents were calculated based on an empirical equation, K1a/sub F/ + a/sub f/ -- 0.10 γ/sub s/ = 0, where K1, a/sub F/, and γ/sub s/ denote first metal ion fluoride complex stability constant, fluoride ion activity, and stoichiometric fluoride ion activity coefficient, respectively. The PuO2 dissolution rates were found to increase linearly with increase in the calculated fluoride ion activities