NP(V) CARBONATES IN SOLID-STATE AND AQUEOUS-SOLUTION

The solubility of NaNpO2CO3(s) in 0.1M perchlorate solution at 25-degrees-C in equilibrium with 1.0% CO2/N2 atmosphere has been investigated as a function of PH/1g [CO32-]. The solid phase was found hexagonal with a = 1008.1+/-0.3 pm and c = 991.1+/-0.2 pm. A solubility product of lg Ksp(NaNpO2CO3) = = -10.22+/-0.02 and a formation constant of the first Np(V) carbonato species of lg beta01 = 4.52+/-0.02 was evaluated. For the dicarbonato species an upper limit of lg lg beta02 < 6.6 was derived. Comparison of the present data with solubility values of Np(V) in equilibrium with 0.03% CO2 partial pressure gave evidence that carbonato species are prevailing in solutions at both 1% and 0.03% CO2 partial.pressures.