Thermodynamic properties for MMoO4 (M = Mg, Sr and Ba) as the end-members of the yellow phases formed in the nuclear fuel waste glasses

Abstract

The standard molar entropyΔ0TSm°, at 298.15 K of MgMoO4(cr) of the end-members of the yellow phases formed in the nuclear fuel waste glasses was determined by measuring Cp,m° at the temperature of 2 K and above using the most recent Debye-Einstein formula. The Δ0TSm° data obtained in our previous study for SrMoO4(cr) and BaMoO4(cr) were re-evaluated using this most recent formula. The standard Gibbs free energies of formation, ΔfGm°, of MgMoO4, SrMoO4(cr) and BaMoO4(cr) were determined by combining the Δ0TSm° data with the reference data for the standard enthalpy of formation,ΔfHm°. The ΔfGm° of MoO42−(aq) was updated from the thermodynamic cycle based on the data obtained in the present work. The unknown standard Gibbs free energy of solution, ΔslnGm°, and the solubility product, Ks, at 298.15 K for MgMoO4 were predicted. The thermodynamic values were obtained as follows:Δ0TSm°(MgMoO4(cr), 298.15 K)/(J K−1 mol−1) = 119.11 ± 1.19;Δ0TSm°(SrMoO4(cr), 298.15 K)/(J K−1 mol−1) = 136.44 ± 1.36;Δ0TSm°(BaMoO4(cr), 298.15 K)/(J K−1 mol−1) = 152.61 ± 1.53;ΔfGm°(MgMoO4(cr), 298.15 K)/(kJ mol−1) = −1295.73 ± 0.91;ΔfGm°(SrMoO4(cr), 298.15 K)/(kJ mol−1) = −1441.32 ± 1.36;ΔfGm°(BaMoO4(cr), 298.15 K)/(kJ mol−1) = −1443.29 ± 1.33;ΔfGm°(MoO42−(aq), 298.15 K)/(kJ mol−1) = −836.63 ± 0.97.ΔslnGm°(MgMoO4(aq),298.15 K)/(kJ (mol of MoO42−(aq))−1) = 3.72 ± 1.88.Ks(MgMoO4(aq), 298.15) = 2.23×10−1± 4.46×10−2The thermodynamic data obtained in this work are expected to be useful for nuclear fuel waste safety management.