Behavior of Molybdenum Chloro-Species in Alkali Chloride-Based Melts: Implications for Spent Nuclear Fuel Treatments

Abstract

Chloro-species of molybdenum in oxidation states (III), (IV) and (V) were studied in a range of alkali chloride melts employing high temperature electronic absorption spectroscopy. The reaction rates of disproportionation of MoCl63- complex ions in various melts between 550 and 750 oC were determined. Mo(IV) species MoCl62- were generated and thermodynamic properties of Mo(IV) chloride in NaCl-CsCl eutectic melt estimated. Absorption spectra of molybdenum(V) MoCl6- were measured in a chloride melt for the first time. Speciation and behavior of molybdenum is required for designing processes for molten salt reprocessing of spent nuclear fuel (SNF).

Electrode and Redox Potentials of Molybdenum and Stability of Molybdenum Chloro-Species in Alkali Chloride Melts

“…33,34 Previous high temperature spectroscopy studies showed that six-coordinated MoCl 6 3ions were formed in the melt irrespectively of the method used for introducing molybdenum ions (anodic dissolution of the metal or dissolution of K 3 MoCl 6 ). 31,35 The concentration of molybdenum in the quenched melt samples was determined photometrically with thiocyanate. 36 Volumetric analysis (oxidimetric titration) was employed to estimate the mean oxidation state of molybdenum in the quenched melts.…”

“…Melts containing Mo(IV) ions can be obtained by reacting MoO 2 with hydrogen chloride. 31 Our previous spectroscopic and spectroelectrochemistry studies showed that Mo(IV) chloro-species are most stable at lower temperatures and in the melts containing low ionic momentum cations (cesium). 31 Electronic absorption spectroscopy allowed clear distinction between Mo(III) and Mo(IV) ions.…”

“…Thus, depending on temperature, the reaction of MoO 2 with HCl produced either Mo(IV) or a mixture of Mo(IV) and Mo(III) ions. The latter were formed as the result of disproportionation of Mo(IV) wavenumber / 10 In a preliminary study, 31 high temperature spectroscopy and spectroelectrochemistry measurements showed that Mo(III)/Mo(IV) oxidation/reduction was a reversible process, and Mo(III)/Mo(IV) redox potential was estimated from the results of spectroelectrochemistry in NaCl-CsCl eutectic. At 823 K the potential found was -(0.83 ± 0.04) V vs. Cl − /Cl 2 or 0.45 ± 0.04 V vs. Ag/AgCl reference electrode.…”

“…Molybdenum(IV) and (V) chloro-species could be formed under certain conditions and were characterised primarily by spectroscopy. [29][30][31] Molybdenum(VI) species can be present in chloride melts only in the form of oxygen containing ions.…”

Effect of Li2O substitution for Na2O on the solubility and water durability of Mo in aluminoborosilicate glass

“…[1][2][3][5][6][7][8][9][10][11][12] Especially the molybdenum with high-field strength (F = Z/d 2 ), one of the main fission products (~10 wt%) in HLW produced during spent fuel reprocessing process has a very low solubility (~1 mol%). 13 niobyl(3+) cation (NbO 3+ ), which enters deform dra (octahedra, tetragonal pyramids) with a co covalent bond to oxygen. 16,17 2 | METHOD 2.1 | Thermodynamic model of…”