Uranyl(VI) Nitrate Salts:  Modeling Thermodynamic Properties Using the Binding Mean Spherical Approximation Theory and Determination of “Fictive” Binary Data

Abstract

This work is aimed at a description of the thermodynamic properties of highly concentrated aqueous solutions of uranyl nitrate at 25 degrees C. A new resolution of the binding mean spherical approximation (BIMSA) theory, taking into account 1-1 and also 1-2 complex formation, is developed and used to reproduce, from a simple procedure, experimental uranyl nitrate osmotic coefficient variation with concentration. For better consistency of the theory, binary uranyl perchlorate and chloride osmotic coefficients are also calculated. Comparison of calculated and experimental values is made. The possibility of regarding the ternary system UO(2)(NO(3))(2)/HNO(3)/H(2)O as a "simple" solution (in the sense of Zdanovskii, Stokes, and Robinson) is examined from water activity and density measurements. Also, an analysis of existing uranyl nitrate binary data is proposed and compared with our obtained data. On the basis of the concept of "simple" solution, values for density and water activity for the binary system UO(2)(NO(3))(2)/H(2)O are proposed in a concentration range on which uranyl nitrate precipitates from measurements on concentrated solutions of the ternary system UO(2)(NO(3))(2)/HNO(3)/H(2)O. This new set of binary data is "fictive" in the sense that the real binary system is not stable chemically. Finally, a new, interesting predictive capability of the BIMSA theory is shown.

Determination of Successive Complexation Constants in an Ionic Liquid: Complexation of UO22+ with NO3− in C4-mimTf2N Studied by UV−Vis Spectroscopy

“…Actually, the use of C 4 -mimNO 3 and UO 2 (Tf 2 N) 2 for the introduction of the reagents suppresses the presence of spectator ions, which is unavoidable in traditional molecular solvents. The values of the stability constants derived in this work are much higher than the values obtained in water for the same system (log 1 ) 0.30 and log 2 ) 0.31 42 ), while they are closer to those derived in acetonitrile 22 (log 1 ) 7.9, log 2 ) 15.0, and log 3 ) 20.0), but no direct correlation can be found with the dielectric constants or polarization abilities of these solvents. 47 Nitrate ions appear to be strong complexing agents of uranyl in C 4 -mimTf 2 N, a situation wich strongly ressembles that of chloride ions toward transition-metal complexes, as evidenced by Dyson and co-workers.…”

Speciation of Uranyl Nitrato Complexes in Acetonitrile and in the Ionic Liquid 1‐Butyl‐3‐methylimidazolium Bis(trifluoromethylsulfonyl)imide

“…In a recent paper, Ruas and co-workers stated that the equilibrium constants for the 1:1 and 1:2 UO 2 2+ /NO 3 -complexes are low, which means that the uranyl trinitrato complex in water can be neglected in our case. [38] The UV/Vis absorption spectrum of the hydrated uranyl ion is well known, [5] although the coordination sphere of the hydrated free uranyl ion has always been a point of discussion. Models with four to six water molecules in the equatorial plane have been proposed, [39,40] although it is generally accepted that the uranyl ion is coordinated by five water molecules in the equatorial plane.…”

Insights into the Mechanism of Extraction of Uranium (VI) from Nitric Acid Solution into an Ionic Liquid by using Tri‐n‐butyl phosphate

“…In addition to the two extraction Equations (5) and (6), we also consider all validated aspects, that is, U VI complexation with nitrates in the aqueous phase, [49] together with HNO 3 transfer in the absence of TBP and metal. [32] In our previous work, [29] our model was built on the assumption that the concentrationso fb oth [Tf 2 N À ]a nd [C 4 mim + ]i ons, which intervene in the two extraction equilibria shown in Equations (3) and (4), N À ]v ariations are strongly dependento nb othT BP and nitric acid concentrations, and that the RTIL cation and anion behave in adifferent way.W e, thus, need to take this fact into accounti no ur new model.Considering the intricate ion exchanges in such biphasic systems, [31,33] we limit ourselves to an empiricalm athematicald escription of the concentration data, by use of ad hoc analytical expressions between [HNO 3 ] = 0a nd 7 m as Equations (7) and (8):…”