Potentiometric and spectrophotometric characterization of the UO₂ ²⁺-citrate complexes in aqueous solution, at different concentrations, ionic strengths and supporting electrolytes

Abstract

Dioxouranium(VI)-citrate / Speciation / Sequestering ability / Dependence on ionic strength / SIT equationSummary. In this paper we report an investigation on the interactions between dioxouranium(VI) and citrate using potentiometry (H + -glass electrode) and UV-spectrophotometry. Potentiometric measurements were carried out in NaCl and KNO 3 aqueous solutions at t = 25 • C in a wide range of experimental conditions (concentrations, ligand/metal molar ratio, pH, titrants). Measurements in NaCl were carried out at different ionic strength values (0.1 ≤ I/mol L −1 ≤ 1.0); different procedures were employed for the acquisition of experimental data and careful analysis of these data performed. In all cases the speciation model that best fits experimental data takes into account the formation of the following species: UO 2 (Cit) − , (UO 2 ) 2 (Cit) 2 2− , (UO 2 ) 2 (Cit) 2 (OH) 2 4− , (UO 2 ) 2 (Cit) 2 (OH) 3− , (UO 2 ) 2 (Cit)(OH) 2 − , (UO 2 ) 2 (Cit)(OH) 0 , (UO 2 ) 3 (Cit) 2 (OH) 5 5− . The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (specific ion interaction theory) approach.Moreover, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO 3 medium) has been calculated to characterise the compounds found by pH-metric refinement.Recommended values for the uranyl-citrate species were proposed for each ionic strength value in NaCl aqueous solution. Comparison with literature stability constants is reported too.

Exploring Actinide Materials Through Synchrotron Radiation Techniques

“…Determining a detailed structure of a metal ion's solution species is a long‐standing and challenging problem, because of the useless of some direct structural probes, such as crystallology and elemental analysis. Many researchers have made great efforts for a number of years to develop a variety of indirect probes of speciation, including potentiometry, polarography, nuclear magnetic resonance (NMR) spectroscopy, as well as visible, infrared (IR), and Raman spectroscopy . The development of EXAFS has recently made available direct structural probes of solution speciation.…”

Binding constant determination of uranyl–citrate complex by ACE using a multi‐injection method

“…The complexation between uranyl and citrate has been studied for more than 60 years , and various efforts have been made using different techniques and instruments, such as potentiometry , polarography , UV/Vis spectroscopy , IR and Raman spectroscopy , ion‐exchange method , nuclear magnetic resonance (NMR) , extended X–ray absorption fine–structure spectroscopy (EXAFS) , X–ray absorption spectroscopy (XAS) , etc. In and , some of the results obtained so far have been summarized and compared. Due to the variation of instruments and experimental conditions, various species of uranyl–citrate complexes have been reported, such as [(UO 2 )‐(Cit)] − , [(UO 2 ) 2 (Cit) 2 ] 2− , and other polymeric, hydrolyzed, or protonated species .…”

“…In and , some of the results obtained so far have been summarized and compared. Due to the variation of instruments and experimental conditions, various species of uranyl–citrate complexes have been reported, such as [(UO 2 )‐(Cit)] − , [(UO 2 ) 2 (Cit) 2 ] 2− , and other polymeric, hydrolyzed, or protonated species .…”

Interaction of N-acetyl-l-cysteine with Na+, Ca2+, Mg2+ and Zn2+. Thermodynamic aspects, chemical speciation and sequestering ability in natural fluids

“…The second approach is a purely chemical model (“weak complex model”), in which the activity coefficients vary with ionic strength according to an equation that is independent of the nature of a species (generally for I < 1 mol dm −3 ), but only on its charge and the medium effect is interpreted in terms of formation of weak species between the molecule under study and the ions of the supporting electrolyte. From this basis, a background electrolyte, that it is assumed to be not (or very weakly) interacting with the molecule under study, is required; for this purpose, when dealing with O- and S- donor ligands, the choice falls on (C 2 H 5 ) 4 NI (aq) or, more rarely, on (CH 3 ) 4 NCl (aq) [ [49] , [50] , [51] , [52] , [53] , [54] , [55] , [56] , [57] , [58] , [59] ]. Moreover, since this approach is based on the direct comparison of data obtained in different media (the so-called Δp K method), the use of the molar concentration scale is more reliable [ 60 , 61 ].…”

“…A direct determination of the stability of these species is often hard since they rarely exceed the value of log K = 1.0. A detailed description of the basic principles of this approach [ 41 , 49 , 51 , 54 ] and some examples can be found, for example, in refs [ 50 , 52 , 55 – 59 ]. Briefly, for a simple monoprotic acid (HL), the lowering effect of the “apparent” protonation constant (log K i H app ) in an “interacting” medium ( e.g.…”