Kinetic investigation of the lanthanide(III)-nitrate complexation reaction

Abstract

Using ultrasonic relaxation technique the kinetics of lanthanide nitrate complexation were investigated in the presence of excess nitrate ion for NdUII), Gd(III), Dy(II1) and Er(II1). The absorption spectra could most simply be interpreted in terms of a double relaxation. At 25°C the complexation rate constants, kS4, were 1.8 x lo8 s-' for Nd(II1) and 0.6 x los s-l for Er(1II). These rate constants were compared with those from earlier lanthanide complexation studies to interpret the overall complexation mechanism. Rate constants could not be obtained for the Dy and Gd systems.

Isopiestic determination of the activity coefficients of some aqueous rare earth electrolyte solutions at 25.degree.C. 3. The rare earth nitrates

“…This factor, together with the reduction in the charge and number of ions in these solutions, accounts for the fact that the rare earth nitrate In y ± values are not as high as the chloride and perchlorate values. This displacement of rare earth Ion Inner sphere water by the nitrate Ion Is also observed in ultrasonic absorption experiments (15,16). If a rare earth nitrate solution is diluted, the amount of outer sphere complexes should increase relative to the amount of Inner sphere complexes.…”

“…The symmetry of the uncomplexed nitrate Ion In aqueous solution is known to be reduced from the expected D3h symmetry, and this reduction In symmetry has been interpreted in terms of the formation of one fairly strong hydrogen bond between the nitrate ion and a water molecule (4). The rare earth nitrates form appreciable amounts of inner sphere complexes (1-3, 5,13,15,16), especially at high concentrations. The formation of inner sphere complexes will result In the displacement of water from the rare earth ion's Inner sphere, and will reduce the charge on the rare earth ion.…”

“…Choppin et al (2,3) have interpreted their spectral and thermodynamic results as indicating that complex formation in dilute rare earth nitrate solutions consists predominantly of outer sphere rare earth nitrate complexes, with a few percent of inner sphere complexes. Ultrasonic absorption results (5, 15,16) suggest that the extent of inner sphere complex formation may be even larger in these solutions. At high concentrations the Journal of Chemical and Engineering Data, Vol. amount of inner sphere nitrate complexes formed appears to be quite large (1,13).…”

Electron spin relaxation as a tool for studying the dynamics in the outer solvation sphere of6S spin state ions

“…There is little literature in favour of the assumption that the molecular motions are slowed up in the outer solvation sphere [37,39], mainly because of the absence of direct experimental evidence. Since it is likely that strong electric fields, of the order of 104-105 volt/cm, are still present at a distance from the ion of ~ 4 A, a reduction of the mobility of solvent molecules is to be expected [40].…”

Acid strength dependent behaviour of Gd(III) ions in aqueous medium and its effect on Gd(III) separation from aqueous phase

“…To improve the efficacy of these processes the knowledge on behavior of lanthanide ions in acidic solution is of great importance. Although thermo-physical, spectroscopic and other properties of rare-earth chlorides, perchlorates and nitrates have been studied by quite a number of groups [21][22][23][24][25][26][27][28][29][30], to the best of knowledge of the authors, such study as a function of acid (ionic) strength of aqueous medium has not been reported so far. The authors therefore felt it worthwhile to explore the behavior of a typical lanthanide ion in medium of nitric acid of varying strength which essentially changed the ionic strength of the medium.…”