Isopiestic determination of the activity coefficients of some aqueous rare earth electrolyte solutions at 25.degree.C. 1. The rare earth chlorides

Apparent molar heat capacities and apparent molar volumes ofY2(SO4)3(aq),La2(SO4)3(aq),Pr2(SO4)3(aq),Nd2(SO4)3(aq),Eu2(SO4)3(aq),Dy2(SO4)3(aq),Ho2(SO4)3(aq), andLu2(SO4)3(aq)atT= 298.15 K andp= 0.1 MPa

“…The effects of the overall hydration increase on thermodynamic and transport properties have been discussed in detail previously. (11,54,66,68,69,73) Values of C p,φ for these R X 3 (aq) electrolytes exhibit slightly more complicated behavior. At constant lower molalities, the values of C p,φ for the RCl 3 (aq) (15,16) and R(ClO 4 ) 3 (aq) (56) at T = 298.15 K are nearly constant from lanthanum to neodymium, increase with atomic number between neodymium and terbium, and then remain nearly constant for the remaining RCl 3 (aq) or increase slowly with increasing atomic number for the R(ClO 4 ) 3 (aq).…”

“…Other thermodynamic properties such as water activities (11,68) of RCl 3 (aq) and R(ClO 4 ) 3 (aq) solutions and the standard ionic entropies (69) of the R 3+ (aq), and transport properties (66) of RCl 3 (aq) and R(ClO 4 ) 3 (aq) such as electrical conductances and viscosities, have an approximately S-shaped variation with ionic radius at constant molality. This is in contrast with the volumetric properties for these systems, which have a reversal in the overall trend between Nd 3+ (aq) and Tb 3+ (aq).…”

“…Values of a w at any constant molality show a slow but regular decrease from La to Nd, and from about Dy to Lu; however, between Nd and around Dy, the a w values also decrease, but they do so much more rapidly with changes in ionic radius. (11,68) The slow decrease of a w with increasing atomic number for the light and for the heavy rare-earths is attributed to the increasing surface charge density of the R 3+ as the lanthanide contraction occurs, which results in an increasing strength of the interaction between the R 3+ ion and the negative end of the dipoles of the nearby water molecules. When an inner-sphere water of hydration is displaced between Nd and Tb, the primary hydration sphere shrinks more rapidly with decreasing ionic radius, and is then less effective in screening the secondary hydration sphere from the central ion.…”

An experimental study of the solubility and speciation of neodymium (III) fluoride in F-bearing aqueous solutions

“…The first involved optimization of U with respect to K sp , b, b NaClO 4 and distances of closest approach for Nd 3+ and NdF 2+ (Model A). In the second procedure, we optimized only K sp , b, and b NaClO 4 , setting the distances of closest approach for Nd 3+ and NdF 2+ at 9 and 4.5 Å , respectively (Model B; Spedding et al, 1976;Gammons et al, 1996). Given that calculation of pH at the temperature of the experiments requires knowledge of H + activity at 25°C, the parameter b for a NaClO 4 -based electrolyte for 25°C was also optimized (back-calculated) to provide the best fit to the experimental data.…”

Activity coefficients in (hydrogen chloride+holmium chloride) (aq) from T=(278.15 to 328.15) K

“…Activity coefficients of some pure aqueous rareearth chloride solutions have been reported based on isopiestic measurements [13][14][15].…”