Apparent molal volumes of aqueous rare earth salts fit to the Pitzer equation

The apparent molal volumes (V_φ) of the trivalent rare earth (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) chlorides, nitrates and perchlorates have been calculated from the density measurements at 25 C and (5 to 80) C and 0.02-4 m. The values of V_φ have been fitted to the Pitzer equations, V_φ = V̄⁰ + (A _vI/(1.2m) ln(1 + 1.2I^0.5) + 2RTm(β^V(0) + β^V(1) g(y) + mC^V), where V̄⁰ is the infinite dilution partial molal volume, A_v is the Debye-Hückel slope, I is the ionic strength, and g(y) = (2/y²)·[1-(1 + y) exp(-y)] where y = 2(I^0.5). The Pitzer volume parameters β^V(0), β^V(1) and C^V are functions of temperature. The values of V̄⁰, β^V(0), β^V(1), and C^V for most of the rare earth chlorides are similar orders of magnitude. These results should be useful in estimating the effect of pressure on the equilibria of rare earths in natural waters over a wide range of temperature.