Solid-Solute Phase Equilibria in Aqueous Solutions IX. Thermodynamic Analysis of Solubility Measurements: La(OH)_m(CO₃)_q•rH₂O

Abstract

Dedicated to Prof. Hitoshi Ohtaki on the occasion of his 60th birthdayThe aqueous solubilities of La(OH)p^(COaJjA 0.1 H20, basic lanthanum carbonate of ancylite type, have been investigated as a function of ionic strength at 25.0 °C. The stoichiometric solubility constants defined by log* K1 0 = log [La3 + ] + 1.1 log pco -3 log [H+1 have the values 11.10, 11.32, 11.42, 11.63, and 11.70 for / = 0.1, 0.25, 1.0, 2.0, and 4.0 mol kg (Na)C104 respectively. The extrapolation to infinite dilution using the Pitzer equations resulted in a "thermodynamic" solubility constant, log* K° 0 = 10.48 ± 0.08. This in turn led to the Gibbs energy of ancylite formation: Af G f98 {La(OH)08(CO3)11 0.1 H20} = -1.531.5 kJ mol-1.

Solid–solute phase equilibria in aqueous solution. XVI. Thermodynamic properties of malachite and azurite—predominance diagrams for the system Cu 2+– H2 O– CO 2

“…The application of the Davies approximation, (30) the specific ion-interaction theory (31) and the Pitzer concept (32) to the extrapolation of the solubility constants to zero ionic strength has been discussed in detail previously. (3,4,27,28) Basically, the Davies approximation suffices to predict the ionic strength dependence of log K I ps0 of transition metal carbonates up to I = 1.00 mol · kg −1 NaClO 4 . It can be expected that the specific ioninteraction theory leads to even better results for the extrapolation of log K I ps0 to infinite dilution than the Pitzer formalism, because the ternary Pitzer parameters for the system Cu(ClO 4 ) 2 -NaClO 4 are unknown.…”

“…Details about the construction of the solubility cells as well as the procedures for the potentiometric measurements and calibration of the glass electrodes (Schott H 1180) can be found elsewhere. (25)(26)(27)(28) The solid phases were checked by x-ray diffraction analyses before and after the solubility measurements. No changes in the x-ray pattern of malachite or azurite were observed.…”

Rare earth element partitioning between Fe oxyhydroxide precipitates and aqueous NaCl solutions doped with NaHCO3: Determinations of rare earth element complexation constants with carbonate ions.

“…We adopted the K d (REE) values in the runs with reaction times of 135~145 hours. Kawabe et al (1999a, b) (c) , (Caro and Lemaitre-Blaise, 1969;Meinrath and Takeishi, 1993;Gamsjäger et al, 1995). These REE phases have been obtained from REE(III) solutions in contact with atmospheric air and CO 2 , and pH of the experimental solutions were 4.0~7.0.…”

(Solid + solute) phase equilibria in aqueous solution. XIII. Thermodynamic properties of hydrozincite and predominance diagrams for (Zn2++ H2O+ CO2)

“…The procedures of the pH measurements, as well as the calibration of the glass electrodes (Schott H 1180), were described in detail previously. (19,20) Reaction (1) was considered to have reached its equilibrium when the drift of the e.m.f. readings did not exceed 0.1 mV per day.…”