Handbook of Solvents - George Wypych - ChemTech - Ventech!

1492 Victor Cherginets
and increase in acidic properties of melt. The increase of KCl molar fraction over 0.6 led to
sharp reduction of ZrO 2 solubility because the decrease of acid (PO 3- ) concentration could
not be compensated by the depolymerization process [21.3.17].
Deanhardt and Stern 47,48 studied solubilities of NiO and Y 2O 3 in molten NaCl and
Na 2SO 4 at 1100 o C. Y 2O 3 solubility product was (1.4-2.2)×10 -36 and (4.5-6.4)×10 -31 in the
chloride and the sulphate melt respectively.
The formation of YO 2-
Figure 21.3.2. The formal ionic moments (I, r X
-1 - ,Å -1 ) and polarizations
(α) of halide-ions.
was observed when oxide ion was
in excess. The formation of peroxide
ions in the presence of O 2 over
melt was favored by thermodynamic
properties. Watson and
Perry 49 have studied ZnO solubility
in molten KCl and found that it
was 2.3×10 -8 mole/kg for ZnO and
3.2×10 -12 for K 2ZnO 2.
We have studied oxide solubilities
in molten CsCl-KCl-NaCl
at 600 and 700 o C in order to estimate
oxide solubility changes
with temperature. 34-36,50 Oxide solubilities
were lower than those
predicted by Shreder’s equation
but estimations of their thermal changes usually were in a good agreement with those calculated
from Shreder’s equation. Oxides solubilities (in molar fractions) in KCl-NaCl and
CsCl-KCl-NaCl have been found to be close at the same temperature.
Some works are related to oxo-acidity studies in alkaline chloride melts with cations
of high acidity: MgO-BaCl 2-CaCl 2-NaCl, 37 CaO-CaCl 2-KCl-NaCl, 51 CeCl 3-KCl-NaCl, 52
ZnO-NaCl-ZnCl. 2.53,54 Acidic cations have been found to affect acid-base interactions by
fixing oxide ions. Oxide solubilities 37,51 were higher than those for alkaline chloride mixtures
without acidic admixtures. The same conclusions came from studies 55 on MgO solubility
in CaCl 2-CaO mixture, K s=10 -6.2 at 1133 K. The oxide solubility products in Ca-based
chlorides are increased by 4 orders of magnitude.
Solubilities (as pP) of MgO (7,61±0,06), NiO (7,44±0,09), CoO (6,25±0,12), MnO
(5,20±0,17), ZnO (4,97±0,07) and CdO (3,21±0,07) in molten eutectic SrCl 2-KCl-NaCl
(0.22:0.42:0.36) at 700 o C have been determined. 56 The precipitation of PbO from solutions
containing Pb 2+ was not observed although these cations demonstrated appreciable acidic
properties (pK=2,58±0,05). The oxide solubility products in molar fractions have been increased
by 1.95 orders of the magnitude for all the oxides.
A similar study was performed in two Ba-based melts: BaCl 2-KCl-NaCl
(0.43:0.29:0.28) and BaCl 2-KCl (0.26:0.74) at 700 o C. 57 Solubility products in molar fractions
of CdO were 5.43 and 5.62, for ZnO these magnitudes were 6.97 and 7.14 in molten
BaCl 2-KCl-NaCl and BaCl 2-KCl, respectively. The corresponding pP in KCl-NaCl were
2.01 and 1.83. The oxide solubility products in alkaline earth and Li-based chlorides are
presented in Table 21.3.2.