Chemical Thermodynamics of Tin - Volume 12 - OECD Nuclear ...

308
A Discussion of selected references
Figure A-22: Solubility isotherms in the system SnF 2 -HF-H 2 O in aqueous solutions at
t = 0, 5, 9.9, 15.4, 20.3 and 30 °C.
SnF 2
%
80
70
60
50
40
SnF 2
*H 2
O 0 °C
SnF 2
0 °C
SnF 2
*2HF 0 °C
SnF 2
5 °C
SnF 2
9,9 °C
SnF 2
15,4 °C
SnF 2
20,3 °C
SnF 2
30,0 °C
30
20
10
0
0 10 20 30 40 50 60
HF %
There are several solubility points, where the sum of HF + SnF 2 exceeds 100%
or is very near 100%. From the scatter of data an accuracy of 2 − 3% can be assumed.
The composition of the solid phase for data above 0 °C seems to comply with
anhydrous tin fluoride. Not all data were used, however, to determine the chemical
composition of the wet residue. From the plot of all data a solubility of 40 − 50% SnF 2
(4.5 to 9.0 mol·kg –1 H 2 O) at t = 25 °C can be estimated. This is in agreement with the
data of [1963HEF]. In a separate table the author reports “solubilities in water” at
different temperatures without further remarks (Table A-18).
These data represent data from Table A-17 with the lowest HF content,
however, still until 9%. In [1972GME] these data were listed as solubility in pure water.
ο
Using the complex formation constants seletected by this review and Δ
fGm
of HF(aq),
HF −
2
and F – ο
in Table IV-1 a Gibbs energy of formation Δ
fGm
of SnF 2 (s) was estimated
by stepwise simulation of solubility as shown in Figure A-23.
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012