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

IX.1 Sulfur compounds and complexes 223
minerals Herzenbergite (SnS), Berndtite (β-SnS 2 ) and Ottemannite (Sn 2 S 3 ) are found.
β-SnS 2 occurs in several polytypic modifications [1974MIT/FUJ]. About the behaviour
of Sn 2 S 3 in contact with aqueous solutions only some general remarks from Moh and
Berndt [1964MOH/BER] are available.
Experimental work with sparingly soluble tin sulfides meets a number of
difficulties. This concerns hydrolysis of aqua complexes of Sn 2+ and Sn 4+ taking place
already in acid solutions, oxidation of tin(II) in solution by dissolved oxygen
(Reaction (IX.6)) or sulfur (Reaction (IX.7)). Sulfur is formed easily by oxidation of
H 2 S by oxygen. Oxidation with sulfur (Reaction (IX.7)) is reversible, especially at
higher pH, prolonged equilibration of Sn 4+ -containing solutions generates sulfur and
through Reaction (IX.8) thiocomplexes. Evaluation of the experimental results is
complicated by the formation of numerous hydrolytic and complex species of tin(II) and
tin(IV).
Sn 2+ + H 2 O(l) + ½ O 2 → Sn 4+ + 2 OH –
Sn 2+ + H 2 S + S Sn 4+ + 2 HS –
SnS 2 (s) + HS – →
(IX.6)
(IX.7)
2
SnS − 3 + H + (IX.8)
IX.1.1.3.1 Solubility of SnS(cr)
Solubility products of SnS mostly cited in literature are those of Latimer (1 × 10 –26 )
[1952LAT] and of Kapustinskii (1 × 10 –27 ) [1940KAP], [1938KAP/MAK] based on
thermodynamic estimations and calculations. A dependence of the SnS solubility on pH
was calculated by Kapustinskii [1940KAP], which yielded values of 9.6 × 10 –7 M at
pH = 3 and 9.7 × 10 –9 M at pH = 5.
An experimental determination of the solubility of SnS in 0.1 and 1.0 M HCl
was performed by Geyer and Mücke [1964GEY/MUC]. Care was taken to avoid
oxidation during preparation of the sulfide and all analytical operations (see Appendix).
Results are listed in Table IX-14.
Table IX-14: Solubility of SnS in aqueous HCl at 293 K.
c HCl /M s SnS /M
0.1 3.9 × 10 –5
0.1 4.0 × 10 –5
0.1 4.0 × 10 –5
1.0 2.7 × 10 –4
1.0 2.6 × 10 –4
1.0 2.4 × 10 –4
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012