On Gold(I) Complexes and Anodic Gold Dissolution in Sulfite–Thiourea Solutions

Processes involving gold(I) complexes were studied in sulfite–thiourea (TU) solutions. It is shown that at pH >5 the complex [ AuTU 2 + ] undergoes irreversible decomposition followed by deprotonation and formation of a solid phase. From the data of pH in mixed solutions, the equilibrium constant...

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Bibliographic Details
Published in:Journal of solution chemistry 2017-04, Vol.46 (4), p.989-1003
Main Authors: Mironov, Igor V., Kal’nyi, Danila B., Kokovkin, Vasiliy V.
Format: Article
Language:English
Subjects:
Anodic dissolution
Chemical equilibrium
Chemistry
Chemistry and Materials Science
Condensed Matter Physics
Dissolution
Geochemistry
Gold
Industrial Chemistry/Chemical Engineering
Inorganic Chemistry
Oceanography
Physical Chemistry
Solid phases
Thioureas
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Summary:Processes involving gold(I) complexes were studied in sulfite–thiourea (TU) solutions. It is shown that at pH >5 the complex [ AuTU 2 + ] undergoes irreversible decomposition followed by deprotonation and formation of a solid phase. From the data of pH in mixed solutions, the equilibrium constants were evaluated: Au ( SO 3 ) 2 3 - + i TU ⇌ Au ( SO 3 ) 2 - i TU i 2 i - 3 + i SO 3 2 - , log 10 β 1  = −1.2, log 10 β 2  = −3.6. Some aspects of the anodic dissolution of gold in mixed sulfite–thiourea solutions are considered. With the help of the carbonate buffer system the change of the anodic current density j a was studied at high pH; j a (pH) has a maximum at pH 11.6–11.9 for E a  = 0.3–0.6 V (vs. NHE). At pH > 12.0, the j a values decrease sharply. Possible mechanisms of anodic gold dissolution, as well as the role of sulfite, are discussed.
ISSN:0095-9782
1572-8927
DOI:10.1007/s10953-017-0616-9