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Deposition and dissolution of metal sulfide layers at the Hg electrode surface in seawater electrolyte conditions

Deposition and dissolution of metal sulfide layers at the Hg electrode surface in seawater... Environmental contextThe electrochemical detection of many sulfur compounds in natural waters is based on the deposition of a HgS layer at the Hg electrode. In samples containing metal ions in excess of sulfide species, electrochemical exchange reactions between the HgS and the metal ion produce metal-sulfide voltammetric peaks. These peaks can easily be misinterpreted as dissolved sulfide species, and hence do not reflect the bulk state of the solution.AbstractCyclic voltammetry on a Hg electrode was used to investigate the influence of metal ion (Zn, Cd, Cu, Fe, Pb, Co) on HgS depositiondissolution in seawater conditions. Due to the exchange of electrons between Hg2 from a HgS layer and free metal (M2) from the solution (HgSlayer M2 2e MSlayer Hg0), the Hg electrode becomes the site for surface metal sulfide (MS) formation. The exchange reaction is reversible, and the surface-formed MS layer reduces at a more negative potential than HgS (MSlayer 2e H M0 HS). The potentials of both electrode reactions, and the formation and reduction of the MS layer, are determined by the MS solubility product. In solutions containing excess of the free metal ions in comparison to the free sulfide, the exchange reaction produces MS voltammetric peaks, which can be misrepresented for the dissolved sulfide species. This research indirectly confirmed that the FeS electrochemical signal, usually recorded in an iron- and sulfide-rich environment at ~1.1V v. Ag/AgCl, is not due to FeS reduction. The connection between the studied MS reduction peak potentials and the solubility products shows that the FeS layer formed by an electrochemical exchange reaction with HgS should be reduced at the Hg surface ~100mV more negative than free Fe2. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Environmental Chemistry CSIRO Publishing

Deposition and dissolution of metal sulfide layers at the Hg electrode surface in seawater electrolyte conditions

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References (43)

Publisher
CSIRO Publishing
Copyright
Copyright © The Author(s). Published by CSIRO Publishing
ISSN
1448-2517
eISSN
1449-8979
DOI
10.1071/EN13056
Publisher site
See Article on Publisher Site

Abstract

Environmental contextThe electrochemical detection of many sulfur compounds in natural waters is based on the deposition of a HgS layer at the Hg electrode. In samples containing metal ions in excess of sulfide species, electrochemical exchange reactions between the HgS and the metal ion produce metal-sulfide voltammetric peaks. These peaks can easily be misinterpreted as dissolved sulfide species, and hence do not reflect the bulk state of the solution.AbstractCyclic voltammetry on a Hg electrode was used to investigate the influence of metal ion (Zn, Cd, Cu, Fe, Pb, Co) on HgS depositiondissolution in seawater conditions. Due to the exchange of electrons between Hg2 from a HgS layer and free metal (M2) from the solution (HgSlayer M2 2e MSlayer Hg0), the Hg electrode becomes the site for surface metal sulfide (MS) formation. The exchange reaction is reversible, and the surface-formed MS layer reduces at a more negative potential than HgS (MSlayer 2e H M0 HS). The potentials of both electrode reactions, and the formation and reduction of the MS layer, are determined by the MS solubility product. In solutions containing excess of the free metal ions in comparison to the free sulfide, the exchange reaction produces MS voltammetric peaks, which can be misrepresented for the dissolved sulfide species. This research indirectly confirmed that the FeS electrochemical signal, usually recorded in an iron- and sulfide-rich environment at ~1.1V v. Ag/AgCl, is not due to FeS reduction. The connection between the studied MS reduction peak potentials and the solubility products shows that the FeS layer formed by an electrochemical exchange reaction with HgS should be reduced at the Hg surface ~100mV more negative than free Fe2.

Journal

Environmental Chemistry – CSIRO Publishing

Published: Sep 20, 2013

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