Response to comment on 'Determination of metal bi sulphide stability of Mn2+, Fe2+,Co2+,Ni2+,Cu2+ and Zn2+ by voltammetric methods

Luther, George W. III, Theberge, S. M., Rickard, David T. and Oldroyd, Anthony 1996. Response to comment on 'Determination of metal bi sulphide stability of Mn2+, Fe2+,Co2+,Ni2+,Cu2+ and Zn2+ by voltammetric methods. Environmental Science and Technology 30 (2) , pp. 3640-3641.

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Abstract

The stoichiometry as well as the conditional and thermodynamic stability constants for the (bi)sulfide complexes of the +2 cations of Mn, Fe, Ni, Co, Cu, and Zn have been determined by voltammetric methods in seawater and chloride solutions of varying ionic strength. Acid−base titrations allowed for the determination of the proton stoichiometry of the complexes. Mn, Fe, Ni, and Co form bisulfide, HS-, complexes of stoichiometry MSH+, M2(SH)3+, and M3(SH)5+, which are labile under diffusion control conditions, in seawater at pH values > 7. These complexes dissociate below pH = 7, releasing H2S from solution. Evidence for sulfide-rich complexes of form M(SH)2 was not found. Cu and Zn form sulfide, S2-, complexes of stoichiometry MS and M2S32-, which are inert (nonlabile) under diffusion control conditions, in seawater at pH values > 7. There is no evidence for metal-rich sulfide complexes of stoichiometry [MxS]2x-2 from the titration data. The M2S32- complexes are tetrameric structures (M4S6) with tetrahedral metal coordination based on known thiolate complex and mineral geometries. The Zn complexes dissociate below pH = 6.7, releasing H2S from solution. However, the Cu complex does not fully dissociate below pH = 2 because of Cu(II) reduction and production of polysulfide, which do not appear to be quantitative. At seawater pH, both Zn and Cu sulfide complexes can be deposited on a mercury drop, indicating that these metal complexes are likely responsible for the presence of nanomolar levels of sulfide in oxic seawater. Determination of metal (Bi)Sulfide stability constants of Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+ by voltammetric methods - ResearchGate. Available from: http://www.researchgate.net/publication/233916517_Response_to_comment_on_Determination_of_metal_%28bi%29sulfide_stability_constants_of_Mn2_Fe2_Co2_Ni2_Cu2_and_Zn2_by_voltammetric_methods [accessed Apr 1, 2015].

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Subjects:	Q Science > QD Chemistry
Publisher:	American Chemical Society
ISSN:	0013-936X
Related URLs:	http://pubs.acs.org/doi/abs/10.1021/es95...
Last Modified:	04 Jun 2017 08:02
URI:	https://orca.cardiff.ac.uk/id/eprint/71920

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