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Refining Thermodyna...
Refining Thermodynamic Constants for Mercury(II)-Sulfides in Equilibrium with Metacinnabar at Sub-Micromolar Aqueous Sulfide Concentrations
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- Drott, Andreas (författare)
- Umeå universitet,Kemiska institutionen
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- Björn, Erik (författare)
- Umeå universitet,Kemiska institutionen
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- Bouchet, Sylvain (författare)
- Umeå universitet,Kemiska institutionen
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- Skyllberg, Ulf (författare)
- Swedish University of Agricultural Sciences,Sveriges lantbruksuniversitet,Institutionen för skogens ekologi och skötsel,Department of Forest Ecology and Management,SLU
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(creator_code:org_t)
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- 2013-04-04
- 2013
- Engelska.
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 47:9, s. 4197-4203
- Relaterad länk:
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https://urn.kb.se/re...
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https://doi.org/10.1...
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https://res.slu.se/i...
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Abstract
Ämnesord
Stäng
- An important issue in mercury (Hg) biogeochemistry is to explore the influence of aqueous Hg(II) forms on bacterial uptake, and subsequent methyl mercury formation, under iron(III) and sulfate reducing conditions. The success of this is dependent on relevant information on the thermodynamic stability of Hg-sulfides. In the present study, we determined the solubility of a commercially available HgS(s) phase, which was shown by X-ray diffraction to be a mixture of 83% metacinnabar and 17% cinnabar. At aqueous sulfide concentrations between 0.060 and 84 µM, well below levels in previous studies, we report a solubility product (log Ksp±SE) of -36.8±0.3 (HgS(s) + H+ = Hg2+ + HS-, I=0, T=25°C, pH 6-10, n=20) for metacinnabar. This value is 0.7 log units higher than previous estimates. Complementing our data with data from Paquette and Helz (1997), we took advantage of a large data set (n=65) covering a wide range of aqueous sulfide (0.06 µM-140 mM), and pH (1-11). Based on this we report refined formation constants (±SE) for the three aqueous Hg(II)-sulfide species proposed by Schwarzenbach and Widmer (1963): Hg2+ + 2HS- = Hg(SH)20; log K = 39.1±0.1, Hg2+ + 2HS- = HgS2H- + H+; log K = 32.5±0.1, Hg2+ + 2HS- = HgS22- + 2H+; log K = 23.2±0.1. Our refined log K values differ from previous estimates by 0.2-0.6 log units. Furthermore, at the low sulfide concentrations in our study we could rule out the value of -10.0 for the reaction HgS(s) + H2O = HgOHSH(aq), as reported by Dyrssén and Wedborg (1991). By establishing a solubility product for the most environmentally relevant HgS(s) phase, metacinnabar, and extending the range of aqueous sulfide concentrations to sub-µM levels, relevant for soils, sediments and waters, this study decreases the uncertainty in stability constants for Hg-sulfides, thereby improving the basis for understanding the bioavailability and mobility of Hg(II) in the environment.
Ämnesord
- NATURVETENSKAP -- Kemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences (hsv//eng)
- LANTBRUKSVETENSKAPER -- Lantbruksvetenskap, skogsbruk och fiske -- Skogsvetenskap (hsv//swe)
- AGRICULTURAL SCIENCES -- Agriculture, Forestry and Fisheries -- Forest Science (hsv//eng)
Nyckelord
- Mercury
- sulfide
- chemical speciation modeling
- metacinnabar
- cinnabar
- solubility
Publikations- och innehållstyp
- ref (ämneskategori)
- art (ämneskategori)
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