The rate of sulfide oxidation by δMnO2 in seawater

Wensheng Yao, Frank J Millero

Research output: Contribution to journalArticle

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Abstract

The rate of oxidation of hydrogen sulfide by manganese dioxide in seawater was determined as a function of pH (2.0-9.0), temperature (5-45°C), and ionic strength (0-4 M). The overall rate constant, k, in seawater at pH = 8.17 was found to be first order with respect to both sulfide and manganese dioxide: - d[H2S]T dt = k[H2S]τ[MnO2]. The rate constant, k, for seawater (S = 35.8, pH = 8.17) at 25°C was found to be 436 M-1 min-1, or 0.0244 m-2 1 min-1 when [MnO2] is expressed in surface area (m2/L). The energies of activation were found to be 14 ± 1 KJ mol-1 and 10 ± 1 KJ mol-1, respectively, for pH = 8.2 and pH = 5.0 in seawater (S = 35). The rate increased from pH 2.0 to a maximum at a pH of about 5.0 and decreased at higher pH. This pH dependence was attributed to formation of a surface complex between >MnO- and H2S. As the concentration of HS- increases above pH = 5 the rate of the reaction decreases. The rate of sulfide oxidation by MnO2 is not strongly dependent on ionic strength. The rates in 0.57 M NaCl were found to be slightly higher than the rates in seawater. Measurements made in solutions of the major sea salts indicated that Ca2+ and Mg2+ caused the rates to decrease, apparently by absorbing on the surface of manganese dioxide. Measurements made in artificial seawater (Na+, Mg2+, Ca2+, Cl-, and SO2- 4) were found to be in good agreement with the measurements in actual seawater. Phosphate was found to inhibit the reaction significantly.

Original languageEnglish (US)
Pages (from-to)3359-3365
Number of pages7
JournalGeochimica et Cosmochimica Acta
Volume57
Issue number14
DOIs
StatePublished - 1993

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Sulfides
Seawater
sulfide
seawater
oxidation
Oxidation
Ionic strength
manganese
Rate constants
Hydrogen Sulfide
rate
sea salt
hydrogen sulfide
Salts
Chemical activation
Phosphates
surface area
phosphate
manganese dioxide

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

The rate of sulfide oxidation by δMnO2 in seawater. / Yao, Wensheng; Millero, Frank J.

In: Geochimica et Cosmochimica Acta, Vol. 57, No. 14, 1993, p. 3359-3365.

Research output: Contribution to journalArticle

Yao, Wensheng ; Millero, Frank J. / The rate of sulfide oxidation by δMnO2 in seawater. In: Geochimica et Cosmochimica Acta. 1993 ; Vol. 57, No. 14. pp. 3359-3365.
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abstract = "The rate of oxidation of hydrogen sulfide by manganese dioxide in seawater was determined as a function of pH (2.0-9.0), temperature (5-45°C), and ionic strength (0-4 M). The overall rate constant, k, in seawater at pH = 8.17 was found to be first order with respect to both sulfide and manganese dioxide: - d[H2S]T dt = k[H2S]τ[MnO2]. The rate constant, k, for seawater (S = 35.8, pH = 8.17) at 25°C was found to be 436 M-1 min-1, or 0.0244 m-2 1 min-1 when [MnO2] is expressed in surface area (m2/L). The energies of activation were found to be 14 ± 1 KJ mol-1 and 10 ± 1 KJ mol-1, respectively, for pH = 8.2 and pH = 5.0 in seawater (S = 35). The rate increased from pH 2.0 to a maximum at a pH of about 5.0 and decreased at higher pH. This pH dependence was attributed to formation of a surface complex between >MnO- and H2S. As the concentration of HS- increases above pH = 5 the rate of the reaction decreases. The rate of sulfide oxidation by MnO2 is not strongly dependent on ionic strength. The rates in 0.57 M NaCl were found to be slightly higher than the rates in seawater. Measurements made in solutions of the major sea salts indicated that Ca2+ and Mg2+ caused the rates to decrease, apparently by absorbing on the surface of manganese dioxide. Measurements made in artificial seawater (Na+, Mg2+, Ca2+, Cl-, and SO2- 4) were found to be in good agreement with the measurements in actual seawater. Phosphate was found to inhibit the reaction significantly.",
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