Computer Science
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.3359y&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 57, Issue 14, pp.3359-3365
Computer Science
5
Scientific paper
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 [ H 2 S ] T / dt = k [ H 2 S ] [ MnO 2 ] . 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 [MnO 2 ] is expressed in surface area (m 2 /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 H 2 S. As the concentration of HS - increases above pH = 5 the rate of the reaction decreases. The rate of sulfide oxidation by MnO 2 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 Ca 2+ and Mg 2+ caused the rates to decrease, apparently by absorbing on the surface of manganese dioxide. Measurements made in artificial seawater (Na + , Mg 2+ , Ca 2+ , Cl - , and SO 2- 4 ) were found to be in good agreement with the measurements in actual seawater. Phosphate was found to inhibit the reaction significantly.
Millero Frank. J.
Yao Wensheng
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