Environ. Sci. Technol. 1989, 23, 209-213
Oxidation of H2S with H202 in Natural Waters Frank J. Mlllero,* Arthur LeFerriere,f Marino Fernandez, Scott Hubinger, and J. Peter Hershey University of Miami, Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, Florida 33149
The oxidation of H2S with H202 has been studied as a function of pH (2-13), temperature (5-45 °C), and ionic strength (0-6 m) in seawater and NaCl solutions. The rate constant, k (min'1 M'1), for the oxidation d[H2S]T/dt = -&[H2S]t[H202] at pH = 8 was found to be given by log k = 8.60 2052/T + 0.084/1/2 in seawater and NaCl solutions ( = 0.07). The energy of activation (AE* = 39 ± 2 kJ mol'1) for the reaction was independent of ionic strength. The rate increased from pH = 2 to 8 due to the increased rate of oxidation of HS" compared to H2S. The rate constant for the oxidation of H^ was found to be zero at every temperature. The rate constant for the oxidation of HS" was found to be 12.0 ± 0.5, 36.2 ± 0.4, and 211 ± 5 min'1 M"\ respectively, at 5, 25, and 45 °C. The energy of activation ( 2?!* = 51 ± 3 kJ) for HS" was higher than the AE* for the overall reaction due to the effect of temperature on Ku the dissociation constant of H2S. Above pH = 8.0, the rate slowly decreased in a near linear manner. The formation of H02", which does not react easily with HS", could be part of the cause of this decrease.
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Introduction The oxidation of hydrogen sulfide, H2S, with hydrogen peroxide, H202, has been studied by a number of workers (1-5). The most extensive measurements in aqueous solutions were made by Hoffmann (5). His interest in the oxidation of H2S by H202 was related to the use of H202 to eliminate odor in sewage waters and other anaerobic environmental systems. The elimination of H2S can also alleviate corrosion in sewer lines. These earlier studies (5) were confined to low ionic strength solutions at 25 °C over a pH range of 2-8. We became interested in the oxidation of H2S by H202 due to the formation of H202 (6-9) in various natural waters that may contain H2S. Although the oxidation of HyS by H202 in surface waters may not be competitive with 02 oxidation, it may be important in rainwater and marine aerosols.
In the present paper, we present measurements of the rates of oxidation of H2S by H202 as a function of pH (2-13), temperature (5-45 °C), and ionic strength (0-6 m) in seawater and NaCl solutions. These results should provide reliable kinetic data valid for a wide range of natural conditions.
Experimental Section Reaction Vessel. The reactions at pH > 8 were carried out in a 500-cm3 jacketed glass beaker under a nitrogen blanket. The temperature was controlled to ±0.05 °C with a Forma bath. Solution samples were taken from the closed vessel with a Rainin automatic pipet. For the measurements at pH
