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Kinetics and Mechanism of Trithionate and Tetrathionate Oxidation at Low pH by Hydroxyl Radicals

Kinetics and Mechanism of Trithionate and Tetrathionate Oxidation at Low pH by Hydroxyl Radicals The oxidation kinetics of trithionate (S3O 6 2- ) and tetrathionate (S4O 6 2- ) with hydroxyl radicals (OH*) have been investigated in systems analogous to acid mine drainage (AMD) environments. The discovery of hydroxyl radical (OH*) formation on pyrite surfaces (Borda et al., 2003) suggests hydroxyl radicals may affect the oxidation kinetics of intermediate sulfur species such as tetrathionate. Cyclic voltammetry experiments in acidic solutions indicate that the reaction of S4O 6 2- with OH* goes through an unknown intermediate, tentatively assigned as S3O 4 n- . An outer-sphere electron transfer mechanism for the reaction of S4O 6 2- with OH* to form S3O 4 n- is proposed based on experimental results. Oxidation rates for trithionate and tetrathionate in the presence of Fenton's reagent (which forms hydroxyl radicals) are too fast to be directly measured using UV-Vis spectrophotometry, electrochemical, or stop-flow spectrophotometry methods. Competitive reaction kinetics within the context of the Haber—Weiss mechanism suggests that the rate constant for the oxidation of trithionate and tetrathionate with OH* is in excess of 108 M-1 sec-1. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aquatic Geochemistry Springer Journals

Kinetics and Mechanism of Trithionate and Tetrathionate Oxidation at Low pH by Hydroxyl Radicals

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References (74)

Publisher
Springer Journals
Copyright
Copyright © 2003 by Kluwer Academic Publishers
Subject
Earth Sciences; Geochemistry; Hydrology/Water Resources; Hydrogeology; Water Quality/Water Pollution
ISSN
1380-6165
eISSN
1573-1421
DOI
10.1023/B:AQUA.0000019495.91752.d7
Publisher site
See Article on Publisher Site

Abstract

The oxidation kinetics of trithionate (S3O 6 2- ) and tetrathionate (S4O 6 2- ) with hydroxyl radicals (OH*) have been investigated in systems analogous to acid mine drainage (AMD) environments. The discovery of hydroxyl radical (OH*) formation on pyrite surfaces (Borda et al., 2003) suggests hydroxyl radicals may affect the oxidation kinetics of intermediate sulfur species such as tetrathionate. Cyclic voltammetry experiments in acidic solutions indicate that the reaction of S4O 6 2- with OH* goes through an unknown intermediate, tentatively assigned as S3O 4 n- . An outer-sphere electron transfer mechanism for the reaction of S4O 6 2- with OH* to form S3O 4 n- is proposed based on experimental results. Oxidation rates for trithionate and tetrathionate in the presence of Fenton's reagent (which forms hydroxyl radicals) are too fast to be directly measured using UV-Vis spectrophotometry, electrochemical, or stop-flow spectrophotometry methods. Competitive reaction kinetics within the context of the Haber—Weiss mechanism suggests that the rate constant for the oxidation of trithionate and tetrathionate with OH* is in excess of 108 M-1 sec-1.

Journal

Aquatic GeochemistrySpringer Journals

Published: Oct 10, 2004

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