Experimental reduction of aqueous sulphate by hydrogen under hydrothermal conditions: Implication for the nuclear waste storage
Sulphate reduction by hydrogen, likely to occur in deep geological nuclear waste storage sites, was studied experimentally in a two-phase system (water + gas) at 250–300 °C and under 4–16 bars H 2 partial pressure in hydrothermal-vessels. The calculated activation energy is 131 kJ/mol and the half-l...
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Published in | Geochimica et cosmochimica acta Vol. 73; no. 16; pp. 4824 - 4835 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier Ltd
15.08.2009
|
Subjects | |
Online Access | Get full text |
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Summary: | Sulphate reduction by hydrogen, likely to occur in deep geological nuclear waste storage sites, was studied experimentally in a two-phase system (water
+
gas) at 250–300
°C and under 4–16
bars H
2 partial pressure in hydrothermal-vessels. The calculated activation energy is 131
kJ/mol and the half-life of aqueous sulphate in the presence of hydrogen and elemental sulphur ranges from 210,000 to 2.7
×
10
9
years at respective temperatures of 90
°C, the thermal peak in the site and 25
°C, the ambient temperature far from the site. The features and rate of the sulphate reduction by H
2 are close to those established for TSR in oil fields. The experiments also show that the rate of sulphate reduction is not significantly affected in the H
2 pressure range of 4–16
bars and in the pH range of 2–5, whereas a strong increase is measured at pH below 2. We suggest that the condition for the reaction to occur is the speciation of sulphate dominated by non symmetric species (
HSO
4
-
at low pH), and we propose a three steps reaction, one for each intermediate-valence sulphur species, the first one requiring H
2S as electron donor rather than H
2. We distinguish two possible reaction pathways for the first step, depending on pH: reduction of sulphate into sulphur dioxide below pH 2 or into thiosulphate or sulphite
+
elemental sulphur in the pH range 2–5. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 ObjectType-Article-2 ObjectType-Feature-1 |
ISSN: | 0016-7037 1872-9533 |
DOI: | 10.1016/j.gca.2009.05.043 |