Fractionation of sulfur and oxygen isotopes in sulfate by soil sorption

Journal Article · Mon Oct 01 00:00:00 EDT 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90016-E· OSTI ID:6264146

van Stempvoort, D R; Reardon, E J ^[1]; Fritz, P ^[2]

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1. Univ. of Waterloo, Ontario (Canada)
2. GSF-Instituet fuer Hydrologie, Neuherberg (West Germany)

Both field and laboratory data indicate that there is no significant isotope fractionation of sulfate during sorption in upland forest Podzols. The dominant sulfate sorption process in these soils is adsorption onto mineral surfaces. In the Plastic Lake watershed, Dorset, Ontario, Canada, fractions of sulfate from Podzol B-horizons have the following mean isotope ({per thousand}) compositions: water soluble sulfate, {delta}{sup 34}S = +6.4; {delta}{sup 18}O = {minus}5.3; bicarbonate-exchange sulfate by two methods, {delta}{sup 34}S = +4.5 and +3.4; {delta}{sup 18}O = {minus}6.2 and {minus}5.6; dissolved sulfate in B-horizon soilwater seepage, {delta}{sup 34}S = +4.8; {delta}{sup 18}O = {minus}5.4. These data indicate that soil sorption enriches dissolved sulfate in {sup 34}S by approximately 1 {plus minus} 1{per thousand} and in {sup 18}O by 0 {plus minus} 1{per thousand} relative to sorbed sulfate. Similar results were obtained by laboratory sorption of sulfate by prepared goethite, which is a mineral representative of soil sorption sites in acidic Podzols like the one at Plastic Lake. The mean fractionation between sorbed and dissolved sulfate was found to be {minus}0.3{per thousand} for {sup 34}S and 0.1{per thousand} for {sup 18}O. Earlier literature has confused the term adsorption; in many cases the more general term sorption, or retention, should be used. Pronounced fractionation of S and O isotopes in sulfate by lake and ocean sediments has been attributed to adsorption or retention but is more likely the result of sulfate reduction. Apparently, at Earth-surface conditions the only substantial isotope shifts in sulfate occur during microbial processes.

• OSTI ID: 6264146
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:10; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540210* -- Environment
Terrestrial-- Basic Studies-- (1990-)
58 GEOSCIENCES
580000 -- Geosciences
ADSORPTION
CANADA
CHEMICAL COMPOSITION
CHEMISTRY
FRACTIONATION
GEOCHEMISTRY
ISOTOPE RATIO
ISOTOPES
NORTH AMERICA
ONTARIO
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
SEPARATION PROCESSES
SOIL CHEMISTRY
SOILS
SORPTION
SORPTIVE PROPERTIES
SULFATES
SULFUR COMPOUNDS
SULFUR ISOTOPES
SURFACE PROPERTIES