Isotopic fractionation of sulfur during formation of basaluminite, alunite, and natroalunite

Jörg Prietzel; Bernhard Mayer

doi:10.1016/j.chemgeo.2004.06.048

Isotopic fractionation of sulfur during formation of basaluminite, alunite, and natroalunite

Jörg Prietzel
, Bernhard Mayer

Chair of Soil Science

University of Calgary

Research output: Contribution to journal › Article › peer-review

24 Scopus citations

Abstract

The extent of fractionation of sulfur (S) isotopes during precipitation of basaluminite and alunite in supersaturated Al₂ (SO₄)₃ solutions was determined in a laboratory synthesis experiment. An acid 0.05 M Al₂ (SO₄)₃ solution was partly neutralized with Ca(OH)₂, NaOH, and KOH to a molar OH/Al ratio of 2.0. Subsequent aging of the precipitates for 15 weeks at temperatures of 20 and 50 °C resulted in the formation of poorly crystalline basaluminite [Al₄(SO₄)(OH)₁₀· 4H₂O], of mixtures of basaluminite with crystalline natroalunite [NaAl₃(SO₄)₂ (OH)₆] or alunite [KAl₃(SO₄)₂ (OH)₆], and of pure crystalline alunite. No significant isotopic fractionation of S was observed during the precipitation of poorly crystalline basaluminite (Δδ³⁴ S_{basaluminite-solution}=+0.04±0.34‰). In contrast, the formation of alunite and natroalunite was accompanied by small but significant isotopic fractionation that favored the incorporation of the heavier isotope, ³⁴S, in the minerals. Sulfur-isotope fractionation (Δδ³⁴ S_{mineral-solution}) was +0.84±0.34‰ for alunite, and +1.72±0.34‰ for natroalunite. The extent of S-isotope fractionation was found to be dependent on (i) the chemical composition and (ii) the crystal structure of the synthesized minerals, and seems to be related to the physico-chemical properties of the involved ions (charge, radius, mass), the energy balance of the reaction, and the reaction rate. The results indicate that S-isotope mass balances in aerated acid soils are not significantly confounded by S isotopic fractionation effects associated with the formation of Al hydroxysulfates.

Original language	English
Pages (from-to)	525-535
Number of pages	11
Journal	Chemical Geology
Volume	215
Issue number	1-4 SPEC. ISS.
DOIs	https://doi.org/10.1016/j.chemgeo.2004.06.048
State	Published - 15 Feb 2005

Keywords

Alunite
Basaluminite
Natroalunite
Precipitation
S-isotope fractionation

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10.1016/j.chemgeo.2004.06.048

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@article{89bcf291a7a84fc69b168bfbfe195cb3,

title = "Isotopic fractionation of sulfur during formation of basaluminite, alunite, and natroalunite",

abstract = "The extent of fractionation of sulfur (S) isotopes during precipitation of basaluminite and alunite in supersaturated Al2 (SO4)3 solutions was determined in a laboratory synthesis experiment. An acid 0.05 M Al2 (SO4)3 solution was partly neutralized with Ca(OH)2, NaOH, and KOH to a molar OH/Al ratio of 2.0. Subsequent aging of the precipitates for 15 weeks at temperatures of 20 and 50 °C resulted in the formation of poorly crystalline basaluminite [Al4(SO4)(OH)10· 4H2O], of mixtures of basaluminite with crystalline natroalunite [NaAl3(SO4)2 (OH)6] or alunite [KAl3(SO4)2 (OH)6], and of pure crystalline alunite. No significant isotopic fractionation of S was observed during the precipitation of poorly crystalline basaluminite (Δδ34 Sbasaluminite-solution=+0.04±0.34‰). In contrast, the formation of alunite and natroalunite was accompanied by small but significant isotopic fractionation that favored the incorporation of the heavier isotope, 34S, in the minerals. Sulfur-isotope fractionation (Δδ34 Smineral-solution) was +0.84±0.34‰ for alunite, and +1.72±0.34‰ for natroalunite. The extent of S-isotope fractionation was found to be dependent on (i) the chemical composition and (ii) the crystal structure of the synthesized minerals, and seems to be related to the physico-chemical properties of the involved ions (charge, radius, mass), the energy balance of the reaction, and the reaction rate. The results indicate that S-isotope mass balances in aerated acid soils are not significantly confounded by S isotopic fractionation effects associated with the formation of Al hydroxysulfates.",

keywords = "Alunite, Basaluminite, Natroalunite, Precipitation, S-isotope fractionation",

author = "J{\"o}rg Prietzel and Bernhard Mayer",

note = "Funding Information: The authors gratefully acknowledge the generous help of Dr. H. Stanjek, who conducted the XRD analyses. M. Englschall and R. Heibl assisted in the synthesis of the minerals and in their chemical analysis. Constructive criticism of two anonymous reviewers and the guest editors was helpful in improving the manuscript and is gratefully acknowledged. The cooperation between the authors was financially supported by the German Federal Ministry for Education and Research (BMBF) as part of the German/Canadian Science and Technology Cooperation Program (Project CAN 98/037). [PD]",

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doi = "10.1016/j.chemgeo.2004.06.048",

language = "English",

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journal = "Chemical Geology",

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T1 - Isotopic fractionation of sulfur during formation of basaluminite, alunite, and natroalunite

AU - Prietzel, Jörg

AU - Mayer, Bernhard

N1 - Funding Information: The authors gratefully acknowledge the generous help of Dr. H. Stanjek, who conducted the XRD analyses. M. Englschall and R. Heibl assisted in the synthesis of the minerals and in their chemical analysis. Constructive criticism of two anonymous reviewers and the guest editors was helpful in improving the manuscript and is gratefully acknowledged. The cooperation between the authors was financially supported by the German Federal Ministry for Education and Research (BMBF) as part of the German/Canadian Science and Technology Cooperation Program (Project CAN 98/037). [PD]

PY - 2005/2/15

Y1 - 2005/2/15

N2 - The extent of fractionation of sulfur (S) isotopes during precipitation of basaluminite and alunite in supersaturated Al2 (SO4)3 solutions was determined in a laboratory synthesis experiment. An acid 0.05 M Al2 (SO4)3 solution was partly neutralized with Ca(OH)2, NaOH, and KOH to a molar OH/Al ratio of 2.0. Subsequent aging of the precipitates for 15 weeks at temperatures of 20 and 50 °C resulted in the formation of poorly crystalline basaluminite [Al4(SO4)(OH)10· 4H2O], of mixtures of basaluminite with crystalline natroalunite [NaAl3(SO4)2 (OH)6] or alunite [KAl3(SO4)2 (OH)6], and of pure crystalline alunite. No significant isotopic fractionation of S was observed during the precipitation of poorly crystalline basaluminite (Δδ34 Sbasaluminite-solution=+0.04±0.34‰). In contrast, the formation of alunite and natroalunite was accompanied by small but significant isotopic fractionation that favored the incorporation of the heavier isotope, 34S, in the minerals. Sulfur-isotope fractionation (Δδ34 Smineral-solution) was +0.84±0.34‰ for alunite, and +1.72±0.34‰ for natroalunite. The extent of S-isotope fractionation was found to be dependent on (i) the chemical composition and (ii) the crystal structure of the synthesized minerals, and seems to be related to the physico-chemical properties of the involved ions (charge, radius, mass), the energy balance of the reaction, and the reaction rate. The results indicate that S-isotope mass balances in aerated acid soils are not significantly confounded by S isotopic fractionation effects associated with the formation of Al hydroxysulfates.

AB - The extent of fractionation of sulfur (S) isotopes during precipitation of basaluminite and alunite in supersaturated Al2 (SO4)3 solutions was determined in a laboratory synthesis experiment. An acid 0.05 M Al2 (SO4)3 solution was partly neutralized with Ca(OH)2, NaOH, and KOH to a molar OH/Al ratio of 2.0. Subsequent aging of the precipitates for 15 weeks at temperatures of 20 and 50 °C resulted in the formation of poorly crystalline basaluminite [Al4(SO4)(OH)10· 4H2O], of mixtures of basaluminite with crystalline natroalunite [NaAl3(SO4)2 (OH)6] or alunite [KAl3(SO4)2 (OH)6], and of pure crystalline alunite. No significant isotopic fractionation of S was observed during the precipitation of poorly crystalline basaluminite (Δδ34 Sbasaluminite-solution=+0.04±0.34‰). In contrast, the formation of alunite and natroalunite was accompanied by small but significant isotopic fractionation that favored the incorporation of the heavier isotope, 34S, in the minerals. Sulfur-isotope fractionation (Δδ34 Smineral-solution) was +0.84±0.34‰ for alunite, and +1.72±0.34‰ for natroalunite. The extent of S-isotope fractionation was found to be dependent on (i) the chemical composition and (ii) the crystal structure of the synthesized minerals, and seems to be related to the physico-chemical properties of the involved ions (charge, radius, mass), the energy balance of the reaction, and the reaction rate. The results indicate that S-isotope mass balances in aerated acid soils are not significantly confounded by S isotopic fractionation effects associated with the formation of Al hydroxysulfates.

KW - Alunite

KW - Basaluminite

KW - Natroalunite

KW - Precipitation

KW - S-isotope fractionation

UR - https://www.scopus.com/pages/publications/14544282428

U2 - 10.1016/j.chemgeo.2004.06.048

DO - 10.1016/j.chemgeo.2004.06.048

M3 - Article

AN - SCOPUS:14544282428

SN - 0009-2541

VL - 215

SP - 525

EP - 535

JO - Chemical Geology

JF - Chemical Geology

IS - 1-4 SPEC. ISS.

ER -

Isotopic fractionation of sulfur during formation of basaluminite, alunite, and natroalunite

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Keywords

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