The mechanisms of reduction of hexavalent chromium by green rust sodium sulphate

Formation of Cr-goethite

L. L. Skovbjerg, S. L S Stipp, Satoshi Utsunomiya, R. C. Ewing

Research output: Contribution to journalArticle

74 Citations (Scopus)

Abstract

The molecular-level processes that control green rust sodium sulphate (GRNa, SO4) reaction with chromate were studied using high-resolution techniques. Changes in solid morphology, structure and composition were observed with atomic force microscopy, transmission electron microscopy and X-ray diffraction. The results suggest the following mechanisms: Chromate replaces sulphate in the GR interlayer and is reduced by Fe(II). Formation of sparingly soluble Cr(III)-solid blocks further chromate entry, but Cr(VI) reduction continues at the GR solid/solution interface. Electron transfer from the centre of the GR crystals to the surface facilitates rapid reaction. Less stable zones of the reacted GRNa, SO4 dissolve and amorphous Cr(III),Fe(III)-solid forms. During equilibration, Cr-substituted goethite evolves in association with remaining GRNa, SO4, fed by material from the amorphous phase and dissolving oxidised GR. In contrast, previous Cr(VI) experiments with the carbonate form of GR, GRCO3, have suggested only reaction and deposition at the surface. From the perspective of environmental protection, these results have important implications. Goethite is sparingly soluble and the inclusion of Cr(III) as a solid-solution makes it even less soluble. Compared to Cr adsorbed at the surface of an Fe(III)-phase, Cr(III) incorporated in goethite is much less likely to be released back to groundwater.

Original languageEnglish
Pages (from-to)3582-3592
Number of pages11
JournalGeochimica et Cosmochimica Acta
Volume70
Issue number14
DOIs
Publication statusPublished - Jul 15 2006
Externally publishedYes

Fingerprint

Chromates
chromate
rust disease
goethite
chromium
sodium
sulfate
solid solution
Solid solutions
atomic force microscopy
Carbonates
Environmental protection
Sulfates
Process control
transmission electron microscopy
Groundwater
Atomic force microscopy
environmental protection
X-ray diffraction
Association reactions

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

Cite this

The mechanisms of reduction of hexavalent chromium by green rust sodium sulphate : Formation of Cr-goethite. / Skovbjerg, L. L.; Stipp, S. L S; Utsunomiya, Satoshi; Ewing, R. C.

In: Geochimica et Cosmochimica Acta, Vol. 70, No. 14, 15.07.2006, p. 3582-3592.

Research output: Contribution to journalArticle

@article{bf444859f66f40fda533bdf1d4a60d9f,
title = "The mechanisms of reduction of hexavalent chromium by green rust sodium sulphate: Formation of Cr-goethite",
abstract = "The molecular-level processes that control green rust sodium sulphate (GRNa, SO4) reaction with chromate were studied using high-resolution techniques. Changes in solid morphology, structure and composition were observed with atomic force microscopy, transmission electron microscopy and X-ray diffraction. The results suggest the following mechanisms: Chromate replaces sulphate in the GR interlayer and is reduced by Fe(II). Formation of sparingly soluble Cr(III)-solid blocks further chromate entry, but Cr(VI) reduction continues at the GR solid/solution interface. Electron transfer from the centre of the GR crystals to the surface facilitates rapid reaction. Less stable zones of the reacted GRNa, SO4 dissolve and amorphous Cr(III),Fe(III)-solid forms. During equilibration, Cr-substituted goethite evolves in association with remaining GRNa, SO4, fed by material from the amorphous phase and dissolving oxidised GR. In contrast, previous Cr(VI) experiments with the carbonate form of GR, GRCO3, have suggested only reaction and deposition at the surface. From the perspective of environmental protection, these results have important implications. Goethite is sparingly soluble and the inclusion of Cr(III) as a solid-solution makes it even less soluble. Compared to Cr adsorbed at the surface of an Fe(III)-phase, Cr(III) incorporated in goethite is much less likely to be released back to groundwater.",
author = "Skovbjerg, {L. L.} and Stipp, {S. L S} and Satoshi Utsunomiya and Ewing, {R. C.}",
year = "2006",
month = "7",
day = "15",
doi = "10.1016/j.gca.2006.02.017",
language = "English",
volume = "70",
pages = "3582--3592",
journal = "Geochmica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "Elsevier Limited",
number = "14",

}

TY - JOUR

T1 - The mechanisms of reduction of hexavalent chromium by green rust sodium sulphate

T2 - Formation of Cr-goethite

AU - Skovbjerg, L. L.

AU - Stipp, S. L S

AU - Utsunomiya, Satoshi

AU - Ewing, R. C.

PY - 2006/7/15

Y1 - 2006/7/15

N2 - The molecular-level processes that control green rust sodium sulphate (GRNa, SO4) reaction with chromate were studied using high-resolution techniques. Changes in solid morphology, structure and composition were observed with atomic force microscopy, transmission electron microscopy and X-ray diffraction. The results suggest the following mechanisms: Chromate replaces sulphate in the GR interlayer and is reduced by Fe(II). Formation of sparingly soluble Cr(III)-solid blocks further chromate entry, but Cr(VI) reduction continues at the GR solid/solution interface. Electron transfer from the centre of the GR crystals to the surface facilitates rapid reaction. Less stable zones of the reacted GRNa, SO4 dissolve and amorphous Cr(III),Fe(III)-solid forms. During equilibration, Cr-substituted goethite evolves in association with remaining GRNa, SO4, fed by material from the amorphous phase and dissolving oxidised GR. In contrast, previous Cr(VI) experiments with the carbonate form of GR, GRCO3, have suggested only reaction and deposition at the surface. From the perspective of environmental protection, these results have important implications. Goethite is sparingly soluble and the inclusion of Cr(III) as a solid-solution makes it even less soluble. Compared to Cr adsorbed at the surface of an Fe(III)-phase, Cr(III) incorporated in goethite is much less likely to be released back to groundwater.

AB - The molecular-level processes that control green rust sodium sulphate (GRNa, SO4) reaction with chromate were studied using high-resolution techniques. Changes in solid morphology, structure and composition were observed with atomic force microscopy, transmission electron microscopy and X-ray diffraction. The results suggest the following mechanisms: Chromate replaces sulphate in the GR interlayer and is reduced by Fe(II). Formation of sparingly soluble Cr(III)-solid blocks further chromate entry, but Cr(VI) reduction continues at the GR solid/solution interface. Electron transfer from the centre of the GR crystals to the surface facilitates rapid reaction. Less stable zones of the reacted GRNa, SO4 dissolve and amorphous Cr(III),Fe(III)-solid forms. During equilibration, Cr-substituted goethite evolves in association with remaining GRNa, SO4, fed by material from the amorphous phase and dissolving oxidised GR. In contrast, previous Cr(VI) experiments with the carbonate form of GR, GRCO3, have suggested only reaction and deposition at the surface. From the perspective of environmental protection, these results have important implications. Goethite is sparingly soluble and the inclusion of Cr(III) as a solid-solution makes it even less soluble. Compared to Cr adsorbed at the surface of an Fe(III)-phase, Cr(III) incorporated in goethite is much less likely to be released back to groundwater.

UR - http://www.scopus.com/inward/record.url?scp=33745927911&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33745927911&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2006.02.017

DO - 10.1016/j.gca.2006.02.017

M3 - Article

VL - 70

SP - 3582

EP - 3592

JO - Geochmica et Cosmochimica Acta

JF - Geochmica et Cosmochimica Acta

SN - 0016-7037

IS - 14

ER -