Capture of molybdenum in pyrite-forming sediments

Role of ligand-induced reduction by polysulfides

Trent P. Vorlicek, Mani D. Kahn, Yasuhiro Kasuya, George R. Helz

Research output: Contribution to journalArticle

139 Citations (Scopus)

Abstract

Capture of Mo by FeS2 is an important sink for marine Mo. X-ray spectroscopy has shown that Mo forms Mo-Fe-S cuboidal clusters on pyrite. Reduction of MoVI must occur to stabilize these structures. Sulfide alone is a poor reductant for Mo, producing instead a series of MoVI thioanions (MoOxS4-x 2-, x = 0-3). In solutions that contain both H2S and S0-donors (i.e. polysulfides; dissolved S8), Mo is transformed to MoIV or MoV 2 polysulfide/sulfide anions. This intramolecular reduction requires no external reducing agent. Remarkably, an oxidizing agent (S0 donor), rather than a reducing agent, stabilizes the reducible MoVI complex. Thiomolybdates and their reduction products do not precipitate spontaneously; solutions supersaturated by 109 with respect to molybdenite, MoS2, produce no precipitate in 40 days. In 10-minute exposures, pyrite can scavenge MoOS3 2- and MoS4 2- weakly at mildly alkaline pH but can scavenge an unidentified product of the S0-induced reduction of MoOS3 2- very strongly. On the basis of these observations, a reaction pathway for Mo capture by pyrite is proposed. Conditions that favor Mo capture by this pathway also favor pyrite growth. Ascribing Mo capture simply to low redox potential is too simplistic and neglects the likely role of oxidizing S0-donors. The aqueous speciation of Mo in anoxic environments will be a function of the activity of zero-valent sulfur as well as the activity of H2S(aq).

Original languageEnglish (US)
Pages (from-to)547-556
Number of pages10
JournalGeochimica et Cosmochimica Acta
Volume68
Issue number3
DOIs
StatePublished - Feb 1 2004
Externally publishedYes

Fingerprint

Molybdenum
molybdenum
ligand
pyrite
Reducing Agents
Sediments
Ligands
Sulfides
sediment
Precipitates
sulfide
molybdenite
redox potential
X ray spectroscopy
Sulfur
Oxidants
X-ray spectroscopy
Anions
anion
sulfur

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Capture of molybdenum in pyrite-forming sediments : Role of ligand-induced reduction by polysulfides. / Vorlicek, Trent P.; Kahn, Mani D.; Kasuya, Yasuhiro; Helz, George R.

In: Geochimica et Cosmochimica Acta, Vol. 68, No. 3, 01.02.2004, p. 547-556.

Research output: Contribution to journalArticle

Vorlicek, Trent P. ; Kahn, Mani D. ; Kasuya, Yasuhiro ; Helz, George R. / Capture of molybdenum in pyrite-forming sediments : Role of ligand-induced reduction by polysulfides. In: Geochimica et Cosmochimica Acta. 2004 ; Vol. 68, No. 3. pp. 547-556.
@article{433bca16fb7347abad1972f91531d767,
title = "Capture of molybdenum in pyrite-forming sediments: Role of ligand-induced reduction by polysulfides",
abstract = "Capture of Mo by FeS2 is an important sink for marine Mo. X-ray spectroscopy has shown that Mo forms Mo-Fe-S cuboidal clusters on pyrite. Reduction of MoVI must occur to stabilize these structures. Sulfide alone is a poor reductant for Mo, producing instead a series of MoVI thioanions (MoOxS4-x 2-, x = 0-3). In solutions that contain both H2S and S0-donors (i.e. polysulfides; dissolved S8), Mo is transformed to MoIV or MoV 2 polysulfide/sulfide anions. This intramolecular reduction requires no external reducing agent. Remarkably, an oxidizing agent (S0 donor), rather than a reducing agent, stabilizes the reducible MoVI complex. Thiomolybdates and their reduction products do not precipitate spontaneously; solutions supersaturated by 109 with respect to molybdenite, MoS2, produce no precipitate in 40 days. In 10-minute exposures, pyrite can scavenge MoOS3 2- and MoS4 2- weakly at mildly alkaline pH but can scavenge an unidentified product of the S0-induced reduction of MoOS3 2- very strongly. On the basis of these observations, a reaction pathway for Mo capture by pyrite is proposed. Conditions that favor Mo capture by this pathway also favor pyrite growth. Ascribing Mo capture simply to low redox potential is too simplistic and neglects the likely role of oxidizing S0-donors. The aqueous speciation of Mo in anoxic environments will be a function of the activity of zero-valent sulfur as well as the activity of H2S(aq).",
author = "Vorlicek, {Trent P.} and Kahn, {Mani D.} and Yasuhiro Kasuya and Helz, {George R.}",
year = "2004",
month = "2",
day = "1",
doi = "10.1016/S0016-7037(00)00444-7",
language = "English (US)",
volume = "68",
pages = "547--556",
journal = "Geochmica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "Elsevier Limited",
number = "3",

}

TY - JOUR

T1 - Capture of molybdenum in pyrite-forming sediments

T2 - Role of ligand-induced reduction by polysulfides

AU - Vorlicek, Trent P.

AU - Kahn, Mani D.

AU - Kasuya, Yasuhiro

AU - Helz, George R.

PY - 2004/2/1

Y1 - 2004/2/1

N2 - Capture of Mo by FeS2 is an important sink for marine Mo. X-ray spectroscopy has shown that Mo forms Mo-Fe-S cuboidal clusters on pyrite. Reduction of MoVI must occur to stabilize these structures. Sulfide alone is a poor reductant for Mo, producing instead a series of MoVI thioanions (MoOxS4-x 2-, x = 0-3). In solutions that contain both H2S and S0-donors (i.e. polysulfides; dissolved S8), Mo is transformed to MoIV or MoV 2 polysulfide/sulfide anions. This intramolecular reduction requires no external reducing agent. Remarkably, an oxidizing agent (S0 donor), rather than a reducing agent, stabilizes the reducible MoVI complex. Thiomolybdates and their reduction products do not precipitate spontaneously; solutions supersaturated by 109 with respect to molybdenite, MoS2, produce no precipitate in 40 days. In 10-minute exposures, pyrite can scavenge MoOS3 2- and MoS4 2- weakly at mildly alkaline pH but can scavenge an unidentified product of the S0-induced reduction of MoOS3 2- very strongly. On the basis of these observations, a reaction pathway for Mo capture by pyrite is proposed. Conditions that favor Mo capture by this pathway also favor pyrite growth. Ascribing Mo capture simply to low redox potential is too simplistic and neglects the likely role of oxidizing S0-donors. The aqueous speciation of Mo in anoxic environments will be a function of the activity of zero-valent sulfur as well as the activity of H2S(aq).

AB - Capture of Mo by FeS2 is an important sink for marine Mo. X-ray spectroscopy has shown that Mo forms Mo-Fe-S cuboidal clusters on pyrite. Reduction of MoVI must occur to stabilize these structures. Sulfide alone is a poor reductant for Mo, producing instead a series of MoVI thioanions (MoOxS4-x 2-, x = 0-3). In solutions that contain both H2S and S0-donors (i.e. polysulfides; dissolved S8), Mo is transformed to MoIV or MoV 2 polysulfide/sulfide anions. This intramolecular reduction requires no external reducing agent. Remarkably, an oxidizing agent (S0 donor), rather than a reducing agent, stabilizes the reducible MoVI complex. Thiomolybdates and their reduction products do not precipitate spontaneously; solutions supersaturated by 109 with respect to molybdenite, MoS2, produce no precipitate in 40 days. In 10-minute exposures, pyrite can scavenge MoOS3 2- and MoS4 2- weakly at mildly alkaline pH but can scavenge an unidentified product of the S0-induced reduction of MoOS3 2- very strongly. On the basis of these observations, a reaction pathway for Mo capture by pyrite is proposed. Conditions that favor Mo capture by this pathway also favor pyrite growth. Ascribing Mo capture simply to low redox potential is too simplistic and neglects the likely role of oxidizing S0-donors. The aqueous speciation of Mo in anoxic environments will be a function of the activity of zero-valent sulfur as well as the activity of H2S(aq).

UR - http://www.scopus.com/inward/record.url?scp=0842269839&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0842269839&partnerID=8YFLogxK

U2 - 10.1016/S0016-7037(00)00444-7

DO - 10.1016/S0016-7037(00)00444-7

M3 - Article

VL - 68

SP - 547

EP - 556

JO - Geochmica et Cosmochimica Acta

JF - Geochmica et Cosmochimica Acta

SN - 0016-7037

IS - 3

ER -