Molybdenum scavenging by iron monosulfide

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

Research output: Contribution to journalArticle

70 Citations (Scopus)

Abstract

Molybdenum profiles in dated sediment cores provide useful historical information about anoxia in anthropogenically impacted natural waters but would be of greater service if Mo fixation mechanisms were better understood. Here, we explore Mo scavenging by precipitated FeS in a model system consisting of an FeIII-bearing kaolinite (KGa-1B) dispersed in NaHS solutions. Test solutions contain 18 μM thiomolybdates (mainly MoOS3 2-). Optically measuring dissolved polysulfides monitors the rate of FeS production from FeIII minerals. Even though the exposed clay surface area is large (450 m2/L), the clay itself sorbs little Mo at pH 8.6. As FeS forms, Mo is taken up in initial Mo/Fe mole ratios of 0.04-0.06, irrespective of HS- concentration (4-40 mM range). After about a day, Mo expulsion from the solids begins, accompanied by net polysulfide consumption. These changes reflect recrystallization of amorphous FeS to more ordered products such as greigite. FeS captures some MoO4 2- but captures thiomolybdates more effectively. Kaolinite accelerates conversion of MoOS3 2- to MoS4 2-, as predicted previously, and thiomolybdates facilitate reduction of FeIII minerals in the clay compared to Mo-free solutions. FeS is a potentially effective, transient scavenging agent for Mo in sulfidic environments, although FeS2 and organic matter appear to be the ultimate sedimentary hosts.

Original languageEnglish (US)
Pages (from-to)4263-4268
Number of pages6
JournalEnvironmental Science and Technology
Volume38
Issue number16
DOIs
StatePublished - Aug 15 2004
Externally publishedYes

Fingerprint

Molybdenum
Scavenging
molybdenum
Kaolin
Polysulfides
Clay
Iron
Kaolinite
iron
clay
kaolinite
Minerals
Bearings (structural)
greigite
anoxia
mineral
Biological materials
fixation
sediment core
Sediments

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Science(all)
  • Environmental Chemistry

Cite this

Molybdenum scavenging by iron monosulfide. / Helz, George R.; Vorlicek, Trent P.; Kahn, Mani D.

In: Environmental Science and Technology, Vol. 38, No. 16, 15.08.2004, p. 4263-4268.

Research output: Contribution to journalArticle

Helz, George R. ; Vorlicek, Trent P. ; Kahn, Mani D. / Molybdenum scavenging by iron monosulfide. In: Environmental Science and Technology. 2004 ; Vol. 38, No. 16. pp. 4263-4268.
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