Adsorption of molybdate and tetrathiomolybdate onto pyrite and goethite: Effect of pH and competitive anions

Nan Xu, Christos Christodoulatos, Washington Braida

Research output: Contribution to journalArticlepeer-review

154 Scopus citations

Abstract

The adsorption of two major molybdenum (Mo) species, molybdate (MoO 42-) and tetrathiomolybdate (MoS42-) onto two main iron minerals pyrite (FeS2) and goethite (FeOOH) is addressed to elucidate the possible mechanisms of molybdenum immobilization in anoxic sediments. Suspensions of MoS42- (or MoO 42-) and goethite (or pyrite) in 0.1 M NaCl solution were equilibrated under anoxic conditions at 25°C in the pH range from 3 to 10. The competitive effects of sulfate, phosphate, and silicate on the adsorption of MoO42- and MoS42- by pyrite and goethite are also addressed. Adsorption of MoO42- and MoS42- on pyrite and goethite is in general well described by a Langmuir model at low pH; the extent of sorption is a function of pH and the surface loading. Maximum sorption is observed in the acidic pH range (pH < 5) at low surface loading. The adsorption of molybdenum (μmol g -1) depends upon Mo species and on the type of iron mineral following the order: MoS42- - goethite>MoO4 2- - goethite>MoS42- - pyrite>MoO 42- - pyrite. Phosphate appears to compete strongly with MoO42- and MoS42- for the sorption sites of pyrite and goethite. The strength of the phosphate competitive effect follows the sequence of MoO42- - goethite∼MoO 42- - pyrite>MoS42- - pyrite>MoS42- - goethite. Silicate and sulfate have a negligible effect on the sorption of MoO42- and MoS 42-. The preferred adsorption by iron mineral of MoS 42-, as well as its behavior in the presence of competitive anions suggests that tetrathiomolybdate species may be an ultimate reservoir and may control Mo enrichment in the sediments.

Original languageEnglish
Pages (from-to)1726-1735
Number of pages10
JournalChemosphere
Volume62
Issue number10
DOIs
StatePublished - Mar 2006

Keywords

  • Adsorption
  • Goethite
  • Molybdate
  • Pyrite
  • Tetrathiomolybdate

Fingerprint

Dive into the research topics of 'Adsorption of molybdate and tetrathiomolybdate onto pyrite and goethite: Effect of pH and competitive anions'. Together they form a unique fingerprint.

Cite this