TY - JOUR
T1 - Adsorption of molybdate and tetrathiomolybdate onto pyrite and goethite
T2 - Effect of pH and competitive anions
AU - Xu, Nan
AU - Christodoulatos, Christos
AU - Braida, Washington
PY - 2006/3
Y1 - 2006/3
N2 - 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.
AB - 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.
KW - Adsorption
KW - Goethite
KW - Molybdate
KW - Pyrite
KW - Tetrathiomolybdate
UR - http://www.scopus.com/inward/record.url?scp=33644511127&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=33644511127&partnerID=8YFLogxK
U2 - 10.1016/j.chemosphere.2005.06.025
DO - 10.1016/j.chemosphere.2005.06.025
M3 - Article
C2 - 16084558
AN - SCOPUS:33644511127
SN - 0045-6535
VL - 62
SP - 1726
EP - 1735
JO - Chemosphere
JF - Chemosphere
IS - 10
ER -