Xu Nan, Christodoulatos Christos, Braida Washington
Center for Environmental Systems, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, NJ 07030, USA.
Chemosphere. 2006 Mar;62(10):1726-35. doi: 10.1016/j.chemosphere.2005.06.025. Epub 2005 Aug 9.
The adsorption of two major molybdenum (Mo) species, molybdate (MoO4(2-)) and tetrathiomolybdate (MoS4(2-)) 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 MoS4(2-) (or MoO4(2-)) and goethite (or pyrite) in 0.1M NaCl solution were equilibrated under anoxic conditions at 25 degrees C in the pH range from 3 to 10. The competitive effects of sulfate, phosphate, and silicate on the adsorption of MoO4(2-) and MoS4(2-) by pyrite and goethite are also addressed. Adsorption of MoO4(2-) and MoS4(2-) 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 (micromol g(-1)) depends upon Mo species and on the type of iron mineral following the order: MoS4(2-)-goethite > MoO4(2-)-goethite > MoS4(2-)-pyrite > MoO4(2-)-pyrite. Phosphate appears to compete strongly with MoO4(2-) and MoS4(2-) for the sorption sites of pyrite and goethite. The strength of the phosphate competitive effect follows the sequence of MoO4(2-)-goethite approximately = MoO4(2-)-pyrite > MoS4(2-)-pyrite > MoS4(2-)-goethite. Silicate and sulfate have a negligible effect on the sorption of MoO4(2-) and MoS4(2-). The preferred adsorption by iron mineral of MoS4(2-), 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.
研究了两种主要钼（Mo）物种，即钼酸盐（MoO4(2-)）和四硫代钼酸盐（MoS4(2-)）在两种主要铁矿物黄铁矿（FeS2）和针铁矿（FeOOH）上的吸附情况，以阐明钼在缺氧沉积物中固定的可能机制。在0.1M NaCl溶液中，将MoS4(2-)（或MoO4(2-)）与针铁矿（或黄铁矿）的悬浮液在25℃缺氧条件下，于pH值3至10的范围内进行平衡。还研究了硫酸根、磷酸根和硅酸根对黄铁矿和针铁矿吸附MoO4(2-)和MoS4(2-)的竞争效应。在低pH值下，MoO4(2-)和MoS4(2-)在黄铁矿和针铁矿上的吸附通常可用Langmuir模型很好地描述；吸附程度是pH值和表面负载量的函数。在低表面负载量下，在酸性pH范围（pH<5）观察到最大吸附量。钼（微摩尔/克）的吸附量取决于钼物种和铁矿物类型，顺序为：MoS4(2-)-针铁矿>MoO4(2-)-针铁矿>MoS4(2-)-黄铁矿>MoO4(2-)-黄铁矿。磷酸根似乎与MoO4(2-)和MoS4(2-)强烈竞争黄铁矿和针铁矿的吸附位点。磷酸根竞争效应的强度顺序为：MoO4(2-)-针铁矿≈MoO4(2-)-黄铁矿>MoS4(2-)-黄铁矿>MoS4(2-)-针铁矿。硅酸根和硫酸根对MoO4(2-)和MoS4(2-)的吸附影响可忽略不计。铁矿物对MoS4(2-)的优先吸附及其在竞争性阴离子存在下的行为表明，四硫代钼酸盐物种可能是最终的储存库，并可能控制沉积物中钼的富集。
