Differential adsorption of molybdate and tetrathiomolybdate on pyrite (FeS2)
Differential adsorption of molybdate and tetrathiomolybdate on pyrite (FeS2)
复制标题
DOI：
10.1021/es0257467
复制
发表时间：
2003-01-15
影响因子：
11.4
通讯作者：
Helz, GR
中科院分区：
文献类型：
--
作者：
Bostick, BC;Fendorf, S;Helz, GR
钼是一种重要的营养素，具有多种生物功能，最显著的是固氮作用。通过吸附反应，钼的可用性是有限的，特别是在富含硫化物矿物的环境中。本研究探讨了两个主要的钼物种，钼酸盐（MoO 42-）和四硫代钼酸盐（MoS 42-），合成黄铁矿（FeS 2）作为溶液组成的函数的吸附。MoO 42-和MoS 42-在一定条件和离子强度下强烈地在FeS 2上分配。钼酸盐和四硫代钼酸盐吸附遵守Langmuir等温线，在酸性和环中性条件下计算的位点密度在2和3个位点/nm（2）之间，在pH 9下降低到小于1个位点/nm（2）。虽然MoO 42-和MoS 42-吸附最强烈的中等酸性条件下，MoO 42-容易解吸，而MoS 42-保持吸附，即使在高pH值。MoO 42-吸附的可逆性表明形成不稳定的表面络合物，而MoS 42-可能形成强大的内球络合物。用X射线吸收光谱测定了表面复合物的结构。钼酸盐形成双齿，单核络合物的FeS 2。黄铁矿上四硫代钼酸盐的Mo-S和Mo-Fe距离与Mo-Fe-S立方烷型簇合物的形成相一致。高亲和力的MoS 42-FeS 2，以及它的抗解吸，支持的假设，thiomolybdate物种是还原沉积物中的活性钼成分，并可能控制钼富集在缺氧的海洋环境。
Molybdenum is a nutrient important for a variety of biological functions, most notably nitrogen fixation. Molybdenum availability is limited through sorption reactions, particularly in environments rich in sulfide minerals. This study examines the sorption of two major molybdenum species, molybdate (MoO42-) and tetrathiomolybdate (MoS42-), on synthetic pyrite (FeS2) as a function of solution composition. Both MoO42- and MoS42- partitioned strongly on FeS2 under a range of conditions and ionic strengths. Molybdate and tetrathiomolybdate adsorption obeyed a Langmuir isotherm with a calculated site density between 2 and 3 sites/nm(2) under acidic and circumneutral conditions, which decreased to less than 1 site/nm(2) at pH 9. Although both MoO42- and MoS42- adsorbed most strongly under moderately acidic conditions, MoO42- readily desorbed while MoS42- remained adsorbed even at high pH. The reversibility of MoO42- adsorption suggests the formation of labile Surface complexes while MoS42- likely forms strong inner-sphere complexes. X-ray absorption spectroscopy was used to determine the structure of the surface complexes. Molybdate formed bidentate, mononuclear complexes on FeS2. The Mo-S and Mo-Fe distances for tetrathiomolybdate on pyrite are consistent with the formation of Mo-Fe-S cubane-type clusters. The high affinity of MoS42- for FeS2, as well as its resistance to desorption, supports the hypothesis that thiomolybdate species are the reactive Mo constituents in reduced sediments and may control Mo enrichment in anoxic marine environments.