Trace Metal Geochemistry in Anoxic Waters: Molybdenum and Mercury

目前的许多研究都是为了了解痕量金属在缺氧水环境中的行为。这些研究产生了对含有还原硫配体的金属络合物的化学计量和稳定性的准确数据的需要。许多现有的稳定常数在数量级上是不确定的，因此远不如它们所应用的现场数据准确。在某些情况下，特别是多硫化物或硫醇配体，不存在数据。当有数据可用时，往往不确定所描述的物种是单核物种还是多核物种。这是一个潜伏的问题，可能会在金属行为的预测中引入巨大的、意想不到的错误。我们完成了与还原的铜-S组合、辉铜矿+闪锌矿和闪锌矿+斜闪石平衡的溶液中铜的形态研究。这包括EXAFS研究，这些研究表明该体系中存在多核配合物。我们还完成了在适合缺氧海洋水域的条件下锌和镉的形态研究。我们将继续这方面的研究，在未来两年将重点放在汞和钼上。具体目标如下：1)水星。在接近缺氧海水的条件下测量朱砂的溶解度，并与偏金砂的溶解度进行比较，以确定是否存在多核络合物。确定汞-多硫化物络合物在自然界中是否重要。研究朱砂在其固溶体范围内的溶解度，以及2)钼。用元素分析、EXAFS和溶解度表征了代表缺氧海水条件下形成的Fe-Mo-S沉淀物。研究硫代钼酸盐作为铜、锌、镉和铁的配体的可能重要性。扩大EXAFS对黑色页岩中钼的初步研究，并寻求实验室生产的产品与保存在古代硫化物海洋盆地页岩中的产品之间的联系。

Much current research is directed toward understanding the behavior of trace metals in anoxic aquatic environments. These studies create a need for accurate data on the stoichiometry and stability of metal complexes containing reduced sulfur ligands. Many existing stability constants are uncertain at the order of magnitude level and thus are far less accurate than the field data to which they are applied. In some cases, especially for polysulfide or thiol ligands, no data exist. When data are available, it is often uncertain whether the species described are mononuclear or polynuclear. This is an insidious problem that can introduce large, unsuspected errors into predictions of metal behavior. We have completed investigations of copper speciation in solutions equilibrated with reduced Cu-S assemblages, chalcocite+djurleite and anilite+covellite. This has included EXAFS studies which demonstrate that multinuclear complexes exist in this system. We have also completed studies of zinc and cadmium speciation under conditions appropriate for anoxic marine waters. We will continue this line of research, focusing in the next two years on mercury and molybdenum. Specific objectives are as follows: 1) Mercury. Measure the solubility of cinnabar under conditions approaching those in anoxic marine waters and compare with metacinnabar solubility to determine if polynuclear complexes exist. Determine if Hg-polysulfide complexes will be important in nature. Investigation the solubility of cinnabar over its solid solution range, and 2) Molybdenum. Characterize Fe-Mo-S precipitates formed under conditions representative of anoxic marine waters by elemental analysis, EXAFS and solubility. Investigate the possible importance of thiomolybdates as ligands for Cu, Zn, Cd and Fe. Extend preliminary EXAFS work on Mo in black shales and seeks links between the products produced in the laboratory and those preserved in shales from ancient sulfidic marine basins.