Trace Metal Geochemistry in Anoxic Waters: Molybdenum and Mercury

目前的许多研究都是为了了解微量金属在缺氧水生环境中的行为。这些研究产生了对含有还原硫配体的金属配合物的化学计量学和稳定性的准确数据的需求。许多现有的稳定常数在数量级上是不确定的，因此远不如应用它们的实地数据准确。在某些情况下，特别是多硫化物或硫醇配体，没有数据存在。当数据可用时，通常不确定所描述的物种是单核还是多核。这是一个潜在的问题，可以在预测金属行为时引入巨大的、意想不到的错误。我们已经完成了铜在还原Cu-S组合、辉铜矿+珠雷岩和亚云母+珠雷岩平衡溶液中的形态研究。这包括EXAFS研究，证明该系统中存在多核配合物。我们还完成了锌和镉在缺氧海水条件下形成的研究。我们将继续这方面的研究，在接下来的两年里将重点放在汞和钼上。具体目标如下：1)水星。测定朱砂在接近缺氧海水条件下的溶解度，并与绿金属砂溶解度进行比较，以确定是否存在多核配合物。确定hg -多硫化物配合物在自然界中是否重要。研究了朱砂在固溶体范围内的溶解度；通过元素分析、EXAFS和溶解度表征在缺氧海水条件下形成的Fe-Mo-S沉淀。探讨硫钼酸盐作为铜、锌、镉和铁的配体的重要性。扩展关于黑色页岩中钼元素的初步EXAFS工作，并寻求实验室生产的产品与古代硫化氢海相盆地页岩中保存的产品之间的联系。

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.