Verifying the Speciation of Molybdenum in Sulfidic and Polysulfidic Natural Waters Using Ion Chromatography with Suppressed Conductivity Detection

Within sulfidic waters, Mo speciation is characterized by the formation of thiomolybdates (MoOnS4-n2- n=1-4). Using thermodynamic constants, Mo speciation in sulfidic basins has been calculated. However, actual speciation in natural waters has not been verified because a suitable analytical method remains elusive. Zero-valent sulfur has been shown to influence Mo speciation and sequestration by pyrite via formation of anionic Mo-polysulfido complex(es). Unfortunately, optical means were not able to identify the complex(es) definitively. We have demonstrated that ion chromatography with suppressed conductivity detection gives linear response down to at least 10-8 M MoO4.. IC methods are developed to quantify contrived mixtures of MoO42- and thiomolybdates at Mo=10-7 in simulated seawater. IC-MS is used to identify and quantify Mo-polysulfido complex(es) formed in polysulfidic test solutions; kinetic and equilibrium constants will be calculated. This research will better define Mo speciation and its relation to Mo fixation in anoxic waters