The effect of super saturation on the Ca and Sr composition in synthetic barite precipitated from seawater

Abstract

<p>An area of intense chemical oceanographic research effort in the past few decades has been the study of marine minerals as there is ample evidence that buried ocean sediments contain important information on past seawater environmental conditions such as temperature, productivity, alkalinity, phosphate, and pH, among others. A key oceanic mineral that could hold robust records of seawater Sr and Ca composition is barite. Marine barites typically contain 1-3% Sr and 0.01-0.1% Ca; concentrations that are evidently controlled by conditions under which barite formation occurs thereby potentially linking sediment composition to oceanic chemistry at the time of formation. The key objective of this work is to develop a better understanding of the connection between solution and solid chemistry that will be applicable to natural marine barites over a broad range of environmental conditions. Recent data from our precipitation experiments from natural seawater spiked with BaCI2 suggest that the Sr/Ca ratio in the barite precipitates is not only a function of the corresponding ratio in seawater via the distribution coefficient, but that super saturation with respect to barite also plays an important role in governing the precipitate composition. We will report the results of barite precipitation experiments carried out in seawater solutions at room temperature as a function of super saturation and as a function of the solution barium ion to sulfate ion ratio. Empirical modeling results from this data will be presented along with the interpretations in terms of the kinetics of ion incorporation during crystallization.</p><p>This presentation occurred at the Wright State University Campus-Wide Celebration of Research, Scholarship and Creative Activities on April 16, 2010</p>