Modeling the dissolution behavior of standard clays in seawater |
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| Institution: | 1. Geocontrols Systems – JETS Contract at NASA Johnson Space Center, Houston, TX 77058, United States of America;2. Houston Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204-5007, United States of America;3. Department of Earth Sciences, University of California Riverside, Riverside, CA 92521, United States of America;1. Department of Earth Sciences, University of Turin, via Valperga Caluso 35, 10125 Torino, Italy;2. NIS - Nanostructured Interfaces and Surfaces Centre, via Quarello 15/A, 10135 Torino, Italy;3. Soprintendenza Archeologia, Belle Arti e Paesaggio per le province di Alessandria, Asti e Cuneo, Piazza San Giovanni 2, 10122 Torino, Italy;4. CNR, Institute of Geosciences and Earth Resources, via Valperga Caluso 35, 10125 Torino, Italy |
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| Abstract: | The present investigation tests a model to explain the behavior of dissolved Si during early diagenesis in sediments. The model assumes that low-Fe clays and other minerals can be treated simply as Al hydroxides, having attached silica. When the minerals are placed in seawater solutions, Si is released, causing exposure of fresh Al-octahedra. which are reactive toward Si and other elements in solution. Standard clays (kaolinite, montmorillonite) and solid silicic acid were suspended in seawater solutions in various combinations and dissolved Al, Si, Ca, pH and alkalinity were determined as a function of time. The theoretical model correctly predicts the behavior of Si in mixtures of the different minerals, based upon the dissolution behavior of the minerals in suspension alone. Further, the decrease in the alkalinity of kaolinitecontaining seawater solutions, where carbonate dissolution, organic matter decomposition and reduced sulfur oxidation are apparently unimportant, can be predicted from a simple extrapolation of the silica model results. The alkalinity changes observed in this study, as well as the pH changes observed in standard clay suspensions by other researchers, can be explained simply by equilibration of the charge on exposed Al-octahedra with the pH of the surrounding waters. The results of this study indicate that theoretical models of Si diagenesis in sediments should have general usefulness for predicting the effects of clay dissolution on sediment properties. |
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