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Multicomponent Transport of Sulfate in a Goethite−Silica Sand System at Variable pH and Ionic Strength

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journal contribution
posted on 19.08.1999, 00:00 by Johannes C. L. Meeussen, Jutta Kleikemper, André M. Scheidegger, Michal Borkovec, Edward Paterson, Willem H. van Riemsdijk, Donald L. Sparks
In this work, existing models for adsorption of protons and sulfate on goethite and silica were used in combination with a one-dimensional mass-transport model to predict the transport of sulfate at variable pH and ionic strength in a goethite−silica system. The predicted multicomponent transport phenomena are discussed, and an evaluation is made of the sensitivity of the results to different input parameters. This information was used to select optimal conditions for independent experimental testing of the model. Column experiments were carried out in which solutions of known pH, sulfate concentration, and salt concentration were infiltrated into a goethite-coated quartz sand column. The agreement between the experiments and the predictions is very good, especially considering the fact that no fitting of model parameters to the actual experimental system was involved. According to the model calculations, transport behavior of sulfate in a goethite system is very sensitive to relatively small amounts of adsorbed sulfate initially present. This could be an explanation for the remaining differences between the predicted and the measured curves. It also implies that, for the application of such mechanistic models to soils, accurate information on the initial composition of the soil is essential.