Author(s): Victoria Barcala; Leonard Oste; Thilo Behrends

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Abstract: Iron-coated sand (ICS) is an iron-based phosphate sorbing material used in filters to remove phosphate from natural and agricultural waters and prevent eutrophication. The objectives of this research were to propose a mathematical and conceptual model for the kinetics of the phosphate diffusion to the inside of the ICS grains. We used columns to calibrate and validate a non-equilibrium adsorption model that fitted the advectiondispersion equation and the mass balance in the solid phase. The interpretation of the model results was supported by scanning electron microscopy images and elemental maps. The adsorption of phosphate by ICS was divided into a fast and a slow process. The fast adsorption described the attraction into the surface of the ICS grains and the slow adsorption described the diffusion of phosphate inside the nanopores of the iron coating. The fast adsorption is in equilibrium, but the slow adsorption is not because it is limited by the phosphorus diffusion inside the iron-coating. Most of the adsorption capacity of the ICS relied on the sorption sites inside the iron-coating, 96.1%. These findings contribute to the design and operation of ICS filters.

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Year: 2022