Dye Adsorption in a Loam Soil as Influenced by Potassium Bromide

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Abstract
FD&C Blue #1 and Rhodamine WT have been used in soils to trace preferential flow paths while bromide has been used to study flow paths of water or nonretarded chemicals. This study quantified the interactions of KBr, FD&C Blue #1, and Rhodamine WT on dye adsorption in Forman loam (fine‐loamy, mixed Udic Argiboroll) soil. The experiment involved characterization of adsorption isotherms and breakthrough curves for various mixtures of tracers at different concentrations. Batch equilibration studies showed that the adsorption of FD&C Blue #1 and Rhodamine WT on Forman loam was not influenced by the presence of each other. The adsorption of FD&C Blue #1 and Rhodamine WT, however, increased with an increase in the concentration of KBr. The slope of linear adsorption isotherm (Kd) increased from 5.0 to 15.0 cm3 g−1 for FD&C Blue #1 and from 4.2 to 5.0 cm3 g−1 for Rhodamine WT on addition of 1000 mg L−1 of KBr. In a flow‐through experiment, FD&C Blue #1 movement was twice as slow in presence of KBr than in absence of KBr. The Kd values from the flow‐through experiment were lower than those from the batch equilibration experiments. We conclude that the retardation coefficients estimated from the batch equilibration studies are not realistic for application to leaching experiments, and the presence of tracer interaction can potentially complicate the interpretation of dye flow patterns observed with the use of multiple tracer technique.
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