Sorption of Brilliant Blue FCF in soils as affected by pH and ionic strength

Brilliant Blue FCF has been frequently used as a dye tracer to stain flow p athways in porous media. As an ionic organic molecule, the dye interacts in a complicated manner with the solid phase. For an adequate interpretation of stained flow pathways, the sorption characteristics of the dye need to b e better understood. In this study, we investigate the suitability of Brill iant Blue FCF as a dye tracer in vadose zone hydrology. The objectives were to test the effect of aqueous solution chemistry on dye absorption spectra , and to evaluate the;effect of ionic strength and type of cations on dye s orption to soils. Batch sorption studies were conducted with three differen t soils and different ionic strengths of the background solution. Ionic str ength was adjusted with either CaCl2 or KCl. Sorption isotherms conformed t o the Langmuir model, with the sorption capacity ranging over one order of magnitude. Substantial sorption was found for the soil sample with the high est clay content and the lowest pH. Increasing ionic strength, led to incre ased sorption of Brilliant Blue FCF. The type of background cation, Ca or K , did not influence sorption. In aqueous solution, the absorption spectrum of Brilliant Blue FCF is not sensitive to pH nor ionic strength. (C) 2000 E lsevier Science B.V. All rights reserved.