RESUMO
The multi-component behavior of fixed-bed adsorption of dioxins (DXNs) was examined through detailed analyses of the concentration profiles of isomers in fixed-bed activated carbon fiber (ACF). Regularities in both adsorption rates and strengths were clarified. (1) The rate of transfer in the adsorption of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCCDs/DFs) tends to increase with decreasing number of chlorine substituents. Axial dispersion also tends to increase with a decreasing number of chlorine substituents under our experimental conditions. (2) Homologues with the same number of chlorine substituents in PCDDs/DFs have similar adsorption strengths. The adsorption strength of PCDD/DF isomers is probably greater than that of co-planar polychlorinated biphenyls (co-PCB) isomers when the number of chlorine substituents is identical. (3) The adsorption strength of isomers depends on their molecular structure. In PCDDs/DFs the toxic isomers, all of which have vicinal chlorine substituents at the 2, 3, 7 and 8 positions, are relatively strong. It is clear, especially in TeCDDs, that isomers with vicinal chlorine substituents are stronger than isomers without. In co-PCBs, isomers without chlorine substituents at ortho positions are stronger than those with, and (4) A close analogy exists between the adsorption strength order for ACF and the elution order in gas chromatography (GC).
