Adsorption and Partitioning of PCDD/F on Flyash from Incinerators

Some of the literature describing the adsorption and formation of PCDD/F and its precursors is examined to see how this influences its partitioning between the gas phase and the surface of ash. Various ashes have widely different capacities to retain chlorinated organics. The application of a kinetic theory adsorption model suggests that the adsorption of gas phase PCDD/F onto the surface of flyash in MSW and medical waste incinerators is minimal at temperatures above 300°C. The external area of the particles appears to be the relevant area for calculating adsorption and reaction rates. When flyash is thermally treated under oxygen both precursors and PCDD/F are formed with single-ring organochlorides such as chlorobenzenes more strongly held than the two-ring species. The strong interaction between precursors and PCDD/F and an ash surface ensures that classical equilibrium is not attained between the gas and solid phases in an operating incinerator.

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