EVALUATION OF GAMMA RADIATION FOR DEGRADATION OF A POLYCHLORINATED BIPHENYL ISOMER IN SOLUTION AND ON ACTIVATED CARBON (RADIOLYSIS, PCB)

JAMES FRANCIS SCHWEITZER, Purdue University

Abstract

This research was conducted to study the application of ionizing radiation in the destruction of a polychlorinated biphenyl (PCB) isomer. Dilute aqueous solutions of PCB which cannot be destroyed effectively by pyrolytic methods were of particular concern. The ability of an activated carbon to adsorb 2,3',4',5-tetrachlorobiphenyl (TCB) from aqueous solution was studied. An adsorption isotherm and carbon column adsorption indicated that the carbon was suitable for TCB removal from water. Aqueous solutions of TCB at 50 (mu)g/L were irradiated by a Co-60 source and received absorbed doses from 28 kilorads to 4.3 megarads. Recovery of the parent TCB was reduced at all levels of irradiation as measured by gas chromatography. At 1 megarad 42% was recovered and 16% was recovered at an absorbed dose of 4.3 megarads. No irradiation byproducts were found on the chromatogram and the method of degradation was not determined. Destruction was also studied in 0.3 M (KOH) alkaline-2-propanol solution which was deaerated with nitrogen prior to irradiation. At 100 mg/L, solutions of TCB were rapidly dechlorinated to yield mono-, di-, and trichlorobiphenyls as well as biphenyl. A dose of 50 kilorads resulted in greater than 98% destruction of the parent TCB and total disappearance of all degradation products. Confirmation of degradation products was provided by mass spectrometry. It has been shown that the mechanism for dechlorination was a free radical chain reaction involving the propoxide radical anion. Adsorption of TCB on activated carbon columns from an acetone standard solution was performed. Solvents such as methylene chloride, hexane, 2-propanol, and p-dioxane were assessed for their ability to desorb TCB from the carbon. Methylene chloride was superior in its desorption properties and was used to recover TCB from the columns after irradiation took place. Columns were loaded with 0.5 to 2.0% TCB on a weight basis. These columns were irradiated alone and with alkaline-2-propanol present. In both cases little or no destruction took place as measured by methylene chloride recovery. Addition of other solvents with the alkaline-2-propanol did not facilitate desorption of the TCB from the carbon and allow destruction to take place in the solution. While the TCB remained on the carbon it was protected from free radical attack and destruction.

Degree

Ph.D.

Subject Area

Environmental science|Radiation

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