Gamma-ray radiolysis of the polychlorinated biphenyls in oil solutio

Polychlorinated biphenyl (PCB) radiolysis was investigated as an alternative to incineration for the remediation of contaminated oils. Radiolysis has inherent benefits over incineration, such as the possibility of in-situ treatment, the selective ability to destroy the PCBs and not the matrix, and the lack of generation of toxic byproducts. The mechanism and kinetics of the reaction were investigated to ensure a knowledge of the reaction products and to provide rate data necessary for process treatment design.;A brief review of the radiolysis of PCBs in isopropanol is presented and contrasted with the results of research using isooctane as a solvent. The mechanism of PCB decomposition was found to be similar in both solvents. Degradation of PCBs occurs by electron capture, with the electrons generated as a result of gamma-ray/solvent interactions. The products are free chloride ion and biphenyl. Biphenyl is stable toward ionizing radiation. The only other products are solvent-PCB adducts, which also decompose by dechlorination.;The kinetics are very different in isooctane than in isopropanol. The kinetics were found to be pseudo-first-order in the nonpolar isooctane, but with a rate constant dependence on the initial PCB concentration. The pseudo-first-order kinetics of an inherently bimolecular reaction were explained by the constant equilibrium electron concentration established during an irradiation. The concentration dependence was explained by the effect of competition between PCB electron capture and geminate recombination of electrons with their parent positive ions in the nonpolar solvent. This was shown mathematically.;The results of an EPA-permitted demonstration experiment are shown. The EPA-mandated treatment goal was achieved in three contaminated waste hydraulic oils using predictable and easily achieved amounts of radiation. Factors influencing the rate of PCB decomposition in these oils were discussed. Finally, a method which both accelerates the rate of PCB decomposition, and isolates the liberated chlorine was examined.