Kinetics and products of PCB28 degradation through a goethite-catalyzed Fenton-like reaction

• PCB28 could be effectively degraded in a goethite-catalyzed Fenton-like system.
• The degradation of PCB28 and H2O2 followed pseudo-first-order kinetics.
• The oxidation rates of PCBs decreased with increasing number of chlorine atoms.
• Four dechlorination and two hydroxylation products of PCB28 were identified.

Efficiencies of 2,4,4′-trichlorobiphenyl (PCB28) degradation in a goethite-catalyzed Fenton-like system under various conditions were investigated. Up to 99% of PCB28 was degraded in the Fenton-like system after 48 h. The hydroxyl radical was responsible for the degradation of PCB28 at pH 3–7. Degradation of PCB28 and H2O2 followed pseudo-first-order kinetics. The rate of PCB28 degradation decreased when the pH increased from 3 to 7, but increased with increasing concentration of goethite and H2O2. The rate of H2O2 decomposition increased at higher pH and goethite concentration, and decreased at lower H2O2 concentration. The half-lives of 4-chlorobiphenyl, 4,4′-dichlorobiphenyl, 2,4,4′-trichlorobiphenyl, and 2,2′,4,4′-tetrachlorobiphenyl were 1.8, 3.5, 4.1, and 11 h, respectively; therefore, the number of chlorine atoms in the biphenyl molecule determined the chemical reactivity of PCBs. By gas chromatography–mass spectrometry, one monochlorobiphenyl, three dichlorobiphenyl, and two hydroxytrichlorobiphenyl derivatives were identified as major products of PCB28 degradation. The decrease in pH of the reaction mixture after 48 h reaction revealed that acidic products might be formed during degradation.