Formation of polychlorinated dibenzo-p-dioxins/dibenzofurans from residual carbon on municipal solid waste incinerator fly ash using Na37Cl

(NaCl)-Cl-37 was used to study the role of chlorine in the formation of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) from carbon. Adding (NaCl)-Cl-37 to fly ash showed that this compound was a (relatively) poor chloride source; chlorine naturally present on the ash - which could include both chlorine in residual carbon and (metal) chlorides - was found to be ca. 17x more reactive. When both (NaCl)-Cl-37 and CuCl2 were added to aqueous extracted fly ash, the percentage of Cl-37 from (NaCl)-Cl-37 included in PCDD/F increased, compared to the combination of (NaCl)-Cl-37/fly ash. When (NaCl)-Cl-37 and CuCl2 were exchanged in water, followed by evaporation of the solvent, and mixed with aqueous extracted fly ash, the percentage of Cl-37 included in PCDD/F was much higher. Apparently, direct transfer of Cl-37 from CuCl2 to carbon and PCDD/F was much faster than transfer of Cl-37(-) from (NaCl)-Cl-37 via a metal chloride (such as CuCl2) to carbon and PCDD/F. In addition to chlorine in PCDD/F originating from exchanged NaCl/CuCl2, chloride left on the fly ash after aqueous extraction and chlorine present in residual carbon could also have been incorporated in PCDD/F. (C) 2001 Elsevier Science Ltd. All rights reserved.