Adsorption of polychlorinated dibenzo-p-dioxins/dibenzofurans on activated carbon from hexane.

Activated carbon is widely used to abate dioxins and dioxin-like compounds from flue gas. Comparing commercial samples regarding their potential to adsorb dioxins may proceed by using test columns, yet it takes many measurements to characterise the retention and breakthrough of dioxins. In this study, commercial activated carbon samples are evaluated during tests to remove trace amounts of dioxins dissolved in n-hexane. The solution was prepared from fly ash collected from a municipal solid waste incinerator. The key variables selected were the concentration of dioxins in n-hexane and the dosage of activated carbon. Both polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) showed very high removal efficiencies (94.7%-98.0% for PCDDs and 99.7%-99.8% for PCDFs). The presence of a large excess of n-hexane solvent had little effect on the removal efficiency of PCDD/Fs. The adsorbed PCDD/Fs showed a linear correlation (R(2) > 0.98) with the initial concentrations. Comparative analysis of adsorption isotherms showed that a linear Henry isotherm fitted better the experimental data (R(2) = 0.99 both for PCDDs and PCDFs) than the more usual Freundlich isotherm (R(2) = 0.88 for PCDDs and 0.77 for PCDFs). Finally, the results of fingerprint analysis indicated that dioxin fingerprint (weight proportion of different congeners) on activated carbon after adsorption did not change from that in hexane.