Modification of activated carbon to enhance the absorption of PCDD/F and dl-PCBs emissions in flue gas in South Africa

Abstract Activated carbon (AC) adsorption is commonly used for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) removal from flue gas. However, the AC available in the market predominantly possesses a substantial specific surface area and numerous micropores leading to significant variations in their adsorption characteristics. In this study, three types of activated carbon (AC) impregnated with different activating agents, namely K 2 CO 3 , KOH, and H 3 PO 4 were evaluated for their effectiveness in removing PCDD/Fs and dl-PCBs compounds. For dl-PCBs, AC impregnated with H 3 PO 4 resulted in a substantial reduction of PCB concentrations with an impressive 98% reduction achieved. Impregnation with KOH proved even more effective attaining a remarkable 99% reduction. In contrast, impregnation with K 2 CO 3 while still effective achieved a slightly lower reduction rate of 95%. For PCDD/F, LAC H3PO4 showed selectivity in achieving high reductions across both CDD and CDF congeners however proved effective in reducing the ∑PCCDF from 403.94 ng/Nm 3 to 3.463 ng/Nm 3 and ∑TEQ from 41.34 ng I-TEQ/Nm 3 to 0.35 ng I-TEQ Nm 3 . LAC KOH proved effective in reducing the ∑PCCDF from 540.45 ng/Nm 3 to 0.25 ng/Nm 3 and ∑TEQ from 57.42 ng I-TEQ/Nm 3 to 0.12 ng I-TEQ Nm 3 obtaining the overall removal efficiency of 99.5%. While the LAC KOH injections were successful in the absorption of PCDD/Fs from the gas phase, it was observed that certain PCDD/F congeners became desorbed and entrapped within the ash necessitating further treatment of the ash residue. The ash underwent a thermal treatment first at 300 °C and 500 °C. The thermal treatment at 500 °C achieved a remarkable degradation of 99.7% removal efficiency rendering the ash and residue safe for disposal in a landfill site. Graphical Abstract