Superfund Research Program
Activated Carbon as a Multifunctional Amendment to Treat PCBs and Mercury
Project Leader: Richard G. Luthy
Grant Number: R01ES016143
Funding Period: 2007-2011
Year: 2010 2009
This year, Dr. Luthy's research team invented a new multifunctional carbon material, polysulfide-rubber (PSR) polymer-coated activated carbon, that has excellent mercury removal efficiency while retaining its polychlorinated biphenyl (PCB) sorption capacity compared to virgin activated carbon. The polymer was synthesized by a simple one-pot reaction and was effectively impregnated in activated carbon with maintaining the micropore volumes and total BET surface area when an optimal amount of PSR was used. Mercury ions are strongly engaged with PSR by chemical bonding and the spatial distribution of mercury and sulfur atoms are positively correlated. The PSR-coated activated carbon can reduce the Hg(II) concentration by three orders of magnitude and remove PCBs as effectively as virgin activated carbon. Both mercury and PCB removal efficiencies depend on the extent of PSR polymer loading.
Nanoscale zerovalent iron particles (nZVI), bimetallic nanoparticles (nZVI/Pd), and nZVI/Pd impregnated activated carbon (nZVI/Pd-AC) composite particles were also synthesized and investigated for their effectiveness to remove polybrominated diphenyl ethers (PBDEs) and/or PCBs. PBDEs were easier to dehalogenate than PCBs by both nZVI and nZVI/Pd. Palladization of nZVI promoted the dehalogenation kinetics for selected mono- to tri-BDEs and 2,3,4-trichlorobiphenyl (PCB 21). The preferential removal of para-halogens on PBDEs and PCBs by nZVI/Pd further lowers their overall toxicity. The change in distribution of products obtained from the debromination pathways of selected PBDEs indicates that a greater role of H atom transfer is induced by Pd, rather than electron transfer by nZVI. A model was developed to study the sorption and dehalogenation kinetics of the reaction by nZVI/Pd-AC. While 2,3,4-tribromodiphenyl ether (BDE 21) was sorbed onto activated carbon composites quickly, debromination was slower compared with freely dispersed nZVI/Pd. This study revealed the retarding effect of activated carbon on the debromination reaction, caused by heterogenous distribution of nZVI and Pd on activated carbon and/or immobilization of hydrophobic organic contaminants at the sorption sites.