Enhanced Heavy Metal Sorption by Surface-Oxidized Activated Carbon Does Not Affect the PAH Sequestration in Sediments

Abstract

We examined the sorption of heavy metals and polycyclic aromatic hydrocarbons (PAHs) to surface-oxidized activated carbon (AC) and its effect on the distribution of those compounds in sediments. Created surface oxygen groups on AC enhanced the sorption of copper, which is superior in sorption competition, in the marine sediments. In case of cadmium, aqueous chemistry altered by AC addition, such as pH, has greater impact on the bioavailability according to the result of a sequential extraction combined with the pore water concentration measurements. Oxidized AC exhibited 2.3 times more adsorption of reduced bioavailable copper while 23% of bioavailable cadmium was adsorbed onto unmodified AC. No significant changes in BET surface area, pore volume, and AC/water distribution coefficient (K (AC)) of PAHs were observed with surface-oxidized AC. The largest difference in K (AC) after the oxidation was only 0.14 log unit. Consequently, freely dissolved aqueous concentrations of PAHs were reduced by more than 96% for all tested ACs in a week despite the increased Cu sorption on AC. This indicates that enhanced metal sorption by surface oxidation of AC is less significant in controlling bioavailability of PAHs in sediments than particle size or sorbent dose.