Effects of humic acid coatings on phenanthrene sorption to black carbon

Black carbon (BC) can strongly adsorb hydrophobic organic compounds (HOCs). The HOC sorption to coated BC could be attenuated in soil and sediment compared with that of the parent BC. To study the potential causes of the sorption attenuation, humic acid (HA) and BC were isolated. Phenanthrene (PHE) was selected as the representative of HOCs. BC was coated with the precipitated HA. The PHE sorption to the HA-coated BC was determined. The HA coatings on BC could result in the significant sorption attenuation of PHE to BC. The attenuation varied in different HA origin and was positively correlated to the aromaticity of HA. The attenuation could be explained by the direct competition between HA and PHE for the available sorption sites on BC and the reduction of the available sorption sites as a result of the pore blockage of BC caused by the HA coatings. Therefore, the HA coatings on BC was one potential cause of the attenuation of HOC sorption to BC in soil and sediment.