Environmental Oxidation Of Black Carbon And Its Effects On Sorption Of Organic Contaminants

Black carbon (BC) derived from incompletely combustion of biomass or fossil fuels is ubiquitous in natural environment. In recent years, manmade BC was largely produced to terrestrial system. In soils/sediment condition, natural oxidation can slowly alter some physicochemical properties of BCs, which can not be ignored.In the present study, BCs were produced from the carbonization of fir-wood at 300,400,500,600 and 700℃, respectively. The obtained BC samples were further oxidized under 60℃ within a period of 12 months. The change of chemical and physical properties of BCs was characterized and its effects on the sorption to organic contaminants (e.g. diquat and phenanthrene) were studied.The change of properties for all of BCs includes the increase of oxygen content, surface acidic groups and CECs but the slight decrease of surface area.After the natural oxidation, the adsorption of ionic organic compounds (e.g. diquat) on BCs produced at 400,500,600 and 700℃ decreases, while that on the low-temperature (300℃) biochar increases.This is due to the change of the electrostatic interaction between BC and diquat. However, the adsorption of hydrophobic organic compounds (e.g. phenanthrene) is different from diquat because that the adsorption of phenanthrene decreased on each BC produced at different temperatures after natural oxidation.The oxidated BCs showed different impacts on adsorption of the ionic and the hydrophobic organic compounds.In special for BC produced at 300℃, the opposite effect on their adsorption was presented. This study will be helpful to better understand the role of the oxidated BCs in soil environment.