Effect Of Surficial Geochemical Processes On Sorptions Of Hydrophobic Organic Contaminants By Black Carbon

Sorption is a main mechanism controlling the migration of hydrophobic organic contaminants(HOCs) in the nature environment. Black carbon is a common component of natural soils, sorption of HOCs by black carbon is important in the overall sorption of HOCs by the bulk soil, its contribution to the overall sorption of HOCs by the bulk soil is remarkable.The compositions and structures of environmental media, e.g. soils, may change continuously during the experience of surficial geochemical processes, sorption-desorption behaviors of HOCs on soils, fate and transport of HOCs, bioavailability and health risk of HOCs in soils change accordingly. It has been recognized that the surficial geochemical process may exert both positive and negative effects on remediation practices of HOCs in nature environments, on the one hand, the desorption ability, bioavailability and environmental risks of HOCs in soils may be reduced after soils had undergone surficial geochemical processes; on the other hand, the surficial geochemical processes may depress sorption abilities of environmental engineering materials once they were introduced into contaminated sites and such undermines the remediation efforts. However, to quantitatively and accurately estimate both effects of the surficial geochemical processes on the fate, transport, bioavailability and environmental risks of HOCs in the environment needs more studies since many key parameters are still lacking by far.This master thesis simulated some common happening surficial geochemical processes in the laboratory, studied effects of these surficial geochemical processes to the surface morphology and physicochemical properties of the black carbon samples and to sorption abilities of phenanthrene and pyrene by the black carbon samples. The surficial geochemical processes simulated in this study mainly includes, the dissolution and precipitation of Fe(OH)3 and Ca CO3 on the black carbon samples, repeating of freezing and thawing, covering and coating by other soil organic matter, and longer interaction time of aqueous solution and the black carbon samples.The thesis study obtained several important results and conclusions list as following:(1) the simulated surficial geochemical processes did change the surface morphology and physicochemical properties of the black carbon samples;(2)the technique of using of syringe with filter membrane is suitable in determining HOCs concentrations in black carbon particle suspending solutions;(3) black carbon samples showed very strong sorption abilities on phenanthrene and pyrene, and black carbon amending can greatly reduce the migration of HOCs in soils;(4) sorption capacities of black carbon samples decreased variously according to the type and strength of surficial geochemical process they had undergone, but sorption capacities of black carbon samples which were covered by other soil organic matter(HA) increased obviously.(5) sorption abilities of the black carbon samples decreased as increasing of precipitating minerals’ concentrations and interaction time of aqueous solution and the black carbon samples, but increased as increasing of the repeating freezing-thawing cycles and other soil organic matter(HA) coating.