Sorption And Desorption Behaviors Of Phenanthrene By Black Carbon From Soil In Danjiangkou Reservoir Water-Level-Fluctioning Zone

Black carbon has strong adsorption capacity towards hydrophobic organic compounds which can be10to1000times higher than the capacity of other organic compounds in sediment. Water-level-fluctuating zone is the transitional area between terrestrial environments and aquatic environments where bank pollution and cross contamination between land and water exist. Therefore, it is of great significance for the control of contamination to develop the research on the adsorption capacity of black carbon towards hydrophobic organic compounds.This research focuses on the water-level-fluctuating zone in Danjiangkou reservoir. Periodic flooded soil sample (with an elevation between149and157meters) and non-flooded soil sample (with an elevation above157meters) are collected as the soil samples in water-level-fluctuating zone. Then black carbon needs to be extracted from soil samples and explore the adsorption and desorption activities of black carbon towards phenanthrene which is a kind of hydrophobic organic compounds. Its adsorption mechanism needs to be discussed and the significant meaning of the black carbon’s controlling contamination in Dan jiang kou reservoir will be explored. Furthermore, this research can provide relative basis for further studies in this field. Mainly conclusions are as follows:(1) The morphology of black carbon has certain heterogeneity. It presents the combination of rectangular and column at a low magnification and smooth, rough, corrugated, stratiform and concave-convex surface structure which includes microporous structures at a high magnification. The IR spectral peaks of black carbon have some similarities as well as slight differences. The surface of all BCs contain groups such as-OH, C-O, C=C, however, Some samples contain carboxyl C=O groups and carbonyl C=O groups stretching vibration at1700cm-1, and carboxylic ester at1560cm-1. The distance between the aromatic structures of black carbon is larger than that in graphite and smaller than that in modern black carbon samples. (2) The adsorption and desorption of black carbon in water-level-fluctuating zone towards phenanthrene can be classified as fast process and slow process. The fast sorption process tends to be into balance after proximately6hours and the rest of the time is slow process. The fast desorption process tends to be into balance after proximately12hours and the rest of the time is slow process.(3) The adsorption and desorption processes were fitted through first order kinetics equation, second order kinetics equation, Elovich kinetic equation and diffusion equation in the granules. All of the results are consistent and the effects of these methods are listed according to accuracy:second order kinetics equation, Elovich kinetic equation, first order kinetics equation, diffusion equation in the granules. According to the results above, the adsorption and desorption of black carbon in water-level-fluctuating zone towards phenanthrene is not a simple mechanism but a complicated process.(4) The fitting parameters in Freundlich model and Langumuir model indicate that both of them can properly fit the adsorption and desorption processes. All of the n values in Freundlich model are less than1, indicating that this adsorption process is not a simple linear distribution but a nonlinear multi-adsorption. On the other hand, the parameters Qmax reflect the black carbon has strong adsorption ability towards phenanthrene, and different samples of BC have different sorption capacity.(5) Hysteresis phenomenon is common in the desorption of phenanthrene from black carbon. With the raise of equilibrium concentration, the desorption hysteresis coefficient tends to increase. When the concentration is low, the increase is fast and when the concentration reach a certain point, the increase will be slow down.(6) The results turn out that distribution effects play the dominating role in the whole adsorption process. From the perspective of the adsorption process as a whole, surface adsorption effect is the mainly performance when the concentration is low and distributional effects play a vital role when the concentration is high.(7) Both of Freundlich model and Langumuir model can be properly fitted in the none flooded soil black carbon’s adsorption and desorption process towards phenanthrene.