Sorption And Desorption Mechanisms Of Naphthalene On Biochars At Presence Of Rhamnoilpid And Sodium Alginate

Biochar is a carbon-rich material produced by pyrolyzing biomass in the absence of oxygen. Due to the presence of well-developed micro-pores and high specific surface area, biochar displays an excellent sorption capacity and hence is deemed as a green environmental sorbent and has been extensively used in the field of agriculture and environment. Polycyclic aromatic hydrocarbons (PAHs) are a typical kind of persistent hydrophobic organic pollutants commonly found in soil and sediments. Thanks to the high affinity of sorbents to PAHs, sorption has become a critical process governing the fate and transport of PAHs in the environment. In the present thesis, Naphthalene is selected as a model compound of PAHs to explore sorption kinetics, sorption isotherm, desorption kinetics and desorption isotherm of PAHs on the biochar prepared through pyrolyzing corn and wheat stalks under different temperatures. The influence of rhamnolipid and sodium alginate on the sorption and desorption of PAHs is also investigated. Different models were used to elucidate the mechanism of sorption and desorption of PAHs on the biochar. The main results and conclusions are as follows:(1) Physicochemical properties of various biochars derived from diffetent feedstocks and pyrolysis temperatures are different. Corn and wheat stalk biochars (C300?C400?C500?C600?M300?M400?M500?M600) pyrolyzed at 400? and 600? were chosen in this thesis.The condensed aromatic carbon content seems to be a little high for corn stalk derived biochar which has well-developed micro-pores and high specific surface area. The biochars produced at low temperature also have higher aromatic carbon content, and have more oxygen-containing organic functional groups.(2) Naphthalene sorption kinetic on corn and wheat stalk biochars pyrolysis temperature (300,400,500 and 600?) were studied. Naphthalene sorption capacity at equilibrium of biochars at the same pyrolysis temperatures varied with feedstocks in an order of wheat>corn. Compared with the pseudo-first-order kinetic model, the pseudo-second-order kinetic model was much better in fitting the sorption kinetic features of the biochars, suggesting that the sorption is related to sorbing sites in biochar, rather than simplex single-layer sorption. Fitting analyses using the intraparticle diffusion model and the Boyd model show that the sorption process was affected by both film diffusion and intraparticle diffusion. And film diffusion is the rate-limiting factor.(3) Naphthalene sorption on corn and wheat stalk biochars pyrolysis temperature (300,400,500 and 600?) was studied. Fitting analyses using Freundlich model, N is less than one showing that the sorption of eight biochars belong to nonlinear. The mechanism of biochars are different due to the contribution rate of partition and adsorption. The contribution rate are various for biochars at diffetent feedstocks and pyrolysis temperatures.(4) Naphthalene sorption to the biochar was studied at the presence of rhamolipid and sodium alginate. Corn stalks biochars (C400, C600) and wheat stalks biochars (M400, M600) pyrolyzed at 400? and 600? were chosen as sorbent. The rhamnolipid is conducive to the sorption of corn stalk biochars, opposite to wheat stalk biochars. And the sodium alqinate is also conductive to corn stalk derived biochar, but has the divergent results for wheat stalk biochar. The concentration of rhamnolipid and sodium alqinate, pryrolysis temperatures and the initical Naphthalene concentration are coefficient to the sorption capacity. Sorption mechanism relate to the physicochemical properties, rhamnolipid and Naphthalene properties.(5)The desorption behavior of Naphthalene was studied based on the corn stalk biochars pyrolyzed at 300? and 600?, both of which were pre-saturated with Naphthalene and at the presence of rhamnoilpid and sodium alginate. The results indicated that there is a desorption hysteresis phenomenon about C300 and C600 suggesting that the sorptions are irreversible. Fitting analyses using Elovich model, the desorption of C300 and C600 belong to heterogeneous diffusion. The desorption process is analyzed with two-compartment first-order rate constant model. C300 C600 are rich in high irreversible difficult desorption components, and the amount of C600 is more than C300. Both of rhamnoilpid and sodium alginate inhibited the desorption of Naphthalene.