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Effect Of Ionic Compounds On Phenanthrene Sorption/Desorption

Posted on:2011-03-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:W L WuFull Text:PDF
GTID:1221330332472494Subject:Environmental Science
Abstract/Summary:PDF Full Text Request
Impact of series ionic compounds, such as NaCl, pentachlorophenol (PCP),4 organic base (n-hexylamine, trimethylamine,1-naphthylamine, aniline), an anionic surfactant sodium dodecylbenzene sulfonate (SDBS), a cationic surfactant dodecyltrimethylammonium chloride (DDTMA), dissolved organic matter (DOM), on the sorption-desorption of phenanthrene (PHE) under various water chemistry condition was studied. (1) Sorption of PCP on geosorbents (soil and sediment) increased with decreasing pH, whereas pH has no obvious effect on PHE sorption. PCP reduced PHE sorption at pH 8, due to the competition of hydrophobic sorption sites on geosorbents, as well as the forming of dimmer of PHE with anionic PCP in aqueous phase. PCP could enhance PHE sorption at pH 5 and 3, because low pH favors PCP sorption on geosorbents via ionic or polar head, and PHE can sorbe on the sorbed PCP throughπ-πinteraction. Moreover, PHE sorption on sorbed PCP was rather stronger than on natural organic matter in geosorbents.At low PHE concentration, PHE had no effect on PCP sorption, while enhanced PCP sorption at high concentration, as a result of more hydrophobic sorption sites andπ-πinteraction provided by the sorbed PHE. (2) Sorption capacity of cationic organic bases is stronger than neutral ones. When existing as the same species, the greater the hydrophobicity, the stronger the sorption. Some cationic organic bases, such as n-hexylamine, enhanced PHE sorption. However, other cationic organic base, such as trimethylamine, had no effect on PHE sorption, because of its low hydrophobicity, and weak sorption ability. Some neutral organic base, such as 1-naphthylamine, could reduce PHE sorption, as a result of competition for hydrophobic sorption sites. And other neutral organic base, such as aniline, due to its low hydrophobicity and weak sorption ability, had no effect on PHE sorption.1-naphthylamine, as a polar compound, reduced PHE sorption, whereas PHE, as an apolar compound, had no effect on 1-naphthylamine sorption. (3) At low DDTMA concentrations, salinity slightly reduced DDTMA sorption. Conversely, at higher DDTMA concentrations, salinity increased DDTMA sorption. Sorption of SDBS increased significantly with salinity. There was practically little or no solubility enhancement for PHE below the critical micelle concentration (CMC) of the surfactants, while the water solubility of PHE was significantly enhanced by the two surfactants above their CMCs. With salinity increasing, PHE solubility enhancement by surfactants increased significantly, and the CMC of surfactants decreased. SDBS reduced PHE sorption, and the reduction extent increased with salinity. DDTMA enhanced PHE sorption, and the extent also increased with salinity. Hence, the change of PHE sorption could not be explained by "salt out" effect only but due to the change of micelle structure at elevated salinity. (4) PHE sorption on carbon nanotubes was much higher than those on natural geosobents, and the sorption isotherms were nonlinear. Single-walled carbon nanotube exhibited the greater sorption ability for PHE than multi-walled carbon nanotube. Both of SDBS and DDTMA reduced PHE sorption on carbon nanotubes. The extent of PHE sorption reduction by surfactants increased with surfactant concentration, and decreased with PHE concentration. Sorption of PHE on carbon nanotubes increased with salinity. The sorption nonlinearity of PHE was weakened by SDBS and DDTMA, and had no change in the present of NaCl. (5) DOM, as a natural surfactant, can form micelles. The electricity conductivity of DOM was higher when it existed as a monor as compared to when it existed as micelles. DOM enhanced PHE solubility at concentrations above CMC, and the extent of PHE solubility enhancement decreased when DOM concentration was too high. This is because the structure of DOM micelle changed at high concentration. The sorption capacity of sediment to DOM decreased with DOM concentration increased. PHE sorption was reduced by DOM in some extent. (6) The extent of solubility enhancement by SDBS for pyrene was greater than for PHE, but the desorption percent of pyrene was smaller than PHE, due to its greater hydrophobicity. The desorption percent of pyrene and PHE was not dependent on their initial concentrations and the coexisting of each other, but increased with SDBS concentration. PHE and pyrene sorbed on geosorbents decreased, and the amount involved in surfactant micelle phase increased with SDBS concentration. Below CMC, PHE sorbed on the teosorbent transferred to surfactant phase with the increasing of SDBS concentration, but not to the water phase. Above CMC, PHE both in the geosorbent and water transferred to the surfactant phase, indicating the strong ability of surfactant to "dissolve" PHE. The partition of PHE and pyrene in soil-surfactant-water system was not dependent on their initial concentration. (7) Desorption of PHE all exhibited hysteresis to some extents. The irreversibility is time-dependent, and the irreversible entrapment in hydrophobic nanopores is the mechanism of sorption-desorption hysteresis, whereas slow kinetic mechanism for pollutant molecule transferring between irreversible and reversible sorption sites can exert effect in short time desorption process. Geosorbent treated by NaOH showed a reduced sequestration ability on PHE than the origin geosorbent did. PHE sorption was enhanced, whereas sorption-desorption hysteresis was weakened with salinity increasing. N2 sorption illustrated that soil organic matter changed to a more condensed conformation at higher salinity, losing lots of its hydrophobic nanopores, which were unfavorable for irreversible sorption.
Keywords/Search Tags:combined pollution, phenanthrene, sorption-desorption, organic acid, organic base, ionic surfactant, dissolved organic matter, sanility
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