Studies On The Sorption Behaviors Of Phenanthrene And Methylene Blue On Marine Sediments

Polycyclic aromatic hydrocarbons (PAHs) and dyes are two kinds of toxic organic pollutants.PAHs are widely ubiquitous in the environment, most of which are carcinogenic and mutagenic and have the role of environmental hormones.Dyes are the basic raw materials of organic chemical industries and largely used in printing and dyeing industry. Because of potential toxic, they, as one of the major pollution sources in industrial wastewater can cause serious contamination to the environment. With the development of modern industry, wastewater and other materials containing PAHs and dyes has been let out to the marine environment by different ways, which not only has a great impact on the marine environment but also cause a great harm to aquatic safety and human health through bioaccumulation and food chain. Chemists and environmental researchers have paid much attention to this.Studies on sorption behavior of these two types of organic pollutants on marine sediments are very essential.On one hand, it is realistically significant to deeply study their transference and marine ecological effects and also provide the theoretical foundation for the pollution control and solution.On the other hand, it definitely provides effective and valuable evidences for marine scientific research and marine environment protection.Phenanthrene and methylene blue are typical representatives of PAHs and dyes, respectively. In this paper, the sorption behaviors of phenanthrene and methylene blue on marine sediments are comprehensively and deeply studied by laboratory simulations.The mechanisms on the sorption of phenanthrene and methylene blue on marine sediments treated by different means, the effect of salinity, temperature and coexisting organic pollutants (surfactants) are discussed respectively.The concrete results are shown as follows:1.Phenanthrene A. The sorption behaviors of phenanthrene on marine sediments reach equilibrium within 30 min, which accords well with pseudo-second-order kinetic equation.The initial rate of sorption, saturation sorption capacity and equilibrium rate constant of sorption change with the intial concentration.B.The sorption behaviors of phenanthrene on different treated sediments accord well with three isotherm model, especially Freundlich isotherm. Organic carbon of sediment plays an important role on the sorption process, the content of which is proportional to sorption capacity.C.The equilibrium time is affected by the media, which in distilled water is longer than that in nature seawater. In different media the content of different types of organic matter is distinguished. Because of their different sorption mechanism, the sorption rate and equilibrium time in different media make a great difference. Seawater contains a variety of ions and organic substances, which will impact on the configuration of humic acid. Humid acid, as a major compoment of organic matter, influences the whole sorption process, which results that sorption capacity of phenanthrene decreases with the increase of the salinity.D.The effect of temperature on the sorption of phenanthrene is obvious. The solubilities of phenanthrene would increase with increasing temperature.The affinity between phenanthrene and water molecules was strengthened. Moreover, the organic matters in sediments were partially dissolved out into solution with increasing temperature and consequently the partition effect of sediment organic carbon decreased. Therefore, the capacity of sorption of sediments decreased. The thermodynamic functions of Gibbs free energy (ΔGθ<0), enthalpy (ΔHθ<0) and entropy (ΔSθ<0) terms were determined, indicating that the sorption was a spontaneous and exothermic process which accompanied with a decrease in the degree of freedom.E. When nonionic surfactant Tween20 is added, the sorption behavior of phenanthrene is affected greatly. The adsorption ability increases with the increase of the concentration of Tween20.2.Methylene blue (MB) A.The sorption behaviors of MB on marine sediments reach equilibrium within 4 h, which accords well with pseudo-second-order kinetic equation. The initial rate of sorption, saturation sorption capacity and equilibrium rate constant of sorption change with the intial concentration.B.The sorption behavior of MB on different treated sediments accords well with the Freundlich isotherm.The content of organic matter is not an important factor on adsorption.The surface and micropore adsorption of clay play an essential role on the sorption behavior.C.Because seawater contains a variety of ions and organic substances, which will produce competitive adsorption with MB,the adsorption capacity decreases with the increase of the salinity. The effect of temperature on the adsorption of MB is not obvious.Because the solubility of MB will increase with increasing temperature, the affinity between MB and water molecules is strengthened.The organic matters in sediments are partially dissolved out into solution with increasing temperature and consequently the partition effect of sediment organic carbon decreases.But because the solubilization of temperature is not obvious with high solubility of MB and the primary reason of adsorption of MB is the surface and micropore adsorption of clay, not patition of organic matter, the change of temperature puts little influences on the adsorbance.D.Addition with different surfactants has different influences on the sorption behavior of MB.In different media the adsorption of MB is not affected by adding Tween20;the adsorption of MB decreases with increasing the concentration of hexadecyltrimethylammonium bromide (CTAB),and the extent of effect is more evident in distilled water. In natural seawater, sodium dodecylbenzenesulfonate (SDBS) has a negative effect on adsorption, while SDBS has a positive effect in distilled water.