Studies On The Sorption Behavior Of Three Kinds Of Typical Surfactants On Marine Sediments

Surfactants are toxic organic pollutants, which are ubiquitous in the environment. They are also the basic raw materials of organic chemical industries. Wastewater containing surfactants has been let out to the marine environment, which has done great harm to the human being and marine organisms. Chemists and environmental researchers have paid much attention to it. Investigation on sorption behavior of surfactants on marine sediments is realistically significant to deeply study their transference and marine ecological effect. It can also provide the theoretical foundation for the pollution control.The study objects of the dissertation referred to three surfactants, which are ubiquitous in marine environment and have carcinogenic harmful properties. There are lots of environmental, biological and geochemical significance on the research of the sorption behavior on marine sediments. Meanwhile, the research results of the thesis will definitely provide an effective and valuable evidence for marine scientific research and marine environment protection.In this work, the sorption behavior of three kinds of typical surfactants, polyoxyethylene (20) sorbitan Monolaurate (Tween20), sodium dodecylbenzene sulfonate (SDBS) and cetyl trimethyl ammonium bromide (CTAB), in the system of marine sediment-seawater were comprehensively and deeply studied. A stress was made on the difference of sorption isotherms of the three surfactants on marine sediments treated by different means and the effect of salinity, acidity, temperature of seawater on their sorption behavior. The concrete results are shown as follows:A. The sorption behavior of surfactants on marine sediments reached equilibrium within 50min, 100min, 1h for Tween20, SDBS, CTAB, respectively no matter what media (Natural Seawater-NSW, Diluted Seawater-DSW and Distilled Water-DW) were utilized. The sorption percentage varied with the media in the sequence of NSW>DSW>DW.B. The sorption behavior of three kinds of surfactants on HCl- and H2O- treated sediments accorded well with the linear isotherm and the partition effect of sediment organic carbon played an important role during the process. At the same time, the behavior for SDBS also accorded with the Freundlich isotherm.C. The sorption isotherms of three kinds of surfactants on H2O2-treated sediments presented nonlinear and could be depicted by the Freundlich model. The surface function and microporous adsorption of the clay significantly influenced the adsorption process.D. The"salting out"effect of seawater led to the decrease in the solubilities of surfactants and the release of the solvable part of sediment organic carbon into aqueous solution. Accordingly, the partitioning coefficients Kd and sorption capacity of surfactants increased with the increase of salinity of seawater.E. The effect of acidity on sorption of surfactants on sediments depended on their types. The effect was slight on Tween20 because it was undissociated in aqueous solutions. The decrease of pH might influence the surface charge of the sediments which became less negative with a consequent increase in electrostatic effect between alkyl chain of SDBS and the sediment surface. As a result, the capacity of adsorption of SDBS increased. The influence on CTAB was just opposite. F. The effect of temperature on the adsorption of surfactants is obvious. The solubilities of surfactants would increase with increasing temperature; The affinity between surfactants and water molecules was strengthened; 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.G. 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.In short, the adsorption process of surfactants on marine sediments is complex. It is influenced by not only the composition of sediments but also some external factors such as salinity, pH, temperature and so on.