Study On Bisphenol A Adsorption Onto Surficial Sediments And Adsorptive Mechanisms

Bisphenol A (BPA) is one of phenolic environmental estrogens. It is mainly used to produce many kinds of high polymer materials. In environment, BPA mainly distributes in soil, water and sediments. The levels of BPA concentration in environment may reach or surpass threshold of endocrine-disrupting properties. The health hazard of BPA to human and animals are gradually brought to people's attention. The study on BPA adsorption onto surficial sediments (natural surface coatings) and adsorptive mechanisms help learn more about the migration and transformation laws of phenolic organic compounds in water environment.The adsorption of BPA onto surficial sediments (natural surface coatings) is affected by many factors. The affection factors include the physical and chemical properties of organic matter and iron/manganese oxides in surficial sediments (natural surface coatings), content, structure, the physical and chemical properties of BPA, co-existing pollutants and natural environment conditions. There are a series of functional groups in organic matters. The functional groups have strong adsorption capacity. Mineral substances are important components of surficial sediments (natural surface coatings), which mainly consist of iron/manganese oxides. The adsorption of organic pollutants especially nonionic organic compounds onto iron/manganese oxides should not be neglected. As the effect of variable charge in the mineral surface and the corresponding interface reaction, such as electroatatic interactions, ion exchange or surface complexation, the adsorption of polar or ionic organic compounds onto the mineral surface becomes very important. The adsorption onto the mineral surface is controlled by the functional groups of mineral surface and the chemical properties of adsorbents. Organic compouds are easily distributed to organic matters, but they are adsorpted by mineral substances within certain limits. In recent research, people could not separate mineral substances and organic matters from sediments without change the physical and chemical properties of mineral substances and organic matters. People could only use different methods to separate sediments and indirectly estimate the relative function of organic compounds and mineral substances. In natural environment, the mineral substances and organic compounds don't solely exist in surficial sediments (natural surface coatings). As a result, the paper mainly studied the content and structure of organic matters and iron/manganese oxides in surficial sediments (natural surface coatings). Surficial sediments before and after extraction were characterized. Selective extraction method was applied to separate primary components. Statistics were applied to estimate contributions of organic matters and iron/manganese oxides about BPA adsorption onto surficial sediments (natural surface coatings). The adsorption of BPA by surficial sediments (natural surface coatings) before and after extraction was determined by Infrared Spectroscopy.In this paper, the following results were obtained:(1) The adsorption of BPA onto surficial sediments (natural surface coatings) coincided with first order chemical kinetics reaction equation and it was a dynamic balance process. The time when adsorption of BPA by surficial sediments (natural surface coatings) was up to the maximum adsorption was 24 hours. After 24 hours, the desorption process occured. The adsorption of BPA doesn't rised all along. During 12 hours adsorption, the adsorption amount of BPA by surficial sediments (natural surface coatings) augmented quickly along with time. The rate of adsorption was very great and this adsorption process belongs to quick adsorption phase of phenolic compounds. After 12 hours, adsorption curves went mild and the adsorption reached stable state. Between 12 hours to 24 hours, the rate of adsorption was relatively small and this adsorption process belonged to slow adsorption phase of phenolic compounds. Between 0 hour and 1 hour, the adsorption rate of BPA by surficial sediments was similar to the adsorption rate of BPA by natural surface coatings. Between 1 hour and 8 hours, the adsorption rate of BPA by surficial sediments was quicker than the adsorption rate of BPA by natural surface coatings. Between 8 hours and 12 hours, the adsorption rate of BPA by surficial sediments was slower than the adsorption rate of BPA by natural surface coatings.(2) The thermodynamics experiments that BPA was adsorbed by surficial sediments (natural surface coatings) and their main components educed the following conclusions: Because BPA is a sort of week acid compound, the adsorption of BPA by surficial sediments (natural surface coatings) was subjected to pH value more. Under acid conditions, the adsorption amounts of BPA by unit surficial sediments (natural surface coatings) decreased with the increace of pH value. Under alkaline conditions, the influence was not distinct. The ratio of surficial sediments (natural surface coatings) to water also influenced the adsorption of BPA by surficial sediments (natural surface coatings). The ratio of BPA adsorption by surficial sediments (natural surface coatings) increased with the ratio of surficial sediments (natural surface coatings) to water. The adsorption process of BPA by surficial sediments (natural surface coatings) was non-linear adsorption and they both accorded with Langmuir and Freundlich equation. When the concentration of BPA was not changed much, there were not many differences between Langmuir and Freundlich equation if two equations were applied to describe non-linear adsorption. Adsorption datas were well fitted with two equations. Significance level both reached p=0.001 (n=8). The functional groups of natural surface coatings were fewer compared with surficial sediments. The adsorption capacity of natural surface coatings for BPA was stronger compared with surficial sediments'. The adsorption capacities of surficial sediments (natural surface coatings) before and after extraction for BPA followed the order: surficial sediments (natural surface coatings) removed Mn oxides > surficial sediments (natural surface coatings) removed Fe-Mn oxides > original surficial sediments (natural surface coatings) > surficial sediments (natural surface coatings) removed organic matters.(3) Three extractants all made the specific surface area, pore structure specific pore volume and particle dispersion of surficial sediments become greater and H2O2 have a great influence on surficial sediments. The adsorption amount of BPA by Surficial sediments before and after extraction was not proportion to its specific surface area.Summation model of statistical analysis method and IR were used to study the adsorption mechanism of BPA by surficial sediments (natural surface coatings) and their components. In Summation model of statistical analysis method, the absolute adsorption capacities (or contributions) of iron oxides for BPA were higher than organic matters'in surficial sediments (natural surface coatings) and manganese oxides had negative effects for the adsorption of BPA; The absolute relative capacities (or contributions) of iron oxides for BPA were higher than organic matters'in surficial sediments (natural surface coatings). The adsorption sites of BPA by surficial sediments (natural surface coatings) were mostly been iron oxides and organic matters. The adsorption amount of BPA was in proportion to the content of organic matters. The adsorption capacities of BPA by surficial sediments (natural surface coatings) which were removed organic matters apparently decreased. The adsorption capacities of BPA by surficial sediments (natural surface coatings) which were removed manganese oxides apparently increased. Because iron oxides had promotions on the adsorption of BPA and manganese oxides had inhibitory effects on the adsorption of BPA, the adsorption capacities of BPA by surficial sediments (natural surface coatings) before and after extraction increaced as a whole.The results of IR indicated that the change of functional groups in spectrograms of unextracted and extracted surficial sediments (natural surface coatings) along with the adsorption of BPA by unextracted and extracted surficial sediments (natural surface coatings) were not significant.