Sorption And Desorption Behaviors Of Heavy Oil On Jiaozhou Bay Sediments And Its Studies Of Effective Factors

Petroleum hydrocarbon is a common organic pollutant in ocean environment, which has become one of the main organic pollutants in the offshore areas. These petroleum contaminants cause serious damage to the marine eco-environment and are harmful to human being through a series of physical, chemical, and biological processes. When oil pollutants enter into water system, the light components will disappear through evaporation, dissolution, emulsification, and so on. However, the heavy contents will be adsorbed onto suspension particle, and then set down to the bottom. Oil pollutants on sediments will release to seawater under certain conditions, and will cause secondary pollution to seawater. The adsorption and desorption of heavy oil in sediment/water interface is an important way to affect their migration, transformation, and biological utilization in marine environment. Therefore, it is very important to study the sorption and desorption behaviour of oil on marine sediments.In this paper, the sorption and desorption behaviors of heavy oil on Jiaozhou bay sediments were comprehensively studied through laboratory experiments. The sediment sample was wet sieved in order to keep the original nature of the particulate. Some related factors were also discussed to study the mechanisms of the sorption and desorption, such as treated method, particle size, salinity, temperature and surfactant. The main conclusions are as follows:1. Sorption process1)The sorption rate of heavy oil on sediment was rapid and the kinetic process was proven to follow the pesudo-second-order kinetic rate equation. The sorption was accelerated remarkably with the addition of anionic surfactant sodium dodecyl benzene sulfonate(SDBS), while was retarded with the presence of nonionic surfactant polyoxyethylene(20)sorbitan Monolaurate (Tween20).2)The sorption isotherms of heavy oil on sediment could be described by the Freundlich equation. The sorption capacity could be enhanced by SDBS obviously, while decreased with the presence of Tween20. 3)The equilibrium experiments of heavy oil sorption on HCl, H₂O and H₂O₂ treated sediments revealed that the isotherms became more linear for sediment with higher organic carbon, which indicated that heavy oil sorption onto sediments was through partition function and surface sorption effect, while the former was dominant. The sorption ability of sediment decreased with increasing particle sizes. The reason may be that sediments with different sizes had different specific surface areas, TOC values, and mineral compositions.4)The sorption capability was increased under higher salinity and lower temperature circumstances. In the presence of SDBS the effect of salinity was significant, while the influence of Tween20 was not clear. The temperature influenced the solubility of heavy oil and the organic matters in sediments, thus affacted the partition effect of sediment.5)Calculation of thermodynamic parameters indicated that the sorption process of heavy oil was spontaneous (ΔG^φ<0), exothermic (ΔH^φ<0) and was a physical process. In the presence of 20 mg·L^-1 SDBS, the│ΔG^φ│and│ΔH^φ│values became higher, while in the presence of 20mg·L^-1 Tween20, the effect was reverse.2. Desorption process1)The desorption rate of heavy oil on Jiaozhou bay sediment was slow, and the kinetic process could be divided into two stages: The first stage was rapid which took place on sediment surface, while the second one was slow and due to the diffusion from the internal micropores of sediment. The desorption process of heavy oil according well with a two-compartment first order kinetic rate equation.2)SDBS and Tween20 could remarkably enhance the desorption of heavy oil from sediment. The desorption rate constant increased with the increasing concentration of surfactants. Under the same circumstances, the influence of Tween20 was more obvious.3)Larger particle size was favourable for the desorption of heavy oil from sediment. Environmental factors research indicated that the desorption capacity and rate constant of heavy oil was significantly increased at lower salinity and higher temperature.