Investigation of thermodynamic and kinetic behaviors of marine sediment at sorption of phthalate esters

Abstract

P esters (PEs) are important classes of chemical endocrine-disrupting compounds. PEs is mainly used as plasticizers. These compounds are easily released into the environment because there is no covalent bond between the phthalates and plastics in which they are mixed. In this study the effect of environmental parameters such as time contact, temperature and salinity on adsorption process of 6 PEs on the sediments of the north-west of Persian Gulf was investigated. Also, the adsorption isotherms and kinetic parameters have been studied. The results showed that the adsorption of PEs is very fast and reach the equilibrium within 6 hours and after this duration only a small change was observed. Among the various PEs, dinormal puthyl phthalate ester (DOP) showed the most adsorption tendency to the studied sediments with average value 613.65 μg, g-1. Several kinetic models have been investigated; pseudo-second order equation was best fitted to the adsorption behavior of PEs with marine sediments at different contact times and film diffusion is the rate limiting step. The sorption equilibrium results could be well described by linear isotherm. This means that in PEs sorption process on marine sediments partition domain is dominated over the whole filling domain. After H2O2 oxidation of sediments, the Kd values were redused by average 64.82%. It means that amorphous organic carbon fraction involve the major part of total organic carbon in sediments. PEs sorption isotherms on treated sediments follow the nonlinear models. By increasing the temperature, the adsorption of PEs on sediments was decreased indicating that the process is exothermic. It was also in thermodynamic study ΔH0<0. The mines value of ΔG0 for these compounds showed the spontaneous sorption process for them. It be noted that mechanism was carried out with decreasing in entropy. These research findings have a prime importance on assessment of the fate and transport PEs in seawater-sediment systems.