Assessment of sepiolite as a low-cost adsorbent for phenanthrene and pyrene removal: Kinetic and equilibrium studies

- The use of sepiolite as a reactive material for construction of PRBs was evaluated.
- High amount of phenanthrene and pyrene removal was obtained.
- The kinetics, adsorption mechanisms and adsorption isotherms were studied.
- The adsorption of PAHs to sepiolite follows pseudo-second order kinetics and the Freundlich isotherm model.
- The exposure to successive batches indicates that sepiolite could be an effective reactive material for use in PRBs.

The objective of this work is to identify and evaluate reactive materials that can serve as permeable reactive barriers to PAHs. The ability to of sepiolite to remove model PAHs, such as phenanthrene and pyrene, was tested in batch assays. The reactive material was assayed for individual PAHs and a mixture of PAHs at concentrations ranging from 50 to 400 μM. Initially, kinetics studies aimed at determining the behaviour of the system and the equilibrium concentration were conducted. The adsorption processes followed pseudo-second-order kinetics, with rate constants of 0.5027 and 0.2478 g μmol−1 h−1 for phenanthrene and pyrene, respectively. Moreover, it was determined that the mechanism that controls the sorption rate was the pore diffusion rate in this study system. Subsequently, equilibrium data were analysed by evaluating their Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms. In all cases, the Freundlich isotherm exhibited the best fit to the experimental sorption data, suggesting that stronger binding sites on a heterogeneous surface are occupied first and that the strength of binding decreases with an increasing degree of site occupation. Finally, several successive batches were assayed using the same sepiolite to evaluate the behaviour of the clay matrix as a permeable reactive barrier. The conclusion of this study is that sepiolite can adsorb phenanthrene and pyrene. This finding has interesting implications for environmental treatment applications, such as providing a source of low-cost reactive material for groundwater treatment using permeable reactive barriers.