Kinetic study of tetracycline adsorption on sludge-derived adsorbents in aqueous phase

This study investigated the global adsorption rate of tetracycline on adsorbents obtained from treatment sludge. Experimental data on tetracycline concentration decay curves were interpreted with kinetic models (first-order, second-order, Langmuir, and intraparticle diffusion) and diffusional models (pore volume diffusion model and surface diffusion model). The first-order kinetic model provided the best interpretation of tetracycline adsorption kinetics on all adsorbents, and its rate constant varied in a linear manner the macro- and mesopore volume of the adsorbents. It was also found that the tetracycline adsorption rate is controlled by intraparticle diffusion and that diffusion in the pore volume represents >80% of total intraparticle diffusion. This indicates that surface diffusion does not play a major role in tetracycline diffusion on the different adsorbents. Furthermore, the effective tetracycline diffusion coefficient in the pore volume gradually increased with greater meso- and macropore volume and larger surface area of the adsorbent, indicating that the tetracycline adsorption rate is directly related to the accessibility of this molecule to the microporous structure of the materials.

► The first-order kinetic fits tetracycline (TC) adsorption on sludge adsorbents.
► The rate constants vary in a linear manner with their macro-and mesopore volumes.
► The TC adsorption rate on all adsorbents is controlled by intraparticle diffusion.
► Pore volume diffusion represents more than 80% of the total intraparticle diffusion.
► Diffusion of TC in the pore volume increases with larger meso and macropore volume.