Sorption behavior of tylosin and sulfamethazine on humic acid: kinetic and thermodynamic studies

Abstract

With the aim to investigate the kinetics and thermodynamics of tylosin (TYL) and sulfamethazine (SMT) sorption on humic acid (HA), batch sorption experiments were performed using batch reactor systems. The results indicated that the Freundlich model was much more suitable for explaining the sorption of TYL/SMT on HA, where the sorption rates for TYL/SMT decreased with the initial concentration and the sorption equilibrium could be attained within 24 h. Based on the intraparticle diffusion model, the sorption process of TYL and SMT on HA could be divided into the fast sorption stage and the slow sorption stage. The kinetic data were well-fitted to the compartment pseudo first order model, where both surface diffusion and intraparticle diffusion may play an important role in rate-controlling processes. At a specific aqueous concentration, the single-point sorption distribution coefficient (k_d) of TYL and SMT decreased when the solution pH and ionic strength increased, which suggested that the sorption of TYL and SMT on HA might be dominated by both ion exchange, surface complexation and hydrophobic interactions. Meanwhile, thermodynamic calculations of sorption of TYL and SMT on HA revealed that the sorption was endothermic and spontaneous at different temperatures and the transportation abilities of TYL and SMT might be weak for soils rich in HA.