Single and competitive removal of sulfachloropyridazine and sulfadimethoxine onto natural kaolinite clay: kinetics, isotherms and thermodynamics studies

Abstract

In this study, local untreated clay was tested for its ability to adsorb sulfonamides, namely, sulfachloropyridazine (SCP) and sulfadimethoxine (SDM) from synthetic wastewater by batch equilibration. The time-dependent adsorption data followed the pseudo-second-order kinetic law while the equilibrium adsorption data were adequately described by the Langmuir model. The monolayer adsorption density (Qo) of the clay was higher for SCP than SDM in single solute system. In binary solute solutions, an antagonistic adsorption process of SDM (Rq,SCP = 0.453) in the presence of SCP (Rq,SDM = 0.915) was observed, suggesting replacement adsorption. Additionally, the calculated thermodynamic parameters, namely: enthalpy (ÄH), Gibbs free energy (ÄG), entropy (ÄS), Arrhenius activation energy (ÄEa), and sticking probability (S*) indicated SCP and SDM adsorption to be spontaneous, exothermic and physical in nature. Based on Langmuir isotherm, the mass of clay required for 99 % removal of the tested sulfonamides for a specified volume of effluent in a single batch system was predicted. The results show the tested clay may be used as a low-cost adsorbent for removal of pharmaceutical compounds from wastewater in its untreated form.