Modelagem do equilíbrio de adsorção bicomponentes: aplicação para atrazina e simazina em carvão ativado

Abstract

This study develops mathematical models to explain the adsorption equilibrium of atrazine and simazine by activated carbon under single and bicomponent experimental conditions. For the experiments, different concentrations were tested at four different temperatures (20, 25, 35 and 45 °C).The tests were developed using the following fixed conditions: 0.038 g of activated carbon, adsorption time of 12 hours and solution volume of 200 mL. The reactors were placed in the Dubnoff Bath SL-157 thermostatic bath and the results of atrazine, simazine concentrations were monitored using the LCESI-MS liquid chromatograph (LC 2020, Shimadzu®).A general model that could explain the multicomponent adsorption equilibrium of the compounds was developed, and from this, several hypotheses of mathematical models were thought and tested to explain the equilibrium of the process. The two-site monolayer model proved to be the best isothermal model to describe the equilibrium of the system. The results indicated a maximum adsorption capacity at 35°C (44.53 mg g -1 ).Thermodynamic parameters and equilibrium constants showed that the process is favorable and spontaneous for atrazine in the S1 active site and for simazine in the S2 active site, revealing that, even with competition for the sites, the two compounds can be efficiently adsorbed in the same aqueous solution. The thermodynamic results suggested two types of surface adsorption mechanisms: physical and chemical. Thus, the study brings an alternative mathematical model to explain the bicomponent adsorption for atrazine and simazine and contributes to a better understanding of the multicomponent adsorption process and system equilibrium that can be tested and applied to other types of pollutants.