Langmuir Isotherm: Kinetic and Equilibrium Considerations

Abstract

Adsorption processes present increasing applications in the most diverse matrices of systems. In this scenario the Langmuir isotherm has highlight and importance. Although it is the simplest isotherm model, in most adsorption studies it is considered, since it is the basis for the formulation of almost all other models proposed in literature. Thus the Langmuir model is applied in the most diverse types of adsorption processes, such as: removal of metallic ions, organic compounds, pollutants generated by agriculture, dyes, mining effluents, among others. The types of adsorbents are also the most varied with highlight: alternative adsorbents, activated carbon and zeolites. Thus, the Langmuir isotherm evaluation, its origin and approximations is of extreme relevance for students and teachers who are interested and / or working with adsorptive processes. The isotherm was first published in 1916 and it parts of simple concepts for its formulation. Thus, this paper presents deductions from the Langmuir equation in two ways: (a) via kinetic considerations and (b) via equilibrium considerations. In addition, it proposes an evaluation of Gibbs energy of the process and some ways of estimating the number of surface adsorption sites.