Beyond Freundlich and Langmuir: the Ruthven–virial equilibrium isotherm for aqueous-solid adsorption systems

Abstract

It is the purpose of this paper to investigate the data fitting attributes of the exponential integral isotherm, which was first derived by Ruthven in 2004 to describe adsorption at gas-solid interfaces. The exponential integral isotherm, a variant of the virial isotherm, incorporates the two fitting parameters of the Langmuir isotherm and has an expandable mathematical structure.model. Furthermore, it is shown that the data fitting performance of the two-parameter Ruthven-virial isotherm is comparable to that of the three-parameter Sips isotherm. The Ruthven-virial isotherm is a hidden gem and a practical alternative to the Freundlich and Langmuir equations in the correlation of hyperbolic adsorption isotherms. We hope that the findings presented here will inspire the research community to evaluate the Ruthven-virial isotherm in the modeling of contaminant adsorption at aqueous-solid interfaces.