The Redlich-Peterson isotherm for aqueous phase adsorption: Pitfalls in data analysis and interpretation

The Redlich-Peterson isotherm, a variant of the Sips isotherm, is widely used to describe the adsorption char-acteristics of water contaminants. Despite its popularity, this isotherm is susceptible to misuse and misinter-pretation. In this article, we aim to bring to light the various deficiencies associated with the Redlich-Peterson equation, encompassing faulty mathematical formulations, unverified mechanistic interpretations, erroneous linearized versions, unnecessary parameter constraints, incorrect parameter units, inappropriate model com-parisons, model misidentifications, and flawed thermodynamic calculations. These deficiencies often stem from a lack of mathematical expertise or a poor understanding of adsorption modeling, and occasionally, from egregious negligence. Our primary goal is to draw attention to these pitfalls and encourage researchers to steer clear of them. By providing guidance and shedding light on these issues, we aim to foster the judicious application of the Redlich-Peterson equation in the analysis and interpretation of adsorption equilibrium data.