Quantification of the limitation of Langmuir model used in adsorption research on sediments via site energy heterogeneity

- The limitation of Langmuir model used in natural sediments was discussed.
- The formula for calculating the error of Langmuir model was developed.
- The error of Langmuir is closely correlated with the site energy heterogeneity.
- The conditions where Langmuir model cannot be used in sediments were obtained.
- This study is vital for further researching the adsorption process of sediments.

The Langmuir model has been extensively introduced into the field of environmental adsorption, while some studies showed that it was difficult for the model to describe the adsorption of sediments. The purpose of this paper is to recognize the applicability of the Langmuir model used in the adsorption of contaminants onto sediments quantitatively through the relationship between the error of Langmuir (δ) and site energy heterogeneity (σ). The formula for calculating δ in sediments was developed based on the heterogeneity parameters (m, n). The data was extracted from papers discussing about the adsorption of pollutants on natural sediments. It was further used to investigate the error of Langmuir and the effect on the error from the site energy heterogeneity. The results indicate that the Langmuir model can be applied in sediments when each one of the conditions below is satisfied, (1) m and n lie in the area which signifies that the relative error is less than 10%, (2) the site energy heterogeneity of sediment is under 5.668. These findings are vital for the proper choice of models fitting the adsorption process of sediments.

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