Searching for optimum adsorption curve for metal sorption on soils: comparison of various isotherm models fitted by different error functions

Péter Sipos

doi:10.1007/s42452-021-04383-0

Abstract

Studies comparing numerous sorption curve models and different error functions are lacking completely for soil-metal adsorption systems. We aimed to fill this gap by studying several isotherm models and error functions on soil-metal systems with different sorption curve types. The combination of fifteen sorption curve models and seven error functions were studied for Cd, Cu, Pb, and Zn in competitive systems in four soils with different geochemical properties. Statistical calculations were carried out to compare the results of the minimizing procedures and the fit of the sorption curve models. Although different sorption models and error functions may provide some variation in fitting the models to the experimental data, these differences are mostly not significant statistically. Several sorption models showed very good performances (Brouers-Sotolongo, Sips, Hill, Langmuir-Freundlich) for varying sorption curve types in the studied soil-metal systems, and further models can be suggested for certain sorption curve types. The ERRSQ error function exhibited the lowest error distribution between the experimental data and predicted sorption curves for almost each studied cases. Consequently, their combined use could be suggested for the study of metal sorption in the studied soils. Besides testing more than one sorption isotherm model and error function combination, evaluating the shape of the sorption curve and excluding non-adsorption processes could be advised for reliable data evaluation in soil-metal sorption system.

Highlights

Metal sorption by soils is of particular interest and having importance from both agricultural and environmental viewpoints
As the metal sorption capacity is the most important parameter for soils, we studied whether models beyond the widely used Langmuir model support more reliable sorption capacity values
Cd and Pb are known for their toxic effects on soil biota, whereas Cu and Zn often show a deficiency in soils requiring artificial fertilization [2]

Summary

Introduction

Metal sorption by soils is of particular interest and having importance from both agricultural and environmental viewpoints. For the exact characterization of the sorption process, it is crucial to provide the most appropriate information on the adsorption equilibrium. This information is fundamental for the reliable prediction of adsorption parameters and comparing the adsorbents’ behavior in varying sorption systems quantitatively [16]. Adsorption isotherms are generally used to describe how adsorbates interact with the adsorbent Their use is crucial for several reasons, like the study of adsorption mechanism pathways, surface properties, and adsorbents’ capacities [12]. The experimental adsorption data are inserted into an equilibrium model to achieve the best fit for the sorption system. The better the model’s fit to the experimental data, the more accurate the calculation can be [10]

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Conclusion