Isotherms for the adsorption of Cu(II) onto lignin: Comparison of linear and non-linear methods

Mirjana Brdar,Dusan Rakic,Aleksandar Takaci,Marina Sciban

doi:10.2298/hemind111114003b

Abstract

Equilibrium studies were carried out for the adsorption of Cu(II) onto Kraft lignin as an adsorbent. The experimental data were fitted to the Freundlich, Langmuir and Redlich-Peterson isotherms by linear and non-linear method. Comparison of linear and non-linear regression method was given in selecting the optimum isotherm for the experimental data. The coefficient of correlation r2 and Chi-square test ?2 was used to select the best linear theoretical isotherm. The best linear model is Redlich-Peterson isotherm model, where r2=0,985 and ?2=0,02. In order to predict the error ERRSQ, HYBRD, MPSD, ARE and EABS were used. Moreover, by minimizing these error functions the optimal values of parameters and also the optimum isotherm was found. The Redlich-Peterson isotherm was found to be the best representative for adsorption of Cu(II) on the adsorbent in the cases when ERRSQ, HYBRD, MPSD functions were used. There coefficients of determination are 0.986, 0.985, 0.984, respectively and Chi-square is 0.02 in all cases. Freundlich isotherms which were obtained by minimization of the ERRSQ, HYBRD, MPSD, ARE and EABS function showed very good agreement with experimental data. In all cases the coefficients of determination are greater than 0.91. Besides, it was observed that non-linear isotherm models were better for representation of equilibrium data than linearized models.

Highlights

Equilibrium studies were carried out for the adsorption of Cu(II) onto Kraft lignin as an adsorbent
All types of linearized Langmuir equation give a lower coefficient of determination and higher values of the chi-squared test compared to Freundlich and Redlich–Peterson isotherms and that suggests that the Langmuir equation is not appropriate to use
High value of r2 and the very small values of χ2 for both Freundlich and Redlich–Peterson isotherms suggest that both models can be used to explain copper adsorption behavior

Summary

Introduction

Equilibrium studies were carried out for the adsorption of Cu(II) onto Kraft lignin as an adsorbent. In order to predict the error ERRSQ, HYBRD, MPSD, ARE and EABS were used By minimizing these error functions the optimal values of parameters and the optimum isotherm was found. The Redlich–Peterson isotherm was found to be the best representative for adsorption of Cu(II) on the adsorbent in the cases when ERRSQ, HYBRD and MPSD functions were used. Their coefficients of determination were 0.986, 0.985 and 0.984, respectively and chi-square was 0.02 in all cases. Freundlich isotherms obtained by minimization of the ERRSQ, HYBRD, MPSD, ARE and EABS function showed very good agreement with experimental data. Linear and non-linear equations of Freundlich, Langmuir and Red-

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