Isotherms for Malachite Green onto rubber wood (Hevea brasiliensis) sawdust: Comparison of linear and non-linear methods

Comparison of linear least-squares method and a trial and error non-linear method of estimating the isotherm parameters was examined to the experimental equilibrium data of Malachite Green, a basic dye onto rubber wood sawdust. The experimental data were fitted to Langmuir, Freundlich and Redlich–Peterson isotherms. The four different linearized forms of Langmuir isotherms are also discussed. Langmuir isotherm parameters obtained from the four Langmuir linear equations are different but they are the same by using non-linear Langmuir equation. The best-fitting isotherms are Langmuir and Redlich–Peterson. Present investigation showed that the non-linear method is more appropriate method to determine the isotherm parameters. Langmuir is a special case of Redlich–Peterson when the constant ‘g’ equals to unity.