General purpose adsorption isotherms

The fitting of adsorption isotherm equations to experimental data is often an important aspect of data analysis. If the Langmuir and Freundlich isotherms are used, then consideration must be given to the proper weighting of the observations. Preferably nonlinear regression (nonlinear least squares) should be used since this enables these isotherms to be fitted directly and also enables other isotherms to be tested with little extra effort. Isotherms described her which are likely to show a wide range of applicability include the Toth, modified Dubinin-Radushkevich, and multisite Langmuir isotherms. These can also describe competitive adsorption (binary exchange) reactions and are well suited for heterogeneous exchangers such as soils and sediments. Specific examples discussed are the adsorption of P and K by soils, Na-Cu exchange by montmorillonite, and Zn adsorption by ferrihydrite.