Derivation and application of a generalised exchange-adsorption isotherm for the adsorption of hydrophobic compounds on soils

Abstract

A general adsorption model able to provide a good description of the multilayer adsorption of ions and molecular compounds under any circumstances is proposed in this paper. In order to reach this goal, a general form of isotherm was deduced based on the Gapon equation and classical isotherm forms. The adsorption of molecular compounds with diverse hydrophobicity and acid-base characteristics were investigated and validated with a new model for the adsorption of four pesticides on different soils. The adsorption capacity and adsorption energy estimated by the new model were found to be related to the organic matter content of the soil. Great differences were found in the isotherm parameters (Ai, Ki, and ni) among both the soils and compounds investigated here.

Keywords

• isotherm parameters
• multilayer adsorption
• organic matter
• pesticide