Natural Organic Matter Sorption by Kaolinite: Modified Langmuir Isotherm

Abstract

This technical note describes the use of the modified Langmuir isotherm (MLI) model recently introduced by Gu and coworkers to describe the adsorption and desorption of natural organic matter (NOM) onto Kaolinite. The MLI was able to describe the adsorption of two different NOM samples with the use of three adjustable parameters. A commercial humic acid adsorbed to a much larger extent than a NOM sample collected from a swamp. The hysteresis coefficient was used to describe adsorption-desorption reversibility. Both samples had similar hysteresis coefficients. Such affinity parameters, however, determined from adsorption and desorption experiments, varied significantly. This study concludes that the new MLI model is better than the traditionally used Langmuir isotherm in describing adsorption-desorption of NOM to Kaolinite and desorption parameters may be considered to describe dissolved organic carbon concentrations in subsurface environments.