Effects of Organic Matter Content on Pore Structure and Water and Organic Vapors Adsorption of Soils

Abstract

Vapor adsorption of water, benzene, hexane, and cyclohexane on three natural solids (a bentonite and two soils) that covered a wide range of soil organic matter (SOM) content were measured to examine the effects of SOM on the adsorption of water and volatile organic compounds (VOCs). The surface area and pore structure of the examined solids were first characterized based on the classical and fractal analyses of the nitrogen adsorption isotherms. The adsorption isotherms of water and VOCs vapor at room temperature were then determined. It was found that the average pore diameter and pore connectivity (surface area, total pore volume, and surface roughness) of solid is proportional (inversely proportional) to the fraction of organic matter in the solids. On the other hand, the high adsorption capacity of polar liquids (water) on bentonite and peat is consistent with the polar nature of the soil mineral and organic matter. Moreover, for benzene (hexane and cyclohexane) adsorption, peat (bentonite) possessed the highest adsorption capacity among the examined solids. The effects of both surface area and pore structure on the organic vapor adsorption characteristics of natural solids are discussed.