Effect of randomly methylated beta-cyclodextrin on physical properties of soils.

Abstract

The application of cyclodextrins in several soil remediation technologies has been increasingly studied, but little is known about their effects on soil physical properties. One of the popular soil remediation additives, randomly methylated beta-cyclodextrin (RAMEB), was found to significantly alter surface and pore properties of soil clay minerals. Therefore, in this paper we studied the effect of various RAMEB doses on physical properties of selected soils, representing a wide range of clay content (3-49%). The results showed that soil physical properties were greatly modified by RAMEB treatment. Analysis of water vapor adsorption isotherms revealed that RAMEB increased water adsorption and surface area in sandy soils and decreased them in clayey soils. An increase in adsorption energy of water in RAMEB-treated soils indicated that desorption of nonpolar pollutants can be enhanced. Water vapor desorption isotherms showed that the volumes and radii of micropores (nanometers range) increased above 1% RAMEB concentration. The micropores became more rough and complex after RAMEB treatment as deduced from an increase in fractal dimensions. The volume of soil mesopores measured by mercury intrusion porosimetry (micrometers range) gradually decreased in most soils with an increase in RAMEB concentration whereas the average mesopore radius increased, indicating that finer mesopores were blocked by RAMEB. Measurements of the granulometric composition of soils by sedimentation analysis showed that the amount of coarse-size soil fractions increased on the expense of finer fractions due to aggregation of smaller particles. Behavior of the studied soils after RAMEB treatment depended on their clay content and the dose of cyclodextrin. In clay-rich soils, strong interactions of cyclodextrins with the soil solid phase governed the resulting soil properties. In clay-poor soils, the cyclodextrin excess (not interacted with clays) played a dominant role. Modification of surface, pore, and aggregation properties of soils by RAMEB can have a significant effect in soil remediation technologies.