U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Determination of Surface Area of Soil Components by Sorption of Nitrogen and Ethylene Glycol Monoethyl Ether Vapors and Evaluation of Adsorption, Partition and Cation Solvation Processes

Abstract

The vapor uptake isotherms of nitrogen and ethylene glycol monoethyl ether (EGME) were determined for soil and soil components. The cross sectional area of EGME was determined to be 40.0 x 10^-20 m² by comparing adsorption isotherms on reference surface area standards. For samples where EGME does not penetrate into the solid (Ottawa Sand, hematite, aluminum oxide, synthetic hydrous iron oxide, and kaolinite), the EGME and nitrogen isotherms show consistent surface uptake and the EGME isotherm can be reasonably estimated from the nitrogen isotherm by multiplying the nitrogen uptake by a factor of 1.3 to account for different molecular area and molecular weight. For other samples where the EGME can penetrate into the solid (peat, Ca-montmorillonite, and illite), the total uptake can be resolved to surface adsorption, partition into soil organic matter, and/or cation solvation. For peat, the nitrogen uptake is very small, resulting in a surface area of 1.3 square meters per gram; uptake of EGME on peat is large and linear, which is indicative of large bulk solubility of EGME in soil organic matter (190 milligrams per gram). For Ca-montmorillonite, the resulting cation solvation isotherm shows a stoichiometric interaction of about 4 EGME molecules per exchangeable Ca ion. Exchange of organic cations for metal ions in montmorillonite sharply decreases the cation solvation effect of EGME. This cation exchange may result in a higher surface area of the clay due to opening of interlayer surfaces.