BET-based mineral surface area quantification comparing nitrogen with water

Abstract

Water is a ubiquitous adsorbate relevant for many natural systems and engineering applications. Water adsorption behavior on clays, sediments, soils, and related geomaterials was studied for over a century and fueled a continuous discussion on the meaning of water sorption as a measure of mineral surface area (MSA). Despite this, MSA quantification using nitrogen established itself as the most widely accepted approach despite the relevance of water for a wide spectrum of in-situ environmental conditions. Many attempts at water-based MSA measurements are reported in dispersed literature. To date, interlaboratory comparison of MSA has been hampered by disparate methodologies for conducting measurements using both water and nitrogen adsorbates. Water and nitrogen-based MSA both using the BET equation for a variety of minerals and mineral matrices relevant for earth, environmental, and clay science was compiled in this contribution. The historical development of water-based MSA determination is also reviewed. The overlay of multitude of factors including mineralogy, interlayer spaces, organic matter, structural water, electrostatic interactions, microstructure, sample preparation and measurement conditions, influencing both nitrogen and water-based MSA quantities are discussed and general guidance is provided on the interpretation of complex MSA datasets.