Specific Surface Area

Abstract

Surface area plays an important role in many soil processes including contaminant adsorption, water retention, and chemical reactions. The specific surface area of soil and soil constituents can range from less than 0.1m2 g−1 (1 × 102 m2 kg−1) for coarse sands to more than 800m2 g−1 (8 × 105 m2 kg−1) for expandable clay minerals such as montmorillonite. The measurement of specific surface area can involve direct physical measurement of particle size and shape, adsorption of probe molecules from either the gas or aqueous phases, or the retention of polar liquids. In general, soils that contain trace amounts of organic matter and clay minerals tend to yield similar specific surface area values regardless of the method applied. In contrast, surface areas values obtained for soils that contain appreciable amounts of organic matter or expandable clay minerals can vary widely. This chapter provides concise descriptions of the different methods that are currently used to determine specific surface area, and a discussion of the advantages and limitation of each approach.