Limitations of EGME retention to estimate the surface area of soils

Abstract

The suitability of two procedures for the measurement of total surface area, based on 'the retention of ethylene glycol monoethyl ether (EGME), was investigated for a wide range of clay fractions and Australian soils. Experimental conditions for optimum precision and convenience of measurement were established. The procedures which utilized a higher vapour pressure of EGME achieved a higher retention of EGME by soils, reached the final condition of measurement more rapidly, and were less dependent on exchangeable cation status of the samples in confirmation of published work with pure smectite. The critical weakness of published procedures for soils is the assumption that the surface area occupied by an EGME molecule on a smectite reference sample can be applied to all soil surfaces. EGME retained per unit area by a range of soil and pure smectites, calculated from total surface area derived from crystal dimensions, and by a range of non-swelling minerals, related to measured BET-N2 areas, varied about fourfold between different mineral groups, and nearly twofold for different smectites. This variation could seriously over- or under-estimate estimates of total surface area, depending on the reference mineral chosen in relation to the mineral species being characterized. Alternatively, for soils free of clay minerals with internal surfaces, an empirical approach based on measured BET-N2 areas of representative soils may be feasible. A consideration of EGME retained in relation to BET-N2 areas may usefully complement X-ray diffraction procedures for characterizing randomly interstratified material in soil clay fractions.