Specific surface area of fine-grained soils
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Date
2011
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Abstract
Clay has a very large specific surface area, which leads to much interaction of ionsand water molecules with the soil particles. However, specific surface area of soilsvariesgreatly because of differences in mineralogy, organic composition, and particle-sizedimension. For example, smectite has the largest SSA among the known clay minerals.Kaolinite has strong bonding forces between layers and they have no significant internalsurfaces.There are various methods to measure specific surface area including gas adsorptionin dry conditions and molecular adsorption in aqueous suspensions. SSA determinationmethods can be grouped into two main categories: gas adsorption and adsorption of polarliquids. Some of these techniques are: EGME, MB, p-Nitrophenol, polyvinylalcoholadsorption methods, etc. Although the physical definition of SSA is very straightforward,its accurate measurement is very difficult. This is because different SSA measuringtechniques yields different SSA values depending on the limitations of each method.Furthermore, some of the SSA measuring techniques are time consuming or requirespecial and expensive instrument.Currently, there is no standard SSA measuring technique for fine-grained soils.Researchers and engineers use the technique that is available in their institutes.Measurement of SSA of fine-grained soils resulted reports of inconsistent SSA values inthe literature. Hence, a simple and easily applicable method, which would yield reliableresults, is greatly needed. To investigate such a SSA measuring technique, one needs tocompare the commonly employed SSA measuring techniques. This is because some SSAmeasuring techniques measures only external SSA whereas other methods measure totalSSA (i.e., both external and internal SSA). For example, nitrogen is non-polar and doesnot penetrate into the interlayers of swelling clays. Thus, the SSA values obtained by thismethod only refer to external crystal surface. However, the retention of polar liquids suchas water, ethylene glycol monoethyl ether (EGME) and methylene blue (MB) is then usedto estimate the total (external + internal) area of expanding layer silicates. These methodsyield widely different estimates of SSA. Therefore, it is important to interpret the resultsaccording to the soil mineral constituents and the method used to determine the SSA. © 2011 Nova Science Publishers, Inc. All rights reserved.