In-Situ Determination of Specific Surface Area of Clays

There are many methods to determine the specific surface area (SSA) of clay minerals. Some of these methods lack accuracy and some are time consuming. There are no methods available for the determination of in situ SSA. In this paper a new approach to predict the SSA of clays is proposed, which has been verified in the laboratory. This method is based on the electrical properties of soils. In this paper the experimental set up and the estimation of specific surface area is presented on the basis of variation of the dielectric constant and the conductivity of the clay–water system when subjected to alternating current in the frequency range of 1–100 MHz. The dielectric constant and conductivity respond differently for different soils with varying surface area corresponding to their mineralogy. When dielectric constants and conductivity were measured for sandy soils, there were no effects with the change of input frequency. The electrical method can identify clays and separate them from fine grained silts. Data are presented which shows a linear correlation between the magnitude of dielectric dispersion and SSA for various clay mixtures. The clay structure determines the value of in situ dielectric dispersion of the clay (Δε _o ) and hence the SSA, making this a good in situ method to estimate SSA of clays.