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Reactions of Surfactants with Montmorillonitic Soils¹

ABSTRACT

Two montmorillonitic soils were treated with each of eight surfactants at three treatment rates: 1%, 0.1%, and 0.01% by weight. The effects of the treatments on certain important physical properties of the soils were investigated by means of aggregate stability analysis, capillary rise measurements, and modulus of rupture.

The surfactants included three anionic, three cationic, and two nonionic compounds. The anionics were not strongly adsorbed by the soils. When the soils were dried in contact with them, they were weakly held and readily released to the liquid phase upon rewetting. Their effects on soil physical properties were directly related to the lowering of surface tension of the liquid phase, and the magnitude of the effect was strongly dependent on treatment rate.

The cationics were strongly adsorbed by the soil exchange complex and not readily released upon rewetting. Their effects on soil physical properties were directly related to the degree of hydrophobicity imparted, which increased with alkyl chain length and amount of material added to the soil.

The nonionics were adsorbed by hydrogen-bonding to clay and other oxygen-rich mineral surfaces. Their sorption energy was somewhat greater than that of water, and they displaced water from the surfaces. Their effects on soil physical properties were small and in proportion to the amount of chemical added. Those effects were related to reduced hydration of surfaces and the hydrophilic centers associated with the nonionic compounds.

¹ Contribution of Soil and Crop Sciences Dep., Texas Agr. Exp. Sta., Texas A&M University, College Station. The research was supported in part by the Procter and Gamble Co., Cincinnati, Ohio.

² Research Assistant in Soil Physics, Head, Soil and Crop Sciences Dep., and Professor of Soil Physics, respectively. Present address of senior author: Robert S. Kerr Water Research Center, Ada, Oklahoma.

Received for publication September 27, 1965. Accepted for publication December 13, 1965.