The effect of certain chemical additives on the physical and chemical properties of montmorillonitic clays

Abstract

The use of surface active chemicals in agricultural applications has greatly increased and continued to become more diversified in recent years. The development and growth of the chemical branch of "agribusiness" has taken place with little apparent concern for the potential effects that certain of the chemical ingredients might have on the physical and chemical properties of the soils upon which they are deposited. One of the primary concerns of this study was to investigate those potential effects and to determine, if possible, the extent to which they might detrimental or possibly beneficial to certain physical and chemical soil properties. Further objectives were: (a) To investigate the effects of the surface active chemicals on the surface reactions of clays, with particular emphasis on the swelling and shrinking of montmorillonite; (b) to develop a better understanding of the absorption mechanisms involved; and (c) to gain further knowledge concerning their influence on soil structural properties. To accomplish those objectives, kaolinite and three montmorillonitic clays were selected for study, along with two soils known to be high in montmorillonite: Houston Black clay soil and Lufkin fine sandy loam subsoil. Three anionic, three cationic, and two nonionic surface active chemicals were selected to cover a wide range of molecular weights. The clays and soils were treated with each surfactant at three well-chosen treatment rates. Quantitative adsorption was determined, and the adsorption mechanisms were studied by x-ray diffraction and thermal methods. Their effect on swelling of montmorillonite was studied by two methods and their effect on certain physical and structural characteristics of the two soils was investigated. The anionic surfactants were adsorbed only in very small quantities and exerted their greatest influence lowering on swelling, and on physical and structural soil properties by their effective lowering of the surface tension of the liquid phase of the soil system. ...