This paper reviews the studies on the adsorption of organic pollutants by clay minerals for a better understanding of the role of clays and the problem of environmental pollution.
Adsoprtion of organic pollutants takes place through various bonding mechanisms to the surface of clay minerals. Among these the most general mechanisms are: cationic exchange, ion-dipole and hydrogen bonding. Ionization of organic bases and acids is greatly affected by solution pH. Cationic species of organic compounds are much more important for the adsorption than the anionic species because of the negatively charged clay surface. Recent studies show that organic molecules can be protonated in the interlayer region of clays even in suspension. Non-ionizing molecules are mostly adsorbed by ion-dipole or hydrogen on the clay surface.
The charge density distribution on the clay surface is an important factor for adsorption when cationic divalent or multivalent organic species are adsorbed. Adsorption of diquat and paraquat clearly shows the difference between montmorillonite and vermiculite. The regularity of the hexagonal network of water molecules on the clay surfaces also affect the adsorption of organic compounds.
The desorption of organic pollutants can be explained on the basis of adsorption studies and is demonstrated by the studies of toxicity of pollutants to plantgrowth and microbial degradation.
Kaolin minerals also become important when organic pollutants are small molecules with high polarity. Kaolinite-formamide complex formed in the interlayer position reveals hydrogen bonding between the clay surface and formamide. Studies of naturally occurring clay samples with organic pollutants have been reported only slightly. More studies in this subject are necessary to understand the real nature of clayorganic pollutants and their interactions.

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Clay mineralogical studies were made of a yellow orange colored soil in the Ishigaki shima Is., Okinawa pref., where the humid sub-tropical climate prevails. The soil is located on the slope (altitude 200 m) of the Mt. Omotodake (525.8 m), and has been derived from biotite granite. The soil is “moist” enough, this being particularly true of the B2 horizon which is derectly underlaid by an impervious bedrock. However the soil has not the characteristics of hydromorphic soils (Pseudogley, Fragiaquult, etc.). The clay minerals were identified by the X-ray, thermal analysis and electron microscope observation after the treatments by Norrish and Taylor's method, Mehra Jackson's method and after heating treatments (180 and 350°).
It was found from the studies that the clays contain an appreciable amount of lepidocrocite (α-FeOOH) together with goethite (γ-FeOOH). Crystalline iron hydroxides (lepidocrocite plus goethite) amount to about 8 percent in the clay fractionsof the A1, B1 and B2 horizons. It is interesting to note that soil lepidocrocites occur in terrestrial soil without any features as associated with wetness because it has so far been reported to form in a hydromorphic soil environments. The mechanism of lepidocrocite formation in soil is get to be investigated hereafter.

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A systematic and automatic X-ray line profile analysis has been planned by the aid of an electronic computer. The system is divided into three parts, (a) data reduction, (b) analysis and estimation, (c) simulation, in which multiple processings are planned in order to confirm the validity of the result. In this first paper, Stokes method for the data reduction, Warren and Averbach method for the estimation of mean particle size and distortion, and Bienenstock method for the particle size distribution are included and systematized. Computer simulation of the profile will be reported in the next paper.

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