Some factors affecting the production and measurement of colors in montmorillonite and kaolinite clays and natural soils

Color is used in describing and classifying soils. How soils acquire color is not fully understood and the measurement of soil color is not precise. Almost every soil contains clay minerals, which affect soil properties. Montmorillonite and kaolinite are two common types of such minerals. The main objective of the study was to investigate the color change of montmorillonite and kaolinite clay minerals with the addition of Fe, organic matter, and Mn, using either NaOH or Ca(OH)₂ for pH adjustment. Further objectives were: (a) To measure the reflectances from the clays and natural soils with particular emphasis on particle size; (b) to convert the reflectance data into International Commission on Illumination (I.C.I.) and Munsell color specification; and (c) to rationalize the color changes in montmorillonite and kaolinite with the addition of Fe, organic matter, and Mn. To accomplish these objectives, montmorillonite and kaolinite clay materials were treated with different levels of Fe, organic matter, and Mn and combinations of organic matter and Mn, organic matter and Fe, and Fe and Mn. The pH of the suspensions were adjusted to different values using either NaOH or Ca(OH)₂. After adjusting the pH the suspensions were washed with water, filtered, air dried and passed through a 0.25 mm sieve. Five natural soils were passed through different sized sieves to study the effect of particle size on reflectance. ..