Decomposition of Minerals by Grinding

Abstract

Soil clay minerals kaolinite and montmorillonite and the closely related mica mineral muscovite are among the most important soil minerals, as the clay minerals largely determine the fertility and physical characteristics of soils. These minerals while of similar composition and structure differ greatly in physical and chemical activities, and their stabilization or alteration is important in soil phenomena. Kaolinite, montmorillonite, and muscovite were dry ground in a ball mill to determine their decomposition products so that the formation of these minerals in the soil might be better understood. Several investigators, including Laws & Page(18l and Shaw (25), have ground certain clay minerals for shorter periods of time; and at the present time it is questioned whether or not some clay mineral can be decomposed by mechanical grinding. Samples ground for various periods of time were analyzed with reference to average particle size, solubility, pH, base-exchange capacity, thermal curves, and x-ray diffraction patterns. The conclusions drawn are from the data collected with these various methods of analysis. The terms kaolin and kaolinite are used interchangeably throughout this paper, as are bentonite and montmorillonite. The ideal chemical formulas for the minerals studied are: Kaolinite-A14 Si4 01,(OH)4 muscovite -KA12 (Al Si3 O10) (OH) 2, and montmorillonite A14Si3O0 (OH) 4 H20. A more correct formula for montmorillonite is 5 A1203.2 MgO.24 SiO .6 H20 (Na2O, CaO) as the isomorphous substitutions are included.