The grinding of kaolinite. II. A more detailed study

Abstract

Abstract The study reported in Part I has been extended in the present Part by grinding a kaolinite for a total of 1000 hours and withdrawing samples at intervals. The samples were examined by all the tests of Part I (except heat of immersion) as well as by a number of additional tests, among which the most important were thermogravimetric analysis and X ‐ray diffraction. The thermogravimetric results show that the lattice is progressively distorted as grinding progresses, but that its chemical composition is unchanged. The specific surface measured by nitrogen sorption increases by some fourfold up to a maximum at 600 hours or so, and then drops to approximately threefold the original value at 1000 hours. Comparison of results for nitrogen sorption and for particle‐size distribution—by sedimentation in water (Andreasen test)—shows that aggregates possessing a considerable internal area are progressively produced by the grinding. The distortion of the lattice and the increase in specific surface each causes a marked increase in the solubility of the ground solid in hydrochloric acid. Both the base‐exchange capacity and the content of adsorbed water (which is driven off at 100°) increase fairly continuously with the time of grinding. The results of this Part thus confirm and extend the conclusions of Part I.