Keikichi Inoue

Solid State Reactions of Dickite and Pyrophyllite with Calcium Oxide

The solid state reactions of dickite and pyrophyllite with CaO at 900°C were investigated paying attention to the direction of diffusion, the preference of reactivity of the two minerals, and to the difference in the reactivity between edge and basal crystal surfaces.Pt-marker method was used for examining the direction of diffusion. The amount of CaO reacted was determined by glycerin-ethanol method.The conclusions obtained are as follows.1. CaO preferentially diffuses into the clay minerals.2. Pyrophyllite is more reactive with CaO than dickite.3. Edge surfaces of dickite is much more reactive than basal surfaces.4. Pyrophyllite shows no noticeable difference in the reactivity with CaO between the two crystal surfaces as of dickite.

Effect of Adsorbed Monovalent Cations on Cristobalite Formation from Kaolinite

The rate of cristobalite formation from a kaolinite saturated with some monovalent cations was studied comparing with the crystallization nature of some amorphous silica, i.e. precipitated-, thermally decomposed-silica gels, and powdered silica glass, to which 1-2 mol% of alkali carbonates had previously been added.The results obtained are summarized as follows.1) The adsorbed cations controlled the nucleation period of cristobalite formation and the Li ion was the most powerful accelerator for the nucleation.2) The nature of crystallization from the silica gels resembled closely to that of the cristobalite formation from the kaolinite except that quartz phase appeared from Li containing-silica gels.3) The crystallization from the kaolinite and the silica gels could be considered as homogeneous nucleation process by reason of the linear growth rate and of that the alkali ions would had been intimately distributed throughout the very fine amorphous silica particles.4) The aspect of crystallization from the coarsely powdered silica glass differed quitely from those of the kaolinite and the silica gels, i.e. Li ion retarded the crystallization and the process could be considered as heterogeneous nucleation.

Negative Surface Charges of Unground Kaolinites

The negative surface charges of some kaolinites from different origins were determined, paying attention to the distribution of the charges on basal and edge surfaces. The relations between the charge density and the particle morphology or crystallinity were considered.The negative charges on the basal and edge surfaces were assessed from the C. E. C. values at pH 4 and from the difference in the C. E. C. values at pH 10 and pH 4, respectively. The crystallinity was evaluated from the ratio of the two peak intensities (I(021)/(I(060)) of X-ray diffraction. The particle shape was observed electron microscopically.The results obtained are summarized as follows;1) The kaolinites of nine species studied could be classified into two groups by the magnitude of the negative charge density.2) Four kaolinites which showed high negative charge densities were poorly stacked to the direction of c-axis. The particles were rather thin shape owing presumably to high degree of isomorphous substitution. The negative charge densities on the basal surfaces, particularly in fine particles, were larger than those on edge surfaces.3) The remaining five kaolinites having low negative chargede nsities were well stacked and the particles were rather thick. The negative charge densities on the basal surfaces were almost same as those on edge-faces.

Density of Water on Kaolinite Surface

The density of water at kaolinite-water interface was estimated by measuring the volumetric change of a clay-organic system which occurred when clay-organic liquid interface was converted into clay-water interface. A definite amount of drops of water which had been previously introduced to the clay-water interface. A definite amount of drops of water which had been previously introduced to the clay-organic system was spread over the clay surface by stirring. The thickness of the layer of the abnormal water molecule on kaolinite was compared with that of pyrophyllite.It was confirmed that the density of water from one to several molecular layers on kaolinite surface was less than that of ordinary water, indicating a looser structure. The density of the abnormal water was the lowest at the completion of coverage on kaolinite and amounted to a few percent less than that of ordinary water. The abnormal water was detected on pyrophyllite, but the thickness of it was shown to be smaller than that of kaolinite.