遊離アルミニウムイオンを含むインドネシアカオリンの表面性状

抄録

Indonesian kaolin have been studied in order to elucidate the influences of hydroxy aluminum ions formed under the weathering circumstance of the tropical hydrometeor on the surface properties of the clay. The effects on both the addition of the dispersant and the de-alumination treatment on the improvement of the surface properties have been discussed.
Indonesian kaolin mainly composed of kaolinite with fine particle size shows a great acidity and a strong aggregation in water by a large amount of hydroxy aluminum ions yielded on the particle surface. Also the positive charge of Al-OH₂⁺ formed on the particle surface by protonation makes the clay to adsorb anions and also acts as the solid acid point.
The anions of sodium pyrophosphate added as the dispersant are adsorbed on the positive sites of the clay, resulting in dispersing the particles. The dispersion of the clay particles has been improved significantly by the de-alumination treatments with hydrochloric acid or sodium citrate, since the hydroxy aluminum ions are removed from the surface and the charge of the clay particles changes from positive to negative.
However, the hydroxy aluminum ions remained in the clay, which is elutriated from the raw are using sodium pyrophosphate, cause the aging phenomena in aqueous system. In case of the de-alumination with hydrochloric acid it is difficult to remove completely the dissolved aluminum ions from the clay suspension, since the aluminum ions change to hydroxy aluminum ions by hydrolysis with increasing the pH of the suspension by washing.
As a result of improvement of the solid acid property, the clay after the de-alumination treatment shows a excellent function of the hard clay as a reinforcement filler in rubber compared with the elutriated clay.