Effects of Solution Chemistry on the Hydrothermal Synthesis of Kaolinite

Ritsuro Miyawaki1, Shinji Tomura1, Soichiro Samejima3, *, Masaharu Okazaki2, Hiroyuki Mizuta1, Shin-ichi Maruyama3 and Yasuo Shibasaki1
1 Ceramic Technology Department, Government Industrial Research Institute, Nagoya, Kita, Nagoya 462, Japan
2 Radiation Research Department, Government Industrial Research Institute, Nagoya, Kita, Nagoya 462, Japan
3 Engineering Research Association for Artificial Clay, Government Industrial Research Institute, Nagoya, Kita, Nagoya 462, Japan
*Present address: Chemical Research Laboratory, TOSOH Corporation, Shin Nan-yo, Yamaguchi 746, Japan.

Abstract: The hydrothermal synthesis of kaolinite was examined in the Al2O3-SiO2-H2O system to study inhibitory effects of additional ions on the formation of kaolinite. Syntheses were carried out with amorphous starting materials and salt solutions of various concentrations in Teflon pressure vessels at 220°C for 5 days. The reaction products were characterized by XRD, IR, DTA-TG, NMR and TEM. In all of the runs using solutions with cation concentrations less than 0.001 M, no significant effect on the formation of kaolinite was observed. The inhibitory effect of the univalent cations Li+, Na+ or K+ was less than that of divalent cations such as Mg2+ or Ca2+. The addition of trivalent Fe3+ or excess Al3+ ions interfered with the formation of kaolinite significantly. Sulfate and acetate solutions interfered with the formation of kaolinite more than chlorides and nitrates. No crystalline product was obtained using a 1.0 M basic solution of carbonate or hydroxide. The addition of the lithium ion to the system affected the crystallization of kaolinite only slightly. The use of 0.1 M LiCl and LiNO3 solutions for the syntheses improved crystallization of kaolinite along the [001] direction.

Key Words: Effect of ions • Hydrothermal synthesis • Kaolinite • Solution chemistry

Clays and Clay Minerals; October 1991 v. 39; no. 5; p. 498-508; DOI: 10.1346/CCMN.1991.0390505
© 1991, The Clay Minerals Society
Clay Minerals Society (www.clays.org)