Synthesis of a 10-A hydrated kaolinite

Abstract--Hydrated kaolinite (d(001) = 10/~) can be synthesized by mild healing of a kaolinite-organic suspension, allowing time for the clay to be intercalated by the organic solvent, and then dissolving a fluoride salt in the liquid. After mild heating of the suspension, the salt and organic solvent are removed by repeated water washings. The kaolinite retains interlayer water in the form of a l 0- & kaolinite hydrate. The influence of the intercalating agent, type of salt, concentration f salt, and the time of treatment on the synthesis of 10- & hydrate was examined for several kaolinites. The most effective salt is NH4F; much smaller yields were obtained using KF and RbF. Not all organic molecules gave high yields of the hydrate; dimethyl sulfoxide, formamide, and hydrazine worked well but N-methyl formamide did not. The reaction between clay and salt resulted in the replacement ofsome hydroxyls by fluoride. This replacement was rapid; after 1 min of fluoride treatment a substantial yield of hydrate was obtained. The intercalation step separated the layers and also disordered the kaolinite, facilitating the F for OH replacement a or near crystallite dges. This replacement weakens the interlayer bonding at the edges and thereby reduces the possibility of layer collapse and attendant dehydration