Kaolinite is a clay mineral with diverse environmental, industrial, and agricultural applications. The influence of the crystallographic properties of kaolinite, e.g. structural disorder, on these applications is of great interest. Qualitative and quantitative analyses of kaolinite structural disordering over the last 70 years have revealed three main sources of layer-stacking disordering: (1) enantiomorphic stacking; (2) dickite-like stacking; and (3) random shift of layers. What influence do these stacking disorders have on the reactivity of kaolinite? The objective of the present study was to investigate the influence of stacking disorder on the intercalation and dissolution of kaolinite layers. To minimize the effect of particle size on reactivity, the 1–2 μm fractions of five geologic kaolinites were used. The 1–2 μm fractions varied in the degree of structural disorder. The kaolinites were: (1) intercalated with saturated CH3COOK solution at room temperature to examine the effect of stacking disorder on intercalation; and (2) dissolved in 4 M NaOH at 80°C to examine the effect of stacking disorder on kaolinite stability in alkaline solution. Samples with a low degree of stacking disorder intercalated twice as much and dissolved >1.5 times as much as the most disordered sample. The infrared spectrum of the undissolved kaolinite residue in 4 M NaOH showed relative intensities of OH-stretching bands characteristic of a kaolinite-dickite mixture. The binding strength (i.e. resistance to intercalation) of the undissolved residue by NaOH was high; the residue could not be intercalated by CH3COOK. Differences in the average interlayer binding strength were attributed to the greater proportions of dickite-like sequences in highly disordered kaolinite compared to ordered kaolinite specimens. These results suggested that the binding strength of kaolinite layers is proportional to the degree of stacking disorder. Dickite-like sequences, a type of stacking defect, contributed to the lower reactivity of highly disordered kaolinite.
