The effect of interlayer cations on the expansion of vermiculite

Three kinds of salt solutions including NaCl, CaCl2 and MgCl2, were used to modify the expansion of vermiculite. X-ray diffraction results indicate that vermiculites have been successfully modified by salt solutions. The d(002) reflection spacings of Na-vermiculite, Ca-vermiculite and Mg-vermiculite corresponding to different salt solution modifications are 1.223 nm, 1.474 nm and1.448 nm, respectively. Expansion ratio experiment results show that the as-obtained vermiculite modified by NaCl solution can lower the beginning expansion temperature, while the vermiculites modified by CaCl2 and MgCl2 solutions can show high expansion ratio. The combined thermogravimetric-differential thermal analysis and infrared spectroscopy analysis reveal that electrostatic attraction force between interlayer cations and interlayer water plays the key factor in the expansion ratio of vermiculite. Compared with Ca and Mg cations, the electrostatic attraction force between Na cation and interlayer water is weak and Na-vermiculite has less interlayer water than that of Ca-vermiculite and Mg-vermiculite.

The figure illustrates the relationship between K% and expansion temperature of Na-vermiculite (A), Ca-vermiculite (B), and Mg-vermiculite (C). Where K% represents the increased percentage of expansion ratio; Km-v represents the expansion ratio of modified vermiculite; Kv represents the expansion ratio of the original vermiculite without modification.Figure optionsDownload as PowerPoint slideHighlights
► Salt solution modification method is originally used for expansion of vermiculite. Na-vermiculite has low beginning expansion temperature at 500 °C.
► Ca-vermiculite and Mg-vermiculite have high expansion ratio at high temperature.