Expandability and layer charge characteristics of diagenetic illite (IMt-1) and hydrothermal sericite (HS) were investigated after alkylammonium ion exchange with potassium, and subsequently, Na, Ca and Mg ion exchange. After the ion exchange, both mica clay minerals clearly exhibited expandability by intercalation of alkylammonium ion, and glycerol and water saturation in their interlayer. Differences in the expandability are mainly attributed to layer charge characteristics of expandable layers, which enabled an estimation of the distribution and amount of layer charge through Xray diffraction (i.e. expansion test). X-ray diffraction patterns after the expansion tests (after alkylammonium ion exchange, after glycerol treatment for Mg-saturated samples and under various relative humidity for Na-and Ca-saturated samples) revealed the following:
1) IMt-1 and HS consist of three and two phases with different expandability, respectively;
2) IMt-1 consists of three types of domains or layers with segregation interstratified structure. The domains or layers have layer charges about 0.5, 0.7 and 1 (esu/half unit cell).
3) HS consists of two types of particles with different layer charges about 0.7 and 1 (esu/half unit cell).
From the result of the expansion tests, the existence of smectitic layers with layer charge of about 0.5 (esu/half unit cell) was confirmed. Such low layer charges have never been recognized by ordinary X-ray diffraction method and chemical analysis of bulk samples. The difference between the components in IMt-1 and HS is presumably due to different degree of alteration.
Atomic Force Microscopy observations reveal the Ca-saturated samples exfoliate thinly about 2 to 3 layers, which behave as thin particles similar to smectites in water. These observations further suggest the formation of thinly exfoliated layers even in non-expandable mica clay minerals through alkylammonium ion exchange with potassium, and subsequently Ca ion exchange.
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