Synthesis and Paragenesis of Na-Beidellite as a Function of Temperature, Water Pressure, and Sodium Activity

Abstract

Abstract--In the chemical system NayO-AIyO3-SiO2-HyO, the stability field of Na-beidellite is presented as a function of pressure, temperature, and Na-and Si-activity. NaoT-beidellite was hydrothermally synthesized using a stoichiometric gel composition in the temperature range from 275* to 475~ and at pressures from 0.2 to 5 kbar. Below 275~ kaolinite was the only crystalline phase, and above about 500~ paragonite and quartz developed instead of beidellite. An optimum yield of 95% of the Nao.7-beidellite was obtained at 400~ and 1 kbar after 20 days. Gels with a Na-content equivalent to a layer charge lower than 0.3 per O20(OH)4 did not produce beidellite. They yielded kaolinite below 325~ and pyrophyllite above 325~ With gels ofa Na-content equivalent to a layer charge of 1.5, the Na-beidellite field shifted to a minimum between temperatures of 275 ~ and 200~ This procedure offers the potential to synthesize beidellite at low temperatures. Beidellite synthesized from NaL0-gel approach a Na~.35 composition and those from Nat. 5-and Nazo-gels a Naj.s composition.

Synthesis of Smectite Clay Minerals: A Critical Review

“…At temperatures below 175~ mainly amorphous material, kaolinite, or zeolites (at lowest gel/solution ratio) were formed (Figure 3). These results represent the lowest pressure and temperature conditions under which beidellite formation has been reported and differ from those of other authors, such as Kloprogge et al (1993b), who found a minimum temperature of 200~ to yield beidellite + amorphous material.…”

“…Kloprogge et al (1993b) also observed this mixed-layer phase in their products synthesized at 2 kbar and higher. Additional experiments (Nakazawa et al, 1992) showed that at 450~ cristobalite also formed, and at 475~ both cristobalite and quartz were present, in agreement with the data of Kloprogge et aL (1993b).…”

“…Kloprogge et al (1993b) also observed this mixed-layer phase in their products synthesized at 2 kbar and higher. Additional experiments (Nakazawa et al, 1992) showed that at 450~ cristobalite also formed, and at 475~ both cristobalite and quartz were present, in agreement with the data of Kloprogge et aL (1993b). Kloprogge et al (1993b) demonstrated that, starting from stoichiometric gels in the system Na~O-A1203-SiO2-H20, the amount of Na determines whether, with increasing Na content, kaolinite + quartz (below 325~ or pyrophyllite (above 325~ beidellite, or paragonite + a S i O 2 phase is formed.…”

“…We note that the metastable persistence of phases is always an important problem when examining clay-mineral synthesis results. A well-known example is the appearance of cristobalite as a secondary phase in clay synthesis or even cristobalite and quartz, where quartz is expected to be the stable phase (Kloprogge et al, 1993b;Nakazawa et al, 1991).…”

“…Pressure-temperature data for synthesis of Na-beidellite. Most of the data are from Kloprogge et al (1990aKloprogge et al ( , 1990bKloprogge et al ( , 1993b) for a starting gel composition of 62.7% SIO2, 34.2% A1203, and 3.1% Na20 (p = .7), with additional data from Ewell and Insley (1935), Granquist et al (1972), De Kimpe (1976, Eberl (1978), Plee et al (1987), Schutz et al (1987), and Yamada et al (1991a, 1991b. Formation of kaolinite occurs at 300~ only when slow heating rates (i.e., <30~ min 1) are used (unpublished data of Kloprogge).…”