CARBON DIOXIDE INCORPORATION INTO SODALITE–LAZURITE GROUP MINERALS

The first experimental data on the relationship between the carbon dioxide content in lazurite-type minerals (LTM) and its partial pressure in the gas phase and temperature in the range corresponding to the lazurite formation process at deposits in the Southern Baikal region have been obtained. The content of structural CO2 species was determined by IR-Fourier spectroscopy. It depends more on temperature than on the partial pressure of CO2 and is maximum for cubic lazurites at 500 °C (0.05–0.07 formula units, f.u.), decreasing to 0.01–0.03 f.u. both when the temperature decreases (460 °C) and when it increases (560 °C). A positive dependence of CO2 content on O2 fugacity in the system has been noted. LTM with an orthorhombic structure (vladimirivanovite) retains CO2 less effectively, with its content decreasing from the initial (natural) 0.08 to 0.01–0.02 f.u. in the specified temperature range of 460–560 °C. The experiments with exposure at 560 °C and subsequent cooling to 460 or 360 °C show the lack of retrograde CO2 solubility in LTM under saturation from gas phase. According to data on CO2 content, cubic lazurites with incommensurate 3D modulation of the structure could have formed at a temperature of about 500 °C, a partial CO2 pressure of ~1.4–2.2 bar, and fO2 at the level of the magnetite-hematite buffer. The high CO2 contents (0.15–0.3 f.u.) recorded in some LTMs may not be related to the direct absorption of CO2 from the gas (fluid) phase but are the product of relatively low-temperature (<400 °C) transformations of carbon forms, leading to the association of CO2 and molecular forms of sulphur. This temperature range and the fugacity of volatile compounds corresponding to such forms of sulphur should be considered as possible conditions for the synthesis or modification of materials based on sodalite, nosean and LTMs, which are promising as carbon dioxide absorbers or indicators.