The Solubility of Tugarinovite (MoO2) in H2O at Elevated Temperatures and Pressures

The solubility of tugarinovite (MoO2) in pure water was investigated at temperatures between 400 and 800 degrees C and at pressures ranging between 95 and 480 MPa by using in situ synchrotron X-ray fluorescence (SXRF) to separately analyze high temperature aqueous solutions in a hydrothermal diamond anvil cell (HDAC). The concentration of molybdenum in the fluid at 400 and 500 degrees C was below detection; however, at temperatures between 600 and 800 degrees C, the solubility of tugarinovite increased with increasing temperature by two orders of magnitude. The molybdenum concentration at 600 degrees C and 800 degrees C is 44 ppm and 658 ppm, respectively. The results complement the data of Kudrin (1985) and provide the first measurement of MoO2 solubility at pressure and temperature conditions comparable to intrusion-related Mo deposit formation. The data are also relevant to the study of water chemistry and corrosion product transport in supercritical-water-cooled reactors, where Mo-bearing steel alloys interact with aqueous solutions at temperatures greater than 600 degrees C. The application of in situ SXRF to solubility measurements of sparingly soluble minerals is recommended because it circumvents analytical uncertainties inherent in determinations obtained by quenching and weight loss measurements.