Measurement of the Solubilities of Scheelite and Ferberite in Hydrothermal Solutions With In-Situ pH Measurement
Tungsten is a metal of strategic importance. Reliable thermodynamic data with which to calculate the solubilities of the most important tungsten ores, scheelite (CaWO4) and ferberite (FeWO4), and the mass transfer of tungsten, in hydrothermal solutions are generally not available. Yet, such data are required to develop comprehensive genetic models of hydrothermal tungsten deposits; these models can guide exploration for new tungsten resources. A study is therefore proposed in which the solubilities of scheelite and ferberite will be measured in non-complexing solutions at saturated water vapor pressure as a function of temperature from 50 degrees to 290 degrees C, pH and ionic strength. The pH will be monitored directly in-situ using a hydrogen electrode concentration cell (HECC) of the type developed and used successfully at Oak Ridge National Laboratory. From the solubilities measured as a function of pH and ionic strength, the solubility products for scheelite and ferberite, and the dissociation constants for tungstic acid (H2WO40), all of which are essential thermodynamic data for the calculation of W mass transfer, can be derived. The project will involve one Ph.D. student who will be trained in hydrothermal geochemistry and high-pressure/high-temperature experimental methods. This project will not only result in the acquisition of high-quality thermodynamic data with which to calculate tungsten mineral solubilities and W mass transfer in hydrothermal solutions, but will also provide the PI with an HECC for future studies of other systems of geochemical interest.