Received: October 31, 2017 Electrochemistry Accepted: December 22, 2017 Published online: January 31, 2018 The Electrochemical Society of Japan https://doi.org/10.5796/electrochemistry.17-00079 Article Electrochemistry, 86(2),61–65 (2018) Solubility of Sodium Tungstate in Molten Sodium Hydroxide Tetsuo OISHI* and Miki YAGUCHI Environmental Management Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan * Corresponding author:
[email protected] ABSTRACT The solubility of sodium tungstate (Na2WO4) in a molten sodium hydroxide (NaOH) bath and its dependence on the partial pressure of water vapor were measured. This was done as part of an ongoing study of a new tungsten (W)- recycling process using molten NaOH. First, the nature of the chemical compound in the equilibrium solid phase in a molten NaOH bath was confirmed by adding excess amount of tungsten oxide as a tungstate ion source into the bath. X-ray diffraction analysis indicated that anhydrous Na2WO4 is the solid phase in equilibrium with the liquid phase of molten NaOH saturated with Na2WO4. Then, the solubility of the anhydrous Na2WO4 was measured under various partial pressures of water vapor. The results revealed that the solubility of anhydrous Na2WO4 drastically increased with the partial pressure of water vapor and the bath temperature from a molar fraction of 0.06–0.17. This value was much higher than those previously reported for molten nitrate and nitrites. © The Electrochemical Society of Japan, All rights reserved. Keywords : Tungsten, Recycling, Molten Sodium Hydroxide, Solubility 1. Introduction of WC and binder metal of cobalt (Co) is anodically dissolved in a molten NaOH, and tungstate ions are accumulated in the melt.