Salt Solubilities in Aqueous Solutions of NaNO3, NaNO2, NaCl, andNaOH: A Hofmeister-like Series for Understanding Alkaline NuclearWaste

摘要

Nonelectrolyte solubility in electrolyte solutions follow the Hofmeister series, but the applicability of theseries to salt solubility has been less appreciated. This study,using solubility data for thirteen sodium-bearing salts, showsthat salts are consistently salted out by electrolytes importantto alkaline nuclear waste in the order NaOH > NaCl >NaNO2 > NaNO3 at 298.15 K, which is the same order as theHofmeister series. Graphical presentation allowed for easyseparation of the common ion effect (caused by the additionof Na+) from the salting-out effect (caused by the presence ofanions) because there is a large difference between thesolubility of a given salt in different background electrolytes ata common Na+ molality. The trend persists even in very highelectrolyte concentrations where essentially all of the water molecules must be in the coordination sphere of an ion, whichmeans that the effect of electrolytes on “bulk water” is not the cause of the trend. These specific interactions more likely resultfrom the sharing of water molecules between ions, augmented by differences in ion-pairing of the electrolytes. The Hofmeisterseries has practical application to the management of alkaline high-level radioactive waste created at nuclear fuel reprocessingfacilities, where a predictive understanding of salt solubility is essential for blending wastes of disparate compositions prior totreatment.