PNNL

Abstract

In aqueous solution, both nitrate and nitrite are polar, planer, monovalent, and have the same elements but different sizes and charge densities. Comparing the viscosity of NaNO2 and NaNO3 aqueous solutions provides an opportunity to determine the relative importance of anion size versus strength of anion interaction with water. The viscosity of aqueous NaNO2 and NaNO3 were measured over a temperature and concentration range relevant to nuclear waste processing. The viscosity of NaNO2 solutions was consistently larger than NaNO3 under all conditions, even though nitrate is larger than nitrite. This was interpreted in terms of recent quantum mechanical charge field molecular dynamics calculations reported in the literature that indicate that nitrite forms more and stronger hydrogen bonds with water per oxygen atom than nitrate. These hydrogen bonds inhibit rotational motion required for fluid flow, thus increasing the nitrite solution viscosity relative to that of an equivalent nitrate solution.