Pitzer Model Anion–Anion and Ternary Interaction Parameters for the Na2C2O4–NaOH–H2O and Na2C2O4–NaNO3–H2O Systems

Abstract

Alkaline high-level nuclear wastes in the United States contain large inventories of sodium oxalate (Na2C2O4) immersed in Na+-, $$ {\text{NO}}_{3}^{ - } $$ - and OH−-bearing electrolyte solutions. Dissolution and precipitation of Na2C2O4 will likely influence the treatment of this waste. The Pitzer model has been widely used to model electrolyte solubility during high-level nuclear waste processing. The present study determines the anion–anion (θ) and ternary cation–anion–anion (ψ) Pitzer interaction parameters for oxalate Na2C2O4–NaNO3–H2O and Na2C2O4–NaOH–H2O systems by fitting the Pitzer model with Na2C2O4 solubility data in aqueous NaNO3 and NaOH solutions. The $$ {\text{C}}_{2} {\text{O}}_{4}^{2 - } $$ – $$ {\text{NO}}_{3}^{ - } $$ and $$ {\text{C}}_{2} {\text{O}}_{4}^{2 - } $$ –OH− θ parameters were found to be 0.02369 and −0.005304, respectively. The Na– $$ {\text{C}}_{2} {\text{O}}_{4}^{2 - } $$ – $$ {\text{NO}}_{3}^{ - } $$ and Na– $$ {\text{C}}_{2} {\text{O}}_{4}^{2 - } $$ –OH− ψ parameters were found to be 0.04069 and 0.017044, respectively. The solubility data could be modeled with temperature independent θ and ψ values over the experimental range investigated, which was 20–75 °C for the Na2C2O4–NaNO3–H2O system and 0–50 °C for the Na2C2O4–NaOH–H2O system.