Pitzer Model Anion–Anion and Ternary Interaction Parameters for the Na 2 C 2 O 4 –NaOH–H 2 O and Na 2 C 2 O 4 –NaNO 3 –H 2 O Systems

lkaline high-level nuclear wastes in the United States contain large inventories of sodium oxalate (Na 2 C 2 O 4 ) immersed in Na + -, NO_3^ - - and OH − -bearing electrolyte solutions. Dissolution and precipitation of Na 2 C 2 O 4 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 Na 2 C 2 O 4 –NaNO 3 –H 2 O and Na 2 C 2 O 4 –NaOH–H 2 O systems by fitting the Pitzer model with Na 2 C 2 O 4 solubility data in aqueous NaNO 3 and NaOH solutions. The C_2O_4^2 - – NO_3^ - and C_2O_4^2 - –OH − θ parameters were found to be 0.02369 and −0.005304, respectively. The Na– C_2O_4^2 - – NO_3^ - and Na– C_2O_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 Na 2 C 2 O 4 –NaNO 3 –H 2 O system and 0–50 °C for the Na 2 C 2 O 4 –NaOH–H 2 O system.