Activity Coefficients, Phase Diagrams of the NaNO₃-Pb(NO₃)₂-H₂O System at 298.2 K, and Its Applications

Abstract

The heavy metal lead will cause serious effects on human living environment and personal health when it enters the ecosystem, and the wastewater produced during the production of lead−chromium pigments may cause lead pollution to the environment. The heavy metals in wastewater can be further treated by studying the thermodynamic properties and phase diagrams of the NaNO 3 and Pb(NO 3 ) 2 systems. The cell potential method and the Pitzer model were used to evaluate the activity coefficients of the NaNO 3 -Pb(NO 3 ) 2 -H 2 O system at 298.2 K. The Pitzer mixed ion parameters were fitted by the activity coefficient data and solubility data, and the theoretical prediction of the solubility of the NaNO 3 -Pb(NO 3 ) 2 -H 2 O system at 298.2 K was made based on the obtained parameters (θ Na,Pb = 0.0462, ψ Na,Pb,NO3 = −0.0056). Phase diagrams predict better results. From the phase diagram, an isothermal evaporation process can be designed to separate NaNO 3 . By conservation calculations, the percentage of NaNO 3 recovered was 71.07%, where NaNO 3 solution can be used to produce KNO 3 products, and the solution after isothermal evaporation has a high Pb(NO 3 ) 2 content, which can be reused in the production of lead−chromium pigments.