Solubility and Solvation of Carbon Dioxide in the Molten Li2CO3/Na2CO3/K2CO3 (43.5:31.5:25.0 mol-%) Eutectic Mixture at 973 K I. Experimental Part

The solubility of CO2 in the molten ternary eutectic mixture Li2CO3–Na2CO3–K2CO3 (43.5, 31.5, 25.0 mol.%) at 973 K has been determined by a titration technique. From the obtained titration curve, the solubility has been found to amount to 9.5·10−2 mol·L−1 (σ= 1.0) under a pressure of CO2 of 1 atm and the pKd value of the carbonate melt has been evaluated to 5.37 (σ5 = 0.24) if the concentrations of the solutes are expressed in mol·L−1. This pKd value is in good agreement with literature data but the solubility value reported in this work is much higher than most of those reported in the literature. A chemical dissolution of CO2 as C2O52– is proposed and the consequences of the occurrence of this species on the acidobasic properties of molten carbonates are discussed. It appears from the experimental results that the CO2/C2O52– equilibrium in the carbonate melt is a slow process.