Determination of the eutectic solubility lines of the ternary system NaHCO 3–Na 2CO 3–H 2O

Abstract

A crystallizer was built and a procedure developed to accurately measure the eutectic solubility lines where ice and salt coexist in equilibrium with the solution, for potential application of Eutectic Freeze Crystallization. The eutectic solubility lines of the ternary system NaHCO 3–Na 2CO 3–H 2O were determined experimentally and calculated with the extended UNIQUAC model. The extended UNIQUAC model describes the experimental data quite well. Anhydrous NaHCO 3 and Na 2CO 3·10H 2O were the only two types of crystals present in equilibrium with ice crystals in the ternary system. At the quadruple point NaHCO 3 and Na 2CO 3·10H 2O are in equilibrium with a solution of about 4.34 wt% of Na 2CO 3 and 4.77 wt% of NaHCO 3 at −3.32 °C. The anhydrous NaHCO 3 crystals were needle shaped with lengths between 5 and 10 μm, that were agglomerated into particles of about 100–300 μm, while the Na 2CO 3·10H 2O crystals were hexagonally shaped with sizes between 100 and 500 μm.