Abstract
Solubilities in the system sodium carbonate + sodium bicarbonate were measured over a range of temperatures from (50 to 90) °C in mixed aqueous solvents containing (50 to 100) mass % (salt-free solvent) ethylene glycol. Mixtures of solid sodium carbonate anhydrate (Na2CO3(s)) and solid sodium bicarbonate (NaHCO3(s)) in different ratios and also trona (Na2CO3·NaHCO3·2H2O(s)) were allowed to recrystallize and equilibrate with the mixed solvents at the given temperatures. The solubility of CO32- was generally found to decrease with increasing ethylene glycol content irrespective of the occurring solid phase, while HCO3- solubility displayed a minimum at (80 to 90) mass % (salt-free solvent) ethylene glycol and then increased sharply. For pure carbonate phases, CO32- solubility displayed little temperature dependence. In equilibrium with mixed carbonate−bicarbonate phases, the CO32- solubility usually decreased with temperature, most likely because it was linked to the HCO3- concentration via the solid's solubility product. The solubility of HCO3- increased significantly with temperature for all sodium bicarbonate containing solid phases. For the temperature range from (30 to 90) °C and an ethylene glycol concentration range of (50 to 100) mass % (of salt-free solvent), the CO32- solubility varied between (0.058 and 1.023) mol/kg solution, and the HCO3- solubility concentration ranged between 0.000 (i.e. the lower detection limit of the analytical method) and 1.153 mol/kg solution. The occurring solid phases were the same as those formed in the aqueous system. They were identified in the recrystallization experiments as sodium carbonate anhydrate (Na2CO3(s)), sodium carbonate monohydrate (Na2CO3·H2O(s)), trona (Na2CO3·NaHCO3·2H2O(s)), wegscheiderite (Na2CO3·3NaHCO3(s)), and sodium bicarbonate (NaHCO3(s)). No solvate phases with ethylene glycol were observed.
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