Crystal Growth Kinetics of Na _<b>2</b> CO _<b>3</b> Hydrate Phases in the Na _<b>2</b> CO _<b>3</b> –NaOH–H _<b>2</b> O System for Sustainable Soda Ash Production

As part of the CODA project, which is laying the foundation for a novel sustainable soda ash (Na₂CO₃) production strategy, this study provides essential parameters and insights for the design, optimization, and scale-up of the required crystallization processes. It investigates the crystal growth kinetics of Na₂CO₃·10H₂O and Na₂CO₃·1H₂O within the Na₂CO₃-NaOH-H₂O system using cooling and vacuum evaporative crystallization, respectively. Experimental studies were conducted utilizing a shortcut method based on seeded batch experiments in a 3 L-scale. The growth rate of Na₂CO₃·10H₂O was studied over a temperature range of 17-6 °C, while Na₂CO₃·1H₂O was examined at a constant temperature of 50 °C under a fixed evaporation rate. Minimal secondary nucleation was confirmed through offline crystal size distribution measurements. Na₂CO₃·10H₂O growth peaked at a critical supersaturation (∼1.03) and afterward slowed despite further increases in supersaturation, alluding to a potential crystal surface roughening mechanism. The presence of NaOH did not alter the crystal habit of Na₂CO₃·10H₂O but did alter that of Na₂CO₃·1H₂O. Despite the relatively low supersaturation, the monohydrate exhibited a higher growth rate than the decahydrate. Furthermore, the monohydrate produced yielded dense (heavy) soda ash, addressing a significant challenge within the soda ash industry.