# Crystal Growth Kinetics of Na 2 CO 3 Hydrate Phases in the Na 2 CO 3 –NaOH–H 2 O System for Sustainable Soda Ash Production

## TL;DR

This study explores the crystal growth of different soda ash forms to improve sustainable production methods.

## Contribution

The paper provides new insights into the growth kinetics of Na2CO3 hydrates under specific conditions for sustainable soda ash production.

## Key findings

- Na2CO3·10H2O growth peaks at a critical supersaturation and then slows down.
- Na2CO3·1H2O grows faster and produces dense soda ash despite lower supersaturation.
- NaOH affects the crystal habit of Na2CO3·1H2O but not Na2CO3·10H2O.

## Abstract

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.