Abstract

Soda values are recovered from waste water and impurities are rejected to bitterns ponds by a low temperature crystallization process. In the process, waste water, typically containing 7-14% equivalent soda ash, is reacted with lime to neutralize bicarbonate. The liquor is subsequently clarified and fed into a multiple effect evaporator cooling circuit where it, along with the recirculating cooling water, is heated. The heated clarified liquid is then fed to an evaporative cooling system. Water is evaporated in the cooling tower and the liquor is cooled. The effluent liquor from this system now contains 17-24% soda ash. Most of this stream is recycled back to the multiple effect evaporator's cooling circuit for reheating. Approximately 10% of this stream is fed forward to an air cooled cooler-crystallizer where sodium carbonate decahydrate is crystallized. The decahydrate crystallized is relatively pure, while the sulfate is concentrated in the mother liquor. The resulting slurry is fed to a solid/liquid separation system where the mother liquor is separated from the decahydrate crystals. The crystals are washed to further remove impurities, dissolved with soda ash liquor, and recycled back to the process. The mother liquor and wash water are recycled to the multiple effect condensate cooling circuit and a portion of the mother liquor is purged to maintain an acceptable impurity level.

Other References

• Olsen, J. C., Unit Process and Principles of Chemical Engineering, D. Van Nostrand Co., NY NY, 1932 pp. 1-3