Product characteristics in simultaneous crystallization of NaCl and CaSO4 from aqueous solution under different evaporation rates

• Published in: Desalination 2019-05, Vol.457, p.85-95
• Main Authors: Zago, G.P., Penha, F.M., Seckler, M.M.
• Format: Article
• Language: English
• Subjects: Calcium sulfate hemihydrate; Evaporative crystallization; Simultaneous crystallization; Sodium chloride; Wastewater treatment; Water reuse
• ISSN: 0011-9164; 1873-4464; 1873-4464
• DOI: 10.1016/j.desal.2019.01.021

Knowledge about simultaneous crystallization in evaporative processes for water reuse is important for the promotion of particles with desirable characteristics. In this work, simultaneous crystallization of sodium chloride and calcium sulfate hemihydrate (HH) from aqueous solutions in unseeded batch mode is addressed. Both the crystallization mechanisms and the resulting particle morphological features have been identified. NaCl particles are generated by heterogeneous primary nucleation in solution, followed by growth and NaCl agglomeration. Calcium sulfate hemihydrate (HH) particles are also formed by heterogeneous primary nucleation in solution followed by crystal growth. HH crystals agglomerate with NaCl in all particle size ranges. Product particles are thus agglomerates with multimodal population densities in submillimetric size ranges, with HH widely dispersed throughout the size span of the particulate product. In comparison with NaCl binary solutions, simultaneous crystallization promotes the formation of larger, less polydisperse NaCl particles. Low supersaturations (low evaporation rates) inhibit HH agglomeration with NaCl. The submillimetric sized particles formed during simultaneous crystallization of NaCl and HH indicate ease in solid-liquid downstream separation. •Simultaneous crystallization is addressed in the context of water reuse operations.•Large NaCl particles, easily separable from the mother liquor, are formed.•Size classification of the product enables recovery of a high purity NaCl stream.•Particles morphology is explained in terms of elementary crystallization phenomena.