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

• 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 super saturations (low evaporation rates) inhibit HH agglomeration with NaCl. The submillimetric sized particles formed during simultaneous crystallization of NaCl and HI-I indicate ease in solid-liquid downstream separation.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering (hsv//eng)

Nyckelord

Simultaneous crystallization; Evaporative crystallization; Sodium chloride; Calcium sulfate hemihydrate; Water reuse; Wastewater treatment

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