PRODUCT CHARACTERISTICS IN SIMULTANEOUS CRYSTALLIZATION OF NaCL AND CaSO4 FROM AQUEOUS SOLUTION WITH SEEDING

• Zero liquid discharge strategies for industrial wastewater treatment have become prominent in recent years. When evaporative simultaneous crystallization is applied, knowledge about the particle crystallization mechanisms and morphology are important to ease solids downstream handling and for recovery of their valuable components. In this work, batch simultaneous crystallization of sodium chloride (NaCl) and calcium sulphate hemihydrate (CaSO4 center dot 0.5H(2)O) from aqueous solution was studied. It was found that CaSO4 center dot 0.5H(2)O is not an effective substrate for NaCl heterogeneous nucleation, but agglomerates with NaCl particles instead. CaSO4 center dot 0.5H(2)O particles on the surface of NaCl crystals sterically hamper agglomeration of NaCl particles with each other and, for a sufficiently high CaSO4 center dot 0.5H(2)O seed load, cover the NaCl crystals so that NaCl supersaturation rises, inducing NaCl primary nucleation. Simultaneous crystallization of CaSO4 center dot 0.5H(2)O and NaCl yields a satisfactory product for downstream handling even for high CaSO4 center dot 0.5H(2)O content in the crystallizer. However, seeding with CaSO4 center dot 0.5H(2)O is not recommended as it reduces the mean size and increases product size dispersion. NaCl seeding may be considered if it is desirable to separate CaSO4 center dot 0.5H(2)O from NaCl downstream the crystallizer by size classification, as it favors CaSO4 center dot 0.5H(2)O to build up in product sizes of 200 mu m and below.

Ämnesord

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

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

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

Nyckelord

Water reuse; Simultaneous crystallization; Batch evaporative crystallization; Sodium chloride; Calcium sulphate

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