Crystallization of spherical common salt in the submillimeter size range without habit modifier

Abstract

Nearly spherical morphology of solution-grown NaCl particles in the size range of 300-1000 µm was achieved at 55-60 °C employing a suitable crystallizer equipped with a butterfly wing-shaped impeller operated at 250 rpm. Morphology control was equally effective with synthetic and natural brines and required no habit modifier. Sieved spherical salt of 350-500 µm size exhibited superior flow (ca. 20% greater mass flow rate through a funnel; angle of repose ~16°)-as compared to commercial vacuum evaporated free flow cubic salt of comparable dimension-upon treatment with potassium ferrocyanide anticaking additive. The superior flow characteristic was retained even after 3 months of storage. Scanning electron microscopic studies revealed that the round polycrystalline particles were derived from the stacking of minute NaCl cubes and the average size of the spheres was amenable to reduction through use of ethanol as antisolvent. The process was successfully scaled up to 10 kg level.