METHOD FOR PURIFYING CRYSTALLINE SUBSTANCE

PROBLEM TO BE SOLVED: To make a continuously crystal-purifying apparatus applicable to raw materials supplied from a relatively wide range and enable continuous operation at high efficiency by specifying the average particle size of a supplied raw material crystal and loading the continuously crystalpurifying apparatus with the crystal. SOLUTION: The average particle size of a raw material crystal supplied to be cast in a crystallizing tower 2 is controlled to be not smaller than 2.5 mm, preferably not smaller than 3 mm, and further preferably not smaller than 5 mm. The raw material crystal is cast in the crystallizing tower 2 from a crystal casting part 3. The cast raw material crystal is dropped to the uppermost part of a mother liquid ascending in the tower and reaches the upper part of a slurry layer and a part of the crystal is dissolved in the mother liquid. Moreover, simultaneously with that, the raw material crystal lowers the ambient temperature to precipitate a crystal. The mother liquid layer formed by such a manner is called as a crystal descending region A. Since the crystal in the slurry layer in the lower part of the crystal descending region A is purified while being descending, the region is called a crystal purifying region B. The crystal purified in the crystal purifying region B and having high purity descends to a crystal melting region C and melted in the region and a part of the molten crystal becomes the mother liquid and the rest is taken out through a product taking out part 8.