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 installing a heating means in a tower upper part of the continuously crystal-purifying apparatus and heating the mother liquid existing in the upper part. SOLUTION: A heating means 9 is installed in an upper part of a crystallizing tower 2 to heat a mother liquid in the part and retard the precipitation speed of a crystal. A raw material crystal is cast in the crystallizing tower 2 from a crystal putting part 3. The cast raw material crystal is dropped to the uppermost part of the 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 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 as 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 extraction part 8.