| 摘要 |
PURPOSE:To enable the operation of a distillation column continuously for a long period without causing the deposition of crystals, by dissolving a Zn-containing composition in a liquid containing NH4OH and (NH4)2CO3, subjecting to the ion exchange, and crystallizing the product, wherein the crystallization is carried out by using a vertical distillation column introducing live steam to the bottom. CONSTITUTION:A Zn-containing composition is dissolved in a liquid containing NH4OH and (NH4)2CO3, and the solution is subjected to the ion exchange and fine-filtration. The obtained raw liquid 3 is crystallized successively in the 1st-4th crystallization tanks 1A-1D by the heat of live steam 7 blasted directly from the distillation column 2. The liquid having low Zn content is discharged from the bottom of the tank 1D and supplied to the top of the column 2. The column 2 is a vertical column furnished with e.g. 20 stages of the plates 2a, 2a..., and live steam 7 is introduced directly to the bottom of the column 2. The crystallization takes place also in the column 2, and the produced slurry of basic zinc carbonate is extracted from the column bottom. Since the heating of the column is carried out by introducing live steam to the column bottom in the present process, the deposition of crystal can be prevented to enable the long-term operation of the facilities.
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