| 摘要 |
PURPOSE:To prevent the increase of impurity concentration caused by over- dissolution of Zn-containing material and to prevent the destruction of zinc carbonate crystal, by controlling the rate of revolution of stirrer of at least one tank selected from dissolution tank, ion-exchange tank and crystallization tank. CONSTITUTION:A Zn-containing material discharged from a plant of iron works is dissolved in a solution containing (NH4)2CO3 and NH4OH in a dissolution tank provided with a stirrer (the reaction of formula I). The solution produced by the above reaction is added with metallic zinc powder in an ion-exchange tank provided with a stirrer to precipitate heavy metal ion in the solution (the reaction of formula II). The obtained solution of Zn(NH3)4CO3 is heated with steam in a crystallization tank provided with a stirrer to separate and evaporate NH3 and CO2 and crystallize 2ZnCO3-3Zn(OH)2 or ZnCO3.3 Zn(OH)2.H2O (reaction of formula IIIA and formula IIIB). In the above process, the rate of revolution of the stirrer of at least one tank in the above tanks is controlled. The increase in impurity concentration caused by over-dissolution of the Zn-containing material can be prevented and the destruction of growing zinc carbonate crystal can be also prevented by this process.
|
