| 摘要 |
PROBLEM TO BE SOLVED: To recover alkali by a compact device while evading the precipitation of alumina (Al<SB>2</SB>O<SB>3</SB>) and the storage of NaCO<SB>3</SB>and heavy metals, and further, to recover alkali even in an alkali etching solution admixed with a hydrolysis preventive. SOLUTION: This invention is composed of: a first stage where an alkali etching solution of aluminum is introduced into an electrolytic cell 1, and a part of free alkali is separated by an ion exchange membrane electrolytic dialysis process; and a second stage where the alkali etching solution from which a part of the free alkali is separated is hydrolyzed in a separation tank 4, so as to be separated into NaOH and Al(OH)<SB>3</SB>, and alkali is recovered. It is preferable that, in the first stage, by separating a part of free alkali, the weight ratio between the concentration of the free alkali and the concentration of metal other than alkali metal is controlled to≤1, and, in the hydrolysis, seed crystals are added. COPYRIGHT: (C)2009,JPO&INPIT
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