Nittetu Chemical Engineering Ltd.

Kabushiki Kaisha Toshiba

Toshiaki Kurihara

Yoshiyuki Imagire

Teruhiko Hirabayashi

Eiichi Akiyoshi

Yoshiaki Kinoshita

Ryoichi Maekawa

A method of regenerating an etching waste fluid, includes the steps of dissolving HCl gas in an etching waste fluid at a temperature falling within a range of 20.degree. C. to 50.degree. C. and crystallizing NiCl.sub.2 and FeCl.sub.2 crystals, the etching waste fluid containing NiCl.sub.2, FeCl.sub.3, and FeCl.sub.2 and being obtained by etching Ni or an Ni alloy with an etching solution consisting of an aqueous solution containing FeCl.sub.3, distilling a mother liquor at the atmospheric pressure after crystallization and separation thereof to reduce the HCl concentration in the mother liquor, and distilling, at a reduced pressure, a concentrate obtained upon distillation at the atmospheric pressure to further reduce the HCl concentration, thereby obtaining an aqueous solution containing FeCl.sub.3, or bringing the concentrate obtained by distillation at the atmospheric pressure into contact with an iron oxide to cause HCl in the concentrate to react with the iron oxide to further reduce the HCl concentration in the concentrate thereby obtaining the aqueous solution containing FeCl.sub.3 with little HCl.

Method of treating nickel-containing etching waste fluid

A process for recovering caustic alkali from spent alkali liquor, in which a spent alkali liquor and iron oxide are roasted to obtain a product containing alkali ferrate and the product of roasting is hydrolyzed at a temperature over 110.degree. C. and under pressurized conditions where liquid phase is retained, thereby recovering caustic alkali in the form of an aqueous solution of a concentration higher than approximately 15 wt% containing dissolved iron in an extremely small concentration.

Process for recovering caustic alkali from spent alkali liquor

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Tokyo, Japan

Toshiaki Kurihara