| 摘要 |
PROBLEM TO BE SOLVED: To prolong the using period of an etching soln. composed of ferric chloride and to reduce the amt. of waste water treatment in an etching treating device in which the etching soln. is sprayed on an alloy contg. iron, and surface treatment is executed. SOLUTION: At the point of time in which the concn. of ferrous chloride in a ferric chloride etching soln. in a reproducing soln. tank 4 reaches a 1st set concn., the spray pressure of the etching soln. is raised. In a state in which the spray pressure is raised, the etching treatment is continued, at the point of time in which the concn. of ferrous chloride in the reproducing soln. tank 4 reaches a 2nd set concn., gaseous chlorine is fed to the ferric chloride etching soln., and, by oxidizing the ferrous chloride into ferric chloride, the dissolving capacity of the ferric chloride etching soln. is recovered. At the point of time in which the concn. of ferric chloride in the ferric chloride etching soln. is recovered to the fixed value, the feed of gaseous chlorine is stopped.
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