| ‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ KAWASAKI STEEL TECHNICAL REPORT No.14 ( March 1986 ) Special Issue on Stainless Steels ‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ |
| A New Acid and Iron Recovery process in Stainless Steel Annealing and Pickling Line Toshio Watanabe, Minoru Hoshino, Kazuhiro Uchino, Yoshio Nakazato |
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Synopsis : A new recovery process was developed for nitric-hydrofluoric acid waster liquor from the stainless steel annealing and pickling line (APL) at Chiba Works. Although the conventional neutralization treatment has dranbacks of generating a large amount of sludge and discharging nitrogen into public waters, the new process has advantages of over-coming these drawbacks and recovering acid and iron contents as well. The process principally consists of (1) the iron separation stage, (2) iron oxide formation stage, (3) nitric-hydrofluoric acid recovery stage and (4) ferrite formation stage. This process is realized in the recovery plant on an industrial scale of 24 m3/day. The plant is composed of mixer-settlers, crystallizers, rotary kilns, pulse columns and others. The plant is in full operation with iron extraction percentage of 95% or more and recovery percentages of 95% or more for nitric acid and 70% or more for hydrofluoric acid. |
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