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An optimal pickling bath composition is a precondition for the realization of constant high-quality steel surfaces. A mixture of HF/HNO(3) is state of the art, but can be harmful to the environment because of the decomposing products in spent air and in discharged pickling baths. Other mixed acids are intimated but, at present, not operational. During pickling, the free acid is bonded to the dissolved metal and the pickling solution loses efficiency and has to be discharged. The usual treatment of discharging pickling bath solutions by neutralization results in high quantities of neutralization sludge. Valuable substances are lost for further use.

In this project, NO(x)-free pickling methods were tested on a laboratory scale and the pickling efficiency was optimised from the viewpoint of the composition of the pickling solution. The efficiency of the different pickling solutions was compared with the traditional and currently used HNO(3)-based mixed-acid pickling method. On the basis of the tests, NO(x)-free pickling in a few cases is competitive with HNO(3)-pickling in terms of efficiency. It is presumed to substitute the NHO(3)-pickling for the austenitic stainless steels 1.4301 and 1.4404, and also for the highly alloyed material 1.4539 when a mixture of HF/H(2)O(2)/H(2)SO($) is used.

For DSS material 1.4467 and the super DSS material 1.4501 relatively good de-scaling reactions were observed in pickling solutions containing KMnO(4).

The recycling methods of the spent pickling acids and the rinse waters were examined. The availability of the membrane technology and the cooptation with the currently used regeneration method were studied. It can be concluded that recycling of the chemicals is possible for the acids HF, HNO(3), H(2)SO(4) and is accentuated by different acid and rinse water treatment methods.hods.

Additional information

Authors: SCHMIDT B, BFI, Düsseldorf (DE);LEVONMAA R, Outokumpu Polarit Oy, Tornio (FI);KRISZT K, Böhler Edelstahl GmbH & Co KG, Kapfenberg (AT)
Bibliographic Reference: EUR 19980 EN (2001), pp. 173. Euro: 26.50
Availability: Available from EUR-OP sales agent URL:
ISBN: ISBN 92-894-1583-5
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