A method of acid pickling iron and iron alloys and a composition for carrying out the method.

摘要

The invention relates to a method of acid pickling metallic material having an iron content of at least about 80 per cent by weight, while simultaneously inhibiting exposed metal surfaces against dissolution by acid attack. The method comprises bringing the material into contact with an aqueous solution containing phosphoric acid and one or both of the mineral acids hydrochloric acid and sulphuric acid. The phosphoric acid concentration is adjusted to at least about 0.01 mole per litre and at most about 1 mole per litre, while the total acid concentration is adjusted to the range between about 0.5 and 4 mole per litre. The invention also relates to a pickling agent for carrying out the method. The agent contains one or both of the mineral acids hydrochloric acid and sulphuric acid and has a total acid concentration of between about 0.5 and 4 mole per litre. The agent contains as an inhibitor phosphoric acid in a amount of at least about 0.01 mole per litre and at most about 1 mole per litre. The agent may also contain Fe(II)-ions.