Waste water-free special steel pickling process

摘要

In a process for oxide layer removal from RSH (stainless, acid resistant and heat resistant) steels by pickling with nitric acid-free, hydrofluoric acid- and sulphuric acid-containing aqueous pickling solutions and then rinsing, the spent pickling solution and used rinse water are adjusted to pH 7-10 by calcium hydroxide addition, preferably as milk of lime of 10-20 wt.% concentration, the precipitate is removed and the resulting water is returned to the pickling/rinsing process.