Removal of nitrogen oxides from pickling bath off-gases - using permanganate or dichromate solutions for oxidation purposes followed by alkali scrubbing

摘要

From the acid treatment bath the off-gases are passed by a fan to a wash column with pumped circulation, in which the NO2 in the gas is taken out by water washing, as weak nitric acid. The gas then flows to a similar circulated column in which it is in contact with the oxidising solution of permanganate or dichromate, which converts the nitric oxide to nitrogen dioxide. There follows a final absorber having a circulation of alkali solution in which the NO2 produced by the NO oxidation is taken up as a nitrate solution. Used for the treatment of the off-gases from metal pickling baths using nitric acid or a mixture of nitric and hydrofluoric acids. The NO content of the gases is removed along with the NO2.