Process for treating waste pickling baths containing metallic salts and acids.

摘要

A spent liquor used for surface treatment of rolled steel products and contg. HF, HNO3, and salts of Fe, Co, Ni etc is worked up and recycled. In this method a cyclic scheme of acid dialysis, membrane electrolysis and evapn. takes place. In the acid dialysis a vol. of spent liquor per unit ion exchange membrane surface area of 0.5-10 1/hr./m2 is used, whilst in the membrane electrolysis a cathode potential of -400 to -1000mVh is employed which corresponds to a cell voltage of 2.8 to 5.0V. In the electrolysis, the catholyte used is the free acid of the depleted spent liquor, the anolyte is up to 1% HF/HNO3 and the freely selected cathode potential is kept at a constant level above a reference electrode by a rectifier.