METHOD FOR REGENERATING PICKLING ACIDS

摘要

The residual acid mixture containing metals which has been produced in the steel pickling process is regenerated to become new HF/HNO3 pickling acid by applying H2SO4 addition and evaporation. The metal sulphate salt produced in evaporation is converted into scarcely soluble iron jarosite Na[Fe3(SO4)2(OH)6] and chrome and nickel hydroxide, the last mentioned metal hydroxide being obtained as a separately utilizable precipitate. The metal sulphate salt is separated from 60% H2SO4 solution, wherein the main part of the salt is also crystallized. For promoting the crystallization, part of the salt is crystallized in a side line where 80% H2SO4 concentration is used. The acid slurry produced is carried back to the crystallizing stage in the main line.