Abstract: A novel process for treating pickling acid residue and recovering sulfates and nickel therefrom has been developed. By lowering the pH of a magnesium compound slurry to 4-5.5 with sulfuric acid containing pickling acid residue in the presence of ammonium sulfate, both magnesium sulfate and nickel sulfate are solubilized. Magnesium sulfate and nickel sulfate solution is separated from the solids by filtration and an iron hydroxide and chromium hydroxide residue is obtained as a precipitate. Magnesium sulfate and nickel sulfate are then separated from the solution.

Abstract: A novel process for treating and recovering valuable metals and other components from pickling acid residue (PAR) has been developed. The metals and other components are recovered by neutralizing the pickling acid residue using a magnesium compound or a mixture of magnesium compounds, and separating components of the resulting mixture (metals and sulfates) into products that can be reused, such as magnesium sulfate, nickel sulfate, iron and chromium phosphate, or various metal hydroxides or oxides.