A study on the treatment of wastes in hot dip galvanizing plants

In this study, a new method to treat the waste pickling liquor and zinc stripping solutions originating from hot-dip galvanizing process was developed. For waste pickling liquor, iron was oxidized to Fe3+ by the addition of H2O2. After the oxidation, iron was precipitated as goethite by NaOH neutralization. Yellow coloured beta-goethite was converted to alpha-Fe2O3 by dehydration at 250degreesC. Iron powder was produced by the reduction of goethite with hydrogen at 1000degreesC. Zinc was completely precipitated by the addition of Na2CO3. Precipitated product was ZnCO3 and ZnO was produced by the calcination of this product at 300degreesC. For de-galvanizing solution, zinc was completely stripped from the galvanized scraps constructing an electrochemical cell with copper electrode in H2SO4. Almost pure ZnSO4.H2O was obtained by the addition of ethyl alcohol from the iron free zinc stripping solution. Ethyl alcohol was recovered by the distillation process.