Metallurgical Evaluation of Liquor Wastes of Galvanizing Plants


Abstract: In this study, the treatment of waste pickling liquor which was taken from a hot dip galvanizing process was investigated. The steps of the process used for the treatment of this solution were goethite precipitation, zinc carbonate precipitation, the production of useful products from precipitates and discharge of the final solution. In the experiments, the optimum parameters of these process steps were investigated. All of the iron was oxidized to Fe^{3+} by the addition of H_2O_2. Following oxidation, NaOH neutralization was performed to increase pH of solution to 2.5, which resulted in complete precipitation of the iron as goethite. The total required time for the complete precipitation of the iron was 20-25 minutes. Yellow-colored \beta-goethite was converted to \alpha-Fe_2O_3 by dehydration at a temperature of 250°C. In the solution from which iron had been eliminated, zinc was precipitated completely by the addition of Na_2CO_3. The precipitated product was ZnCO_3 and relatively pure ZnO was produced by the calcination of this product for 0.5 hr at 300°C.

Keywords: Hot galvanizing, Waste pickling liquors, Goethite precipitation, Zinc precipitation

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