| During the production of iron smelting, a large amounts of blast furnace flue dust which contains high zinc and low iron is produced. The dust returning to sintering process as mixture of sinters will affect the permeability of bed of materials and reduce the taste of iron in sinter lump for thin granularity of the dust and the low melting point of zinc. At the same time, the accumulation of zinc causes the knot and reduces blast furnace using life in the process of the ironmaking. Currently the main treatment method of the blast furnace flue dust is rotary evaporation process, which has some disadvantages, such as high energy consumption, the kiln knot and environmental pollution. Meanwhile, some high concentration of waste sulfuric acid is produced during the TiO2production by sulfate method. According to the features of the Pangang Company, we proposed the process including waste acid leaching, iron precipitation, solvent extraction and electrowinning to recover metal zinc from blast furnace flue dust. This article researched systematically on the process of acid leaching, iron precipitation, solvent extraction and oil removal. The cathode zinc plate has high purity.The optimized leaching conditions were chose as the following, the amount of waste acid855L/t (or sulfate acid65g/L), room temperature, liquid-solid ratio of4mL/g and reaction time of2h. Under the optimum conditions the leaching percentages of zinc and iron were97.94%and only6.52%respectively. The content of the total iron and Fe2+in the filtrate was8g/L and5g/L respectively. The optimized conditions for iron precipitation by similar goethite process were the mass ratio of1.3for hydrogen peroxide and Fe2+, reaction temperature of50℃and limestone as neutral reagent. Under the optimum conditions the loss rate of zinc was controlled at about2.90%.The ZnSO4solution after iron precipitation contained low zinc and some impurities, such as Cu2+, Ni2+, Co2+, Cd2+, et al, which could not be directly used in electrowinning. The solvent extraction process comprised of three countercurrent solvent extraction steps, two countercurrent washing steps and two countercurrent stripping steps. The optimized conditions of solvent extraction steps were40%P204in260#kerosene, O/A=2and at temperature40℃, washing steps used diluted waste electrolyte at pH≈2by adding deionized water and then returned to the first washing step at temperature40℃, O/A=5, stripping steps used zinc spent electrolyte (Zn2+50g/L, H2SO4160g/L) at temperature40℃, O/A=4-5. The extraction and stripping percentage of zinc was57.03%and99.83%respectively. The extraction equilibrium pH was0.35. The enriched solution contained about90g/L of zinc and100g/L of H2SO4.To meet the requirement of zinc electrowinning, removal of entrained organic phase in the enriched ZnSO4solution was conducted by a step of fiber ball absorption and two steps of activated carbon (2g/L) absorption. The solution after oil removal was used in zinc electrowinning. The cathode zinc plate contained99.97%and the current efficiency was90.48%. If without considering Al content in the zinc plate, the content of zinc was more than99.99%.The four cyclic experiments showed that the process could work all right, the cathode zinc plates were dense and smooth. The average recovery rate of zinc was85.82%and the average current efficiency was90.56%. |
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