Abstract
The sludge from a wet-off gas cleaning system of the iron blast furnace (BF) contains significant amounts of iron; however, they cannot be recycled due to their high content of zinc and alkalis. These compounds are detrimental to the optimal performance of iron and steelmaking furnaces. In this work, a comparative laboratory study to reduce zinc and alkali contained in the blast furnace sludge (BFS) is presented. The effect of leaching parameters such as oxidant (i.e., ferric ion, oxygen or ozone), aqueous solution media (i.e., 0.2 M NH4Cl, 0.2 M HCl and 0.1 M H2SO4) and temperature (i.e., 27 and 80 °C) on Zn and alkalis (Na2O and K2O) removal were studied by applying an experimental design. The results obtained show that Zn and K2O removal of 85% and 75% were achieved under the following conditions: Ozone as an oxidant agent and 0.1 M H2SO4 as an aqueous medium, temperature had no significant effect. The results are supported by thermodynamic diagrams and the possible chemical reactions are mentioned. Although the results also indicate that leaching under the above conditions dissolves up to 9% of iron, this loss is much less than leaching without the oxidizing conditions generated by the ozone. The BFS obtained from this treatment could be recirculated to the iron or steelmaking processes to recover iron values.
Highlights
The iron and steelmaking processes have been always related to the generation of dust/sludge, slag and other wastes or byproducts
The fundament of zinc and alkalis dissolution into strong or weak acid media using ozone or oxygen is that aqueous media react with the oxides of zinc and alkalis, incorporating them with the oxygen is that aqueous media react with the oxides of zinc and alkalis, incorporating them with the media as aqueous ions, just like it is shown by the average chemical analysis of the blast furnace sludge (BFS) with and media as aqueous ions, just like it is shown by the average chemical analysis of the BFS with and without ozone treatment
The high content of undesirable elements in iron blast furnace sludge generated a loss of valuable units of iron, to the potential environment hazards and the cost by handling and disposal/confinement
Summary
The iron and steelmaking processes have been always related to the generation of dust/sludge, slag and other wastes or byproducts. Dust and sludge from the gas cleaning systems of the blast furnace (BF) and the basic oxygen furnace (BOF) contains significant amounts of iron, carbon and other elements. Such materials cannot be recycled because of its impurities (nonferrous metals, mainly zinc) and represent a loss of 2% of the iron and coal contained in the raw material. In 2018, the world mine production was of 2.5 billion tons of iron ore; dust and sludge can be representing a loss of 15 to 20 million tons of Fe units annually) [1,2].
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