Abstract
Depending on the operation of the blast furnace (BF), the main outlet of zinc from the furnace is more or less via the BF dust and sludge. As the dust is recycled to the BF, the sludge has to be de-zinced prior to recycling to prevent the accumulation of zinc in the BF. De-zincing and recycling of the low-zinc fraction via sinter have been reported. However, no research concerning recycling of upgraded BF sludge via cold-bonded briquettes has been performed. In the present study, a fine-grained BF sludge with low zinc content, generated by a BF operating on a ferrous burden of 100% pellets, was upgraded using the tornado process. The process simultaneously dried and separated the BF sludge into a high-zinc and a low-zinc fraction. The feasibility of recycling the low-zinc fraction to the BF using cold-bonded briquettes was studied on a laboratory-scale BF shaft simulator. On comparison with a reference briquette, the experiments indicated that 10 wt% of the upgraded BF sludge can be added to the briquette without negatively affecting the reducibility. Higher additions were found to render the briquette less reduced compared to the reference under test conditions corresponding to the central part of the BF. The strength of the briquettes was not compromised with the addition of the upgraded BF sludge, and a decision to study the briquettes in the LKAB experimental blast furnace was made in order to evaluate the behavior under actual BF conditions.
Highlights
Ore-based steelmaking generates a variety of residues including dusts, sludges, scales, and slags
The tumble indices after 24 h of curing were determined to be 42, 47, and 48% for the reference, B1, and B2 briquettes, respectively. These results suggest that a higher strength after 24 h of curing can be achieved by adding the upgraded blast furnace (BF) sludge
Zinc compounds slow the cement setting time by forming a protective layer on cement grains [25], and the hydrophobic nature of carbon disturbs the wetting and induce an effect of set retardation in the cement [26]. These two factors would contribute to a lower tumbling index with the increasing amount of upgraded BF sludge added as the sludge additions resulted in higher zinc and carbon contents, Table 3
Summary
Ore-based steelmaking generates a variety of residues including dusts, sludges, scales, and slags. The feasibility of recycling different amounts of the low-zinc fraction of the upgraded BF sludge to the BF using cold-bonded briquettes was studied experimentally using a laboratory-scale BF shaft simulator. These two factors would contribute to a lower tumbling index with the increasing amount of upgraded BF sludge added as the sludge additions resulted in higher zinc and carbon contents, Table 3.
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