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Ore-based steelmaking generates a variety of residues including dusts, sludges and slags. Recycling of these residues within the process or via other applications is essential for sustainable production from both environmental and economic aspects. In blast furnace (BF) ironmaking, there are generally two residues leaving the gas cleaning equipment; namely, BF dust and BF sludge. Traditionally, the dust is recycled via the sinter or, in the case of pellet based BF, via cold bonded agglomerates and injection. As the main output of zinc from the BF is the top gas, the sludge has to be dezinced prior to recycling to prevent accumulation of zinc in the furnace. Although dezincing of BF sludge has been successfully accomplished using e.g., hydrocycloning, the studied sludges are generally coarse sized and high in zinc. Furthermore, information is lacking regarding the efficiency of separation of different hydrocyclone setups. In the present work, hydrocycloning of a fine sludge, with low zinc content, generated by a pellet based BF has been studied. The gas cleaning equipment used to produce the sludge was running a primary aerocyclone and a scrubber. A characterization of the sludge has been conducted together with an evaluation of the separation efficiency of the hydrocyclone in order to assess the hydrocyclone performance and limitations. Furthermore, the dezincing using the hydrocyclone has been compared to that of sulfuric acid leaching. The results suggest that 51 to 93% of the sludge can be recycled depending on the demand on zinc removal and the chosen dezincing route.

Ore-based ironmaking generates a variety of residues, including slags and fines such as dust and sludges. Recycling of these residues within the integrated steel plant or in other applications is essential from a raw-material efficiency perspective. The main recycling route of off-gas dust is to the blast furnace (BF) via sinter, cold-bonded briquettes and tuyere injection. However, solely relying on the BF for recycling implicates that certain residues cannot be recycled in order to avoid build-up of unwanted elements, such as zinc. By introducing a holistic view on recycling where recycling via other process routes, such as the desulfurization (deS) station and the basic oxygen furnace (BOF), landfilling can be avoided. In the present study, process integration analyses were utilized to determine the most efficient recycling routes for off-gas dust that are currently not recycled within the integrated steel plants of Sweden. The feasibility of recycling was studied in experiments conducted in laboratory, pilot, and full-scale trials in the BF, deS station, and BOF. The process integration analyses suggested that recycling to the BF should be maximized before considering the deS station and BOF. The experiments indicated that the amount of residue that are not recycled could be minimized.

Ore-based steelmaking generates various residues including dusts, sludges, scales and slags. Recycling of these residues within the process or via other applications is essential for sustainable production of steel. In blast furnace (BF) ironmaking, the gas-cleaning equipment generally recovers the particles in the off-gas as dust and sludge. Traditionally, the dry dust is recycled via the sinter or, in the case of pellet-based BF operation, via cold-bonded briquettes and injection. As the BF sludge mainly consists of iron and carbon, this residue is of interest to recycle together with the BF dust. However, depending on how the BF is operated, these two residues are more or less the major outlet of zinc from the furnace. Thus, to limit the recycled load of zinc, both materials cannot be recycled without dezincing the sludge prior to recycling. Dezincing and recycling of the low-zinc fraction of BF sludge via sinter have been reported whereas recycling via cold-bonded briquettes has not been performed. In the present study, cold-bonded briquettes containing the low-zinc fraction of dezinced BF sludge were charged as basket samples to the LKAB Experimental Blast Furnace (EBF). The excavated basket samples from the quenched EBF suggested that additions of up to 20 wt.% of upgraded BF sludge was feasible in terms of reducibility and strength. Based on these results, BF sludge were added to cold-bonded briquettes and charged in industrial-scale trials. The trials indicated that the annual generation of BF sludge, after dezincing, could be recycled to the BF.

This paper investigates the distribution of elements between slag and hot metal from a blast furnace through calculation of distribution coefficients from actual production data. First, samples of slag and hot metal tapped from a commercial blast furnace were taken continually at 10-minute intervals for a production period of 68 hours. Distribution coefficients of manganese, silicon, sulphur and vanadium were then calculated from the results of the sample analyses.A major conclusion drawn from examination of the results was that the behaviour of the studied elements was as could be expected when approaching the equilibrium reactions from thermodynamic theory. The distributions of the elements in the slag-metal system showed clear tendencies which did not appear to be influenced by the operational conditions of the furnace. For example, for manganese, vanadium and sulphur, it was found that a higher basicity led to a decreased distribution coefficient LMn and Lv, but an increased Ls, which is according to theory. Another observed relationship was that slag basicity increased with an increased carbon content in the hot metal, which indicated that Si0 2 was reduced to [Si] when the oxygen potential decreased. Furthermore, it was found that sulphur and silica behaviour likened that of acidic slag components, while the manganese oxide and vanadium oxide behaviour was similar to that of basic slag components. Theoretical backgroundThe first part of the paper describes the thermodynamic theory used in the determination of distribution coefficients as well as the procedure used in obtaining the production data. In the second part, investigation results regarding the variation in distribution coefficients during tapping and between taps are presented and discussed.where parentheses indicate slag phase and brackets indicate metal phase of element i. The distribution coefficients provide information about how the elements behave in the blast furnace, i.e. how much oxide remains in the slag and how much oxide is reduced to the elements contained in the hot metal. The equilibrium distribution coefficients are influenced by three factors: temperature, oxygen potential and basicity. In the present work the basicity is expressed asThe main reactions in a blast furnace are heterogeneous slag-metal-gas reactions. Although the reactions normally go through the gas phase, a common way to present the degree of the reduction of oxides is to use distribution coefficients. This is possible due to the fact that most of the elements of interest leave the furnace through the slag or the hot-metal phase. Among the components that leave the furnace with the top gas are CO, C02, N2, H2 H20 and some S. Since the blast furnace is assumed to operate at steady state, the distribution coefficient, Li; for a general slag-metal distribution can be expressed on the form (1) (2) (%i) L · --I - [%i] (%CaO)