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Original Article
DOI: 10.1016/j.jmrt.2019.09.047
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Available online 19 October 2019
Experimental evaluation of the usage of residues for sintermaking
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Victor Freire de Oliveiraa,
, Maurício Covcevich Bagatinib,**
a Process and Technology, Paul Wurth SMS Group, Belo Horizonte, Brazil
b Department of Metallurgical and Materials Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
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Tables (7)
Table 1. Mass percentage composition of the used sinter feed and residues in dry basis.
Table 2. Generation of selected residues in the metallurgical process [11].
Table 3. Mass percentage composition of the sintering mixes for the study cases.
Table 4. Mass variation percentages for the different study cases.
Table 5. Chemical composition of high temperature experiment products (mass percentage).
Table 6. Mass percentage distribution per particle type of the studied mixtures.
Table 7. Resulting charging rates of negative elements in the studied blast furnace.
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Abstract

The shifts in quality of global reserves of iron ore, as well as the progressive advances in environmental legislations, are tendencies that have motivated researches on the usage of iron and carbon-bearing residues in the production of sinter for blast furnace ironmaking. These residues, however, are commonly limited in use due to their physical (particle size distribution) and chemical (heavy metals, alkali and zinc contents) properties as compared to sinter feed. In that sense, it is necessary to verify the impact of these materials on sinter quality and on sintering process parameters. In order to assess the recycling potential of residues via sintermaking, mixtures with increasing proportions (4.5–50%) of iron and steelmaking residues were prepared and tested in controlled laboratory conditions representing those of the sintering machine. The effect of residues on sinter mineral phases and chemical quality was evaluated and showed few differences in sinter quality for a mixture resulting from recycling 100% of a plant’s residue generation (4.5% of the mix). The greatest impact was an increased presence of wustite in the produced sinter, beyond 25% of residues in the mixture. The results indicated that there are opportunities, in the industry, for increasing the recycling of residues via sintermaking.

Keywords:
Sintermaking
Residues
Iron Ore
Recycling
Full Text
1Introduction

Stable blast furnace operation and productivity require control of raw material chemistry, metallurgical quality and size distribution. However, the availability of high-grade iron ores has progressively decreased over the years and the properties of the available ores vary widely [1]. Agglomeration routes such as sintering and pelletizing allow for controlling these parameters via blending of different ores [2], and sintering allows also for the recycling of metallurgical residues. Studies in the field of steelmaking [3], nevertheless, also indicate that around 40% of selected residues are still landfilled, a solution which is not sustainable in the long run, especially when environmental constraints exert pressure on steelmakers for better recycling performance [4]. Recycling of residues through the sintering process is, however, limited due to loss of sinter machine productivity resulting from compromised permeability (the residues usually are fine materials and agglomeration efficiency might be harmed), environmental constraints in the sinter plant (dioxines resulting from using oily mill scales, heavy metals coming from steel shop residues), operational limits in the sinter plant gas treatment system (alkali and chlorides reducing the efficiency of eletrostatic precipitators), besides quality requirements for blast furnace operation. Charged sinter is an important source of elements such as alkali and zinc that recirculate in the blast furnace, causing problems such as scaffolds, burden slips, productivity losses and fuel rate increases [5,6,7]. The alkali input in European furnaces, for example, is limited to 1,5–5,0kg/tHM and the zinc and lead inputs are limited to 0,05–0,25kg/tHM [8]. In the USA, zinc inputs are reported to be limited to 0,5–1,0kg/tHM [7]. All these trends and constraints have motivated researches on the usage of iron and carbon-bearing residues in the production of sinter for blast furnace ironmaking [9,10]. Even those studies, however, do not focus on the proportion with which residues are added to the sintering mix, nor on the proportion with which such a produced sinter could be used in a blast furnace.

The present study aimed at evaluating the recycling potential of iron and steelmaking residues in sintermaking, regarding the chemical quality of the product. More specifically, the study intended to investigate the impact of increasing residue proportion in sintering mixes on sinter chemical quality and mineral phases, parameters which directly impact their usage in blast furnaces.

2Materials and methods

Samples of blast furnace (BF) dust, BF sludge, basic oxygen furnace (BOF) dust, fine BOF sludge and mill scale were obtained from a Brazilian integrated steel plant. The characterization of these materials, as well as the conducted laboratory experiments are hereby detailed.

2.1Raw materials

Additional material samples to the residues were sinter feed, limestone, dolomite and lime. The chemical compositions of the residues and of the sinter feed are presented in Table 1, whilst their size distribution is presented in the graphic of Fig. 1. Atomic Absorption Spectroscopy (AAS) was used to quantify Ca, Mg, K, Na, Al, Mn, Zn, Cr. X-ray Fluorescence (XRF) was used to quantify CaO/CaOH, Pb and Cd. Titration with TiCl3 was used to quantify Total Fe/FeO. Gravimetry was used to quantify Si, according to ISO 2598-1. Ti was quantified by diantipyrylmethane spectrophotometry (ISO 4691/2011). P was quantified using molybdenum blue spectrophotometry (ISO 4687-1). Carbon was quantified by means of immediate analysis according to ASTM D3174. The sinter feed was an itabirite ore from the Minas Gerais iron quadrangle region in Brazil.It was a hematite-martitite with incipient recrystallization.

Table 1.

Mass percentage composition of the used sinter feed and residues in dry basis.

Parameter  Sinter feed  Mill scale  BOF dust  BF sludge  Fine BOF sludge  BF dust 
FeT  63.59  73.84  53.85  43.66  71.65  34.56 
Fe  0.00  0.00  0.00  0.00  46.09  0.00 
Fe2O3  89.09  38.79  73.22  60.42  0.00  44.82 
FeO  1.65  60.09  3.40  1.81  32.88  4.13 
SiO2  7.56  0.60  7.13  6.38  1.10  7.80 
Al2O3  1.170  0.078  1.372  3.107  0.107  2.365 
Mn  0.155  0.159  0.168  0.076  0.158  0.054 
P2O5  0.146  0.052  0.115  0.125  0.208  0.117 
CaO  0.034  0.107  5.932  0.599  15.294  5.632 
MgO  0.069  0.016  0.617  0.347  3.019  0.522 
TiO2  0.001  0.000  0.000  0.305  0.000  0.164 
Na20.027  0.033  0.016  0.037  0.061  0.035 
K20.001  0.001  0.001  0.001  0.001  0.005 
0.02  0.02  0.03  0.22  0.05  0.41 
ZnO  0.004  0.000  0.021  0.213  0.430  0.321 
Cd  <0.01  <0.01  <0.01  <0.01  <0.14  <0.01 
Cr  0.002  0.010  0.003  0.005  0.014  0.009 
Pb  0.00  <0.01  <0.01  <0.04  <0.01  <0.09 
0.00  0.00  7.89  26.09  0.00  33.21 
Moisture  10.874  2.606  9.641  16.949  29.941  9.074 
Fig. 1.

Size distribution of the analysed materials.

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In terms of general chemical quality, the residues show comparable parameters to those of sinter feed. Mill scale and fine BOF sludge have even higher iron contents than sinter feed. In terms of slag components, the SiO2 content of the residues are comparable or lower than that of the sinter feed. With the exception of mill scale, the residues contain much higher ZnO levels (50–100 times higher) than those of the sinter feed, whilst the alkali contents are comparably low. Heavy metals such as Cd, Cr and Pb are comparable between sinter feed and the residues, with the exception of the fine BOF sludge that has a 7 times higher chrome content than that of the sinter feed. Furthermore, BF dust and BF sludge present appreciable carbon contents, which might lead to coke breeze savings in the sinter plants. In terms of size distribution, the residues present, in general, a narrower and finer range than that of sinter feed, concentrating under 710μm.

2.2Preparation of samples

In order to assess the recycling potential of the investigated residues, laboratory scale experiments were conducted with four study cases. For each of them, a mixture of materials was prepared:

Case 1 - Sinter without residues in the mixture

Case 2 - Sinter with 4.5% residues in the mixture

Case 3 - Sinter with 25% residues in the mixture

Case 4 - Sinter with 50% residues in the mixture

Mixture 1 was taken as a control experiment to evidence changes caused by the residues and was prepared only with sinter feed, limestone, lime and dolomite. Mixture 2 focused on evaluating what would be the impacts of recycling 100% of each of the residue generated in the plant where the samples were obtained, which pointed to a maximum of 4.5% of residues in the mixture. The generation rate was assumed as the reference of specialists [11], which is reproduced on Table 2. Mixtures 3 and 4 focused on amplifying possible impacts of negative elements for the blast furnace such as zinc and alkali. For mixture 2, a mass balance taking the residue generation, the sinter proportion in the BF ferrous burden (normally 70% for the reference plant), hot metal and steel compositions, besides a binary basicity aim (B2=CaO/SiO2) of 1.77 for the produced sinter was conducted to reach the adequate proportions of each residue, sinter feed and fluxing agents. The other ferrous materials that are charged into the blast furnace were also taken into account to reach a slag balance and the dolomite proportion in the sintering mix was calculated to ensure a proper quaternary basicity for the BF slag (B4=CaO+MgO/SiO2+Al2O3). Lime was fixed to a 4% mass percentage of lime as a typical value for industrial practice [12] and to reduce the number of variables, since the focus was on the effect of residues in the mixes. The missing CaO was completed with limestone. For the calculation of mixtures 3 and 4, which aimed at amplifying possible negative impacts of alkali and zinc, 100% sinter proportion in the blast furnace burden was assumed, as well as the fixed residue proportions of 25 and 50%, respectively, and a mass balance similar to the one for mixture 2 was done. This was done as a “worst case scenario”. The mass balance is summarized by the flow sheet of Fig. 2 and the resulting raw material proportions for each mix are presented on Table 3. The main points of the mass balance were closing the iron balance with sinter feed to cover the iron not supplied by residues, adjusting limestone to complete the required CaO quantity to reach the desired B2 value and adjusting dolomite to reach the desired B4 value. For each mixture, 120g were prepared weighing the raw materials with an analytical balance. The mixture was then homogenised in a horizontal mixing drum at 26RPM for 6min. It was then transferred into a 1000mL beaker were a previously weighed water quantity was gradually sprayed to reach 8% moisture simultaneously to manual mixing. The humid mass was then homogenized by means of two successive quarterings. The homogenized humid mass was then pressed into eighteen briquettes of 4g each with a diameter of 11.5mm using a hydraulic press with a pressure of 10MPa maintained for 1min before the briquette was removed from the die. The methods were based in other references [13,14,15].

Table 2.

Generation of selected residues in the metallurgical process [11].

Residue  Generation  Unit 
Blast furnace dust  kg/tHM 
Blast furnace sludge  9.5  kg/tHM 
BOF dust  kg/tsteel 
Fine BOF sludge  17  kg/tsteel 
Mill scale  20  kg/tsteel 
Fig. 2.

Summarized mass balance flow sheet for the calculation of the analysed mixtures.

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Table 3.

Mass percentage composition of the sintering mixes for the study cases.

Parameter  Case 1  Case 2  Case 3  Case 4 
BF dust  0.00  0.55  3.07  6.15 
BF sludge  0.00  0.75  4.17  8.34 
BOF dust  0.00  0.44  2.48  4.96 
Fine BOF sludge  0.00  1.26  7.02  14.04 
Mill scale  0.00  1.48  8.26  16.52 
Sinter feed  81.86  78.28  61.99  42.12 
Lime  3.41  3.45  3.62  3.84 
Limestone  10.79  9.98  6.12  1.44 
Dolomite  3.94  3.82  3.27  2.60 
TOTAL  100.00  100.00  100.00  100.00 
Percentage of residues  0.00  4.47  25.00  50.00 
Percentage of sinter in the blast furnace ferrous burden  70.26  71.11  100.00  100.00 
2.3High temperature tests

The produced briquettes were dried in a stove at 110°C for 3h [13]. Each test was conducted in duplicates with nine briquettes each. The test followed controlled temperature and gas composition profiles, exemplified on Fig. 4 (which was the profile for one of the test replica), using a resistive furnace represented on Fig. 3. The furnace was a Lindberg 54459 resistive furnace (12.6W 240V 50/60Hz, max. temperature 1500°C) with a 1245mm DN65 AISI 310S tube. The sample holder was fitted with a thermocouple (S-type) to measure the temperature in close contact with the briquettes. The sample holder allowed for positioning the samples in different temperature regions of the furnace, whilst mass flowmeters were used to adjust the gas composition. The maximum temperature was 1300°C and the gas composition was, in the heating step, a low oxygen potential mix (1% CO, 24% CO2 and 75% N2) and atmospheric air in the cooling step [13]. The gas flow rate was kept at a total of 2.5L/min all throughout the test. The low oxygen potential mix was blown into the furnace for 8min to homogenize the test atmosphere before the sample holder was moved into the high temperature zone, where it was kept for a total of 5min. 3min at 1300°C and 2min at 1140°C, when the gas mixture was changed to 100% air. The atmosphere was changed 20s before the end of the 1300°C step. Fig. 4 also highlights the 1100°C temperature threshold, which is mentioned by other studies [16] as highly influential over key sintering phenomena such as liquid phase formation and iron species oxidation/reduction. The amount of time that the sample holder (also indicated in the figure) is above that temperature influences product mineral phases and sinter quality. The briquettes were weighed before and after the experiment so the mass variation could be obtained.

Fig. 3.

Tubular resistive furnace used for the high temperature experiments.

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Fig. 4.

Temperature and gas composition profiles of the high temperature experiments.

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The chemical composition of the test products was analysed by titration (total Fe and FeO), X-ray fluorescence (SiO2, Al2O3, CaO, MgO, TiO2, Na2O, K2O, P, Mn, Cr2O3, PbO, ZnO), inductively coupled plasma—optical emission spectroscopy (Cd) and the sulphur content was measured using LECO equipment. The mineral phases of the products were also investigated, using X-ray diffraction analysis.

3Results and discussion3.1High temperature experiments

After the high temperature tests, the processed briquettes presented a homogeneous and porous macroscopic aspect. The porosity might be attributed to residual moisture evaporation, carbon dioxide liberation during the calcining of limestone and dolomite or liquid phase formation. There was no appreciable dimensional variation as compared to the crude briquettes and they were found to be non-friable. The homogeneous aspect of the briquettes indicated that other cold agglomeration methods to prepare the samples might not lead to appreciably different results. In the industrial sintering process, sintering mixes are also cold agglomerated before charging into the sintering strand and material particles are in close contact which, in this experiment, was emulated by briquetting the samples. The observations also suggested that the small dimensions of the samples and the steep heating curves were sufficient to provide proper kinetic conditions for the reactions to take place over the whole sample in the given test time. The mass loss percentages of the experiments are presented on Table 4. The mass variation during sintering are explained by evaporation of moisture, calcination of limestone and dolomite, carbon oxidation (when it is present) and also due to the change in the oxidation state of iron, which involves gain or loss of oxygen. Since the calcination reactions must be responsible for the main weight decreases in these experiments and they are essentially the same for all the studied cases, the progressive increase of carbon-bearing residues should account for the increasing mass variation of the samples. The results indicate, thus, that the experimental method was consistent during different experiments.

Table 4.

Mass variation percentages for the different study cases.

Study case  Experimental average 
Case 1—0% residues  11.6 
Case 2—4.5% residues  12.3 
Case 3—25% residues  13.5 
Case 4—50% residues  14.8 

The chemical composition of the obtained products is shown on Table 5. In general, the results indicate that the iron content increased with increasing residue proportions. This is in good agreement with the higher proportion of steel shop residues, which have higher iron contents than the sinter feed. Alkali contents did not increase for 4.5% residues proportion, but K2O increased from 0.03 to 0.05% in mass for the 25 and 50% proportion mixes. As for ZnO, the results indicate a progressive increase as the percentage of residues increases, even though the levels remain below 0.10% in mass percentage. This result agrees with other studies [6] that have indicated that the removal of zinc in the sintering process is negligible. Hence, the higher input of zinc brought by the residues will imply in a higher outlet content. No increase of heavy metals contents was observed, which was expected as the residues and sinter feed had comparable levels of those elements. Even the chrome content, which was higher for fine BOF sludge as compared to sinter feed, remained on the same level as the residue-less sample. Phosphorus contents also remained unaltered, also because its contents in the used residues were comparable to that in the sinter feed they substituted. In terms of sulphur, the contents increased with increasing proportions of residues. Comparing the results for case 1 and 2 indicated that 4.5% residues in the mixture caused no impact on the chemical composition of the produced samples.

Table 5.

Chemical composition of high temperature experiment products (mass percentage).

Parameter  Case 1 0% residues  Case 2 4.5% residues  Case 3 25% residues  Case 4 50% residues 
FeT  57.28  57.39  59.64  63.14 
SiO2  6.97  6.58  6.17  5.47 
Al2O3  1.02  1.01  0.96  1.06 
CaO  10.6  10.2  9.29  7.97 
MgO  0.94  0.93  1.01  1.15 
TiO2  0.07  0.06  0.08  0.08 
Na20.1  0.1  0.1  0.1 
K20.03  0.03  0.05  0.05 
P2O5  0.119  0.115  0.113  0.118 
MnO  0.15  0.19  0.35  0.56 
Cd  <1ppm  <1ppm  <1ppm  <1ppm 
Cr2O3  <0.01  <0.01  <0.01  <0.01 
PbO  <0.01  <0.01  <0.01  <0.01 
ZnO  <0.01  0.02  0.05  0.07 
0.01  0.02  0.03  0.04 
B2  1.52  1.55  1.51  1.46 
B3  1.66  1.69  1.67  1.67 
B4  1.44  1.47  1.44  1.40 

Fig. 5 shows the X-Ray Diffractograms obtained from the products. The results indicate little or no difference between the present mineral phases of cases 1 and 2, which are mainly magnetite, hematite and silico-ferrites of calcium and aluminium (SFCA). A peak for quartz was also identified for case 1. For cases 3 and 4, however, wustite also appears. This might be attributed to the higher carbon content of the mixes, a result of using BF dust and BF sludge. As described in section 2.3, all the experiments were conducted in the same temperature and atmosphere conditions, so the increasing presence of carbon for mixtures 3 and 4 might further decrease the oxygen potential during the heating step of the experiment, creating conditions for further reduction of hematite into magnetite and wustite. Furthermore, Table 1 indicated that steel shop residues contain wustite in their composition and other studies indicate that increased contents of wustite in the sintering mixes lead to a corresponding higher content in the sinter product [17]. Peaks for quartz were also identified on case 3. The comparison the results of cases 1 and 2 indicates that 4.5% residues in the sintering mix caused no impact in the mineral phases of the produced samples.

Fig. 5.

X-ray diffractograms of the products of cases 1(a), 2(b), 3(c) and 4(d) – M: magnetite, H: hematite, Q: quartz, SFCA: silico-ferrites of calcium and aluminium.

(0.53MB).
3.2General remarks

In general, the use of residues in sintermaking is considered a challenging practice, as it might lead to sinter bed permeability loss and blast furnace sinter quality constraints. As previously discussed, recycling 100% of the residue generation of the studied steel plant would not surpass 4.5% of the sintering mix (case 2). Cases 3 and 4, evaluated in this study, would only be possible using residues from external companies.

According to specialists in the area of cold agglomeration for sintering [18,19], the agglomeration behaviour of particles can be classified according to their size. In light of that, the size distributions from section 2.1 were coupled with the mixture compositions of Table 3, yielding the particle size distributions of Table 6 for the different studied cases. Even though the residues have a narrower size distribution range and their particles concentrate in smaller sizes (<710μm) as compared to sinter feed, the results indicate no change in size distribution with 4.5% residues, as compared to a residue-less case. For 25 and 50% residues, the intermediate and adhering ranges increase whilst superfines and super coarse ranges decrease. These results, especially for case 2 with 100% recycling rates, indicate that no negative impact on sinter bed permeability should be expected, which is an important factor affecting sintering machine productivity levels.

Table 6.

Mass percentage distribution per particle type of the studied mixtures.

Parameter  Particle size range [mm]  Case 1 0% residues  Case 2 4.5% residues  Case 3 25% residues  Case 4 50% residues 
Super coarse  >6.3 
Nucleating  1.0–6.3  24  24  23  22 
Intermediate  0.3–1.0  11  16 
Adhering  0.1–0.3  18  19  23  27 
Superfine  <0.1  26  26  24  22 
Total (without lime, limestone and dolomite)82  83  87  92 

Concerning the quality of the produced samples, the obtained chemical composition and mineral phases results indicated no sensible differences between cases 1 (without residues) and 2 (4.5% residues in the mixture). Iron contents were comparable for the residue-bearing mixes. Zinc levels and wustite contents only increased beyond 25% of residues (case 3). Whilst a higher wustite content might lead to increased sinter strength [2,20], it also negatively impacts sinter reducibility. Sulphur increased slightly with increasing contents of residues, but that should not be troublesome as the most important source of sulphur in the blast furnace charge is coke, not sinter. Phosphorus contents remained constant for the different mixes, indicating no impact on hot metal quality concerning this element. The mass balance of section 2.2, combined with the chemical composition of the produced sinter samples would lead to the results of Table 7 for the charging rate of negative elements in the studied blast furnace. An increase in the loads of zinc is present and they follow the increase in proportion of residues. The results indicate that, according to European standards, the zinc/ZnO charging limits would not be satisfied for cases 3 and 4, but cases 1 and 2 would be within common practice. For USA standards [7,21], zinc charging would be within limits for all the tested cases. Concerning alkali, the calculated values would be within limits for all the tested cases. For case 2, the increased loads of both zinc and alkali resulting from recycling 100% of the generation of residues via the sintering route were still within acceptable limits. For cases 3 and 4, it is noteworthy that 100% sinter was assumed in the blast furnace burden and, still, values were within USA acceptable limits. Though different plants worldwide adopt different practices for charging limits of zinc and alkali, as well as different sinter proportions in the ferrous burden, the presented results for the tested mixtures indicate that there are opportunities for increasing recycling rates in the sintermaking process.

Table 7.

Resulting charging rates of negative elements in the studied blast furnace.

Parameter  Unit  Case 1  Case 2  Case 3  Case 4 
Residue proportion in the sintering mix  Mass percentage  4.5  25  50 
Sinter proportion in the blast furnace ferrous burden  Mass percentage  70  71  100  100 
Specific sinter consumption  kg/tHM  1154  1165  1577  1489 
ZnO charging  kg/tHM  0.12  0.23  0.79  1.04 
Zn charging  kg/tHM  0.09  0.19  0.63  0.84 
Alkali charging (Na2O+K2O)  kg/tHM  1.50  1.51  2.37  2.23 
European limits for zinc charging [8]  kg/tHM  0.05–0.25
USA limits for zinc charging [7,21]  kg/tHM  0.5–1.0
European limits for alkali charging [8]  kg/tHM  1.5–5.0

A remark should be made that the observed results might vary for other raw materials and with fluid dynamic aspects of the actual sintering process. It was observed that an increase in zinc inputs will increase the zinc content in the sinter. Whilst the used materials in this research were not particularly high in zinc, that might not be the case for other plants in the world. Hence, a mass balance considering the zinc content of the inlet residues is crucial to evaluate the allowable proportion of zinc-bearing materials in the sintering mix. Furthermore, the used sinter feed was an itabirite ore, which is naturally higher in SiO2. For other ores, different requirements for CaO balancing might be required. However, since the calculations indicate that, for most cases in steel plants, the residue proportion would not surpass 5% in the sintering mix, such an impact should not be large. Pot grate analysis are an experimental route that allow to evaluate the effect of fluid dynamics in the results and address sinter metallurgical quality (RDI, RI, TI, etc.). If the results, compared to a residue-less mixture, prove advantageous, industrial tests could be conducted stepwise, running the sinter plant for controlled periods of time with increasing residue proportions, monitoring the sinter quality, sinter plant off-gas ducts for zinc and alkali accretions, blast furnace process parameters, especially those concerning zinc contents in off-gas dust and sludges, sinter fines percentage in the stockhouse and blast furnace permeability. For that purpose, a period of constant (or close to constant) sinter proportion in the blast furnace burden is recommended. If no impacts are observed, or those observed are manageable, the proportion of materials being directed to landfills might be sensibly reduced, whilst also allowing for savings on raw materials such as sinter feed.

4Conclusions

The present study investigated the recycling potential of iron and steelmaking residues via sintermaking, a practice that is commonly limited due to sintering bed permeability loss and to harmful elements. Recycling 100% of the residue generation of a given steel plant would lead to no more than 4.5% residues in the sintering mix. High temperature experiments indicated no relevant impacts of using residues on sinter chemical quality: iron contents were either equal to those of a residue-less mixture or increased with increasing proportions of steel shop residues. There was no increase in heavy metal contents, whilst zinc and alkali contents remained in the same levels, with small increases for mixtures containing 25 and 50% of residues, much higher proportions than the viable 4.5%. The results also indicated no impacts on the mineral phases of the obtained products for 4.5% residues in the mixture, which were hematite, magnetite, wustite and silico-ferrites of calcium and aluminium. Wustite contents increased for the 25 and 50% residue mixtures, though, a result of using wustite-bearing steel shop residues. Regarding size distribution, residues have a narrower size distribution and smaller particle size (<710μm) than the sinter feed used in this study. However, the particle size distribution of the resulting mixes presented no evidence of a possible negative impact of using residues in the tested proportions of the sintering mix on cold agglomeration, which indicates there might not be related sinter bed permeability or productivity losses. Therefore, the set of obtained results showed that there are opportunities in the steel industry for increasing the recycling of residues in sintermaking.

Declaration of interest

The authors declare that there is no potential conflict of interest.

Acknowledgements

The authors would like to thank Paul Wurth SMS Group, CAPES-PROEX, CNPq and FAPEMIG for the invaluable support to research.

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Journal of Materials Research and Technology

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