metals Article
The Macroscopic Flow direction and Microscopic Distribution of Mg in Sintered Products and Its Influence Shengli Wu, Weili Zhang *, Mingyin Kou
and Heng Zhou
School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijng 100083, China;
[email protected] (S.W.);
[email protected] (M.K.);
[email protected] (H.Z.) * Correspondence:
[email protected]; Tel.: +86-178-0100-1120 Received: 2 November 2018; Accepted: 29 November 2018; Published: 1 December 2018
Abstract: Magnesium flux is an indispensable part of sintering materials. Its distribution and reaction behavior have an important influence on the quality of the sinter. Studying the macroscopic flow direction and microscopic distribution of MgO in sintered products is important for guiding the matching of ore for sintering and adjusting sintering technical parameters. The macroscopic flow direction situation of MgO in all sintered products was studied using X-Ray diffractometer and X-Ray fluorescence analyzer. In addition, the microscopic distribution characteristics of Mg element in the main sintered products were studied using scanning electron microscope and energy dispersive spectrometer. The results of this research are as follows. The Mg contents of sintered products are in the following increasing order: sinter ore, sinter internal return ore, and blast furnace return ore. The Mg content of the 1 to 2 mm grain size is the highest in the sinter internal return ore and blast furnace return ore, which is related to the granular distribution of magnesium flux. Moreover, the Mg content of sintered minerals are in the following decreasing order: magnetite; silico-ferrites of calcium and aluminium (SFCA); and silicate and hematite, and the Mg dissolving in the SFCA has a tendency to make the SFCA morphology coarse. The diffusion range of Mg in a large dolomite particle is much narrower, and it mainly stays at the position where the dolomite is located. In the actual sintering process, Mg increases the viscosity of the sintering liquid phase and prevents the oxidation of magnetite, which is not conducive to the improvement of the strength of the sinter. Keywords: sinter; magnesium; flow direction; microscopic distribution; SFCA
1. Introduction Blast furnace ironmaking requires basic slag with excellent metallurgical properties. These properties are necessities for a high-quality, high-yield and low-consumption ironmaking process. Appropriate MgO content in the slag facilitates the improvement of its metallurgical properties [1–5]. In general, the magnesium content in iron ore is too low to meet the demand for blast furnace ironmaking [6]. Therefore, it is necessary to add an extra magnesium source, such as dolomite, to ironmaking materials. Since adding dolomite to the blast furnace will bring a series of adverse effects [7–9], magnesium-containing fluxes are usually added during the sintering process. As for the effects of magnesium flux on the sintering process, previous studies have shown that MgO has a negative effect on the strength and reducibility index and a positive effect on the reduction degradation index of the sinter [10–15]. It can be seen that the reaction behavior of MgO is closely related to the quality index of sintering production. The distribution of Mg in sintered products can reflect the reaction behavior of Mg in the sintering process, to some extent. Thus, the distribution of Mg in sintered
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products is worth clarifying. However, there is little to report on the macroscopic flow direction of Mg during the actual sintering process. Moreover, the research on the magnesium microscopic reaction behavior and its influence in the sintering process is mostly limited to high temperature simulation laboratory experiment. Its temperature, atmosphere, and kinetic environment may differ from that of the actual sintering process. As a result, the practical reaction behavior and influence degree of Mg on the actual sintering process are difficult to fully observe. This research aims to clarify the macroscopic flow direction, the microscopic reaction, and distribution characteristics of Mg with actual sintered products. This will lay a foundation for reducing the adverse effect of Mg on the quality index of sintering by regulating the distribution of Mg in sintering. In this research, the macroscopic flow direction of Mg in all sintered products was studied using X-Ray diffractometer (XRD) produced by Rigaku Corporation, Tokyo, Japan and X-Ray fluorescence analyzer (XRF). produced by panalytical B.V., Almelo, The Netherlands, in addition, some microscopic reaction and distribution characteristics of Mg in main sintered products were studied using scanning electron microscope and energy dispersive spectrometer (SEM-EDS) produced by FEI, Hillsboro, OR, United States. 2. Materials and Methods 2.1. Properties of Raw Materials During the sintering process, the magnesium flux, such as dolomite, is mixed with other sintering materials and granulated. After sintering, the sintered body is crushed and sieved to divide into sinter ore (SI-ore) and sinter internal return ore (return fine, IN-re). The dust formed during crushing is collected using a bag filter to form tail bag ash (TBS). During the process of transporting the sinter ore to the blast furnace, blast furnace return ore (BF-re) will form from its breaking. In addition, some materials will enter the sinter flue gas during sintering and be collected by the first, second, and third sinter electric precipitators to form first, second, and third sinter electrostatic dust (SED1, SED2, and SED3), respectively. The SED1 and TBS are mixed with the sinter mixture again to return them to the sintering process. Meanwhile, SED2 and SED3 were sent to the dump. Therefore, there are seven flow directions of Mg in the sintering process: SI-Ore, IN-re, BF-re, TBS, SED1, SED2, and SED3. The samples used in the experiment (i.e., SI-Ore, IN-re, BF-re, TBS, SED1, SED2, and SED3) were produced by Meishan Iron & Steel Group in China. The sintering raw materials ratio, chemical composition of mixed mine and dolomite, and the dolomite granular distribution of products from the Meishan Iron & Steel Group are shown in Tables 1–3, respectively. The ratio of dolomite in sinter raw materials is 2.76%, which is determined by the difference between the Mg content required for the blast furnace and the Mg content of the ironmaking raw material. The −0.5 mm grain size of dolomite is the greatest, followed by the 1–2 mm grain size. Table 1. Raw materials ratio of products form the Meishan Iron & Steel Group. Materials
Mixed Mine
IN-re
BF-re
Dolomite
Limestone
Quicklime
Fuel
ratio (%)
55.6
25.0
8.12
2.76
2.08
3.11
3.33
Table 2. Chemical composition of mixed mine and dolomite from the Meishan Iron & Steel Group. Composition
TFe
FeO
SiO2
CaO
Al2 O3
MgO
LOI
mixed mine (%) dolomite (%)
62.19 -
3.1 -
4.52 2.46
0.77 30.95
1.59 0.26
0.21 19.85
3.78 44.97
Table 3. Granular distribution of dolomite from the Meishan Iron & Steel Group. Granularity (mm)
−0.5
0.5–1
1–2
2–3.15
+3.15
Proportion (%)
32.61
20.79
27.96
17.92
0.72
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Figure 1 shows the macroscopic morphology of the seven samples. A few white particles were 1 shows theSI-ore macroscopic morphology of the shows. seven samples. A few white particles found onFigure surface of some samples, as the picture Similarly, a certain number were of white found on surface of some SI-ore samples, as the picture shows. Similarly, a certain number of white particles existed in the IN-re and BF-re samples. While most of the white particles existed in the form particles existed in the IN-re and BF-re samples. While most of the white particles existed in the form of separate particles in IN-re samples, most of the white particles were inlaid on the BF-re samples, of separate particles in IN-re samples, most of the white particles were inlaid on the BF-re samples, as evident in the pictures shown. The mineral phases of white particles in SI-ore, IN-re, and BF-re as evident in the pictures shown. The mineral phases of white particles in SI-ore, IN-re, and BF-re werewere detected using XRD. The minerals calciumoxide oxideand and magnesium oxide, which detected using XRD. The mineralswere were mainly mainly calcium magnesium oxide, which shows thatthat thethe white the main sintered products (i.e., SI-ore, IN-re and BF-re) shows whiteparticles particles existing existing ininthe main sintered products (i.e., SI-ore, IN-re and BF-re) were had undergone an incomplete reaction. weredolomite dolomitethat that had undergone an incomplete reaction.
Figure 1. Macroscopic morphologyofofthe thesintered sintered products. ore; IN-re: sinter internal Figure 1. Macroscopic morphology products.SI-ore: SI-ore:sinter sinter ore; IN-re: sinter internal return BF-re: blast furnace returnore; ore; SED1, SED1, SED2, SED2, and andand third sinter return ore; ore; BF-re: blast furnace return andSED3: SED3:first, first,second, second, third sinter electrostatic dust; TBS: tail bag ash. electrostatic dust; TBS: tail bag ash.
2.2. Experimental Methods
2.2. Experimental Methods
In order to study the macroscopic material flow direction of Mg in all sintered products, the SI-Ore,
In order study thesieved macroscopic material flow ofsieved Mg ininto all sintered the SIIn-re, andto BF-re were into five grain sizes. Thedirection SI-Ore was five grainproducts, sizes of 5–10, Ore, 10–16, In-re, 16–25, and BF-re were grain sizes.were The sieved SI-Oreinto wasfive sieved sizes of 25–40, and sieved +40 mm.into Thefive IN-re and BF-re graininto sizesfive of −grain 0.5, 0.5–1, 1–2, 2–3.15, and +3.15 mm. Then, all the grain sizes of SI-ore, In-re, BF-re, and TBS, and three kinds of -0.5, 5–10, 10–16, 16–25, 25–40, and +40 mm. The IN-re and BF-re were sieved into five grain sizes of were made into all a −the 0.074grain mm powder. mineral phases of each sample wasthree 0.5–1,sinter 1–2,electrostatic 2–3.15, anddust +3.15 mm. Then, sizes of The SI-ore, In-re, BF-re, and TBS, and tested using an X-Ray diffractometer, and the MgO content of each sample was tested using an X-Ray kinds of sinter electrostatic dust were made into a −0.074mm powder. The mineral phases of each fluorescence analyzer. According to the Mg content in each grain size of SI-ore, In-re, and BF-re and sample was tested using an X-Ray diffractometer, and the MgO content of each sample was tested the proportion of each grain size, the integral MgO content of SI-ore, In-re and BF-re were calculated. using an X-Ray fluorescence analyzer. According to the Mg content in each grain size of SI-ore, In-re, Through comparative analysis, the macroscopic flow direction of Mg in the sintering process was and BF-re and the proportion of each grain size, the integral MgO content of SI-ore, In-re and BF-re clarified, and attempts were made to analyze the reasons for the flow direction. were calculated. comparative thedistribution macroscopic flow direction of in Mg in the sintering In order Through to study the microscopicanalysis, reaction and characteristics of Mg main sintered process was clarified, and attempts wereselected, made toground, analyze thepolished reasonstofor the light flowsheets. direction. products, typical SI-ore samples were and make The Mg In order to study the microscopic reaction and distribution characteristics of Mg in main distribution condition in different mineral types of SI-ore were then analyzed using point analysis sintered and products, typical SI-ore samples ground, and polished light sheets. The Mg surface scanning of EDS. At thewere sameselected, time, we examined the Mg contentto inmake silico-ferrites of calcium and aluminium (SFCA) minerals mineral with different recover the relationship between distribution condition in different typescrystalline of SI-orestates weretothen analyzed using point analysis the Mg content and the crystalline state of SFCA. Additionally, surface scanning was performed on of and surface scanning of EDS. At the same time, we examined the Mg content in silico-ferrites the area where the magnesium flux was located to recover the Mg distribution characteristics around calcium and aluminium (SFCA) minerals with different crystalline states to recover the relationship dolomite. On content the otherand hand, typical samplesstate of IN-re and BF-re were selected to try scanning to explore, was between the Mg the crystalline of SFCA. Additionally, surface through SEM-EDS, the reasons for the insufficient consolidation strength of IN-re and BF-re from the performed on the area where the magnesium flux was located to recover the Mg distribution perspective of Mg distribution characteristics. characteristics around dolomite. On the other hand, typical samples of IN-re and BF-re were selected to try to explore, through SEM-EDS, the reasons for the insufficient consolidation strength of IN-re and BF-re from the perspective of Mg distribution characteristics. 3. Results and Discussions 3.1. Mineral Phases of Sintered Products
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3.1. Mineral Phases of Sintered Products
Figure 2 shows the mineral phases of the seven samples tested using XRD. The mineral phases Figure 2 shows mineral phases of the seven samples tested usingwere XRD.hematite, The mineral phases of and of the SI-ore, IN-re, andthe BF-re were similar. The main mineral phases magnetite, the SI-ore, IN-re, and BF-re were similar. The main mineral phases were hematite, magnetite, and a a certain amount of calcium ferrite. Interestingly, a little of MgO was found, which further supported certain amount of calcium ferrite. Interestingly, a little of MgO was found, which further supported the existence of unreacted dolomite in the main sintered products. In addition to the hematite and the existence of unreacted dolomite in the main sintered products. In addition to the hematite and magnetite, the three kinds of sinter electrostatic dust also contained a large amount of potassium magnetite, the three kinds of sinter electrostatic dust also contained a large amount of potassium chloride. This is because the potassium chloride existing in sintering materials is a low boiling point chloride. This is because the potassium chloride existing in sintering materials is a low boiling point substance. It will volatilize into gasatatthe the sintering temperature then captured substance. It will volatilize intosintering sintering flue flue gas sintering temperature and isand theniscaptured by by the sinter electric precipitators. Therefore, the potassium chloride will mainly exist in sinter the sinter electric precipitators. Therefore, the potassium chloride will mainly exist in sinter electrostatic electrostatic dust. The potassium chloride content lowest in SED1, highest in SED3 according dust. The potassium chloride content was lowestwas in SED1, highest in SED3 according to the X-ray to the X-ray diffraction intensity ofSED2, SED1,and SED2, and SED3.toSimilar to SI-ore, mineral phases of tail diffraction intensity of SED1, SED3. Similar SI-ore, the mineralthe phases of tail bag ash were mainly hematite and magnetite, and no potassium chloride or MgO was found. bag ash were mainly hematite and magnetite, and no potassium chloride or MgO was found.
Figure 2.2.Mineral sinteredproducts. products. Figure Mineralphases phases of sintered
3.2. Macroscopic Flow Direction of Mg
3.2.Macroscopic Flow Direction of Mg
3.2.1. Mg Flow Direction in All Sintered Products
3.2.1. Mg Flow Direction in All Sintered Products
Figure 3 shows the MgO content in different sintered products obtained by XRF. The content of Figure shows MgO content in different products obtained content MgO in3the SI-orethe is slightly lower than that of thesintered IN-re, and BF-re. The contentby ofXRF. MgO The in SI-ore is of the content of MgO in than the IN-re BF-re is 1.71 andBF-re. 1.78%.The Thiscontent is 3.64 and 7.88%in higher MgO1.65%, in theand SI-ore is slightly lower thatand of the IN-re, and of MgO SI-ore is than that the SI-re,ofrespectively. is detrimental to 1.71 the consolidation of theissintered body by the 1.65%, and theofcontent MgO in theMgO IN-re and BF-re is and 1.78%. This 3.64 and 7.88% higher liquid phase. On one hand, MgO and its reaction products in the sintering process (e.g., magnesium than that of the SI-re, respectively. MgO is detrimental to the consolidation of the sintered body by silicate and magnesia iron peridot) are high-melting point substances which will increase the liquid the liquid phase. On one hand, MgO and its reaction products in the sintering process (e.g., phase formation temperature to some extent, then reduce liquid phase production [16]. On the other magnesium silicate and magnesia iron peridot) are high-melting point substances which will increase hand, the MgO will increase the viscosity of the liquid phase, which will narrow the bonding range the liquid phase formation temperature to some extent, then reduce liquid phase production [16]. On of the sinter liquid phase [17]. Thus, the MgO is not conducive to the effective consolidation of the the other hand, the MgOAs will increase viscosity the high liquid phase, which willtonarrow the bonding sintering materials. a result, the the sintered bodyofwith MgO content tends enter IN-re and rangeBF-re of the sinter liquid phase [17]. Thus, the MgO is not conducive to the effective consolidation because of its poor consolidation, which leads to a relatively higher MgO content in IN-re and of the sintering materials. As a to result, the the sintered high MgO of content tends to enter IN-re BF-re. The authors tried analyze reasonbody whywith the Mg content BF-re is higher than that of and BF-reIN-re. because of are its poor consolidation, leadsistothe a relatively higher MgO content in IN-re There two sources of IN-re.which One source powder produced during the crushing of and the sintered body, andtothe Mg content of IN-re from this source is relatively according to the BF-re. The authors tried analyze the reason why the Mg content of BF-rehigher is higher than that of INanalysis Anotherofsource the upper-most layer of the sinter minerals, which into the re. There areabove. two sources IN-re.isOne source is the powder produced during theenter crushing of the
sintered body, and the Mg content of IN-re from this source is relatively higher according to the analysis above. Another source is the upper-most layer of the sinter minerals, which enter into the IN-re without selectivity due to the deficiency of heat, and the Mg content of IN-re from this source is at the average MgO level of the sinter minerals. However, the only source of the BF-re is the sintered
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IN-re without selectivity due to the deficiency of heat, and the Mg content of IN-re from this source is at the average MgO level of the sinter minerals. However, the only source of the BF-re is the sintered body with insufficient strength, which means a relatively higher Mg content to some extent. Therefore, Metalsthe 2018, 8, x FOR PEERcontent REVIEW integral MgO of IN-re composed of two sources is lower than the Mg content of BF-re.5 of 12 At the same time, compared with the existing form of residual dolomite in IN-re and BF-re, the separate uppermost of the sinter in derived which the not participate in the dolomitelayer particles existing in minerals, IN-re may be fromdolomite the secondalmost source,does i.e., the uppermost layer sintering due toin a which deficiency of heat.almost The SED1, SED2, and SED3 contain much alkali of thereaction sinter minerals, the dolomite does not participate in the sintering reaction duemetal a deficiency of heat.chloride. The SED1,Alkali SED2, and SED3 contain much alkalithe metal [18],electrostatic such as potassium [18], tosuch as potassium metal selectively entering sinter dust will chloride. Alkali metal dustiswill the so percentage of reduce the percentage of selectively MgO. Theentering contentthe of sinter alkali electrostatic metal in SED3 thereduce highest, the percentage MgO. The content of alkali metal in SED3 is the highest, so the percentage of MgO is the lowest. of MgO is the lowest.
MgO content (%)
2.0 1.8 1.6 1.4 1.2 1.0 0.8 SI-ore IN-re BF-re SED 1SED 2SED 3 TBS sinter products Figure Distributionof ofMgO MgO in products. Figure 3. 3. Distribution in different differentsintered sintered products.
3.2.2. Mg Flow Direction in Various Grain Sizes of Main Sintered Products
3.2.2. Mg Flow Direction in Various Grain Sizes of Main Sintered Products Figure 4 shows the MgO content in different grain sizes of SI-ore, IN-re, and BF-re obtained by Figure shows the MgO content different grain sizes of SI-ore,1.6 IN-re, and BF-re obtained by XRF. The4 MgO content in each graininsize of SI-ore fluctuates between and 1.7%. Interestingly, XRF.the The MgO content in each of SI-ore fluctuates between 1.6 and 1.7%. Interestingly, Mg content of IN-re and grain BF-re size present the same trend with the granularity. As the grain size the Mg content of IN-re and BF-re present the same trend with the granularity. As the grain size increases, increases, the Mg content first rises, then falls and peaks at the grain size of 1 to 2 mm. Coincidentally, the Mg content first then falls and peaks the grainissize of 1 as to the 2 mm. Coincidentally, the variation of Mgrises, content with IN-re and BF-reat granularity the same granular distribution the of theof dolomite (except for the −0.5 mmBF-re graingranularity size). As shown in same Figureas 5, the granular variation Mg content with IN-re and is the granulardistribution distribution of proportion(except first rises, then with thegrain grain size increasing, and in theFigure proportion of 1granular to 2 mm grain size the dolomite for thefalls −0.5 mm size). As shown 5, the distribution is the highest (except for the − 0.5 mm grain size). A conjecture is put forward about this coincidence. proportion first rises, then falls with the grain size increasing, and the proportion of 1 to 2 mm grain mineralization performance the dolomite is not very A ideal, so residual is inevitable size The is the highest (except for theof−0.5 mm grain size). conjecture is dolomite put forward about this during a relatively short sintering time at high temperature. The more dolomite there is in a certain coincidence. The mineralization performance of the dolomite is not very ideal, so residual dolomite grain size, the more residual dolomite there is in this grain size in general. Since the residual dolomite is inevitable during a relatively short sintering time at high temperature. The more dolomite there is cannot be consolidated well, it mostly enters IN-re during crushing or BF-re during transport. As a in a result, certainthere grain thecorrelation more residual dolomite there is in this grain in general. is asize, certain between the Mg content in each grain size size of IN-re and BF-reSince and the residual dolomite cannot be of consolidated it mostly enters IN-re during crushing or BF-re during the granular distribution the dolomite.well, Under the same reaction conditions, a high proportion of transport. As a result, there is a certain correlation between the Mg content in each grain size in of INdolomite in the 1 to 2 mm grain size leads to more residual dolomite in this grain size, which results re and BF-re theingranular dolomite. the the same reaction conditions, a higher Mgand content the 1 to 2distribution mm grain sizeofofthe IN-re and BF-re.Under Although dolomite proportion of 0.5 mm grain is the highest, dolomite in thistograin size is relatively less, which high−proportion of size dolomite in the 1the to 2residual mm grain size leads more residual dolomite in thisisgrain shown by the less MgO content of IN-re and BF-re in this grain size, because of its excellent chemical size, which results in higher Mg content in the 1 to 2 mm grain size of IN-re and BF-re. Although the reaction kinetics conditions. Therefore, the peak value of the the Mg content in dolomite the IN-re and BF-regrain and the dolomite proportion of −0.5mm grain size is the highest, residual in this size is peak proportion of dolomite granular distribution (except for the − 0.5 mm grain size) all coincidentally relatively less, which is shown by the less MgO content of IN-re and BF-re in this grain size, because arise at 1 to 2 mm grain size.
of its excellent chemical reaction kinetics conditions. Therefore, the peak value of the Mg content in the IN-re and BF-re and the peak proportion of dolomite granular distribution (except for the 0.5mmgrain size) all coincidentally arise at 1 to 2 mm grain size.
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2.1 2.0
BF-re
2.1
1.9 2.0
IN-re
SI-ore
BF-re
1.8 1.9 MgO (%)
MgO (%)
IN-re
SI-ore
1.7 1.8 1.6 1.7 1.5 1.6 1.5+40 40-25 25-16 16-10 10-5 +40 40-25 25-16 16-10 10-5
+3.15 3.15-2 2-1 1-0.5 -0.5
+3.15 3.15-2 2-1 1-0.5 -0.5
+3.15 3.15-2 2-1 1-0.5 -0.5(mm) +3.15 3.15-2 2-1 1-0.5 -0.5 sinter product grain sizes
sinter product grain sizes (mm) Figure 4. MgO content sizesofofSI-ore, SI-ore, IN-re, and BF-re. Figure 4. MgO contentinindifferent different grain grain sizes IN-re, and BF-re.
40 Mass percentage (%)
Mass percentage (%)
Figure 4. MgO content in different grain sizes of SI-ore, IN-re, and BF-re.
40
30 30 20 20 10 10 0 0 +3.15 +3.15
3.15-2 2-1 1-0.5 -0.5 3.15-2 2-1 1-0.5 -0.5 dolomite grain sizes (mm) dolomite grain sizes (mm)
Figure 5. Granular distribution of dolomite.
Figure dolomite. Figure5.5.Granular Granular distribution distribution ofofdolomite.
3.3. Microscopic Distribution of Mg 3.3. Microscopic Distribution of Mg
3.3. Microscopic Distribution of Mg
3.3.1. Mg Mg Distribution Distribution in in Different Different Minerals Minerals 3.3.1.
3.3.1. Mg It Distribution in Different Minerals wellknown known that sinter is a heterogeneous structure of multiple and, It isiswell that the the sinter ore isore a heterogeneous structure of multiple mineralsminerals and, therefore,
therefore, the Mg distribution may exhibit in different regions because the content It isMgwell known thatexhibit the sinter ore isa asegregation structure multiple minerals the distribution may a segregation inheterogeneous different regions because theofcontent of Mg varies of in and, 2+ can easily enter the magnetite crystal lattice from Mg varies in different minerals. For example, Mg 2+ different For example, canaeasily enter theinmagnetite lattice from the gangue or of therefore, theminerals. Mg distribution mayMg exhibit segregation differentcrystal regions because content 2+ and Fe2+ are gangue or external dolomite at sintering temperature because the ionic radius Mg 2+ andof 2+ are 2+ external dolomite at sintering temperature because the ionic radius of Mg Fe similar and Mg varies in different minerals. For example, Mg can easily enter the magnetite crystal lattice from similar andisthe is the same [19]. the valence thevalence same [19]. gangue or external dolomite at sintering temperature because the ionic radius of Mg2+ and Fe2+ are Typical SI-ore samples were selected to to study study the the relationship relationship between Typical SI-ore samples were between Mg Mg content content and and mineral mineral similar andthrough the valence is theFigure same selected [19]. types SEM-EDS. 6a,c are the graphs of two different regions of the SI-ore types through SEM-EDS. Figure 6a,c are the graphs of two different regions of the SI-ore sample sample Typical SI-ore samples were selected toboth study the relationship between Mgblack content andand mineral obtained using SEM. The two regions are composed of gray calcium ferrite, silicate, obtained using SEM. The two regions are both composed of gray calcium ferrite, black silicate, typeswhite through SEM-EDS. Figure 6a,c to are graphs of two different regions of the SI-ore sample bright ironiron oxide. According thethe dissolution characteristics ofofMg and white bright oxide. According to the dissolution characteristics Mgions ionsintroduced introducedabove, above, hematite and magnetite can be distinguished by the Mg content in the mineral obtained using EDS. obtained using SEM. The two regions are both composed of gray calcium ferrite, black silicate, hematite and magnetite can be distinguished by the Mg content in the mineral obtained using EDS. and When theiron Mg content content is in in aa relatively relatively high range, the is otherwise ititisishematite. white bright oxide. is According to the dissolution characteristics of Mg ions introduced above, When the Mg high range, the mineral mineral is magnetite, magnetite, otherwise hematite. Figure 6b,d are the corresponding Mg distribution maps of Figure 6a,c, respectively, obtained by hematite and can be distinguished by the Mgofcontent in the mineral obtained using Figure 6b,dmagnetite are the corresponding Mg distribution maps Figure 6a,c, respectively, obtained by EDS.EDS. EDS. It can be seen that the distribution of Mgthe in mineral the sinter ore has an otherwise obvious segregation When the Mg content is in a relatively high range, is magnetite, it is hematite. It can be seen that the distribution of Mg in the sinter ore has an obvious segregation phenomenon phenomenon that may relate to the different dissolution characteristics of Mg in various minerals. that6b,d mayare relate the different dissolution characteristics of Mg in various minerals. The Mgobtained content by Figure thetocorresponding Mg distribution maps of Figure 6a,c, respectively, The Mg content of various minerals in Figure 6a,b are shown at Figure 7. Apparently, in the SFCAof various minerals in Figure 6a,b are shown at Figure 7. Apparently, in the SFCA-iron oxide-silicate EDS. It can be seen that the distribution of Mg in the sinter ore has an obvious segregation iron oxide-silicate structure, the Mg content of sintering minerals are in the following decreasing structure, the content of sintering minerals dissolution are in the following decreasingoforder: magnetite, SFCA, phenomenon thatMg may relate to the Mg in various minerals. order: magnetite, SFCA, silicate, anddifferent hematite. Meanwhile,characteristics in contrasting the Mg content of the same silicate, and hematite. Meanwhile, in contrasting the Mg content of the same kind of minerals (SFCA The Mg content of various minerals in Figure 6a,b are shown at Figure 7. Apparently, in the kind of minerals (SFCA or silicate) in two regions, it is evident that the Mg content in Figure 6a SFCAis or silicate) in two regions, it is evident that the Mg content in Figure 6a is higher than that in Figure 6c iron oxide-silicate thewhether Mg content of sintering minerals the following decreasing higher than thatstructure, in Figure 6c the mineral is SFCA or silicate. are Thisin means that when the Mg whether the mineral is SFCA or silicate. This means that when the Mg content rises in a region, the Mg
order: magnetite, SFCA, silicate, and hematite. Meanwhile, in contrasting the Mg content of the same kind of minerals (SFCA or silicate) in two regions, it is evident that the Mg content in Figure 6a is higher than that in Figure 6c whether the mineral is SFCA or silicate. This means that when the Mg
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content of rises a region, the Mg an content of all minerals will show an upward However, content all in minerals will show upward However, relative order trend. of the Mg contentthe of content rises in a region, the Mg content of trend. all minerals will the show an upward trend. However, the relative order of the Mg content of various minerals in the same region does not change. various minerals in the same region does not change. relative order of the Mg content of various minerals in the same region does not change.
Figure 6. 6. Sinter map of of Mg. Mg. (a) Figure Sinter graphs graphs under under SEM SEM and and the the distribution distribution map (a) SEM SEM graph graph of of region region 11 (b) (b) Mg Mg Figure 6. Sinter graphs under SEM and the distribution map of Mg. (a) SEM graph of region 1 (b) Mg distribution map region 1 (c) SEM graph of region 2 (d) Mg distribution map region 2. distribution map region 1 (c) SEM graph of region 2 (d) Mg distribution map region 2. distribution map region 1 (c) SEM graph of region 2 (d) Mg distribution map region 2.
Mgcontent content(%) (%) Mg
2 2 1.5 1.5 1 1 0.5 0.5 0 0
magnetite SFCA-1 SFCA-2 silicate-1 silicate-2 hematite magnetite SFCA-1 mineral SFCA-2types silicate-1 silicate-2 hematite mineral types Figure 7. Distribution of Mg in different mineral types. Figure 7. Distribution of Mg in different mineral types.
3.3.2. Mg Distribution Distribution in in Different Different SFCA 3.3.2. Mg SFCA 3.3.2. Mg Distribution in Different SFCA According to the the SFCA According to the morphology morphology of of crystal crystal particles, particles, the SFCA can can be be divided divided into into acicular-SFCA acicular-SFCA According to the morphology ofcolumnar-SFCA crystal particles, the SFCA can platy-SFCA be divided into acicular-SFCA with fine crystal particles (Figure 8a), (Figure 8b), and with with fine crystal particles (Figures 8a), columnar-SFCA (Figures 8b), and platy-SFCAcoarse with crystal coarse with fine crystal particles (Figures 8a), columnar-SFCA (Figures 8b), and platy-SFCA withand coarse particles (Figure 8c) [20–23]. this section, thesection, relationship between the morphology SFCA the crystal particles (Figures 8c)In[20–23]. In this the relationship between the of morphology of crystal particles (Figures 8c) [20–23]. In this section, the relationship between the morphology of Mg content was studied. The Mg content of SFCA in different morphologies was obtained using EDS. SFCA and the Mg content was studied. The Mg content of SFCA in different morphologies was SFCA and the Mg content was studied. The Mg content of SFCA in different morphologies was In order tousing avoidEDS. individual error, the Mg content oferror, each morphology wasofmeasured at 10 different obtained In order to avoid individual the Mg content each morphology was obtained using EDS. In order to avoid individual error, the Mg content of each morphology was points, andatthe content three kinds of SFCA are three shown in Figure 9. Itare can be seen measured 10 average differentMg points, and of thethe average Mg content of the kinds of SFCA shown in measured at 10 different points, and the average Mg content of the three kinds of SFCA are shown in from Figure 9 that the higher the Mg content, the coarser the crystal particle. Previous studies have Figure 9. It can be seen from Figure 9 that the higher the Mg content, the coarser the crystal particle. Figure that 9. It the can be seen from Figure 9 that the higher the Mg content, the coarser the crystal particle. shown crystallization process is divided into two steps: crystal formation Previous studiescrystal’s have shown that the crystal's crystallization process is divided intonucleus two steps: crystal Previous studies have shown that the crystal's crystallization process is divided into two steps: crystal and crystal growthand [24,25]. When the amount liquid is constant, largerisnumber ofacrystal nucleus formation crystal growth [24, 25]. of When thephase amount of liquid aphase constant, larger nucleus formation and crystal growth [24, 25]. When the amount of liquid phase is constant, a larger nuclei are associated with a smaller crystal size. Generally, the large melt viscosity has a negative number of crystal nuclei are associated with a smaller crystal size. Generally, the large melt viscosity numberonofthe crystal nuclei arecrystal associated with aone smaller crystal size. Generally, the large viscosity impact formation nuclei. hand, harmful tomelt theisdiffusion has a negative impact onofthe formation ofOn crystal nuclei.the Onhigh one viscosity hand, theishigh viscosity harmful has a negative impact on the formation of crystal nuclei. On one hand, the high viscosity is harmful to the diffusion of liquid particles to the surface of the microcrystals, which is not conducive to the to the diffusion of liquid particles to the surface of the microcrystals, which is not conducive to the formation of primary nucleus [26]. On the other hand, the reduction of fluidity likely reduces the formation of primary nucleus [26]. On the other hand, the reduction of fluidity likely reduces the
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primary nucleus [26]. On the other hand, the reduction of fluidity likely reduces the dendritic fracture,
dendritic becomes the secondary nucleus after fracturing reduces whichfracture, probably which becomes the secondary nucleus fracturing and reduces amount and of secondary dendritic fracture, which probably probably becomes theafter secondary nucleus after the fracturing and reduces the the amount of aa high point substance, increase the nucleus [25]. MgO, nucleus a high melting point substance, will increase viscositywill of the liquid phase to a amount of secondary secondary nucleus [25]. [25]. MgO, MgO, high melting melting pointthe substance, will increase the viscosity viscosity large extent. Thus, a the liquid phase with athe higher Mgphase content is favorable for thecontent formation favorable of coarse of of the the liquid liquid phase phase to to a large large extent. extent. Thus, Thus, the liquid liquid phase with with aa higher higher Mg Mg content is is favorable for for SFCA crystal particles. the formation of coarse SFCA crystal particles. the formation of coarse SFCA crystal particles.
contentofofMg Mg(%) (%) content
Figure 8. Morphology of different calciumand and aluminium (SFCA). (a) Acicular-SFCA; Figure 8. Morphology differentsilico-ferrites silico-ferrites of of (SFCA). (a) Acicular-SFCA; Figure 8. Morphology of of different silico-ferrites ofcalcium calcium andaluminium aluminium (SFCA). (a) Acicular-SFCA; (b) columnar-SFCA; (c)(c) platy-SFCA. (b) columnar-SFCA; platy-SFCA. (b) columnar-SFCA; (c) platy-SFCA.
1.0 1.0 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0.0 0.0
acicular acicular
columnar columnar SFCA SFCA types types
platy platy
Figure in different differentSFCA. SFCA. Figure9.9.Mg MgContent Content in Figure 9. Mg Content in different SFCA.
3.3.3. Mg Distribution around Dolomite
3.3.3. 3.3.3. Mg Mg Distribution Distribution Around Around Dolomite Dolomite Due to the weak mineralization ability of dolomite, the Mg in a large dolomite particle may not be Due weak ability dolomite, the Mg in dolomite particle may uniformly dispersed in the sintered products and participate in Mg the sintering reaction. Theparticle distribution Due to to the the weak mineralization mineralization ability of of dolomite, the in aa large large dolomite may not not be uniformly dispersed in the sintered products and participate in the sintering reaction. The characteristics of Mg around a large dolomite particle in the actual sintering process is worthy of study. be uniformly dispersed in the sintered products and participate in the sintering reaction. The distribution characteristics around large dolomite in sintering process A large dolomite particle of was found in theaasinter and theparticle graph obtained using SEM is shown in is distribution characteristics of Mg Mg around largeore, dolomite particle in the the actual actual sintering process is worthy of A large particle in ore, and graph obtained Figure 10a. The map of the Mgwas and found Ca around thesinter dolomite, surface scanningusing worthy of study. study. Adistribution large dolomite dolomite particle was found in the the sinter ore,obtained and the theby graph obtained using arein shown in Figure 10b,c respectively.map It can clearly seen from Figure 10b,c that theobtained Mg SEM shown Figures 10a. distribution of the Mg Ca around the dolomite, SEMofis isEDS, shown in Figures 10a. The The distribution map ofbe the Mg and and Ca around the dolomite, obtained element is mostlyoflocated where the dolomite particle is located, andItthe diffusion range offrom the Mg by surface scanning EDS, are shown in Figure 10b,c respectively. can be clearly seen by surface scanning of EDS, are shown in Figure 10b,c respectively. It can be clearly seen from Figure Figure element isMg far less than that of Ca located element.where This may be becauseparticle the calcium fluxes, e.g., CaO and 10b,c that element is mostly the dolomite is located, and the diffusion 10b,cCaCO that the the Mg element is mostly located where the dolomite particle is located, and the diffusion to generate point substances, e.g., SFCA and calcium olivine, easily 3 , tend range of Mg is low-melting far than Ca This be because thewhich calcium fluxes, range of the the Mg element element far less lesstemperature. than that that of ofThen, Ca element. element. This may may because calcium fluxes, forms a liquid phase at is sintering the migration of Ca be mainly takesthe place through e.g., CaO and CaCO 3, tend to generate low-melting point substances, e.g., SFCA and calcium olivine, e.g., the CaO andofCaCO 3, tend to generate low-melting e.g., SFCA calciumasolivine, flow the liquid phase [14], so the distributionpoint rangesubstances, of Ca is relatively wide.and However, a which easily forms aa liquid phase at sintering temperature. Then, the migration of Ca mainly takes which easily forms liquid phase at sintering temperature. Then, the migration of Ca mainly high-melting point material, MgO cannot yet generate a low-melting point substance that melts at thetakes place through the liquid phase [14], so the distribution range relatively wide. place through the flow flow of of the the phase of [14], distribution range of of Ca Ca is isMgO relatively sintering temperature [27], so liquid the migration Mg so canthe almost only be achieved through particlewide. However, aa high-melting material, MgO cannot yet aa low-melting point substance thermalas which haspoint an extremely limited moving range. As such, the Mg element stays in However, asmotion, high-melting point material, MgO cannot yet generate generate low-melting pointonly substance that melts at the sintering temperature [27], so the migration of Mg can almost only be achieved the original position of the dolomite. that melts at the sintering temperature [27], so the migration of Mg can almost only be achieved through through MgO MgO particle particle thermal thermal motion, motion, which which has has an an extremely extremely limited limited moving moving range. range. As As such, such, the the Mg element stays only in the original position of the dolomite. Mg element stays only in the original position of the dolomite.
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Figure 10. Distribution map of Mg and Ca around large dolomite particle. (a) SEM graph of large Figure10. 10.Distribution Distributionmap mapof ofMg Mgand andCa Caaround aroundaaalarge largedolomite dolomiteparticle. particle.(a) (a)SEM SEMgraph graphof ofaaalarge large Figure dolomite particle; (b) Mg distribution map around dolomite particle; (c) Ca distribution map around dolomiteparticle; particle;(b) (b)Mg Mgdistribution distributionmap maparound arounddolomite dolomiteparticle; particle;(c) (c)Ca Cadistribution distributionmap maparound around dolomite dolomite particle dolomiteparticle. particle dolomite
3.3.4. 3.3.4. Mg Distribution characteristics in BF-re. 3.3.4.Mg MgDistribution Distributioncharacteristics characteristicsin inBF-re BF-re. As As mentioned above, there was larger portion of residual dolomite inlaid on the BF-re. In order Asmentioned mentionedabove, above,there therewas wasaaalarger largerportion portionof ofresidual residualdolomite dolomiteinlaid inlaidon onthe theBF-re. BF-re.In Inorder order to study the distribution of Mg in the BF-re and its effects on the sintered body, typical BF-re samples to study the distribution of Mg in the BF-re and its effects on the sintered body, typical BF-re samples to study the distribution of Mg in the BF-re and its effects on the sintered body, typical BF-re samples inlaid residual dolomite werewere selected, mounted, and polished into a light sheet. Its morphology, inlaid with residual dolomite selected, mounted, and into aa light sheet. inlaidwith with residual dolomite were selected, mounted, and polished polished into light sheet. Its Its seen under the SEM is shown in Figure 11a. dolomite should be shown right side morphology, seen under the isisshown in Figure Residual dolomite should be shown on the morphology, seen under theSEM SEM shown inResidual Figure11a. 11a. Residual dolomite shouldon bethe shown on the of theside sample, but it fell off the mounting due to its poor bonding. is shown right of sample, but itit fell the mounting process due bonding. As isis right side of the the sample, butduring fell off off during during the process mounting process due to to its its poor poorAs bonding. Asin Figure 11, the sample is divided into two areas by the white line. The left area is a dense interwoven shown shown in in Figure Figure 11, 11, the the sample sample isis divided divided into into two two areas areas by by the the white white line. line. The The left left area area isis aa dense dense structure composed of calcium ferrite and iron oxide. Additionally, its local enlarged graph is shown in interwoven structure composed of calcium ferrite and iron oxide. Additionally, its local enlarged interwoven structure composed of calcium ferrite and iron oxide. Additionally, its local enlarged Figure 11b. It is self-evident that the liquid phase is sufficient and consolidation is better. Meanwhile, graph graphisisshown shownin inFigure Figure11b. 11b.ItItisisself-evident self-evidentthat thatthe theliquid liquidphase phaseisissufficient sufficientand andconsolidation consolidationisis the right area is a loose porous structure its local enlarged graph isenlarged shown ingraph Figure 11c. It in is better. Meanwhile, the area isisaaloose porous structure and isisshown better. Meanwhile, theright right area looseand porous structure andits itslocal local enlarged graph shown in apparent that the liquid phase is deficient and the pores are large, which leads the area to become Figure 11c. It is apparent that the liquid phase is deficient and the pores are large, which leads the Figure 11c. It is apparent that the liquid phase is deficient and the pores are large, which leads the the weak link of the body strength. Thebody element composition of the two structuresof area to weak of strength. The composition the area to become become the sintered weak link link of the the sintered sintered body strength. The element element composition ofobtained the two two through region analysis of EDS are shown in Table 4. are It isshown evidentin the4. main composition structures obtained through region analysis of Table ItIt isischemical evident the structures obtained through region analysis of EDS EDS are shown inthat Table 4. evident that that the main main in the twocomposition regions is similar, except for the Mg content. Accordingly, different Mg content should chemical in two isis similar, for Mg content. Accordingly, the chemical composition in the the two regions regions similar, except except for the thethe Mg content. Accordingly, the be responsible for the opposite structures. This is because the MgO will increase the liquid viscosity, different differentMg Mgcontent contentshould shouldbe beresponsible responsiblefor forthe theopposite oppositestructures. structures.This Thisisisbecause becausethe theMgO MgOwill will resulting in decreased flow range, making the liquid phase deficient in the some areas. Thedeficient deficiency increase liquid resulting in flow range, making phase in increase the the liquid viscosity, viscosity, resulting in decreased decreased flow range, making the liquid liquid phase deficient in of the liquid phase leads to a porous structure and poor consolidation strength. Therefore, such a some some areas. areas. The The deficiency deficiency of of the the liquid liquid phase phase leads leads to to aa porous porous structure structure and and poor poor consolidation consolidation mechanism by which the Mg influences the sintered body strength exists in the actual sintering process. strength. strength.Therefore, Therefore,such suchaamechanism mechanismby bywhich whichthe theMg Mginfluences influencesthe thesintered sinteredbody bodystrength strengthexists exists In area in contact with the dolomite, the relatively high Mg content increases the liquid phase in the actual sintering process. In the area in contact with the dolomite, the relatively high Mg content in the actual sintering process. In the area in contact with the dolomite, the relatively high Mg content viscosity, leadsphase to a porous structure. becomes a limiting link ofarea the strength increases the viscosity, which leads to porous structure. Then, this becomes increaseswhich the liquid liquid phase viscosity, whichThen, leadsthis to aaarea porous structure. Then, this area becomesofaa the sintered limiting link of limiting linkbody. ofthe thestrength strengthof ofthe thesintered sinteredbody. body.
Figure 11. SEM micrographs of typical BF-re sample. typical BF-re sample; (b) local Figure Figure11. 11.SEM SEMmicrographs micrographsof ofaaatypical typicalBF-re BF-resample. sample. (a) (a) Graph Graph of ofaaatypical typicalBF-re BF-resample; sample;(b) (b)local local enlarged graph 1;1;(c) (c) local enlarged graph 2.2. enlarged enlargedgraph graph1; (c)local localenlarged enlargedgraph graph2.
Region Region region region11 region region22
Table 4. Element composition of region 1 and region 2 (wt%). Table Table4.4.Element Elementcomposition compositionof ofregion region11and andregion region22((wt% wt%).). Region Fe O Si Al Mg Ca
Fe Fe region 1 60.15 60.15 region 2 55.34 55.34
O O
60.15 17.26 17.26 17.26 55.34 15.81
15.81 15.81
3.3.5. 3.3.5.Mg MgDistribution DistributionCharacteristics Characteristicsin inIN-re IN-re
Si Si 6.76 6.76 6.76 6.41 6.41 6.41
Al Al
1.97 1.970.73 1.97 1.88 4.49
1.88 1.88
Mg Mg
13.13 0.73 0.73 16.07
4.49 4.49
Ca Ca 13.13 13.13 16.07 16.07
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As Asmentioned mentioned above, above, the the Mg Mg content content in inthe theIN-re IN-reisishigher higherthan thanthat thatof ofSI-ore. SI-ore.The Themechanism mechanism of influence of this extra Mg content on the strength of the sintered body is worth studying. of influence of this extra Mg content on the strength of the sintered body is worth studying. Typical Typical IN-re IN-resamples sampleswere wereselected, selected,mounted, mounted,and andpolished polishedinto intoaalight lightsheet. sheet. Its Its morphology, morphology,as asseen seenunder under the SEM, is shown in Figure 12a, and the local enlarged graph is shown in Figure 12b. The minerals the SEM, is shown in Figure 12a, and the local enlarged graph is shown in Figure 12b. The minerals of consist of of the the gray graySFCA SFCAand andwhite, white,bright bright iron oxide. Additionally, porosity of of this this area area consist iron oxide. Additionally, the the porosity of this this IN-re sample is relatively highthe and the interconnected irregular pores are dominant, which IN-re sample is relatively high and interconnected irregular pores are dominant, which indicates indicates the insufficiency of the liquid phase. The chemical composition of the SFCA and iron oxides the insufficiency of the liquid phase. The chemical composition of the SFCA and iron oxides in in Figure 12b were obtained by EDS toto try to clarify the reason forinsufficiency the insufficiency the liquid Figure12b were obtained by EDS to try clarify the reason for the of the of liquid phase. phase. As is shown in Table 5, the Ca content of SFCA and the Mg content in the iron oxide region As is shown in Table 5, the Ca content of SFCA and the Mg content in the iron oxide region are as are as as high as 26.06 2.08% respectively. Thus, amount calciumflux fluxisis sufficient sufficient and high 26.06 and and 2.08% respectively. Thus, thethe amount of ofcalcium and not not responsible responsiblefor forthe theinsufficiency insufficiencyof ofliquid liquidphase. phase.A Aconceivable conceivablereason reasonisisthat thatmassive massiveMgO MgOdissolving dissolving in inthe themagnetite magnetitehinders hindersthe theoxidation oxidation of ofmagnetite magnetite to to hematite hematite [20], [20],then thenthe theforming formingof ofSFCA SFCAwas was blocked. Therefore, preventing the oxidation of magnetite is another mechanism through which blocked. Therefore, preventing the oxidation of magnetite is another mechanism through whichthe the Mg Mg reduces reduces the the formation formation of of the the liquid liquid phase, phase, leading leading to to aa decline decline of of sintered sintered body body strength strength in in the the actual actualsintering sinteringprocess. process.
Figure 12. SEM micrographs of a typical IN-re sample. (a) Graph of a typical BF-re sample; (b) local Figure 12. SEM micrographs of a typical IN-re sample. (a) Graph of a typical BF-re sample; (b) local enlarged graph. enlarged graph. Table 5. Element composition of point 1 and point 2 (wt%).
Table 5. Element composition of point 1 and point 2 (wt%). Point Fe O Si Al Mg Ca
Point pointFe 1 67.50 O 29.20 point 1 point 67.50 29.2017.41 2 48.71 point 2 48.71 17.41
Si 0.06 0.06 5.61 5.61
Al 0.29 0.29 1.58 1.58
2.08 Mg0.87 0.63 2.08 26.06
0.63
Ca 0.87 26.06
4. Conclusions 4. Conclusions Through the study of the macroscopic flow direction and microscopic distribution of magnesium Through the study of the knowledge macroscopic direction and microscopic distribution of in sintered products, the following wasflow obtained. magnesium in sintered products, the following knowledge obtained. In the main sintered products, the Mg contents are in thewas following increasing order: SI-ore, IN-re, In theInmain products, Mg contents are2 in the following INand BF-re. IN-resintered and BF-re, the Mgthe content of the 1 to mm grain size is increasing the highest,order: whichSI-ore, is related re, and BF-re. In IN-re and BF-re, the Mg content of the 1 to 2 mm grain size is the highest, which is to the granular distribution of the magnesia fluxes. related to the granular distribution of the magnesia fluxes. The solid solution characteristics of Mg in various minerals are different and their order from The solid solution characteristics Mg insilicate, various minerals areMg different and their easy to difficult to dissolve is magnetite,ofSFCA, and hematite. dissolving in theorder SFCAfrom has easy to difficult to dissolve is magnetite, SFCA, silicate, and hematite. Mg dissolving in the SFCA has a tendency to make the SFCA morphology coarse. The diffusion range of the Mg in large dolomite a tendency to make the SFCA morphology coarse. The diffusion range of the Mg in large dolomite particle is much narrower than that of Ca, and the Mg mainly stays at the position where the dolomite is much narrower than that of Ca, and the Mg mainly stays at the position where the dolomite isparticle located. is located. Two mechanisms through which Mg reduces the strength of the sintered body exist simultaneously through which the strength the viscosity sintered and body exist in theTwo actualmechanisms sintering process. On one hand,Mg the reduces MgO increases the liquidofphase reduces simultaneously in the actual sintering process. On one hand, the MgO increases the liquid phase viscosity and reduces the consolidation range of liquid phase. On the other hand, Mg2+ entering the magnetite crystal lattice hinders the oxidation of magnetite, thereby blocking the formation of SFCA.
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the consolidation range of liquid phase. On the other hand, Mg2+ entering the magnetite crystal lattice hinders the oxidation of magnetite, thereby blocking the formation of SFCA. Author Contributions: Conceptualization, S.W. and W.Z.; Data curation, S.W.; Formal analysis, W.Z.; Funding acquisition, S.W.; Investigation, W.Z.; Methodology, W.Z.; Project administration, S.W.; Resources, S.W.; Software, M.K.; Supervision, S.W.; Validation, W.Z., M.K. and H.Z.; Visualization, W.Z.; Writing—original draft, W.Z.; Writing—review & editing, S.W. Funding: This work was supported by the National Natural Science Foundation of China (Grant Number 51804027), the China Postdoctoral Science Foundation (Grant Number 2017M610769). Acknowledgments: The authors would like to thank the financial support of Fundamental Research Funds for the Central Universities (Grant Number FRF-IC-18-010). Conflicts of Interest: The authors declare no conflict of interest.
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