Preparation of Carbon-Containing Iron Ore with Enhanced Crushing

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Preparation of Carbon-containing Iron Ore with Enhanced Crushing Strength from Limonite by Impregnation and Vapor Deposition of Tar Recovered from Coke Oven Gas Yuuki Mochizuki, Megumi Nishio, Naoto Tsubouchi, and Tomohiro Akiyama Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00651 • Publication Date (Web): 14 Jul 2016 Downloaded from http://pubs.acs.org on July 14, 2016

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Preparation of Carbon-containing Iron Ore with Enhanced Crushing Strength from Limonite by Impregnation and Vapor Deposition of Tar Recovered from Coke Oven Gas Yuuki Mochizuki, Megumi Nishio, Naoto Tsubouchi *, Tomohiro Akiyama Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan *Corresponding author: [email protected] Highlight ・Mesopores were filled with carbonaceous materials by impregnation and vapor deposition of tar. ・High-carbon composites were obtained by both methods. ・Crushing strength was improved by depositing tar-derived carbonaceous materials. Abstract The optimum conditions for preparing carbon-containing iron ore (composites), in which coke-oven-gas-(COG)-tar-derived carbonaceous materials completely filled the pores in Indonesian limonite (IL), are investigated using impregnation (IM) and vapor deposition (VD). A peak around 2 nm is observed in the pore-size distribution profiles for the as-received IL and IL absolutely heated to a predetermined temperature. The intensity of the peak decreased with increasing ratio of tar to IL (tar/IL) for the IM-prepared composites, and it completely disappeared for the composites prepared with tar/IL > 1.0; the corresponding SBET and VBJH are < 1 m2/g and < 0.01 cm3/g, respectively. The peak at 2 nm in the pore size distribution profiles for the VD-prepared composites almost disappears for treatment times longer than 60 min for any combination of conditions for tar pyrolysis temperature (TPT) and VD temperature (VDT). The composite prepared using a combination of TPT-VDT = 700-350 oC for 60 min shows the highest carbon content and crushing strength. The C content and crushing strength of the IM- and VD-prepared composites increase with increasing in tar/IL and VD time. The composite prepared with tar/IL= 3.0 and VD time = 240 min shows a C content and crushing strength of 48-50 wt%-dry and 10 daN, respectively. The cross-sectional analyses of composite particles prepared using both methods show that the tar-derived carbonaceous materials has completely filled the pores. 1

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Key words: Low rank iron ore, Limonite, Carbon, COG tar, Crushing strength, Composite

1. Introduction In Japan, the iron/steel-making industry faces many challenging problems. Among the most important are the consumption of large quantities of energy, the depletion of and /or increasing prices of resources, and the emission of large amounts of CO2. Thus, there is a demand to develop technology that can simultaneously solve all three. It is believed that reducing the temperature of the thermal reserve zone will reduce the CO2 emission and/or energy consumption of blast furnaces [1]. Therefore, it is very important to develop of iron-making materials showing rapid reduction reactivity. On the other hand, iron materials having a low reduction disintegration index (RDI) are required for use in blast furnaces because in the upper part of a blast furnace, reduction disintegration occurs owing to the reduction of hematite to magnetite in lump/sinter iron ores - which volumetrically expand causing permeability loss in the blast furnace [2]. In general, it is believed that low-RDI lump/sinter iron ores have high crushing strength and low reducibility. It is thus very important to develop low-RDI and high–reducibility iron materials for making iron in blast furnaces. On the other hand, it is necessary to develop methods of effectively using low-rank materials such as limonite, lignite and/or biomass in iron making to solve the resource problem. In an effort to simultaneously solve all three problems, low-rank carbonaceous materials and iron ore have been used to produce carbon-containing iron ores by impregnation and/or chemical vapor infiltration (CVI) [3-8]. Although such carbon-containing iron ores have rapid reduction reactivity, their crushing strength has not been researched so far. In addition, the carbon content of CVI-prepared samples is very low (3-5 wt%-dry), and the complete filling of pores with carbonaceous materials is very difficult to achieve using the experimental conditions proposed in References [6-8]. Our research group has been investigating the production of carbon-containing pellet/sinter by coke oven gas (COG) tar impregnation, and it has been clarified that 2


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the carbonaceous materials derived from COG tar could be completely filled into pores in samples [9-11]. In addition, it has been found the composites have high crushing strength and high reducibility, and the composites could be assumed as having low RDI. If a composite containing large amounts of carbon in limonite pores can be prepared by using COG, including gaseous tar from coke making and/or the pyrolysis of biomass or lignite, the resulting composite by vapor deposition of gaseous-tar can be applied to various iron-making methods (e.g., providing material for sintering machines and electric furnaces whereas conventional iron materials can only be used in blast furnaces) because carbon-containing composites are good energy carriers and/or sources. In this study, therefore, we first investigated the optimum conditions for preparation of high crushing strength composites in which COG-tar-derived carbonaceous materials completely filled the pores in limonite by impregnation (IM) and vapor deposition (VD). The IM method was used to compare the results of VD because it has been found that IM can completely fill the mesopore in the cold-bonded pellets with carbonaceous materials in our previous work [11]. The particle distribution of the carbonaceous materials and the crushing strength of the composites were then investigated against IM- and VD-prepared composites.

2. Experimental 2.1. Samples Indonesian limonite (IL), a low-rank iron ore, consisting of 3.4-4.0 mm particles was used in this study. The composition of the dry basis limonite was Fe, 43; Si, 3.2; Al, 1.8; Ni, 1.1; and Mg, 0.6 wt%. COG tar recovered from a commercial coke oven was used as the carbon source. The composition of the dry ash-free (daf) basis was C, 91; H, 5.3; N, 1.1; S, 0.5; and O, 2.1 wt%. The O content of the tar was estimated by difference. The iron form in the IL was goethite (α-FeOOH), as determined by powder X-ray diffraction (XRD), and its content was calculated based on a dry sample as 68 wt%. The other minerals except for SiO2 were not detected by XRD. The specific surface area (SBET) and pore 3


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volume (VBJH) values of the IL were 75 m2/g and 0.15 cm3/g, respectively. The tar composition was investigated by sequential extraction with toluene (T) and methanol (M), which have different Hildebrand solubility parameters δ=18.2 and 29.7 (MPa)0.5, respectively [12,13]. TS, TI, TI–MS, and TI–MI were 85, 15, 7, and 8, respectively, where, “S” and “I” mean “soluble” and “insoluble”, respectively. According to previous work, COG tar consists of a mixture of 2-9 ring aromatic compounds [14].

2.2. Preparation of composites by IM The IM composites were prepared in a quartz reactor (internal diameter (i.d.) : 38 mm) following the method described in References [9-11]. An alumina cell was charged with 0.5 g of IL and then a predetermined amount of tar was loaded into the cell. The mass ratio of tar to IL (tar/IL) was varied from 0 to 4.0. The mixture was then pyrolyzed at 10 oC/min to 500 oC in helium under ambient pressure in order to obtain the composites. In the present study, above method was defined as impregnation method.

2.3. Preparation of composites by VD Fig. 1 illustrates the VD apparatus. The composites were prepared in a cylindrical flow-type fixed-bed quartz reactor consisting of tar pyrolysis (TP) (i.d., 27 mm) and gaseous-tar-to-IL vapor deposition (VD) (i.d., 17 mm) sections. A toluene solution containing 50 wt% tar was first pumped at 0.4 mL/min onto quartz wool in the upper part of the reactor by high-performance liquid chromatography (HPLC) pump (JUSCO, PU-980). Helium was loaded at 200 mL/min as an inert carrier gas. The mixture was pyrolyzed on the wool to generate tar-containing pyrolysis gas. The tar pyrolysis temperature (TPT) ranged from 350 to 700 oC. The generated gas was continuously loaded onto 2.0 g of IL in the VD section. The height of the IL phase, including the space between the particles, was approximately 30 mm. The vapor deposition temperature (VDT) was varied between 4


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350 and 600 oC. The experimental run was started after the TPT and VDT had reached a predetermined temperature in the helium. The VD was varied from 10 to 240 min to prepare the composite. In this work, the combination of TPT and VDT is abbreviated as TPT-VDT.

2.4. Characterization The pore structure of the samples was measured using N2 adsorption analysis (QUANTACHROME, NOVA1200e). The samples were first dried at 108 oC under vacuum for 1 h in a glass cell and then high-purity N2 (>99.9999 %) gas was adsorbed/desorbed in liquid nitrogen of -196 oC. The specific surface area and the pore volume were estimated using the BET and BJH methods, respectively. The analysis was repeated to ensure that the results could be reproduced. XRD measurements were performed using a conventional powder diffraction apparatus (SHIMADZU, XRD6000) with Mn-filtered monochromatized Fe-Kα radiation generated at 40 kV and 30 mA. Crushed samples were first loaded into a glass holder, and the XRD patterns were collected for 2θ over the range 20-70 o at 2 o/min in steps of 0.01 o. For the thermogravimetric (TG) analysis (ADVANCED RIKO, TGD9000), samples were placed into a platinum pan and heated at 10 °C/min to 1000 °C in a helium stream flowing at 200 mL/min. The carbon form in the prepared composites was examined using a Raman spectrometer (RENISHAW, WOTTON-UNDER-EDGE) equipped with a charge-coupled device (CCD) detector. The samples were scanned using a laser excitation wavelength of 532 nm and a 20 × objective lens. The laser power was set below 7.5 mW, and samples were only exposed to the laser for 10 s to prevent irradiation damage. The spectra were collected in the range of 900-2000 cm-1. The obtained spectra were fitted to a curve according the method described in a previous report in order to determine the carbon forms in the composites [15]. The carbonaceous materials deposited in the prepared composites were analyzed using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS) (JEOL, JSM-7400F) probe operated at 15 eV and an acceleration of 3 nA. SEM-EDS samples were prepared by filling composite particles with a 5


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low-melting alloy and then polishing the cross-sections of the filled particles with sand paper. The carbon content in the prepared composites was determined using an elemental analyzer (LECO, TRUSPEC-CHN) employing combustion method defined in Japanese Industrial Standard (JIS M 8813). The crushing strength, which is the maximum load (daN) at the breaking point of a material, of the particulate samples was determined using a tensile and compression testing machine (MINEBEA, LTS-500NB) according to the method defined JIS M 8718. In this examination, it was difficult to stably reproduce the crushing strength data because the IL particles were heterogeneous. Therefore, the crushing strength was measured 10-20 times per sample, and the average crushing strength and the associated standard deviation are presented.

3. Results and discussion 3.1 Change in IL pore structure with heat treatment Fig. 2 shows the changes in the pore-size distribution and the SBET and VBJH for the as-received IL heated in helium. The 2 nm-peak intensity increased beyond 350 oC and then decreased with increasing temperature above 800 oC. The SBET of the as-received IL significantly increased above 300 oC to a maximum of 135 m2/g at 350 oC and decreased to 115 m2/g at 500 oC. On the other hand, VBJH increased above 250 oC to a maximum of 0.23 cm3/g in the range 400-800 oC (Fig. 2b). The changes in the iron form with heating temperature were determined by XRD, and the results are summarized in Table 1 and Figure S1 in the Supporting Information. Peaks attributed to α-FeOOH in the as-received IL were observed until 250 oC, and weak signals attributed to Fe2O3 were observed beyond 300 oC. SBET increased with increasing temperature in this range of iron transformation temperatures. The thermogravimetric and derivative curves of the as-received IL were measured while the samples were heated under helium and are shown in Figure S2 in the Supporting Information. The IL sample started losing weight above 100 oC, and the derivative curve of the relative weight showed the main peak around 250 oC. As is well known, heated α-FeOOH decomposes into Fe2O3 and H2O, 6


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and pores form around 250-400 oC owing to the dehydration ofα-FeOOH in limonite [16]. Therefore, limonite dehydration caused the pores to develop, which affected SBET and VBJH accordingly.

3.2. Pore structure and iron form in IM-prepared composites Fig. 3 presents changes in the pore size distribution, SBET and VBJH for the composites prepared using IM with different tar/ILs. When the IL was absolutely heated to 500 oC in helium (denoted as He/500) (Fig. 3a), the intensity of the pore-size-distribution peak around 2 nm increased. On the other hand, the peak intensities for the composite obtained from tar/IL = 0.1 drastically decreased, whereas the intensities of the peak ≥ 8 nm did not significantly change. The peak intensities at 2 nm for the composites obtained from tar/IL = 0.5 slightly decreased and significantly decreased > 3 nm. Almost no pore-size peaks were observed for tar/IL ≥ 1.0. SBET for He/500 significantly decreased with increasing tar/IL to < 1 m2/g for tar/IL = 2.0 (Fig. 3b). VBJH exhibited a trend similar to SBET. The TG and derivative curves of the tar used in this study are also shown in Figure S2 in the Supporting Information. When the tar was absolutely heated in helium, the main peak in the derivative curve of the relative weight occurred at around 250 oC, and the tar continued losing weight until 500 oC. The main peaks of the derivative curves corresponding to those of the IL occurred in the same temperature range, suggesting that tar loaded at room temperature can impregnate and/or vapor-infiltrate into the mesopores inherently present in as-received IL or into the mesopores in de-hydrated IL pyrolyzed to 500 oC and that the tar-derived carbonaceous materials can be deposited into the mesopores. In addition, as shown in Fig. 3a, the intensity of the peak attributed to the 2 nm pores initially decreased, and the intensities of those attributed to pores larger than 2 nm decreased to zero with increasing tar/IL, which may indicate that approximately 2 nm tar molecular (i.e., low molecular compositions such as kata-type 2-3 ring aromatic compounds (molecular size: approximately 1.0-3.0 nm)) are first loaded into 2 nm pores and become deposited there and then > 2 nm tar molecules become deposited in > 2 nm pores during pyrolysis. 7


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Table 2 and Figure S3 in the Supporting Information summarize the iron form identified by XRD in the composites prepared using IM at different tar/ILs. Some of the Fe2O3 in the He/500, generated by α-FeOOH de-hydration, was reduced to Fe3O4 in the composite prepared at tar/IL = 0.1. The peak attributed to Fe2O3 was still observed for tar/IL ≤ 0.5, whereas only the XRD signals corresponding to Fe3O4 appeared for tar/IL = 1.0. The changes in the XRD patterns with increasing tar/IL indicate that the iron oxide in the IL was reduced during pyrolysis of the mixture, and this reduction occurs mainly for tar/IL ≥ 1.0. The Fe2O3 may be reduced to Fe3O4 in the composites owing to carbonaceous materials being deposited and/or to the gases generated during TP.

3.3. Pore structure, iron form, and crushing strength of VD-prepared composites The

IL

was

treated

with

tar-containing

gases

by

VD

under

conditions

TPT(350-700 oC)-VDT(350-600 oC) for 60 min. This treatment resulted in a significant decrease or almost disappearance in the intensities of 2-nm pores observed in the IL absolutely heated at 10 oC/min in helium to 350, 500, and 600 oC (denoted as He/350, He/500, and He/600), as shown in Fig. 2. Fig. 4 illustrates SBET and VBJH for the composites prepared by VD for 60 min. SBET and VBJH drastically decreased after VD under different TPT-VDT conditions. SBET and VBJH decreased more at VDT = 350 oC than at 500 and 600 oC and were < 1m2/g and < 0.01cm3/g, respectively, at TPT-VDT = 700-350oC. Fig. 5 shows the XRD patterns for the same composites. As previously mentioned, the XRD pattern for the He/350 only showed a medium-intensity peak attributed to Fe2O3, whereas that for the composite prepared at TPT-VDT = 350-350 oC (Fig. 5a) shows peaks attributed to Fe3O4. The patterns for the TPT(500-700 oC)-VDT(350 oC) composites showed similar peaks. (Figs. 5b, d, g) When the VDT was increased to 500 oC for TPT in the range 500-700oC (Figs. 5c, e, h), the Fe2O3 in the composites was completely reduced to Fe3O4. At TPT-VDT = 600-600 oC (Fig. 5f), the XRD signals corresponding to Fe3O4 were extremely weak and peaks attributed to FeO, α-Fe, and Fe3C appeared. 8


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Furthermore, the pattern for the composite prepared at TPT-VDT = 700-600 oC also showed peaks attributed to FeC, as shown in Fig. 5i. Fig. 5i also shows that the peak corresponding to α-Fe is more intense than that in the pattern for TPT of 600 oC (Fig. 5f), even at the same VDT. The production of metallic Fe indicates that the iron oxides in the samples were reduced by the carbonaceous materials deposited in pores and/or by the pyrolyzed gases. In addition, the formation of iron carbides (Fe3C and FeC) suggests that a solid-solution phase had formed between the deposited carbonaceous materials and the metallic Fe reduced from the iron oxides during tar VD. Therefore, longer reaction times (i.e., ≥ 60 min) at TPT and VDT ≥ 600 oC may favor the formation of iron carbides and α-Fe. The carbon content and crushing strength of the composites were determined in order to identify the optimum conditions for producing high strength composites. The C content of the composites prepared at various TPT-VDTs for 60 min was approximately 15-20 wt%-dry, except for those prepared at TPT-VDT = 350-350 oC (10 wt%-dry C) and 700-350 oC. The composite prepared at TPT-VDT = 700-350 oC showed the highest C content (30 wt%-dry). Fig. 6 presents the crushing strengths of the composites prepared at various TPT-VDTs for 60 min. The strengths (0.7-2.2 daN) of the composites were all higher than that (< 0.5daN) of the as-received IL. The strengths of the composites prepared in the ranges TPT(500-700 oC)-VDT (500-600 oC) were almost identical (i.e., 1.3 daN). The strength increased with increasing TPT at VDT = 350 oC. The composite prepared at TPT-VDT = 700-350 oC showed the highest strength (2.2 daN) of all composites, suggesting that TPT-VDT = 700-350 oC may be the optimum condition for the carbonaceous materials to fill the IL mesopores. The C content and crushing strength were both low for the composite prepared at TPT-VDP = 350-350 oC, which may be because low molecular composition were not generated during TP. When only toluene was used for VD, the crushing strength of the prepared composites was ≤ 1.0 daN, suggesting the single-ring aromatic compounds (approximately < 1.0 nm molecule) had only a slight effect on filling the macro, meso, and micropore in the heated IL. For TPT > 350 oC, the tar was completely pyrolyzed thereby generating low molecular compositions suitable for deposition in the mesopores. Moreover, at heating 9


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temperatures > 350 oC, the SBET of the heated IL decreased with increasing temperature, as shown in Fig. 2, which possibly resulted in low C deposition and low crushing strength for VDTs in the ranges 500-600 oC. According our previous work, the C content and crushing strength of composites tends to decrease with decreasing SBET in the original samples [10]. Therefore, SBET decreasing causes low C deposition and low crushing strength for VDTs in the range 500-600 oC, which may also suggest that carbonaceous material is deposited by cracking among the gaseous-tar molecules formed during pyrolysis and that this mechanism is dominant for TPT(600-700 oC)-VDT(500-600 oC). In particular, the reaction rate is too high at high temperature, so it is possible that C deposition starts from the outer pores and that the deposited C prevents the tar from infiltration into the particle interior. This speculation is supported by the C distributions of composites obtained in the ranges TPT(600-700 oC)-VDT(500-600 oC) because the amount of C deposited on the outside of the particles was greater than that deposited on the inside when the C content of composite prepared at TPT-VDT = 700-350 oC was compared with the C content of the crushed samples. On the other hand, tar vapor diffusion into IL mesopores was dominant at low temperature as well as for VDT = 350 oC, which supports the finding that the C contents and crushing strengths of the composites prepared at TPT-VDT = 700-500 oC and 700-600 oC were lower than those of the composite prepared at TPT-VDT=700-350 oC. Moreover, as previously mentioned, the Fe2O3 in the He/500 and He/600 was reduced to Fe3O4, FeO, and α-Fe, and iron carbides after VD (Fig. 5), which shows that carbon was reduced at the contact area between the deposited carbonaceous materials and the iron oxide in the pores. Therefore, the C contents of the composites prepared at VDTs in the range 500-600 oC may be lower than that of the one prepared at VDT = 350 oC. The iron form is not an important factor in obtaining high-strength composites because the strengths of the composites prepared in the range TPT(700-350 oC)-VDT(600-500 oC) are lower than that of the one prepared at TPT-VDT = 700-350 oC. The aim of this study was to prepare composites in which IM- and VD-prepared tar-derived carbonaceous materials completely filled the pores in limonite. Therefore, the TPT-VDT = 700-350 oC 10


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was used for the subsequent experiments.

3.4. Carbon content and crushing strength of IM- and VD-prepared composites Fig. 7 shows the change in the pore size distribution of the VD-prepared composite for various holding times at TPT-VDT = 700-350 oC. In Fig. 7a, the peak corresponding to the 2-nm pores in He/350 almost disappeared for the composite prepared by VD for 10 min whereas the distribution of pores ≥ 7 nm remained about the same. When the holding time was increased above 10 min, the distribution of 3-10 nm pores steadily declined with increasing holding time, and the mesopores disappeared completely above 60 min. SBET and VBJH (Fig. 7b) of VD-prepared composites also drastically decreased at 10 min to < 1 m2/g and 0.01 cm3/g, respectively, up to 60 min. These results may suggest that gaseous tar first

preferentially filled the filled 2 nm mesopores by vapor infiltration

and then the tar-vapor-derived carbonaceous materials filled the > 2 nm pores only after completely filling the 2 nm pores because the 2 nm pores disappeared before > 2 nm ones, as shown in Fig. 7a. Fig. 8 shows the crushing strengths of the IM- and VD-prepared composites plotted as functions of tar/IL and VD holding time. Although the crushing strengths of the composites barely increased up to tar/IL = 0.5 and VD time = 30 min, they dramatically and linearly increased for tar/IL > 0.5 and VD time > 40 min and then leveled off at 10 daN around tar/IL = 3.0 and VD time = 240 min. The relationship between the C content and the crushing strength (Figs. 8a and b) of the composites was further investigated, and the results are shown in Fig. 9. The crushing strengths of both composites only slightly increased until 20 wt%-dry C, the point at which the C content dramatically increased in Fig. 8a, but they exponentially increased beyond 20 wt%-dry C to 10 daN at 50 wt%-dry C. As previously mentioned, the peak attributed to the 2 nm pores disappeared at 30 wt%-dry C, as shown in Figs. 3a and 7a. Therefore, the tar-derived carbonaceous materials may have first preferentially filled the 2 nm pores and then the crushing strength of the composites may have increased by the tar filling the > 2 nm pores. It is possible that for IM- and VD-prepared composites, the carbonaceous materials 11


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are 1. initially deposited inside particles and are then 2. gradually deposited outward, filling pores along the way. When the mesopores have been completely filled, the carbonaceous materials are then 3. deposited on the outside of the particles. The three differently sloped lines in Fig. 9 may indicate that the carbonaceous materials are deposited in these three steps. The crushing strengths of the IMand VD-prepared composites for tar/IL = 3.0 and VD time = 240 min are comparable to those of coke (95-98 wt%-daf C, 8-14 daN), which has the same particle size fraction and a drum index (DI1506) of 51-87. In addition, the crushing strengths of the composites prepared by both methods are higher than that (2.5 daN) of carbon-containing cold-bonded-pellets (Fe, 34; C, 19; Ca, 9.5; Si, 4.0; Al, 1.9; and Mg, 0.6 wt%-dry), whose particles are the same size as those prepared from iron-making dust and which have been used for blast furnaces, Therefore, the composites prepared by both IM and VD may provide viable alternatives to using the existing cold-bonded-pellets in blast furnaces. Fig. 10 shows the SEM-EDS analyses of cross-sections in the IM- and VD-prepared composites for tar/IL = 3.0 and VD time = 240 min. Figs. 10a and e show SEM images of a cross-section of each sample particle. Figs. 10 b and f present the line analyses for Fe and C in the regions corresponding to the broken lines in Figs. 10a and e. The Fe and C mappings of the cross-section of each samples are also shown in Figs. 10 c, d, g and h. Fe was uniformly distributed at the cross-sections. Although a large amount of C was deposited on the particle surfaces, C was also uniformly deposited in large amounts inside the particles. When the deposited C is hypothesized as amorphous C, a theoretical amount of C filling the pores in IL can be calculated based on VBJH for He/350 or He/500, which produced 40 or 45 wt%-dry C for the IM- and VD-prepared composites, respectively. The actual carbon contents of the IM- and VD-prepared composites were 48 and 46-50 wt%-dry C, respectively, which were significantly higher than the theoretical C contents because of the carbonaceous materials deposited on the particle surfaces. These results suggest that IM and VD can be used to prepare high-strength IL-based composites whose pores are completely filled with tar-derived carbonaceous materials. Further, the results suggest that the strength of the composites depends more on the IL 12


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mesopores being filled with enough carbonaceous materials than on the chemical structure of the carbon and the form of iron form in composite. In other words, the C content and distribution in the IL mesopores is the most important factor in determining the strength of the composites. The composites prepared in the present study will be reduced and investigated in future work.

4. Conclusion The optimum conditions for preparing composites in which tar-derived carbonaceous materials completely filled Indonesian limonite (IL) pores were investigated using tar impregnation (IM) and vapor deposition (VD). The crushing strength of the composites and the distribution of the carbonaceous material were then analyzed and compared against those of the composites prepared using IM and VD methods. The following conclusions are summarized, (1) The pore –size-distribution peak was located around 2 nm, and SBET and VBJH for the as-received IL decreased with increasing tar/IL. The peak attributed to the 2-nm pores almost completely disappeared and SBET and VBJH decreased below 1 m2/g and 0.01 cm3/g, respectively, for the IM-prepared composite when tar/IL > 1.5. (2) The XRD signals attributed to Fe2O3 in the IM-prepared composites completely disappeared and were replaced with only signals attributed to Fe3O4 when tar/IL > 1.5. (3) When the as-received IL was treated by VD at different combinations of tar pyrolysis temperature (TPT)( 350-700 oC) and vapor deposition temperature (VDT) (350-600 oC) for 60 min, the composite prepared using the TPT-VDT combination of 700-350 oC showed the highest carbon content and crushing strength. The pore-size-distribution peak located at 2 nm, SBET and VBJH for the original sample drastically decreased after VD. (4) For tar VDT = 350 oC, only part of the Fe2O3 in the samples was reduced to Fe3O4 whereas for tar VDT = 500 oC, the Fe2O3 was completely reduced to Fe3O4 regardless of the pyrolysis temperature. On the other hand, FeC, Fe3C, and α-Fe were formed at TPT = 700 oC and VDT = 500-600 oC. 13


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(5) The carbon contents and crushing strengths of the IM- and VD-prepared composites increased with increasing tar/IL and VD time to 50 wt%-dry C and 10 daN when tar/IL ≥ 3.0 and VD time = 240 min, respectively. (6) The tar-derived carbonaceous material was detected on the composite particle surface as well as inside the particles, and the composite contained 50 wt%-C, which was above the theoretical C content calculated based on the pore volume of the IL heated at 350 and/or 500 oC.

References (1) Sato, T.; Sato, M.; Takeda, K.; Arima, T. Testu-to-hagane, 2006, 92, 1006. (2) Murakami, T.; Kodaira, T.; Kasai, E. ISIJ Int. 2015, 55, 1181 (3) Miura, K.; Miyabayashi, K.; Kawanari, M.; Ashida, R. ISIJ Int. 2011, 51, 1234. (4) Kawanari, M.; Matsumoto, A.; Ashida, R.; Miura, K. ISIJ Int. 2011, 51, 1227. (5) Hata, Y.; Hosokai, S.; Hayashi, J.-i.; Akiyama, T. CAMP-ISIJ 2007, 20, 923. (6) Hata, Y.; Purwanto, H.; Hosokai, S.; Hayashi, J.-i.; Kashiwaya, Y.; Akiyama, T. Energy Fuels 2009, 23, 1128. (7) Hosokai, S.; Matsui, K.; Okinaka, N.; Ohno, K.-i.; Shimizu, M.; Akiyama, T. Energy Fuels 2012, 26, 7274. (8) Cahyono, R.B.; Saito, G.; Yasuda, N.; Nomura, T.; Akiyama, T. Energy Fuels 2014, 28, 2129. (9) Mochizuki, Y.; Tsubouchi, N.; Akiyama, T. Fuel Process. Technol. 2015, 138, 704. (10) Mochizuki, Y.; Nishio, M.; Tsubouchi, N.; Akiyama, T. Fuel Process. Technol. 2015, 142, 287. (11) Mochizuki, Y.; Nishio, M.; Tsubouchi, N.; Akiyama, T. Energy Fuels 2016, 30, 2102. (12) Hildebrand, J.; Scott, R.L., The Solubility of Nonelectrolytes, 3rd Ed. Reinhold, New York, 1950. (13) Mochizuki, Y.; Sugawara, K., Fuel 2011, 90, 2974. (14) Wang, H.; Takarada, T., Fuel Process. Technol. 2003, 81, 247. (15) Li, X.; Hayashi, J.-i.; Li, C.-Z. Fuel 2006, 85, 1700. (16) Naono, H.; Fujiwara, R. J. Colloid Int. Sci., 1980, 73, 406.

Tables and Figure captions Fig. 1 Scheme of apparatus for vapor deposition of tar Fig. 2 Changes in pore size distribution (a), SBET and VBJH (b) of IL with heating temperature. Fig. 3 Changes in pore size distribution (a), SBET and VBJH (b) of composites prepared by IM with tar/IL. 14


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Fig. 4 Changes in SBET and VBJH of composites prepared by VD with combinations of different TPT-VDT for 60 min. Fig 5 XRD patterns of composited prepared by VD at combination of different TPT-VDT. TPT-VDP : (a) 350-350 oC, (b) 500-350 oC, (c) 500-500 oC, (d) 600-350 oC, (e) 600-500 oC, (f) 600-600 oC, (g) 700-350 oC, (h) 700-500 oC, (i) 700-600 oC. Fig. 6 The crushing strength of composites prepared by VD at different combinations of TPT-VDT for 60 min. Fig. 7 Change in pore distribution (a), SBET and VBJH (b) of composites prepared by VD with treatment time at TPT-VDT of 700-350 oC. Fig. 8 Changes in carbon contents (a) and crushing strength (b) of composites prepared by IM with tar/IL and VD with holding time. Fig. 9 Relationship between carbon content and crushing strength of composites prepared by IM and VD. Fig. 10 SEM image (a, e), line analyses (b, f) and elemental mapping of Fe and C (c, d, g, h) for the cross-section of the composites prepared by IM at tar/IL of 3.0 and VD time of 240min Table 1Summaries of the iron forms in IL before and after heat treatment in helium Table 2 Summaries of the iron forms in composites prepared by the IM method at different tar/IL.

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Fig. 1 Scheme of apparatus for vapor deposition of tar

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Fig. 2 Changes in pore size distribution (a), SBET and VBJH (b) of IL with heating temperature.

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Fig. 3 Changes in pore size distribution (a), SBET and VBJH (b) of composites prepared by IM with tar/IL.

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Fig. 4 Changes in SBET and VBJH of composites prepared by VD with combinations of different TPT-VDT for 60 min.

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Fig 5 XRD patterns of composited prepared by VD at combination of different TPT-VDT. TPT-VDP : (a) 350-350 oC, (b) 500-350 oC, (c) 500-500 oC, (d) 600-350 oC, (e) 600-500 oC, (f) 600-600 oC, (g) 700-350 oC, (h) 700-500 oC, (i) 700-600 oC.

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Fig. 6 The crushing strength of composites prepared by VD at different combinations of TPT-VDT for 60 min.

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Fig. 7 Change in pore distribution (a), SBET and VBJH (b) of composites prepared by VD with treatment time at TPT-VDT of 700-350 oC.

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Fig. 8 Changes in carbon contents (a) and crushing strength (b) of composites prepared by IM with tar/IL and VD with holding time.

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Fig. 9 Relationship between carbon content and crushing strength of composites prepared by IM and VD.

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Fig. 10 SEM image (a, e), line analyses (b, f) and elemental mapping of Fe and C (c, d, g, h) for the cross-section of the composites prepared by IM at tar/IL of 3.0 and VD time of 240 min

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Table 1 Summaries of the iron forms in IL before and after heat treatment in helium Fe species by XRD measurement a Heating temperature, oC As-received IL

200

250

α-FeOOH (s)

α-FeOOH (s)

α-FeOOH (m)

a

300 α-FeOOH (vw) Fe2O3(vw)

350

400

450

500

Fe2O3(m)

Fe2O3(m)

Fe2O3(m)

Fe2O3(m)

XRD intensities designated as vw (very weak), w (weak), m (medium), s (strong)

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Table 2 Summaries of the iron forms in composites prepared by the IM method at different tar/IL. Fe species by XRD measurement a Mixture ratio of tar to IL 0 Fe2O3(m) a

0.1

0.25

0.5

Fe2O3(m) Fe2O3(m) Fe2O3(vw) Fe3O4(w)

Fe3O4(w)

Fe3O4(m)

1.0

1.5

2.0

3.0

4.0

Fe2O3(m) Fe2O3(m) Fe2O3(m) Fe2O3(m) Fe2O3(m)

XRD intensities designated as vw (very weak), w (weak), m (medium)

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Preparation of Carbon-Containing Iron Ore with Enhanced Crushing

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