A novel method for Fe-Al2O3 composites prepared from high sulfur Bayan Obo iron concentrate: Effectively eliminate the emission of SO2

Journal Pre-proof A novel method for Fe-Al2 O3 composites prepared from high sulfur Bayan Obo iron concentrate: Effectively eliminate the emission of SO2 Yuxin Chen, Saiyu Liu, Shunli Ouyang, Yu Shi, Baowei Li

PII:

S0304-3894(19)31832-1

DOI:

https://doi.org/10.1016/j.jhazmat.2019.121878

Reference:

HAZMAT 121878

To appear in:

Journal of Hazardous Materials

Received Date:

10 September 2019

Revised Date:

3 December 2019

Accepted Date:

9 December 2019

Please cite this article as: Chen Y, Liu S, Ouyang S, Shi Y, Li B, A novel method for Fe-Al2 O3 composites prepared from high sulfur Bayan Obo iron concentrate: Effectively eliminate the emission of SO2 , Journal of Hazardous Materials (2019), doi: https://doi.org/10.1016/j.jhazmat.2019.121878

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A novel method for Fe-Al2O3 composites prepared from high sulfur Bayan Obo iron concentrate: Effectively eliminate the emission of SO2

Yuxin Chen a,b , Saiyu Liu c , Shunli Ouyang a, Yu Shi a,b, Baowei Li a,*,

Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Inner Mongolia University of

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a

Science and Technology, Baotou 014010, China b

School of Material and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China

c School

of Science, Inner Mongolia University of Science and Technology, Baotou 014010, China

*corresponding author.

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E-mail address: [email protected] (Baowei Li)

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Graphical Abstract

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Highlights:

Fe-Al2O3 composites were prepared by using iron concentrate and bauxite.

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No sulfur dioxide is discharged during sintering.

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Sulfur is precipitated in the samples as the form of FeS or MnS.

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Mechanical properties and acid resistance were effectively improved by

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MnS instead of FeS.

Abstract 2

Fe-Al2O3 composites with different carbon contents were prepared by reactive sintering from high sulfur iron concentrate, bauxite, Al2O3 powder mixture. The effects of different carbon contents on emission form of sulfur were studied. The thermo gravimetric-infrared radiation results showed there were no gaseous compounds containing sulfur discharged during the sintering except CO2 and H2O. It is indicated that sulfur precipitates around the metal phase in the form of sulfide by the phases and microstructures analysis. And with an increase in carbon contents, sulfide gradually transformed from FeS to MnS. The mechanical properties and acid resistance of

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materials can be improved by MnS rather than FeS. Samples with higher carbon content had optimal physical and chemical properties with bending strength of 295MPa,

hardness of 13.0 GPa, acid resistance of 94.89% and alkali-resistance of 98.45%. This study provides a novel cleaner method for the high sulfur iron concentrate that avoids

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the emission of sulfur-containing substances while ensuring the performance of the composite.

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Keywords: iron concentrate, sulfur dioxide, emission reduction, clean technology

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1.Introduction

Although China is rich in iron ore reserves, with its complexity of metallogenic conditions and variety of ore deposits, the grade of most iron ore is low and tends to

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contain sulfide ore [1- 3], such as pyrite, pyrrhotite or chalcopyrite. Because pyrrhotite and magnetite have similar magnetism, and the natural floatability of magnetite is poor [5]. Therefore, current desulfurization processes at home and abroad cannot remove all

[6,7].

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sulfur in iron concentrate, leading to the inevitable residual sulfur in iron concentrate

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Generally, sulfur content is one of the important indicators to quality measurement

of iron concentrate [8]. In iron and steel production, every 0.1% increase in sulfur content of iron ore, coke ratio goes up by 5%, which will lead to both costly smelting, and harmful effects on blast furnace ironmaking [9]. At the same time, some sulfur will remain in the pig iron. During heat treatment, sulfur-containing pig iron brings about a "hot embrittlement", which will reduce the quality of steel [10,11]. In addition, another part of the sulfur in iron concentrate will be generated in the form of harmful gaseous 3

sulfur compounds [12], by which the steel industry has become one of the major sources of sulfur pollution [13]. At present, air pollution has been considered as one of the common concerns of the world. Gaseous sulfide, as a typical exhaust gas compound, is also among the main culprits of events such as acid rain and optical smoke [14, 15]. Therefore, iron concentrates with a high sulfur content must be desulfurized before smelting [16]. The main desulfurization processes currently used are wet method, semi-dry method, dry method, adsorption method, etc [17, 18], which fail to fundamentally solve sulfur pollution, largely stemming from the following problems [19, 20]. Firstly, high

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equipment investment and operating costs that reduce the economic benefits of

enterprises. Secondly, because magnetite and pyrite have similar magnetism, it is impossible to separate them completely by magnetic separation. Thirdly, there is no efficient use of resources in terminal management, resulting in the waste of natural

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resources. Due to the above problems, the sulfur cannot completely wipe off during the

desulfurization process of iron concentrate before smelting. Table 1 shows the sulfur

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dioxide emissions in different years in China [21], in which industrial sources of sulfur dioxide emissions account for more than 80% of total emissions. Table 2 shows the

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sulfur dioxide emissions of different industries [22]. The sulfur dioxide emissions from ferrous metallurgy are the second largest source of emissions, accounting for more than

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12% of industrial sulfur dioxide emissions.

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Table 1. Sulfur dioxide emissions in China Total sulfur dioxide Year emission/ million tons 2001 19.47 2005 25.49 2011 21.85 2015 18.59

Sulfur dioxide emissions from industrial sources/ million tons 15.66 21.68 18.96 14.00

Table 2. Sulfur dioxide emissions from different industries Industrial sulfur dioxide Industrial sulfur dioxide emission in 2011 emission in 2015 No. Industry Emissions/ Emissions/ proportion proportion million tons million tons Industry in total 18.96 100% 14.00 100% 1 Thermal power 9.01 47.52% 5.06 36.14% 4

3 4 5 6 7 8

2.51

13.24%

1.74

12.43%

2.02

10.65%

2.034

14.53%

1.27

6.70%

1.35

9.64%

1.14

6.01%

1.21

8.64%

0.81

4.27%

0.65

4.64%

1.20

6.33%

0.98

7.00%

1.00

5.27%

0.98

7.00%

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industry Smelting and mangling process of ferrous metal Nonmetallic mineral Chemical engineering Non-ferrous metal Oil industry Paper, food and textile industry Other industry

In summary, the complex desulfurization refers to a prerequisite for high sulfur iron concentrates before smelting. Even so, some of the sulfur remains in the iron

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concentrate, which eventually causes environmental pollution during the smelting

process. This study proposes a novel cleaner process for the treatment of high-sulfur

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iron concentrates. According to the previous work, we believe that it is not limited to the desulfurization process, but a new cleaner means to treat the iron concentrate and

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to prepare a new product. The main advantage of this method is that the composites are directly prepared from minerals and all harmful substances remain in the materials,

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which means no waste residue is generated [23]. It is within the tolerable range if the harmful substance as no or slight influence on the performance of the material. The harmful substances can be effectively solidified in the material to reduce the emission

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of waste gas and waste residue during preparation, forming an environmentally friendly cleaning process. It is well known that alumina (Al2O3) is one of the most famous oxide

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ceramics [24, 25]. With a variety of advantages, such as high melting point, high level of hardness, excellent heat and corrosion resistance and good electrical insulation [26]. Meanwhile, high grade bauxite contains about 90% alumina. In order to make full use of mineral raw materials, bauxite is used to replace part of alumina. The iron concentrate powder is mixed with the bauxite powder and the reducing agent is added to prepare the Fe-Al2O3 composite material, which has the hardness of the ceramic and 5

the toughness of the metal, and can be effectively used as an inexpensive wear-resistant material in the metallurgy, construction and other industries [27]. 2.Materials and methods 2.1 Materials Fig.1 shows the X-ray diffraction (XRD) patterns of the high sulfur Bayan Obo iron concentrate powder and bauxite. The main mineral phases were Fe3O4, Fe2O3, and bauxite mainly contains Al2O3 and TiO2. Other chemicals (Al2O3 and activated carbon)

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were supplied by Macklin as analytical grade reagents.

Fig. 1 X-raw diffraction patterns of iron concentrate and bauxite

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2.2 Preparation of composite samples The components of Fe-Al2O3 composites were shown in Table 2. The raw materials were mixed in a ball milling for 6h at 250 rpm, with a ball powder ratio of 5:1. Anhydrous ethanol was added as the ball milling medium. The mixed slurry was dried at 95℃ for 24 h. Samples were formed by pressing in a hydraulic machine at a pressure of 25- 30MPa. The shaped samples were fired in a pressureless sintering furnace with 6

argon as a protective atmosphere, the gas flow was 50ml/min. The sintering temperature was 1380℃ with heating rate of 3℃/min and under holding time of 240 min. Fig.2 shows the flowchart of preparing composites from high sulfur Bayan Obo iron concentrate and bauxite. Fig. 3 shows the appearance of the samples C1-C5. It can be seen that sample C5 has undergone obvious deformation. It indicates that the carbon content of sample C5 is too high under this process condition. Therefore, only samples C1-C4

Table 1. Chemical composition of raw materials (wt%) Fe2O3

FeO

SiO2

CaO

MgO

K2O

Na2O

MnO2

S

Al2O3

REO

TiO2

Ig

60.29

25.1

2.13

1.00

0.65

0.14

0.15

2.76

2.67

0.5

1.2

—

3.41

Bauxite

1.84

—

4.71

0.23

0.26

—

—

—

0.7

88.54

—

3.72

—

Alumina

0.1

—

0.2

—

—

—

0.1

—

99.5

—

0.1

—

Iron

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concentrate

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have been studied.

Table 2. The mixture proportion of Fe-Al2O3 composites (wt%)

Bauxite

Al2O3

41 40 39 38 37

23 22 21 20 19

27 26 25 24 23

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Iron concentrate

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Sample number C1 C2 C3 C4 C5

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Activated carbon 9 12 15 18 21

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2.3 Instruments

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Fig.3 The Fe-Al2O3 samples C1-C5

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Fig.2 Flowchart of preparing composites from Bayan Obo iron concentrate

The mineralogical and chemical compositions of the Fe-Al2O3 composites were determined by X-ray diffractometer (XRD), model X’pert Pro. The chemical contents

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were measured on an X-ray fluorescence spectrometer (XRF, ARLAdvant’ X 3600). The morphology and the elemental distribution of the samples were analyzed with a

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Scanning Electron Microscope (SEM, SUPRA 55), equipped with energy dispersive spectrometer (EDS, X-max 20) and electron backscatter diffraction (EBSD, Nordlys

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Nano) images analysis system. Density values of the sintered samples were measured in distilled water using the

Archimedes principle. Linear shrinkage (LS) was determined using the length difference between the green (L1) and the fired sample (L2), and calculated as shown in Eq. (1): 𝐿𝑆(%) = 100 × (𝐿1 − 𝐿2 )/𝐿1

(1)

Vickers Hardness tester was used to measure the hardness of the Fe-Al2O3 8

composites. The bending strength was measured by the three-point method (on specimens 3mm × 4mm × 30mm in size). Corrosion experiments were carried out by using Chinese standard JC/ T258-93. In order to determine the reaction process, thermal analysis was carried out in a differential scanning calorimeter (DSC, Mettler Toledo) instrument using 20 mg powder that after ball milling. The DSC analysis was done in a N2 atmosphere with heating rate of 10°C/min. Thermo gravimetric-infrared radiation (TG-IR, Mettler Toledo -Thermo Nicolet

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6700) technology was used to analyze the composition of reaction sintering gas. 1h of

argon was passed before the test to eliminate air interference, gas flow rate was 25ml/min.

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3. Results and discussion

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3.1 Sintering process

Fig. 4 The DSC results of samples C1-C4

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Fig. 5 The TG results of samples C1-C4

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DSC analysis was carried out to study the sintering process of Fe-Al2O3 composite. Since more attention for sulfur was drawn in this study, the composition of the gas

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product during sintering was analyzed by TG-IR to determine if gaseous sulfide was produced. Fig. 4 shows the DSC results of samples C1-C4, while Fig. 5 shows the TG

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results of samples C1-C4. As can be seen in Fig. 4, no reaction is detected up to 665°C in DSC curve, while Fig. 5 shows a slight drop in the TG curve before 665 °C. This should only be the removal of free water and crystal water in the system, so there is no

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thermal disturbance to the system. At 665 °C, an exothermic reaction is detected, while the slope of the TG curve has varied slightly at 668°C. Combined with the

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characteristics of the system, this reaction is related to the reduction of Fe2O3 by activated carbon [28]. Due to the low Fe2O3 content in the system, resulting the tiny changes of heat flow and weight loss rate moves were detected. After this exothermic reaction, an endothermic reaction occurs at 910 °C. It can be found from the TG curve that following 870 °C around, the slope of the curve becomes large, which shows that the weight loss rate of the system increases significantly. This reaction is related to a 10

large amount of Fe3O4 is reduced to FeO by activated carbon in the system [29]. On the DSC curve, the second endothermic peak appeared at 1010 °C, which should be the reduction of FeO in the system. It can be seen from the DSC curve that the endothermic peak at 1010 ° C of the sample C1 is weak, for which one reason is low carbon content in the sample C1, so the reduced reaction of FeO in the sample C1 is weak [30]. No obvious peaks appeared in the DSC curve after 1015 ℃, indicating that the completed reduction follows this temperature. The TG curve shows that at 1015 ℃, the system still maintains a large weight loss rate, and it phenomenally come down after 1080 ℃.

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In situ TG-IR technology was used to investigate the composition of gas products in sintering process. As the reaction process of the four samples is basically similar,

TG-IR analysis is performed on two extreme samples, namely C1 and C4. Fig.6 shows the 3D TG-IR spectra of samples C1 and C4. As can be seen in the figure that the

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evolved gas products for the samples C1 and C4 exhibit characteristic bands of 6001000 cm-1, 1300-1700 cm-1, 2100-2500 cm-1, 3500-3800 cm-1. According to DSC

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results, infrared results of 500 °C, 700 °C, 900 °C and 1100 °C were selected to illustrate the gas composition in the whole sintering process. Fig. 7 shows the infrared absorption

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spectra of sample C1 at different temperatures and the library spectra of CO2, H2O and SO2. As shown in the figure, only CO2 and H2O are discharged throughout the sintering,

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without gaseous compounds related to sulfur.

DSC analysis shows that no reduction reaction occurs before 665°C. However, TG-IR shows that a small amount of CO2 was discharged at 500°C. This can be

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explained that the reaction of iron oxide with activated carbon generally occurs at 470 °C [31], which is not reflected in the DSC curve for its weakness. A handful of

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water is released at 500 °C, 700 °C, 900 °C and 1100 °C, since the free water and hydration water contained in iron concentrate. The free water can be released at a low temperature, while the hydration water needs a high temperature to be released. Fig. 8 shows the TG-IR results for the sample C4. Even when the carbon content is high, no other gas discharged except CO2. The library spectra of SO2 are shown in Fig.7 and Fig.8, indicating that the infrared 11

peak of sulfur dioxide is 1150 cm-1 and 1360 cm-1 [32-35]. But infrared absorption peaks

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of SO2 fail to find during the sintering of the Fe-Al2O3.

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Fig.6 3D TG-IR spectra of samples C1 (a) and C4 (b)

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Fig. 7 The TG-IR results of sample C1

Fig. 8 The TG-IR results of sample C4

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3.2 Phases and microstructures

The above results indicated that the sulfur was not discharged from the system in form

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of gaseous. It can be inferred that sulfur should be latent in form of sulfur-containing compound in the system. In order to investigate the existing forms of sulfur, the phase identification and microstructure analysis of samples were carried out. XRD analysis for the Fe-Al2O3 samples with different carbon contents can be seen from the Fig.9. The XRD patterns of samples C1-C4 reveal that there are no relevant diffraction peaks of Fe2O3 and FeO. It is indicated that all iron oxides in raw materials 13

were reduced. The diffraction peaks relative to sulfur compounds were not found in

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XRD patterns as the content of sulfide is too low to be detected by XRD.

Fig.9 X-raw diffraction patterns of samples C1-C4

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The microstructure of Fe-Al2O3 composites with different C/O ratios are observed by SEM. Fig. 10 (a)-Fig.10 (d) shows the microstructure of samples C1–C4,

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respectively. The white particles in the figure are metal phase, while the black regions are alumina matrix and glass phase. The microstructure of the four samples show that the metal phases are uniformly distributed in the alumina matrix. In samples C1 and C2,

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the metal phases are irregularly distributed in the ceramic phase. However, in sample C3, part of metal phases is circular or oval. Almost all metal phases are elliptic in

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sample C4. The content of activated carbon in the sample nudges upward, which speeds up carburizing reaction of the metal phase. According to the Fe-C phase diagram, a rise carbon content will lead to the decrease in melting point of Fe-C alloy, and the metal liquid with low melting point has better fluidity. Therefore, as activated carbon content goes up, the metallic phase particles gradually turn into a circle. An interesting phenomenon can also be found in Fig. 10, where there are distinct 14

precipitates around the metal particles, as indicated by the red circle. Moreover, a phenomenon for these precipitates can be observed tangibly. As the content of activated carbon increases in the sample, the size of the precipitates gradually comes down. The precipitates around the metal phases of sample C1 were large size and irregular shape. In the samples C2 and C3, the size of precipitates gradually decreased and transitioned to thin films. In the sample C4, the precipitates were wrapped in a thin film around the

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metal phase.

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Fig.10 SEM images of samples C1 (a), C2 (b), C3 (c) and C4 (d) Fig. 11 shows the EDS results of sample C1, indicating that the precipitates were

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indeed a substance containing sulfur and iron. Fig. 12 shows EDS results of sample C4, and the precipitates largely consist of sulfur and manganese. EDS results cannot serve as an evidence for phase identification since only the distribution of elements can be analyzed. Therefore, the analysis of crystal structure of precipitates is conducted by EBSD. Fig. 13 (a) -(c) shows the EBSD results of the precipitates in sample C1. Through the analysis of the Kikuchi pattern, a hexagonal structure for the precipitate is 15

determined. The distribution of the elements is combined to pin down that the precipitate is FeS. By the same principle, it is concluded that the precipitate refers to MnS according to Fig.13 (d) -(f). Combined with the sintering process analysis mentioned above, it is concluded that the sulfur in the mineral is not discharged in the form of gaseous compounds during the sintering process by studying the precipitates from different samples, but is precipitated around the metal phase in the form of sulfide. It is well known that in the process of steelmaking, sulfur in molten steel will precipitate as sulfide in the cooling process of molten steel [36], which is consistent

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with the formation of sulfide in this study. The main reason for the precipitation of sulfur is that the solubility of sulfur in iron decreases significantly with the solidification of iron [37]. Therefore, the sulfur is bound to precipitate as sulfide when the

temperature drops. Compared with the reduction of iron oxide, manganese oxide is not

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easy to be reduced [38]. Increasing the carbon content of the system causes manganese to be reduced. When manganese is present in the system, sulfur combines with

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manganese instead of iron [39]. Therefore, in this study, with the increase of carbon

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content in the system, more sulfur was precipitated as MnS.

Fig.11 The elemental composition of sample C1

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Fig.12 The elemental composition of sample C4

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Fig.13 The structure and element composition of precipitation in sample C1(a) EBSD pattern; (b) indexed EBSD pattern; (c) EDS spectra; and sample C4 (d) EBSD pattern; (e) indexed EBSD pattern; (f) EDS spectra

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Table 3 shows the XRF results of samples C1-C4. It can be seen that sulfur is present in all four samples, and the content is basically equivalent. It shows that the

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carbon content does not affect the efficiency of sulfur fixation, and most of the sulfur is precipitated in the samples rather than in the gaseous state. This is consistent with the previous analysis. It has been calculated that approximately 96% of the sulfur in the raw materials is fixed in the sample. The iron concentrate treated by the traditional desulfurization process has a desulfurization rate of 50-80% [40]. Flotation is usually used for 17

desulfurization treatment, which will lead to various desulfurization rate depending on different desulfurizer and desulfurization parameters [41]. The other desulfurization treatment is heat treatment. Although the desulfurization ratio of this method was more than 80%, SO2 is discharged and needs to be recycled again [40]. Table 3 The main elements of samples C1-C4 detected by XRF Al2O3

Fe2O3

SiO2

SO3

MnO

CaO

MgO

Na2O

K2O

TiO2

Other

C1 C2 C3 C4

52.74 56.34 55.08 52.62

26.37 24.74 26.78 25.75

10.28 11.00 12.26 13.05

3.15 3.04 3.18 3.16

0.991 1.001 0.982 0.994

0.767 0.900 1.00 1.07

1.08 1.20 1.29 1.41

0.709 0.863 0.931 1.12

0.386 0.440 0.253 0.494

0.118 0.159 0.206 0.241

3.409 3.317 2.038 1.191

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3.3 The infulence of the precipitates

In order to determin the infulence of the precipitates, the crack propagation of samples was analyzed. Fig.14 (a) shows the propagation path of cracks in sample C1, and the

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relevant element distribution is shown below. As can be seen in the figure, when the

crack encounters the metal iron and precipitates, there is no significant impediment to

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the precipitates on the cracks propagation. The crack continues to propagate through the phase interface between FeS and Fe, which means that FeS does not hinder

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propagation of the crack, and even provides the crack with an propagation path for the instability of the phase interface. Fig.14 (b) shows propagation path of cracks in sample

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C4, and the relevant element distribution is shown below. It is shown in the figure, the crack was obviously hindered when it encounters the precipitates of MnS. In order to further support this conclusion, the fracture surfaces of samples C1 and C4 were

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analyzed. Fig. 15 (a) shows the fracture surfacesof sample C1, and the element distribution of point A is shown below. As can be seen in the figure, the crack passes

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through the phase interface between the metal particle and precipitates A. Fig. 15 (b) shows the fracture surface of sample C4, and it is found that MnS has a remarkable effect of crack propagation curb. This phenomenon indicates that sulfur precipitates in the form of sulfide in the sample, which does lead to a certain influence on the mechanical properties of the samples. Through the analysis of crack propagation and fracture surface, it is found that 18

when sulfur precipitates in the form of FeS, any positive effects on the performance of the sample are provided. Furthermore, the instability of the interface between Fe and FeS offers a path for crack propagation. When the amount of carbon increased and sulfur is precipitated in a form of MnS, the positive effects on the mechanical properties

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of the sample come.

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Fig.14 The effect of precipitates on the crack propagation (a) SEM of sample C1, (b) SEM of sample C4

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Fig.15 Fracture surface of samples C1 (a) and C4 (b) 3.4 Mechanical properties

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Fig.16 shows the density and linear shrinkage of the samples C1-C4, both density and linear shrinkage increase monotonically. As the carbon content increases, the melting

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point of the Fe-C alloy decreased. As a result, more liquid phase is produced during sintering, which serves to densification of samples.

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As shown in Fig. 17, as the increase in carbon content, bending strength and Vickers hardness increased, which largely rests with two factors, a rise in sample densification and existence around the metal phase in the form of MnS, which can

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effectively hinder the crack growth.

As can be seen from Fig. 18, samples have excellent alkali resistance, coming of

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the resistance of ceramic phase and metal phase in the samples to alkali corrosion. However, there were significant differences in acid resistance among the four samples. The metal phase in the samples is easily corroded by acid. The acid resistance of the sample builds as the carbon content grows, which mainly depends on the form of sulfur precipitation. FeS does not prevent corrosion of metal phase. With an increase in carbon distribution, FeS is gradually replaced by MnS. In this way, the acid resistance of 20

sample C4 reaches 94.89%, a pivotal conclusion. Traditional iron-containing composites have poor acid resistance, and costly composites containing Co, Ni and Mo generally used in acidic environment. This study provides a new method to offset the poor acid resistance of iron-containing composite materials and expand the application space of the materials. Through the above results, it can be found that carbon content has a significant impact on the comprehensive performance of the samples. The essence of carbon content affecting the performance of samples is the symbiotic elements sulfur and

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manganese in iron concentrate. When the carbon content is high, MnS precipitates around the metal phase, which inhabits both the crack propagation and hinders the reaction between the sample and the acid. The mechanical properties and acid resistance

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of the material are simultaneously improved.

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Fig.16 The density and linear shrinkage of samples C1-C4

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Fig.17 The bending strength and hardness of samples C1-C4

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Fig.18 The alkai resistance and acid resistance of samples C1-C4

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4. Conclusions

Regarding the investigation in this study, the following conclusions are made: (1) Most of the iron concentrates have to be desulfurized before smelting, and the current desulfurization process cannot be completely removed, resulting in difficulties in handling many high-sulfur iron concentrates. (2) A composition of Fe-Al2O3 designed for novel composite to use Bayan Obo iron concentrate and bauxite. 22

(3) Sulfur is not discharged in the form of gaseous compounds, but precipitates in the form of the sulfide during the cooling. Moreover, the precipitates depend on the amount of reducing agent in the original material. With an increase in reducing agent, the precipitates were MnS instead of FeS. The sulfur fixation ratio was above 96%. (4) Samples with higher carbon content had optimal physical and chemical properties with bending strength of 295MPa, hardness of 13.0 GPa, acid resistance of 94.89% and alkali-resistance of 98.45%. Due to its excellent mechanical properties and

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chemical stability, the composite can be widely used in metallurgy, construction and other industries.

(5) A further work is needed to investigate processes and get consistence in scale-up

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production.

Author Contribution Statement

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Declaration of interests

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Yuxin Chen: Investigation, Writing- Original draft preparation, Writing - Review & Editing Saiyu Liu: Investigation Shunli Ouyang: Supervision, Resources Yu Shi: Software Baowei Li: Funding acquisition, Project administration

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The authors declare that they have no known competing financial interests or personal

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relationships that could have appeared to influence the work reported in this paper.

Acknowledgements: This work has been financially supported by the National Natural Science Foundation of China (No. 51774189, 11564031, 11964025), The open project for key basic research of the Inner Mongolia Autonomous Region (No.20140201), Key 23

Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources of Inner Mongolia Autonomous Region (2016CXYD-KYPT), Young talents of science and

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technology in universities of Inner Mongolia Autonomous Region (No. NJYT-17-B10).

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References

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