Boron-Iron Separation and Boron Enrichment from Boron-Bearing Iron Concentrate at Low-Temperature Enhanced by Supergravity

Abstract

Boron-bearing iron concentrate, as the tailings of boron concentrate otained from ludwigite, still contains more than 5 wt.% of B₂O₃, which can hard to be utilized. In this study, low-temperature separation compared with high-temperature melting separation of boron and iron from boron-bearing iron concentrate, and the migration, transformation, separation and enrichment behaviors of boron in both processes were studied. High-temperature melting separation of iron and slag could be accomplished at 1823 K for 60 min, where the boron mainly distributed in a form of glass phase in the slag with a B₂O₃ content of 22.69 wt.%, while 0.35 wt.% of [B] was melted into the liquid iron. In contrast, iron and slag were efficiently separated at a low temperature of 1573 K for 10 min enhanced by supergravity, almost all of boron was enriched into suanite phase in the slag with a significantly higher B₂O₃ content of 35.61 wt.% and a high recovery ratio of 99.37%, and the content of B was decreased to 0.15 wt.% in the iron. Compared with high-temperature melting separation, low-temperature separation greatly improved the enrichment of boron in slag and avoided the melting of boron into iron.

1. Introduction

Boron compounds process favorable physical properties such as fire retardant, heat resistance, high hardness and high strength and have been widely used in the aerospace and military fields, which leads to a rapid increase of boron consumption.^1,2,3) China has made an enormous contribution to the growth of the total world consumption of boron, and causes the imminent depletion of high grade ascharite resources. Alternatively, there are affluent low grade ludwigite ores in Liaoning province, which contains 28.43 Mt B₂O₃ resources and accounts for 57% of boron resources in China.^4,5) However, the average content of B₂O₃ in ludwigite ore is only 8.4 wt.%,^6,7) and the boron, iron, magnesium and gangue minerals are intergrowth, which is currently difficult to be utilized efficiently.^8,9)

Recently, the ludwigite ore has been primarily disposed by mineral processing of multistage fine-grinding combined with magnetic-flotation separations to produce boron concentrate with a higher boron content of 12 wt.%, which can be used as the raw material to prepare boracic acid and borax.^10,11) Meanwhile, the boron-bearing iron concentrate, as the tailings of boron concentrate, was massively produced from the mineral processing, which still contains more than 5 wt.% of B₂O₃ that can hard to be efficiently utilized.¹²⁾ So far, the boron-bearing iron concentrate was mainly stockpiled in landfill, which led to a great deal of waste for boron resources and also contributed to several environmental pollution problems. A variety of hydrometallurgical methods have been proposed aim to separate boron and iron from boron-bearing iron concentrate, while the massive use of acid would also cause the erosion of equipment and pollution of environment.¹⁰⁾

In recent years, lots of high-temperature reduction combined with mineral processing and melting separation processes have been proposed for the separation of boron and iron in boron-bearing iron concentrate. Most of which were focused on the recovery of metallic iron, while the further utilization of boron was limited. Li,¹³⁾ Fu¹⁴⁾ and Han¹⁵⁾ studied the reduction and magnetic separation of iron form boron-bearing iron concentrate, and reported that the iron minerals can be fully reduced to metallic iron by various reducing agent of carbon, H₂ and CO, while most of boron was occurred in the gangue.¹⁶⁾ However, the fine particles of metallic iron and boron minerals were dispersive distribution in the gangue, it was difficult to separate boron and iron efficiently through the magnetic separation.¹⁷⁾ Liu¹⁸⁾ reported the high-temperature reduction and melting separation of liquid iron and boron-bearing slag from the ludwigite ore in an industrial scale blast furnace, where a high coke ratio was needed and some brasque erosion was occurred in the blast furnace. The results showed that only 11.98 wt.% of B₂O₃ was transformed into the slag while 1.00 wt.% of [B] was melted into the liquid iron.¹⁹⁾ Chu,²⁰⁾ Wang^21,22,23,24) and Ding²⁵⁾ reported the reduction combined with melting separation of iron and slag by electric furnace from boron-bearing iron concentrate, the boron-bearing slag and liquid iron could be efficiently separated at the high temperature of 1823 K in this process, where the B₂O₃ content in the slag was 10.8 wt.% and the [B] content smelted into the iron was 0.74 wt.%.²²⁾

The previous studies indicated that the high-temperature melting separation of iron and slag by blast furnace and electric furnace was an effective way for the separation of boron-bearing slag and liquid iron from the boron-bearing iron concentrate. However, a certain amount of boron would be melted into the liquid iron at high temperature, which limited the purity of iron.^26,27) On the other hand, the addition of other fluxing agents was needed in the high-temperature melting separation process which would cause a low content of boron in the slag,²⁸⁾ where most of boron transformed into the amorphous phase which caused a low activity of the boron-bearing slag and limited the sustainable utilization of slag.²⁹⁾ Compared with the high-temperature melting separation, low-temperature separation of boron and iron may greatly improve the enrichment of boron in the slag and limit the melting of boron into iron.

In this study, low-temperature separation compared with high-temperature melting separation of boron and iron from the boron-bearing iron concentrate was investigated, and the supergravity field was conducted to enhance the boron-iron separation and boron enrichment at a low temperature, based on the previous studies of significant improvement on phase separation of complex systems by supergravity.^30,31,32,33) Moreover, the migration, transformation and separation behaviors of boron in both processes were reported in this study, which verified the enrichment of boron in slag and avoided the melting of boron into iron at low-temperature.

2. Materials and Methods

2.1. Materials

The boron-bearing iron concentrate employed in current study was produced from Dandong, Liaoning Province, China, and obtained through multistage magnetic-flotation separation process of ludwigite ore with the particle size of ≤ 0.15 mm. The chemical composition of boron-bearing iron concentrate was measured by inductively coupled plasma-atomic emission spectrometer (ICP-AES, Plasma1000, NCS Testing Technology Co., Ltd.) and the content of FeO in boron-bearing iron concentrate was measured by the potassium dichromate titrimetric method in accordance with GB/T 6730.8-2016, as shown in Table 1, where the B₂O₃ and TFe contents were 6.10 wt.% and 51.08 wt.% respectively. The X-ray diffractometer (XRD, Smartlab, Rigaku) and the scanning electron microscope with energy-dispersive X-ray spectroscope (SEM-EDX, MLA250, FEI Quanta) were utilized to analyse the mineral composition and microscopic morphology of the boron-bearing iron concentrate, and the results are presented in Figs. 1, 2(a) and Table 2. It was clear that the primary mineral phases of boron-bearing iron concentrate were magnetite (Fe₃O₄), szaibelyite (Mg₂(OH)[B₂O₄(OH)]), serpentine (Mg₃[Si₂O₅](OH)₄) and ludwigite ((Mg,Fe)₂FeBO₅). The majority of boron was distributed in the szaibelyite and ludwigite with iron.

Table 1. Chemical compositions (wt.%) of boron-bearing iron concentrate before and after reduction.

Composition	TFe	MFe	FeO	B2O3	SiO2	MgO	CaO	Al2O3	S	P
Before reduction	51.08	–	24.35	6.10	9.17	20.11	0.40	0.30	1.21	0.034
After reduction	67.34	67.30	–	6.76	12.76	24.50	0.62	0.57	1.25	0.036

Fig. 1.

XRD patterns of boron-bearing iron concentrate before and after reduction.

Fig. 2.

SEM images of boron-bearing iron concentrate before and after reduction: (a) before reduction; (b) after reduction. (Online version in color.)

Table 2. EDX data (wt.%) of various phases in boron-bearing iron concentrate before and after reduction.

	Pt.	Fe	B	Si	Mg	Ca	Al	O	Phases
Before reduction	1	72.85	–	–	–	–	–	27.15	Magnetite
	2	47.34	6.84	–	10.57	–	–	35.25	Ludwigite
	3	–	–	44.41	22.86	2.09	–	30.63	Serpentine
	4	3.18	13.56	–	31.13	–	–	52.13	Szaibelyite
After reduction	5	100	–	–	–	–	–	–	Metallic iron
	6	–	–	37.77	33.33	–	–	28.90	Olivine
	7	–	10.59	9.60	24.96	1.80	1.14	51.91	Slag phase

In this study, the reduction of boron-bearing iron concentrate was firstly accomplished in a tube-type furnace. The boron-bearing iron concentrate was heated to 1323 K in a Ar atmosphere with a gas flow rate of 0.5 L/min, subsequently maintained and reduced at 1323 K in a H₂ atmosphere for 240 min with a gas flow rate of 0.2 L/min. The chemical composition, mineral composition and microstructure of the boron-bearing iron concentrate after reduction are presented in Table 1, Figs. 1, 2(b) and Table 2. It was indicated that there are two mineral phases of metallic iron (MFe) and olivine (Mg₂SiO₄) included in the boron-bearing iron concentrate after reduction. Obviously, the magnetite was fully reduced into metallic iron, the serpentine was decomposed into olivine (Mg₂SiO₄), and the ludwigite and szaibelyite transformed into the slag phase, all of which were closely included and difficult to separate from each other are presented in Fig. 2(b).

2.2. Apparatus

A crucial part of this study relies on the supergravity field to enhance the boron-iron separation and boron enrichment from boron-bearing iron concentrate at low temperature, which was created by a centrifugal apparatus incorporating with the heating function as shown in Fig. 3. The high-temperature centrifugal apparatus could realize the heating while rotating, and a conductive slip ring connected with an R-type thermocouple (within ± 3 K) and a programmed controller (KSY-6-16A) was used to realize the real-time control of heating and temperature in the rotated furnace, as shown in Fig. 3(a).

Fig. 3.

Schematic diagram of high-temperature centrifugal apparatus: (a) schematic diagram, (b) internal structure of heating furnace, 1 - counterweight, 2 - heating furnace, 3 - conductive slipping ring, 4 - temperature controller, 5 - resistance wire, 6 - graphite crucible, 7 - graphite felt, 8 - thermocouple. (Online version in color.)

2.3. Methods

2.3.1. In-situ Study of Mineral Evolution and Migration Behavior of Boron with Temperature

Transformation and migration behavior of boron between iron and slag is the basis for boron-iron separation from boron-bearing iron concentrate. In-situ study on mineral evolution and migration behavior of boron in the reduced boron-bearing iron concentrate with temperature was conducted through hot-quenching and ex-situ analysis. 20 g of the reduced boron-bearing iron concentrate were heated to different temperatures of 1473 K, 1573 K, 1673 K and 1823 K in a tube-type resistance furnace under Ar atmosphere. The samples were quenched in water after holding at each temperature for 60 min. Subsequently, the samples obtained at the different temperatures were split into two halves along the vertical centerline, and the mineral evolution and migration behavior of boron with temperature were analyzed by the SEM and Electron Probe Microanalysis (EPMA, EPMA-1720H, Shimadzu).

2.3.2. Low-temperature Separation Compared with High-temperature Melting Separation of Boron and Iron

Based on the transformation and migration behavior of boron with temperature, the low-temperature separation compared with high-temperature melting separation of boron and iron from the reduced boron-bearing iron concentrate were investigated.

For the low-temperature separation, an amount of 20 g of reduced boron-bearing iron concentrate were placed on a graphite felt with a pore size of 0.01 mm which was embedded in the graphite crucible as a filter, as shown in Fig. 3(b). The graphite crucible covered with a graphite lid was put into the heating furnace of centrifugal apparatus and heated to 1573 K. Subsequently, the rotating speed of centrifugal apparatus was adjusted to 1036 r/min, 1465 r/min and 1795 r/min to achieve different gravity coefficients (G) of 300, 600 and 900, as calculated via Eq. (1). The rotation was shut down after 10 min, and the crucible with sample was quenched in water or by cooling in furnace, respectively.   

$$G=\frac{\sqrt{g^2+{({\omega }^{2}R)}^2}}{g}=\frac{\sqrt{g^2+{\left(\frac{N^2{\pi }^{2}R}{900}\right)}^2}}{g}$$(1)

where, g presents the gravitational acceleration (g = 9.8 m/s²), R expresses the distance between centrifugal axis and sample center (R = 0.25 m), ω denotes the angular velocity (rad/s), and N represents the rotating speed of the centrifuge (r/min).

For the high-temperature melting separation, an amount of 20 g of the reduced boron-bearing iron concentrate were put in the same graphite crucible and covered by the graphite lid, which was heated to 1823 K in the tube-type furnace under Ar atmosphere. After melting separation for different time of 10, 30 and 60 min, the samples were also water-quenched or by furnace-cooling, respectively.

After both experiments, the samples obtained at different temperatures were symmetrically cut into two parts along the vertical centerline, and the separated samples were performed by XRD, SEM-EDX and EPMA methods to determine the mineral composition, microstructure and element distribution of iron and slag phases. The B₂O₃ content in iron and slag phases were measured respectively using the ICP-AES. The recovery ratios of B in slag phase were calculated by the Eq. (2).   

$$R_B=\frac{m_S\times {\omega }_{B-S}}{m_S\times {\omega }_{B-S}+m_I\times {\omega }_{B-I}}\times 100\%$$(2)

where, R_B represents recovery ratios of B in slag phase, m_S and m_I denote the mass of slag and iron phases, ω_B−S and ω_B−I present the B₂O₃ contents in slag and iron phases.

3. Results and Discussion

3.1. Mineral Evolution and Migration Behavior of Boron with Temperature

Figure 4 shows the melting behavior of reduced boron-bearing iron concentrate with temperature for 60 min. It was clear that the sample maintained a loose and porous state at a low temperature of 1473 K, as depicted in Fig. 4(a). The sample became smaller and more compact due to the melting of slag as the temperature increased to 1573 K, while the iron and slag can hardly separate from each other, as presented in Fig. 4(b). A small amount of slag was separated from the bottom of the sample with further increase of temperature to 1673 K, as depicted in Fig. 4(c). The melting separation of slag and iron occurred at the high temperature of 1823 K for 60 min, and the molten slag moved on top of the liquid iron depending on their density difference.

Fig. 4.

Melting behavior of reduced boron-bearing iron concentrate with temperature for 60 min: (a) T = 1473 K, (b) T = 1573 K, (c) T = 1673 K, (d) T = 1823 K. (Online version in color.)

The mineral evolution and migration behavior of B and Fe in iron and slag was indicated from the EMPA-mapping results in Fig. 5. It was clear that the metallic iron particles were dispersedly included among the slag at 1473 K, and the B was mainly existed in the slag phase, as exhibited in Fig. 5(a). Some iron particles started to aggregate together as the melting of slag at 1573 K, and the B maintained in the molten slag, as indicated from Fig. 5(b). As the increase of temperature to 1673 K, a large area of aggregated iron was formed with the fully melting of the slag, and the B was evenly distributed in the molten slag, as shown in Fig. 5(c). Compared to 1573 K, the concentration of B in the slag was significantly decreased at 1673 K, which was resulted from the melting of olivine into the slag. The iron-slag melting separation was completed at 1823 K, and an obvious interface was appeared between the liquid iron and molten slag, where most of B was distributed in the slag and some has been melted into the iron, as shown in Fig. 5(d).

Fig. 5.

EMPA-mapping results of B and Fe in slag and iron with temperature: (a) T = 1473 K, (b) T = 1573 K, (c) T = 1673 K, (d) T = 1823 K. (Online version in color.)

3.2. Low-temperature Separation Compared with High-temperature Melting Separation of Boron and Iron

3.2.1. Iron-slag Separation Behavior

The vertical sections of samples for high-temperature melting separation at 1823 K with time are showed in Fig. 6. Although the iron and slag were fully melted at 1823 K, while the two melted phases can be hardly separated from each other within 10 min, as shown in Fig. 6(a). With the increase of time, more liquid iron was separated and gathered to the bottom, while the molten slag gradually moved to the upper, and a layered structure was formed clearly for 60 min as presented in Fig. 6(c). It was demonstrated that melting separation of iron and slag can be achieved at a high temperature above their melting points, while enough time was needed for the melting separation of molten slag from liquid iron based on their density difference.

Fig. 6.

Vertical sections for high-temperature melting separation of iron and slag at 1823 K with time: (a) t = 10 min, (b) t = 30 min, (c) t = 60 min. (Online version in color.)

In contrast, the vertical sections of samples for low-temperature separation at 1573 K with gravity coefficient are shown in Fig. 7. Obviously, not any melted slag can be separated from the iron at 1573 K under the normal gravity of G = 1 even for 60 min, and a uniformly mixed structure was maintained in Fig. 7(a). As shown in Figs. 7(b) to 7(d), the samples were separated into two parts enhanced by supergravity just for 10 min. The molten slag was successfully separated from the iron and went through the filter into lower crucible, which presented in a glassy state after water-quenching. While the solid iron was fully intercepted by the filter, which showed an obvious metallic luster. Moreover, the mass of the separated slag was significantly increased with the increase of gravity coefficient from G = 300 to G = 900. It was confirmed that the supergravity can significantly enhance the migration of molten slag, and greatly improve the separation between iron and molten slag at low temperature.

Fig. 7.

Vertical sections for low-temperature separation of iron and slag at 1573 K with gravity coefficient: (a) G = 1; t = 60 min, (b) G = 300; t = 10 min, (c) G = 600; t = 10 min, (d) G = 900; t = 10 min. (Online version in color.)

3.2.2. Mineral Composition for Boron-iron Separation

The XRD patterns of the iron and slag phases separated from boron-bearing iron concentrate at the low temperature separation of T = 1573 K and high-temperature melting separation at T = 1823 K are compared in Fig. 8. It was clearly found from Fig. 8(b) that the diffraction peaks of metallic iron were appeared significantly in the iron phase through high-temperature melting separation. However, the olivine (Mg₂SiO₄) was the main phase formed in the cooled slag after melting separation, only some diffraction peaks of kotoite (Mg₃B₂O₆) were found in the cooled slag, while the peak intensity of olivine was much higher than that of kotoite. This indicated that most of boron was mainly distributed in a form of glass phase in the slag through melting separation, which caused a low activity and greatly limited the further utilization of the slag. Compared to the high-temperature melting separation, the main crystalline phase changed to the suanite (Mg₂B₂O₅) in the separated slag, and the intensity of diffraction peaks of suanite (Mg₂B₂O₅) was extremely high after low-temperature separation, as presented in Fig. 8(a). It was indicated that the enrichment of boron in the slag was greatly improved through low-temperature separation by stopping most of olivine in the iron phase, and the fully enrichment of boron into suanite was beneficial for sustainable utilization of the slag.

Fig. 8.

XRD patterns of the iron and slag phases by low-temperature separation compared with high-temperature melting separation: (a) T = 1573 K; (b) T = 1823 K. (Online version in color.)

3.2.3. Element Distribution for Boron-iron Separation

The SEM images, EDX data of the separated slag and iron phases, and the EMPA-mapping of B in slag phases by low-temperature separation at T = 1573 K compared with melting separation at T = 1823 K are showed further in Fig. 9 and Table 3. As shown in Fig. 9(d), the metallic iron was fully melted into liquid iron at the high temperature of 1823 K, which was efficiently separated from the slag through melting separation. However, through comparing the SEM and EMPA-mapping of B in the molten slag by water-quenching as shown Figs. 9(b) and 9(e), there were not any crystalline phase in the molten slag and the concentration of B in the separated slag phase at low temperature of 1573 K was greatly higher than that of high-temperature melting separation at 1823 K, it was confirmed that the boron was fully enriched into slag via low-temperature separation.

Fig. 9.

SEM images and EMPA-mapping of B in the separated iron and slag phases by low-temperature separation compared with high-temperature melting separation: (a) iron phase for 1573 K; (b) molten slag for 1573 K; (c) cooled slag for 1573 K; (d) iron phase for 1823 K; (e) molten slag for 1823 K; (f) cooled slag for 1823 K; 1- metallic iron; 2 - olivine; 3 - suanite; 4 - kotoite; 5 - slag phase. (Online version in color.)

Table 3. EDX data (wt.%) for various phases obtained by low-temperature separation compared with high-temperature melting separation.

Temperatures	Samples	Pt.	Fe	B	Si	Mg	Ca	Al	O	phase
1823 K	Iron phase	3	100	–	–	–	–	–	–	Metallic iron
	Slag phase	2	–	–	36.93	34.59	–	–	28.48	Olivine
		4	–	9.75	–	39.81	–	–	50.62	Kotoite
		5	2.56	10.28	6.77	12.42	6.53	6.11	55.33	Glass phase
1573 K	Iron phase	3	100	–	–	–	–	–	–	Metallic iron
		2	–	–	36.25	35.12	–	–	28.63	Olivine
	Slag phase	1	–	15.02	–	31.54	––	–	53.44	Suanite
		2	–	–	36.24	34.61	–	–	29.15	Olivine
		5	0.48	5.61	11.82	6.51	2.11	3.94	69.53	Glass phase

Moreover, the cooled slag of melting separation was tightly mixed by amounts of large olivine with a size of 150–300 μm and some small kotoite with a size of 50–100 μm, while the boron was evenly distributed in the glass phase and kotoite, as presented in Fig. 9(f). In contrast, amounts of large suanite with a crystal size of 100–300 μm were formed significantly in cooled slag of low-temperature separation, in which almost all of boron was fully enriched into the suanite with a high B₂O₃ concentration of 46.67 wt.%, as shown in Fig. 9(c). Compared to high-temperature melting separation, the concentration of B in the slag was increased significantly and was fully enriched into suanite through low-temperature separation, which was conductive to the sustainable utilization and boron recovery of the slag.

3.3. Mechanism for Boron-iron Separation and Boron Enrichment at Low-temperature

The variations of B₂O₃ content in slag phase and B content in the iron phase through low-temperature separation with gravity coefficient are showed in Fig. 10. With the gravity coefficient increasing from G = 1 to G = 900, the content of B in the iron phase was decreased significantly from 2.11 wt.% to 0.15 wt.% with the gradually removal of slag, while the content of B₂O₃ in the slag phase was up to 35.33 wt.%–35.61 wt.%, and the recovery ratio of B in slag phase was increased from 41.81% to 99.37% through low-temperature separation. This confirmed that the super-gravity greatly enhanced the boron-iron separation at the low temperature, almost all of boron was fully enriched into the slag and be efficiently separated from the iron phase. The contents of B₂O₃ in slag phase and B in iron phase through low-temperature separation and high-temperature melting separation are compared further in Fig. 11. It was found that 0.35 wt.% of [B] was melted into the liquid iron at the high temperature of 1823 K, and the content of B₂O₃ in the slag phase was only 22.69 wt.% through melting separation. By contrast, it was confirmed that low-temperature separation can greatly improve the enrichment of boron in slag and avoid the melting of boron into iron.

Fig. 10.

Variations of B₂O₃ content in slag phase and B content in iron phase through low-temperature separation with gravity coefficient. (Online version in color.)

Fig. 11.

Contents of B₂O₃ in slag phase and B in iron phase by low-temperature separation compared with high-temperature melting separation. (Online version in color.)

Figure 12 shows the mechanism for boron-iron separation and boron enrichment by low-temperature separation compared to high-temperature melting separation. Generally, the high-temperature melting separation method is used for the iron-slag separation from the boron-bearing iron concentrate.^34,35,36) At the high temperature about 1823 K, both the iron and slag can be fully melted and separated from each other for enough time, while some B₂O₃ in molten slag will melt into the liquid iron as [B] at the high temperature, as shown in Fig. 12(b). Moreover, the B₂O₃ content in molten slag will decrease further due to the common addition of other fluxing agents,¹⁸⁾ and most boron will convert into the amorphous state in the slag during cooling process,^37,38) which will cause the low activity of the slag and greatly limit the further sustainable utilization of the slag.³⁹⁾ On the contrary, the low-temperature separation can significantly limit the melting of boron into iron, and greatly improve the enrichment of boron in the slag by trapping most olivine in the iron, as shown in Fig. 12(a). Due to the high concentration of boron in the slag phase at low temperature, almost all of boron can be sufficiently enriched into suanite with a high B₂O₃ content of 46.67 wt.% in the slag during cooling process. Compared to high-temperature melting separation process, this study provides an efficient way to achieve boron-iron separation and enrichment of boron from boron-bearing iron concentrate, which is beneficial for the sustainable utilization of boron-bearing slag.

Fig. 12.

Mechanism for boron-iron separation and boron enrichment by low-temperature separation compared with high-temperature meting separation: (a) T = 1573 K, (b) T = 1823 K. (Online version in color.)

4. Conclusions

In this study, low-temperature separation compared with high-temperature melting separation of boron and iron from boron-bearing iron concentrate were studied.

(1) Melting separation of iron and slag could be accomplished at 1823 K for 60 min. The boron was mainly distributed in a glass phase in the slag with a B₂O₃ content of 22.69 wt.%, while 0.35 wt.% of [B] was melted into the liquid iron.

(2) Low-temperature separation of iron and slag was completed at 1573 K for 10 min enhanced by supergravity, almost all of boron was enriched into suanite phase in the slag with a significantly higher B₂O₃ content of 35.61 wt.% and a high recovery ratio of 99.37%, and the content of B was decreased to 0.15 wt.% in the iron.

(3) Compared with high-temperature melting separation, low-temperature separation greatly improved the enrichment of boron in slag and avoided the melting of boron into iron.

Acknowledgments

This study is supported by the National Natural Science Foundations of China (No. 51774037 and No. 51404025).

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