Selective Chlorinated Extraction of Iron and Manganese from

Research Article pubs.acs.org/journal/ascecg

Selective Chlorinated Extraction of Iron and Manganese from Vanadium Slag and Their Application to Hydrothermal Synthesis of MnFe2O4 Shiyuan Liu,†,‡ Lijun Wang,*,†,‡ and Kuochih Chou†,‡ †

State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083, China ‡ Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083, China ABSTRACT: Several valuable elements, including V, Cr, Fe, Mn, and Ti, exist in vanadium slags. In this paper, an innovative way to extract Fe and Mn selectively and destroy the typical encompassed structure with NH4Cl has been proposed. Fe and Mn are then used to synthesize MnFe2O4, and the residue is an enriched Cr−V−Ti−O mixture. Moreover, the chlorination agent NH4Cl can be recycled in this process. Vanadium slag was mixed with various amounts of NH4Cl and NaCl in a temperature range from 300 °C to 900 °C for 1 to 8 h. The optimal conditions for the chlorination of Mn and Fe are NH4Cl−slag mass ratio of 2:1, NaCl−NH4Cl mass ratio of 0.308:1, 800 °C and 4 h. The manganese and iron chlorination ratio can be reached at 95% and 72%, respectively. The presence of NaCl can enhance the chlorination rate of manganese and iron. Manganese ferrite powders were prepared via hydrothermal treatment of iron and manganese in the leaching solution at a temperature of 140−200 °C. The synthesized MnFe2O4 exhibits high saturation magnetization (Ms, 55.85 emu/g) and low coercivity (Hc, 38.4 Oe). The possible mechanisms involved in these findings are explored. KEYWORDS: Vanadium slag, Sodium chloride, Ammonium chloride, Magnetic properties, Mechanisms

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INTRODUCTION In China, large amounts of vanadium slag are generated each year. Since it contains several valuable elements including V, Cr, Fe, Ti, and Mn, the utilization of such slags have attracted great attention. The difficulty for extraction also lies in how to destroy the typical encompassed structure, such as fayalite, manganoan ((Fe,Mn)2SiO4), titanomagnetite (Fe2.5Ti0.5O4), and vuorelainenite ((Mn,Fe)(V,Cr)2O4). And the spinel particles are encompassed by a fayalite phase. The destruction of the structure of fayalite contributes to the decomposition of the spinel.1 The traditional processes proposed are mainly focused on the V and Cr extraction and utilization.2−5 The residue containing iron after salt roasting contains a high sodium content, which is used in ironmaking leading to promote a thicker wall, knot, and damage to the brick lining. Thus, the residue containing iron is not suitable for ironmaking.6 In the case of Fe and Mn extraction, a recovery of manganese from vanadium slag was reported as 76% by H2SO4 leaching, while the leaching behavior of iron in vanadium slag was not mentioned.7 With NaOH molten salt roasting, 22.8% of manganese was leached out.4 Li et al.8 also employed pressure acid leaching for iron extraction from vanadium slag, but in addition to iron, © XXXX American Chemical Society

vanadium, chromium, and titanium may also get extracted in this process, which would harm the subsequent valorization of the leachate, resulting in high impurity levels and making purification more difficult. From another side, manganese and iron are both important elements largely used in synthesizing MnFe2O4.9,10 The low grade manganese ores as well as secondary sources become increasingly important to recover manganese, due to the world’s rapidly growing demand for manganese.11 Thus, an attempt to selectively extract manganese and iron from vanadium slag to synthesize MnFe2O4 has been made in the present work. The residue is enriched Cr, Ti, and V oxides instead of a spinel crystalline structure. Figure 1 shows the flowchart of this new process. NH4Cl is a nontoxic and noncorrosive solid chlorinating agent.12 The vanadium slag is first selectively chlorinated by NH4Cl. After chlorination roasting and water treatment, the FeCl2 and MnCl2 were separated from V, Cr, and Ti concentrate slag as solution. Afterward, the MnFe2O4 has been synthesized with limited Received: July 28, 2017 Revised: September 13, 2017

A

DOI: 10.1021/acssuschemeng.7b02573 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering

Cr2O3, 37% FeO, 20.88% SiO2, 11.38% TiO2, 5.93% MnO, 3.39% Al2O3, 3.15% MgO, and 2.38% CaO. NH4Cl is a nontoxic and noncorrosive solid chlorinating agent, which could be decomposed to NH3 and HCl gases over 230 °C.12 The reagents used in this work, namely sodium chloride, MnCl2·4H2O, ammonium hydroxide, and ammonium chloride, were of analytical grade. Experimental Procedure. In each experiment, 10.0 g of vanadium slag was mixed well with certain weighed amounts of chlorinating agents, viz., NH4Cl or/and NaCl, heated to the targeted temperature in an alumina crucible with a lid, and held for a fixed time. High purity grade argon was introduced as the protective gas. After that, the crucible was taken out of the furnace and cooled down in air. The products of the experiment were immersed in 200 mL of deionized water contained in a glass breaker with glass for 30 min. After that the breaker solution was filtered, the volume of the filtrate was measured, and the concentrations of valuable metals (Fe and Mn) were analyzed by ICP-AES. The percentage of chlorinated valuable metals (Fe and Mn) was calculated based on the following equation:

Figure 1. Flowchart of a new process for the efficient utilization of vanadium slag.

Mn (or Fe) chlorination (%) =

impurities. The residues containing vanadium, chromium, and titanium were not only enriched but also the typical encompassed structure of vanadium slag was destroyed, which facilitated vanadium extraction by molten salt electrolysis. Previously, simultaneous extractions of Cr, V, and Ti from slag by molten salt electrolysis were achieved.13 This paper would provide a new insight into utilizing resources with the aim of obtaining functional materials.

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[Mn] × V × 100 WMn

(1)

where WMn is the mass of manganese (or iron) in milligrams from the original vanadium slag; [Mn] is the concentration of manganese (or iron) from the filtrate in mg/L; and V is the volume of the filtrate in liters. The Fe:M (Mn and Ca) molar ratio in the target filtrate was founded to be about 4.8, while the ratio needed for the synthesis of Mn-ferrite should be 2.0. It was suggested that compounds such as MnCl2·4H2O should be added. The Fe in the filtrate exhibits bivalency. However, Fe in the structure of MnFe2O4 is trivalent while Mn remains bivalent. H2O2 was used to selectively oxidize the Fe cation. In this work, H2O2 (30%) was successively dripped into the filtrate under stirring, Subsequently, MnCl2·4H2O and NH3·H2O were added into the filtrate. The pH was adjusted to 10, and a precipitate was formed. The mixed solution was transferred into a Teflon-lined stainless-steel autoclave with a filling degree of 80%. After heating at

EXPERIMENTAL SECTION

Materials. The chemical composition of the vanadium slag with a particle size fraction of 49−74 μm was analyzed using inductively coupled plasma optical emission spectroscopy (ICP-AES, SPECTRO ARCOS EOP, SPECTRO Analytical Instruments GmbH). The chemical composition of the vanadium slag was 10.05% V2O3, 5.84%

Figure 2. Plots of standard Gibbs free energy change as a function of temperature (a) reactions 2−7, (b) reactions 8−11, and (c) reactions 13−17 B


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ACS Sustainable Chemistry & Engineering different temperatures for 12 h, the autoclave was cooled to room temperature. The product was obtained by washing several times with deionized water and absolute ethanol and finally dried in vacuum oven at 100 °C for 5 h. X-ray diffraction patterns of the powder of samples were recorded with a Rigaku TTRIII X-ray diffractometer equipped with a Cu Kα radiation source (λ = 0.15405 nm). The SEM observation was performed with the SEM (Zeiss Ultra 55). The mineralogical phases of products were examined by X-ray diffraction, and the magnetic properties of the synthesized ferrites were tested by a physical property measurement system (PPMS, America, 9T (EC-II).

HCl +

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RESULTS AND DISCUSSION Thermodynamic Consideration. As mentioned in the previous section, the main crystalline phases of the vanadium slag are fayalite, manganoan ((Fe,Mn)2SiO4), titanomagnetite (Fe2.5Ti0.5O4), and vuorelainenite((Mn,Fe)(V,Cr)2O4).13 Here the valence of Fe exhibited two states, Fe2+ in (Fe,Mn)2SiO4, (Fe,Mn)(V,Cr)2O4, and Fe2.5Ti0.5O4 phases and Fe3+ in Fe2.5Ti0.5O4 phase. The possible reactions involved in the chlorination of the vanadium slag process are according to reactions 2−15. On the platform of FactSage software, changes with temperature in the standard Gibbs free energy of reactions 2−11 were calculated by the FactSage 6.4 program, and the data were plotted against the temperature change shown in Figure 2a,b. It is clearly shown that with increasing temperature, NH4Cl decomposes to NH3 and HCl. Thus, the possibilities of HCl to react with different components in vanadium slag were examined. In the case of components bearing Fe2+, the ferrous ion can be chlorinated in the forms of FeCl2, and with increasing temperature, the standard reaction Gibbs energy is increased. The tendency of chlorination is ranked as the sequence Fe2O3 < FeCr2O4 < FeV2O4 < Fe2TiO4 < Fe2SiO4. It is difficult to chlorinate FeCl3. In the case of components bearing divalent manganese, Mn2+ can be chlorinated in the forms of MnCl2, and with increasing temperature, the standard reaction Gibbs energy is increased. The tendency of chlorination is ranked as the sequence Mn2SiO4 < Mn2TiO4. Meanwhile, it can be seen from reaction 10 that FeCl2 as the chlorination agent can react with Mn2TiO4. The possibilities of V2O3, Cr2O3, and TiO2 reacting with chlorinating agent HCl were evaluated from the thermodynamic viewpoint as shown in eqs 13−15. It can be seen from Figure 2c that V2O3, Cr2O3, and TiO2 cannot be chlorinated by HCl. Thus, from the thermodynamic equilibrium, selective chlorinated extraction of iron and manganese can be achieved. NH4Cl = NH3 + HCl

HCl +

1 1 1 1 Fe2TiO4 = SiO2 + H 2O + FeCl 2 4 4 2 2

1 1 1 1 HCl + Fe2SiO4 = SiO2 + H 2O + FeCl 2 4 4 2 2

1 1 1 1 Mn2SiO4 = SiO2 + H 2O + MnCl 2 4 4 2 2

HCl +

1 1 1 1 Mn2TiO4 = TiO2 + H 2O + MnCl 2 4 4 2 2

(8) (9)

FeCl 2 +

1 1 Mn2TiO4 = MnCl 2 + FeO + TiO2 2 2

(10)

FeCl 2 +

1 1 Mn2SiO4 = MnCl 2 + FeO + SiO2 2 2

(11)

HCl +

1 1 1 1 MnV2O4 = V2O3 + H 2O + MnCl 2 2 2 2 2

(12)

HCl +

1 1 1 TiO2 = TiCl4 + H 2O 4 4 2

(13)

HCl +

1 1 1 V2O3 = VCl3 + H 2O 6 3 2

(14)

HCl +

1 1 1 Cr2O3 = CrCl3 + H 2O 6 3 2

(15)

NaCl +

1 1 1 1 MnO + SiO2 = Na 2SiO3 + MnCl 2 2 2 2 2

(16)

1 1 1 1 FeO + SiO2 = Na 2SiO3 + FeCl 2 (17) 2 2 2 2 Selective Chlorination Using NH4Cl. Figure 3 gives the chlorination ratio of Mn and Fe solely by NH4Cl in the NaCl +

Figure 3. Effect of temperature on chlorination of iron and manganese (NH4Cl−slag mass ratio of 3:1 and 4 h in the absence of sodium chloride).

(2)

(3)

temperature range from 300 °C to 800 °C. It is clear that with increasing temperature, iron extraction has been reduced, while chlorination of Mn was enhanced in the range from 300 °C to 600 °C, and then reduced afterward. The leaching residue in vanadium slag after chlorination was characterized by SEM-EDS and XRD, which are presented in Figures 4, 5, and 6. Figure 4 shows the residual vanadium slag, with the help of EDS analysis, and the chemical compositions of section A indicated in Figure 5. It is seen that the bright sections contain V, Cr, Fe, Mn, and Ti, while the gray sections contain Si, Fe, Mn, and Ca. XRD patterns of chlorinated vanadium slag at 400 °C are shown in Figure 6. It was observed

(4)

HCl +

1 1 1 1 FeCr2O4 = Cr2O3 + H 2O + FeCl 2 2 2 2 2

(5)

HCl +

1 1 1 1 FeV2O4 = V2O3 + H 2O + FeCl 2 2 2 2 2

(6)

HCl +

1 1 1 Fe2O3 = H 2O + FeCl3 6 2 3

(7) C


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that Mn2SiO4 peaks cannot be detected in XRD. It implies that Mn2SiO4 has reacted with HCl to form MnCl2 and SiO2. As analyzed from the thermodynamic aspect, the reaction is not favored in elevating temperature. But commonly, the reaction kinetics between HCl and MnO would be favored by increasing temperatures. However, the chlorination of Mn rapidly decreased between 600 °C and 800 °C. This may be because the NH4Cl quickly decomposes to NH3 and HCl gases, and HCl cannot fully react with vanadium slag. The chlorination of Fe decreased quickly as the chlorination temperature increased from 300 °C to 800 °C. Figure 6 shows that Fe2.75Ti0.25O4 appears at 400 °C. The molar ratio of Fe2+/ Fe3+ in the Fe2.5Ti0.5O4 phase is 1.5:1, then, the molar ratio of Fe2+/Fe3+ in the Fe2.75Ti0.25O4 phase is 0.83:1. It is suggested that iron in the Fe2.5Ti0.5O4 phase is probably partially chlorinated. Meanwhile, from the thermodynamic equilibrium, FeCl2 as the chlorination agent can react with Mn2TiO4, leading to the low chlorination ratio of Fe. The elements Fe and Mn are uniformly distributed in spinel and fayalite. From the thermodynamic equilibrium, MnO is more readily chlorinated than FeO during the chlorination. Iron in the titanomagnetite (Fe2.5Ti0.5O4) phase consisted of bivalent and trivalent iron. The Fe2O3 cannot be chlorinated by NH4Cl at the experimental temperature.14 Meanwhile, FeCl2 as the chlorination agent can react with Mn2TiO4. Thus, the chlorination ratio of Mn was higher than that of Fe in the temperature range from 300 °C to 800 °C. According to Figure 3, it is clear that the extraction of manganese and iron are not complete. Selective Chlorination Using NaCl−NH4Cl. Figure 7 shows the chlorination of Fe and Mn with NH4Cl−NaCl in

Figure 4. Backscatter electron image of water leaching residue of the vanadium slag after vanadium slag chlorination for 4 h at 400 °C (chlorinating condition: NH4Cl−slag mass ratio of 3:1).

Figure 5. Elemental distribution images of section A (in Figure 4) by EDS.

Figure 7. Effect of temperature on chlorination of iron and manganese (NH4Cl−slag mass ratio of 3:1, NaCl−NH4Cl mass ratio of 0.308:1 and 4 h).

700−900 °C. Both chlorination ratios of Fe and Mn have been improved remarkably by addition of NaCl compared with the cases of NH4Cl alone. The highest chlorination ratio of Fe and Mn have been achieved as 72% and 98%, respectively. Meanwhile, the effect of the chlorinating temperature, viz. from 700 °C to 900 °C, is presented in Figure 7. The chlorination ratio of manganese remarkably increased with increasing temperature in the temperature range from 700 °C to 900 °C. The chlorination of Fe decreased steadily as the chlorination temperature increased from 700 °C to 900 °C.

Figure 6. XRD patterns of water leaching residues of the vanadium slag after vanadium slag chlorination for 4 h at 400 °C (NH4Cl−slag mass ratio of 3:1).

D


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which would explain the fact that the chlorination ratio of Fe and Mn reached 72% and 95%, respectively. It is interesting that the combined chloride agent (NH4Cl + NaCl) chlorinating at the temperature examined had a higher extraction of Mn and Fe than that of a single chloride agent chlorinating using NH4Cl. In order to explain the effect of NaCl as additive, NaCl as the chlorination agent in the absence of NH4Cl was examined to chlorinate vanadium slag in the temperature range from 700 °C to 850 °C, and the chlorination ratio of Mn and Fe at NaCl−slag mass ratio of 0.66:1 were less than 2% and 1%, respectively. From thermodynamic viewpoint as shown in eqs 16 and 17, it can be seen from Figure 2c that NaCl cannot chlorinate the Fe and Mn in vanadium slag. Thus, the chlorination role of NaCl is not the real reason why addition of NaCl can achieve a high extraction of Fe and Mn. Instead of acting as a chlorination agent, the role of NaCl might contribute to reduce the activities of NH4Cl, FeCl2, and MnCl2 as a molten flux. As for NH4Cl, the molar ratio of NaCl/ (NaCl + NH4Cl) of 0.22 for the experiment, they can form a liquid phase at 438 °C (eutectic point) in Figure 9a. Once the liquid occurred, the activity of NH4Cl is lower than 1, resulting in reducing the fast decomposition of NH4Cl at high temperature. From the phase diagram of NaCl−MnCl2, as shown in Figure 9b, there is a compound formed as Na6MnCl8 when the molar ratio of NaCl in this binary system is about 0.875, which also confirmed the presence of Na6MnCl8 by XRD patterns in Figure 8. Obviously, the MnCl2 has been stabilized in terms of the new compound. As for FeCl2, Figure 9c indicated that the liquid phase of NaCl−FeCl2 was formed

The chlorinated vanadium slag without and with water leaching was characterized by XRD. As can be seen in Figure 8, the main

Figure 8. XRD patterns of the sample of the vanadium slag after vanadium slag chlorination for 4 h at 800 °C (NH4Cl−slag mass ratio of 3:1 and NaCl−NH4Cl mass ratio of 0.308:1).

crystalline phases are NaAlSi3O8, Fe2.942O4, (V0.5Ti0.5)2O3, SiO2, Fe2.75Ti0.25O4, NaCl, FeCl2(H2O)2, Na6MnCl8, and FeCr2O4. It is suggested that Fe in the FeV2O4 and Fe2SiO4 phases and Mn in the MnCr2O4 phase were chlorinated by NH4Cl at 800 °C,

Figure 9. Phase graph (a) NaCl−NH4Cl, (b) NaCl−MnCl2, and (c) NaCl−FeCl2. E


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ACS Sustainable Chemistry & Engineering above 400 °C, which can also reduce the activity of FeCl2 and facilitate the chlorination of the iron-containing phase. Thus, NaCl as flux increases the chlorination of iron and manganese. However, the iron extraction ratio was only 72%. The reason can be explained from two aspects. Besides Fe3+ cannot be chlorinated by HCl at the experimental temperatures, the the NaAlSi3O8 phase enveloping the surface of the unreacted oxides during the chlorination roasting process, would make the HCl diffusion through the unreacted core containing iron difficult to some extent.15 The effect of 1−3 NH4Cl/slag mass ratio on the chlorination of Mn and Fe from the chlorinating samples was investigated. Figure 10 shows that the chlorination ratio of Mn and Fe

Figure 11. Effect of time on chlorination of iron and manganese from the chlorinating samples (NH4Cl−slag mass ratio of 2:1 and NaCl− NH4Cl mass ratio of 0.308:1 and 800 °C).

Figure 10. Effect of NH4Cl−slag mass ratio on chlorination of iron and manganese from the chlorinating samples (NaCl−NH4Cl mass ratio of 0.308:1, 800 °C, and 4 h).

significantly increased with increasing NH4Cl/slag mass ratios up to 2.0 and then reached a plateau, which could be attributed to the increased concentration of chlorinating agents, assuming FeO, MnO, CaO, and MgO in vanadium slag and NH4Cl completely react to form FeCl2, MnCl2, CaCl2, and MgCl2, at a NH4Cl/vanadium slag mass ratio of 0.77. With the NH4Cl− slag mass ratio reaching 3, the extraction of manganese and iron hardly increased. Taking into account the cost of treatment, the optimal NH4Cl/slag mass ratio is 2. The effect of 1−8 h chlorination time at a NH4Cl−slag mass ratio of 2:1, the NaCl−NH4Cl mass ratio of 0.308:1 and 800 °C on the chlorination of Mn and Fe in vanadium slag was investigated. Figure 11 shows that the chlorination ratio of Mn increased with time up to 4 h and reached a plateau between 4 and 8 h. This may be because the chlorination of the manganese-containing phase was restrained by a diffusion step. The chlorination ratio of Fe increased steadily between 1 h and 8 h. When the extraction time was short, the reaction was not complete and could not destroy the structure of spinel and fayalite, and most of the manganese and iron could not be chlorinated. The optimal time was 4 h. Hydrothermal Synthesis of Manganese Ferrite. The target filtrate without adding MnCl4·4H2O was heated at 200 °C for 12 h, and the XRD patterns are shown in Figure 12. It can be seen that the main crystalline phases are MnFe2O4 and Fe2O3. This result further indicated that MnCl4·4H2O should be added into the target filtrate for the synthesis of singlecrystal MnFe2O4.

Figure 12. XRD patterns of target filtrate without adding MnCl4· 4H2O heated at 200 °C for 12 h.

XRD patterns of Manganese ferrite are shown in Figure 13a. It is apparent that the single-crystalline ferrites for each temperature were synthesized. The intensity of the major ferrite peak increases as the reaction temperature increases from 140 °C to 200 °C. The experiments have shown that a higher temperature may contribute to crystallization of the ferrite particle. The crystallite size of manganese ferrite was estimated by the Scherrer equation:16 d=

0.9λ β cos θ

where d is the average crystallite size of the manganese ferrite, λ is the wavelength of the X-ray radiation (0.15405 nm), β is the half-peak width of the (3 1 1) diffraction peak in the experiment, and 2θ is the position of the highest diffraction peak (3 1 1). The estimated crystallite size was in agreement with that observed from the TEM images.16,17 The crystallite size of manganese ferrite at 140 °C, 160 °C, and 200 °C are 14.25, 21.09, and 23.42 nm, respectively. F


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Figure 13. (a) XRD patterns, (b) room temperature hysteresis loops, (c) an expand view at low field, and (d) the Ms and Hc values of synthesized (Mn0.952Ca0.048)Fe2O4 ferrites under different hydrothermal temperature at Fe:(Mn + Ca) molar ratio of 2:1 for 12 h.

Figure 14. Collected powders along the upper portions of reactor tube after chlorination: (a) typical photo and (b) X-ray diffraction patterns.

Recycle Analysis of Chlorinating Agent. NH4Cl is a very good solid chlorinating agent because it decomposes to NH3 and HCl above 230 °C and recombines from NH3 and HCl below 112 °C.12 With this advantage, NH4Cl can be reused in this process. Meanwhile, new and green processes including chlorination of iron and manganese by NH4Cl, selective oxidation of Fe cation, and hydrothermal synthesis can be achieved by recycling utilization of NH4Cl. Reactions involved in the hydrothermal synthesis of manganese ferrite from vanadium slag are according to reactions 18−24. Figure 14a shows the photo of collected product in the condensing zone. The collected product was analyzed by the XRD pattern. The XRD patterns in Figure 14b indicated that the collected product was NH4Cl. Although one of the chlorination products is H2O vapor, according to Banic’s24 findings, water vapor acts as a catalyst instead of entering into the reaction NH3 + HCl = NH4Cl. Although the

The hysteresis loops of manganese ferrite are shown in Figure 13b,c, while the Figure 13d represents the relationship between hydrothermal temperature and both saturation magnetization and coercivity. Saturation magnetization increased from 51.34 to 55.85 (emu/g) in the temperature range from 140 °C to 200 °C. This may be explained as the saturation magnetization is directly proportional to particle size.18 The Hc of the ferrite is enhanced with the elevating temperature from 140 °C to 200 °C, which may be attributed to the increasing particle size. The coercivity increases as the single domain particle size increases, however, the size of the particle size attains a value of critical diameter at which it becomes multidomain, and the covercivity starts decreasing.19−21 A single crystal will theoretically become a single domain when its size is reduced below a critical value of a few hundred angstroms.22 The formed single-phase MnFe2O4 synthesized from vanadium slag exhibited better magnetic properties compared to those synthesized from pure reagents.23 G


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Figure 15. Produced NH4Cl powders: (a) typical photo and (b) X-ray diffraction patterns.

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optimal NH4Cl/slag mass ratio was 2.0, the condensed NH4Cl can be reused after the grinding. NH3 gas can be absorbed by water to produce ammonia− water.12 Ammonia−water was added into the FeCl3 solution, and a precipitate of Fe(OH)3 was formed. After that the mixed solution was filtered through Whatman GF-A membrane. The filtrate was evaporated at 125 °C for 8 h. Figure 15a,b shows a photo of the precipitate and its XRD patterns. It is apparent that the precipitate is NH4Cl. The chlorinating agent NH4Cl was produced and recycled. 2NH4Cl + FeO = FeCl 2 + H 2O + 2NH3

(18)

2NH4Cl + MnO = MnCl 2 + H 2O + 2NH3

(19)

NH3 + H 2O = NH3·H 2O

(20)

2FeCl 2 + H 2O2 + 2HCl = 2FeCl3 + 2H 2O

(21)

FeCl3 + 3NH3·H 2O = Fe(OH)3 + 3NH4Cl

(22)

MnCl 2 + 2NH3·H 2O = Mn(OH)2 + 2NH4Cl

(23)

2Fe(OH)3 + Mn(OH)2 = MnFe2O4 + 4H 2O

(24)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (L.W.). ORCID

Lijun Wang: 0000-0003-2094-3228 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for the financial support of this work from the National Natural Science Foundation of China (No.51474141, 51774027), the China Postdoctoral Science Foundation (2014M560046), and the Beijing Higher Education Young Elite Teacher Project (YETP0349), as well as the Fundamental Research Funds for the Central Universities (FRF-TP-15-052A3).

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REFERENCES

(1) Liu, B.; Du, H.; Wang, S. N.; Zhang, Y.; Zheng, S. L.; Li, L. J.; Chen, D. H. A Novel Method to Extraction Vanadium and Chromium from Vanadium Slag using Molten NaOH-NaNO3 Binary System. AIChE J. 2013, 59, 541−552. (2) Li, H. Y.; Fang, H. X.; Wang, K.; Zhou, W.; Yang, Z.; Yan, X. M.; Ge, W. S.; Li, Q. W.; Xie, B. Asynchronous Extraction of Vanadium and Chromium from Vanadium Slag by Stepwise Sodium RoastingWater Leaching. Hydrometallurgy 2015, 156, 124−135. (3) Jing, X. H.; Ning, P. G.; Cao, H. B.; Sun, Z.; Wang, J. Y. Separation of V(V) and Cr(VI) in leaching solution using annular centrifugal contactors. Chem. Eng. J. 2017, 315, 373−381. (4) Chen, D. S.; Zhao, L. S.; Liu, Y. H.; Qi, T.; Wang, J. C.; Wang, L. N. A Novel Process for Recovery of Iron, Titanium, and Vanadium from Titanomagnetite Concentrates: NaOH Molten Salt Roasting and Water Leaching Processes. J. Hazard. Mater. 2013, 244-245, 588−595. (5) Sanchez-Segado, S.; Makanyire, T.; Escudero-Castejon, L.; Hara, Y.; Jha, A. Reclamation of reactive metal oxides from complex minerals using alkali roasting and leaching−an improved approach to process engineering. Green Chem. 2015, 17, 2059−2080. (6) Yang, Z.; Li, H. Y.; Yin, X. C.; Yan, Z. M.; Yan, X. M.; Xie, B. Leaching kinetics ofcalcification roasted vanadium slag with high CaO content by sulfuric acid. Int. J. Miner. Process. 2014, 133, 105−111. (7) Peng, H.; Fang, L.; Liu, Z. H.; Tao, C. Y. Study on leaching behavior of manganese in converter vanadium slag, National conference on physical chemistry of metallurgy. NanNing. 2016. (8) Li, X.; Yu, H. H.; Xue, X. X. Extraction of iron from vanadium slag using pressure acid leaching. Procedia Environ. Sci. 2016, 31, 582− 588.

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CONCLUSIONS Mn and Fe extraction from vanadium slag to synthesize MnFe2O4 have been achieved in the current study. Selective chlorination of Fe and Mn to form FeCl2 and MnCl2 by NH4Cl were performed under optimal conditions (NH4Cl−slag mass ratio of 2:1, NaCl−NH4Cl mass ratio of 0.308:1, 800 °C, and 4 h), and iron and manganese chlorination ratio reached 72% and 95%, respectively. The combined chloride agent (NH4Cl + NaCl) chlorinating had a higher extraction of Mn and Fe than that of single chloride as the chlorinating agent. Using Fe and Mn extracted from vanadium slag, manganese ferrite powders were obtained by a hydrothermal synthesis method. Good magnetic properties of saturation magnetization (Ms, 55.85 emu/g) and coercivity (Hc, 38.4 Oe) at 200 °C are achieved. A green route for recovery of Mn and Fe existing in vanadium slag to synthesize MnFe2O4 is reported for the first time in this paper. Meanwhile, vanadium, chromium, and titanium were enriched in the residue for other utilizations. H


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Selective Chlorinated Extraction of Iron and Manganese from

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