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Simultaneous extraction of vanadium and titanium from vanadium slag using ammonium sulfate roasting-leaching process
Journal of Alloys and Compounds 742 (2018) 504e511
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Simultaneous extraction of vanadium and titanium from vanadium slag using ammonium sulfate roasting-leaching process Guoquan Zhang, Dongmei Luo, Chenhui Deng, Li Lv, Bin Liang, Chun Li* School of Chemical Engineering, Sichuan University, Chengdu 610065, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 October 2017 Received in revised form 6 January 2018 Accepted 22 January 2018
Sodium and calcification roasting processes are traditional technologies to recover vanadium from vanadium slag. However, these processes are associated with many drawbacks, including high energy consumption, serious environment pollution, and the inability to simultaneously extract associated titanium resources. In this paper, a novel technology for simultaneous extraction of vanadium and titanium from vanadium slag was proposed, in which the vanadium slag was roasted with recyclable (NH4)2SO4 (AS) at moderately high temperatures followed by dilute H2SO4 leaching. To enhance the extraction, an activation pretreatment of the vanadium slag through high-temperature water quenching was employed. The results demonstrated that the activation significantly accelerated the extraction, with the vanadium and titanium extraction increasing by 16% and 12%, respectively, compared with the raw vanadium slag. The extraction of vanadium and titanium were 91% and 77%, respectively, after roasting at an AS-to-vanadium slag mass ratio of 4:1 and 370 C followed by leaching in a 6% H2SO4 solution. X-ray diffraction analysis indicated that the spinel phases in the vanadium slag, such as FeV2O4, Fe2TiO3, and Fe2MnO4, began to transform into (NH4)3V(SO4)3, (NH4)3Fe(SO4)3, (NH4)2Mn(SO4)2, and TiSO4 at 320 C and a nearly complete conversion could be achieved at 370 C. The mass ratio of AS to vanadium slag significantly affected the extraction of both vanadium and titanium, which increased with the increasing mass ratio until an 8:1 ratio was achieved, after which, the extraction decreased. A stratification phenomenon of the vanadium slag and ammonium bisulfate at high AS/slag mass ratios was observed, which could be responsible for the decreasing extraction. © 2018 Elsevier B.V. All rights reserved.
Keywords: Vanadium Titanium Vanadium slag Ammonium sulfate Roasting
1. Introduction Vanadium is an important strategic metal and is widely used in the iron and steel industry, as well as in non-ferrous alloys due to its excellent hardness, tensile strength, and corrosion resistance [1]. Vanadium accounts for only 0.02% of the crustal weight, which although is a higher abundance than that of copper, zinc, and nickel, and ranks 22nd in the known elements, it does not naturally occur in its pure state [2]. Research has confirmed that vanadium initially presents in igneous rocks and gathers in a water-insoluble state of V(III) [3]. Because the ion radii of V(III), Mn(III), Fe(III), and Ti(III) are close, it is quite common for these ions to form a polymetallic symbiotic ore. Vanadium-titanium magnetite ore is a typical polymetallic symbiotic ore that is primarily found in Russia, China, and South Africa. In China, vanadium slag, a by-product of vanadium-
* Corresponding author. E-mail address: [email protected] (C. Li). https://doi.org/10.1016/j.jallcom.2018.01.300 0925-8388/© 2018 Elsevier B.V. All rights reserved.
titanium magnetite in the converter steelmaking process, is a typical vanadium metallurgical raw material, which contributes to more than 40% of V2O5 production in the country [4]. In general, it is almost impossible to separate vanadium from vanadium slag in an unenhanced procedure because there is little vanadium in vanadium slag that could dissolve in water, alkali, or acid directly [5,6]. Further, vanadium primarily occurs in the very stable spinel phase in vanadium slag. Theoretically, it is necessary to recover vanadium from vanadium slag by transforming the lowvalence insoluble vanadium in the spinel phase into high-valent soluble vanadium [7e9]. The traditional commercial methods for vanadium extraction from vanadium slag are sodium roastingwater leaching and calcification roasting-acid leaching [10,11]. In the two methods, the vanadium slag is roasted with an additive, such as NaCl or CaO, above 850 C to decompose the spinel phase structure and vanadium extraction of about 75e80% is obtained [12]. Recently, several studies have been conducted to enhance vanadium extraction. Li et al. researched the process of extracting
G. Zhang et al. / Journal of Alloys and Compounds 742 (2018) 504e511
vanadium by calcification roasting and ammonium carbonate leaching and obtained 96% vanadium recovery [6]. Rashchi et al. revealed the effect of alkaline roasting and H2SO4 leaching on vanadium extraction from vanadium slag using surface response methodology [13]. Xie et al. investigated the oxidation behavior of the vanadium phase in vanadium slag using the sodium roasting process and achieved 90% vanadium extraction [14]. Although over 90% vanadium extraction could be obtained in these studies, a roasting temperature of at least 800 C was required, which is energy intensive. The sodium-roasting and calcification-roasting processes also involve the emission of harmful gases and high additive consumption [15]. In addition, both the sodium and calcification roasting processes seldom allow for the simultaneous extraction of titanium, a high-value-added metal associated in vanadium slag, since the titanium cannot be dissolved during vanadium extraction. Therefore, it is necessary to develop a new extraction route. The obvious advantages of the ammonium sulfate roastingleaching (ASRL) process are high efficiency, low energy consumption (roasting temperatures of only 300e400 C), and environmental friendliness (ammonium sulfate is a recyclable extractant), especially in dealing with low-grade symbiotic minerals [16,17]. Saleh et al. researched the technology of extracting zinc by the ASRL process and obtained a 95% zinc extraction rate at 350 C [18]. Highfield et al. investigated magnesium extraction from serpentine using the ammonium sulfate roasting process and determined that the silicate minerals could decomposed at 350 C [19]. Li et al. used ammonium sulfate to decompose low-grade nickel laterite at 400 C, where 90.8% nickel and 85.4% cobalt could be selectively extracted [20]. In this study, we proposed a novel ASRL process that can be used to simultaneously extract and recover vanadium and titanium from vanadium slag under mild conditions for comprehensively utilizing vanadium slag. In order to enhance the extraction, raw vanadium slag was melted and water quenched for activation, which could be easily realized in industry. The decomposition behavior and microstructure morphology of vanadium slag in the presence of ammonium sulfate at different roasting temperatures is investigated. Furthermore, the effect of the ammonium sulfate dosage on the extraction is discussed. The mineral composition of leaching residues is also characterized.
2. Experimental 2.1. Materials
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Fig. 1. XRD analysis of raw vanadium slag.
2.2. Procedure In the water quenching process, the raw vanadium slag was placed in a high-purity SiO2 crucible, which was positioned centrally and heated by MoSi2 rods in an electric furnace (laboratory customization). When heated to 1500 C in air atmosphere, the slag was dropped rapidly into a bucket located immediately below the hearth through a specially designed outlet and cooled by water in the bucket. After being crushed and milled, the water quenched vanadium slag was dried at 110 C for 12 h. In each roasting test, the vanadium slag sample was evenly mixed with (NH4)2SO4 (AS) at a predetermined mass ratio. The mixture was placed in a porcelain boat, heated at a rate of 10 C/min until 370 C, and then annealed for 90 min in an electric furnace (KSL-1200X, Heifei Kejing Materials Technology Co., Limited, Heifei, China). The roasted slag was then withdrawn and cooled in a desiccator to room temperature. The roasted samples were leached in 6 vol% H2SO4 at a liquid-tosolid mass ratio of 8:1 and 60 C for 1 h. The obtained slurry was run through a vacuum filter. The leaching solution and residues were collected and analyzed to determine the leaching ratio of both vanadium and titanium. The simultaneous extraction of vanadium and titanium from vanadium slag using ammonium sulfate roasting-leaching process was shown in Fig. 2. The ratio could be calculated by following equation (1):
a ¼ f1 ðm2 w2 Þ=ðm1 w1 Þg 100%
The vanadium slag used in this research was provided by Panzhihua Steel & Iron Co., Ltd, Sichuan province, China. The vanadium slag was crushed and milled to a thickness of 75 mm by a ball mill after drying at 110 C for 12 h. The chemical composition of the slag is shown in Table 1. The X-ray diffraction (XRD) patterns of vanadium slag are shown in Fig. 1. The XRD patterns indicate that FeV2O4 (Ref. code: 01-075-0317), Fe2TiO4 (Ref. code: 01-071-1141), FeMn2O4 (Ref. code: 01-075-0035), and Ca(Fe, Mg) (SiO3)2 (Ref. code: 00-024-0204) occur as the primary phase of the vanadium slag. (NH4)2SO4 and H2SO4 were of analytical grade.
(1)
where m1(g) is the mass of the vanadium slag used in the roasting procedure; w1(wt.%) is the content of vanadium or titanium in the vanadium slag; m2(g) is the mass of the leaching residue obtained from the leaching procedure; and w2(wt.%) is the content of vanadium or titanium in the leaching residue. 2.3. Characterization The XRD (DX-2007, Fangyuan Instrument Factory, China), with
Table 1 Chemical composition of the vanadium slag used in this study (wt./%). Composition
V2O5
TiO2
Fe2O3
MnO
SiO2
MgO
CaO
Al2O3
Others
Wt./%
17.52
13.10
36.73
10.00
14.91
2.34
2.26
2.20
0.93
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G. Zhang et al. / Journal of Alloys and Compounds 742 (2018) 504e511
Fig. 2. Simultaneous extraction of vanadium and titanium from vanadium slag using ammonium sulfate roasting-leaching process.
Cu Ka radiation (l ¼ 0.154056 nm), was used to confirm the mineral phase of the solid samples under the condition of 1 /min from 10 to 75 . The surface morphologies of the solid samples were observed by scanning electron microscopy (SEM) (JSM-7500F, JEOL, Japan) at a 5 kV accelerating voltage. The element content of the roasted samples was detected by an energy dispersive X-ray spectrometer (EDS, IS250, Oxford, Japan). 3. Results and discussion 3.1. Thermal decomposition process of ammonium sulfate Fig. 3 shows the thermogravimetry-differential scanning calorimetry (TG-DSC) curves of pure AS from room temperature to 570 C. The experiment was conducted at a heating rate of 10 C/ min and N2 flow rate of 100 mL/min. Three obvious endothermic peaks were observed at
Fig. 3. TG-DSC curve of the AS.
approximately 360 C, 370 C, and 510 C, which could be assigned to the decompositions of AS, ammonium bisulfate, and ammonium pyrophosphate, respectively [21]. The three stage reactions could be expressed as follows: (NH4)2SO4(s)]NH4HSO4(l) þ NH3(g)[,
(2)
2NH4HSO4(l)](NH4)2S2O7(s) þ H2O(g),
(3)
(NH4)2S2O7(s)]2NH3(g)[ þ 2N2(g)[ þ 6SO2(g)[ þ 9H2O(g).
(4)
The experimental rate of lost weight for AS was 13.69%, which is consistent with the 12.87% theoretical value. Clearly, the intermediate product, ammonium bisulfate, is acidic due to ionization of HSO 4 , which plays a key role in mineral decomposition. Therefore, the control of the roasting temperature in a suitable range is very important for the decomposition of minerals to maximize the
Fig. 4. XRD analysis of water-quenched vanadium slag.
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recycling of AS. 3.2. Effect of water quenching on the vanadium slag Fig. 4 presents the XRD pattern of water-quenched vanadium slag. Although the slag had almost the same diffraction peaks as the raw vanadium slag, the peaks appeared to become a little weak and were wider than those of the raw vanadium slag. This was because the rapid water cooling process could lead to incomplete nucleation growth. Additionally, the characteristic peaks of the Ca(Fe, Mg)(SiO3)2 phase were also changed in the 13.47, 31.51, 32.43 , and 33.03 positions. Fig. 5(a) and (b) show the back-scatter electron (BSE) analysis of the raw vanadium slag and water-quenched vanadium slag, respectively. Owing to rapid cooling, the particles were smaller in the water-quenched vanadium slag than that in raw vanadium slag. Fig. 5 (c) and (d) present the EDS analysis of points 1 and 2 in the raw vanadium slag. It indicates that the white bright area (point 1) was enriched in the spinel phase, and the dark black area (point 2) was enriched in the olivine phase. 3.3. Effect of roasting temperature on conversion of vanadium slag Fig. 6 presents the XRD patterns of the water-quenched slags roasted with AS at different temperatures. At 270 C, diffraction peaks of both ammonium sulfate and vanadium slag appeared in the roasted sample; no new phases were observed, which indicates no decomposition of the slag. Significant decomposition of the slag occurred above 320 C. At 320 C, the original spinel phases in vanadium slag, such as FeV2O4, Fe2TiO3, and Fe2MnO4, initiated a transformation into (NH4)3V(SO4)3, (NH4)3Fe(SO4)3, (NH4)2Mn(SO4)2, and TiSO4. However, there still existed some characteristic peaks of the spinel phase and AS, which indicate that
507
the decomposition was not complete. When the temperature increased to 370 C, all the diffraction peaks of the original spinel phase and AS disappeared, demonstrating complete decomposition of the slag at this temperature. Clearly, 370 C was a suitable reaction temperature for simultaneous extraction of vanadium and titanium from the vanadium slag. In addition, it was noticed that various double salts were formed by AS with various metals present in the slag; i.e., V, Fe, and Mn remained in the same stoichiometry in the temperature range from 320 C to 370 C and no decomposition of these salts occurred. However, when the temperature was further increased to 420 C, all the double salts decomposed into the ones with a low molar ratio of NH4 to metal ions; some double salts decomposed to those with no ammonium ion. According to our previous study [16], notable decomposition of TiOSO4 into acidresistant TiO2 would start at temperatures over 420 C. Therefore, to simultaneously recover vanadium and titanium, a suitable roasting temperature should be controlled in the range of 370e400 C. The SEM images of roasted samples at various temperatures were shown in Fig. 7. The SEM results indicate that both the vanadium slag and ammonium sulfate still existed and no roasting reaction occurred at 270 C, which was in agreement with the XRD results. When the roasting temperature achieved 320 C, the roasted particles acquire surface roughness; this could result from the overflow of product gases, indicating that the roasting reaction initiated, which was in good agreement with the XRD results at 320 C. At 370 C, the roasted product particles had a more porous and loose surface, indicating further overflow of gas products. The results appear to suggest that the vanadium slag was completely converted, as demonstrated by the XRD analysis. When the roasting temperature was elevated to 420 C, the roasted particles become smaller and a slight fusion was observed.
Fig. 5. BSE-EDS analysis of the vanadium slag: (a) raw vanadium slag; (b) water-quenched vanadium slag; (c) EDS analysis of point 1; (d) EDS analysis of point 2.
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Fig. 6. XRD analysis of roasted samples at different temperatures: (a) 270 C; (b) 320 C; (c) 370 C; (d) 420 C.
3.4. Effect of ammonium sulfate dosage on the vanadium and titanium extraction The effect of the mass ratio of AS to vanadium slag, which ranged from 0 to 16:1, on the extraction of vanadium and titanium, from both the raw and water quenched vanadium slags, was investigated under otherwise identical conditions. The results are shown in Fig. 8. The results demonstrate that the extraction of both vanadium and titanium increased with an increasing AS-to-vanadium slag mass ratio for both the raw and water-quenched vanadium slag. In the absence of AS, the raw vanadium slag had low vanadium and titanium extractions (both 35%), which considerably increased to 54% and 42%, respectively, upon extraction of the water-quenched vanadium slag. The maximum for the vanadium and titanium extraction was obtained at a mass ratio of 8:1. The respective percentages were 75.60% and 65.45% for the raw vanadium slag, with a rapid increase to 91.44% and 77.43% for the water-quenched slag. Clearly, water quenching significantly increased the extraction by 16% for vanadium and 12% for titanium. When the mass ratio was greater than eight, the extraction gradually decreased; the reason for this was discussed later. Fig. 9 shows the evolution of the contents of vanadium and titanium in the leaching residue, which was obtained by dissolution of the roasted slags in 6% H2SO4, with the AS-to-vanadium slag mass ratio. In the absence of AS, the respective contents were 11% and
15% for the raw vanadium slag, which decreased to 7.0% and 12%, respectively, for the water-quenched vanadium slag. With increasing AS/slag mass ratio, the contents of vanadium and titanium gradually decreased, and the minimum was obtained at a mass ratio of 8:1 for both the raw and water-quenched vanadium slags. When the mass ratio increased beyond 8:1, the contents of vanadium and titanium increased. The trend was in good agreement with the results shown in Fig. 7. As shown in Figs. 7 and 8, the extraction of both vanadium and titanium decreased when the mass ratio of AS to slag became greater than 8:1. During the roasting experiment, a large amount of foam formed at high mass ratios. The foam was formed due to the gas products [NH3(g) and H2O(g)] passing through the viscous liquid intermediate product, ammonium bisulfate, the melting point of which was less than 150 C. The higher the mass ratio, the more the foam. A large difference in the density of the foam and vanadium slag particles led to stratification of the two reactants. The ammonium bisulfate floated in the upper layer of the reaction system, while the vanadium slag submerged into the lower layer, which deteriorated the extraction. The process mechanism was shown in Fig. 10. 3.5. Characterization of leaching residues Fig. 11 shows the XRD patterns of the leaching residues from both the raw and water-quenched vanadium slags roasted at the
G. Zhang et al. / Journal of Alloys and Compounds 742 (2018) 504e511
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Fig. 7. SEM analysis of roasted samples at various temperatures: (a) 270 C; (b) 320 C; (c) 370 C; (d) 420 C.
phases in the water-quenched slag disappear after AS roasting followed by dilute H2SO4 leaching. The result was in good agreement with the high extraction of vanadium demonstrated in Fig. 7. Fig. 12 shows the image of leaching residue from the waterquenched vanadium slag. Compared with the vanadium slag particles shown in Fig. 5, which were smooth and compact, the leaching residue became irregular and porous. Clearly, the roasting and subsequent leaching completely destroy the original spinel structure.
4. Conclusion
Fig. 8. Effect of the mass ratio of AS/V-slag on vanadium and titanium extraction (roasting temperature, 370 C; roasting time, 60 min; leaching time, 60 min; leaching temperature, 60 C; sulfuric acid concentration, 6%).
AS-to-slag mass ratio of 8:1. The primary phases of the leaching residues from raw vanadium slag were CaFeSi2O6, Fe2TiO4, FeV2O4, and FeMn2O4; no crystal phases occurred in the leaching residue of water-quenched vanadium slag. Clearly, compared with the XRD patterns of the vanadium slags shown in Fig. 4, almost all the spinel
A novel environmentally friendly process, based on (NH4)2SO4 roasting and dilute H2SO4 leaching, to simultaneously extract vanadium and titanium from vanadium slag was proposed. The method of high-temperature water quenching pretreatment for the vanadium slag has been proven to be effective for vanadium and titanium separation. In detail, compared with the raw vanadium slag, the extraction rate of water-quenched vanadium and titanium increased by 16% and 12%, respectively. Furthermore, the optimized condition for the simultaneous extraction of vanadium and titanium was an AS-to-vanadium slag mass ratio of 4:1 and 370 C roasting, followed by leaching in a 6% H2SO4 solution. Meanwhile, the spinel phases in the vanadium slag, such as FeV2O4, Fe2TiO3, and Fe2MnO4, initiated conversion into (NH4)3V(SO4)3, (NH4)3Fe(SO4)3, (NH4)2Mn(SO4)2, and TiSO4 at 320 C, and a nearly complete transformation could be achieved at 370 C. The effect of the AS to vanadium slag mass ratio on the extraction of both vanadium and titanium was positive until 8:1. However, because of
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Fig. 9. Content of vanadium and titanium in the leaching residue.
Fig. 10. Stratification of the vanadium slag and ammonium bisulfate during the roasting process.
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Sichuan University Postdoctoral Research and Development Fund (NO. 2017SCU12017). References
Fig. 11. XRD analysis of leaching residues.
Fig. 12. BSE analysis of leaching residue from water-quenched vanadium slag.
the stratification of the vanadium slag and ammonium bisulfate at higher AS/slag mass ratios, the extraction decreased. Acknowledgements This work was financially supported by the National Key Research and Development Program (No. 2016YFB0600904) and
[1] R.R. Moskalyk, A.M. Alfantazi, Processing of vanadium: a review, Miner. Eng. 16 (2003) 793e805. [2] Y. Zhang, S. Bao, T. Liu, T. Chen, J. Huang, The technology of extracting vanadium from stone coal in China: history, current status and future prospects, Hydrometallurgy 109 (2011) 116e124. [3] S. Yang, Vanadium Metallurgy, Metallurgical Industry Press, Beijing, 2010. [4] G. Zhang, T. Zhang, G. Lü, Y. Zhang, Y. Liu, W. Zhang, Effects of microwave roasting on the kinetics of extracting vanadium from vanadium slag, JOM 68 (2016) 577e584. [5] H. Li, H. Fang, K. Wang, W. Zhou, Z. Yang, X. Yan, W. Ge, Q. Li, B. Xie, Asynchronous extraction of vanadium and chromium from vanadium slag by stepwise sodium roastingewater leaching, Hydrometallurgy 156 (2015) 124e135. [6] H. Li, K. Wang, W. Hua, Z. Yang, W. Zhou, B. Xie, Selective leaching of vanadium in calcification-roasted vanadium slag by ammonium carbonate, Hydrometallurgy 160 (2016) 18e25. [7] M.R. Tavakoli, D.B. Dreisinger, The kinetics of oxidative leaching of vanadium trioxide, Hydrometallurgy 147e148 (2014) 83e89. [8] M. Wang, P. Xian, X. Wang, B. Li, Extraction of vanadium from stone coal by microwave assisted sulfation roasting, JOM 67 (2015) 369e374. [9] G. Zhang, T. Zhang, G. Lü, Y. Zhang, Y. Liu, G. Xie, Extraction of vanadium from LD converter slag by pressure leaching process with titanium white waste acid, Rare Metal Mater. Eng. 44 (2015) 1894e1898. [10] X. Zhou, C. Wei, M. Li, S. Qiu, X. Li, Thermodynamics of vanadiumesulfurewater systems at 298K, Hydrometallurgy 106 (2011) 104e112. [11] X. Zhu, Y. Zhang, J. Huang, T. Liu, Y. Wang, A kinetics study of multi-stage counter-current circulation acid leaching of vanadium from stone coal, Int. J. Miner. Process. 114e117 (2012) 1e6. [12] X. Zhang, F. Liu, X. Xue, T. Jiang, Effects of microwave and conventional blank roasting on oxidation behavior, microstructure and surface morphology of vanadium slag with high chromium content, J. Alloys Compd. 686 (2016) 356e365. [13] M. Aarabi-Karasgani, F. Rashchi, N. Mostoufi, E. Vahidi, Leaching of vanadium from LD converter slag using sulfuric acid, Hydrometallurgy 102 (2010) 14e21. [14] X. Li, B. Xie, G. Wang, X. Li, Oxidation process of low-grade vanadium slag in presence of Na2CO3, Trans. Nonferrous Met. Soc. China 21 (2011) 1860e1867. [15] G. Zhang, T. Zhang, Y. Zhang, G. Lv, Y. Liu, Z. Liu, Pressure leaching of converter vanadium slag with waste titanium dioxide, Rare Met. 35 (2016) 576e580. [16] W. Liu, X. Wang, Z. Lu, H. Yue, B. Liang, L. Lu, C. Li, Preparation of synthetic rutile via selective sulfation of ilmenite with (NH4)2SO4 followed by targeted removal of impurities, Chin. J. Chem. Eng. 25 (2017) 821e828. [17] S.W. Li, W.H. Chen, S.H. Yin, A.Y. Ma, K. Yang, F. Xie, L.B. Zhang, J.H. Peng, Impacts of ultrasound on leaching recovery of zinc from low grade zinc oxide ore, Green Process. Synth. 4 (2015) 323e328. [18] H.I. Saleh, K.M. Hassan, Extraction of zinc from blast-furnace dust using ammonium sulfate, J. Chem. Technol. Biotechnol. 79 (2004) 397e402. [19] J. Highfield, H. Lim, J. Fagerlund, R. Zevenhoven, Activation of serpentine for CO2 mineralization by flux extraction of soluble magnesium salts using ammonium sulfate, RSC Adv. 2 (2012) 6535e6541. [20] J. Li, Z. Chen, B. Shen, Z. Xu, Y. Zhang, The extraction of valuable metals and phase transformation and formation mechanism in roasting-water leaching process of laterite with ammonium sulfate, J. Clean. Prod. 140 (2016) 1148e1155. [21] K. Liu, C. Lang, Thermal decomposition of ammonium sulfate, Chem. Res. Appl. 14 (2002) 737e739.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Simultaneous extraction of vanadium and titanium from vanadium slag using ammonium sulfate roasting-leaching process Guoquan Zhang, Dongmei Luo, Chenhui Deng, Li Lv, Bin Liang, Chun Li* School of Chemical Engineering, Sichuan University, Chengdu 610065, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 October 2017 Received in revised form 6 January 2018 Accepted 22 January 2018
Sodium and calcification roasting processes are traditional technologies to recover vanadium from vanadium slag. However, these processes are associated with many drawbacks, including high energy consumption, serious environment pollution, and the inability to simultaneously extract associated titanium resources. In this paper, a novel technology for simultaneous extraction of vanadium and titanium from vanadium slag was proposed, in which the vanadium slag was roasted with recyclable (NH4)2SO4 (AS) at moderately high temperatures followed by dilute H2SO4 leaching. To enhance the extraction, an activation pretreatment of the vanadium slag through high-temperature water quenching was employed. The results demonstrated that the activation significantly accelerated the extraction, with the vanadium and titanium extraction increasing by 16% and 12%, respectively, compared with the raw vanadium slag. The extraction of vanadium and titanium were 91% and 77%, respectively, after roasting at an AS-to-vanadium slag mass ratio of 4:1 and 370 C followed by leaching in a 6% H2SO4 solution. X-ray diffraction analysis indicated that the spinel phases in the vanadium slag, such as FeV2O4, Fe2TiO3, and Fe2MnO4, began to transform into (NH4)3V(SO4)3, (NH4)3Fe(SO4)3, (NH4)2Mn(SO4)2, and TiSO4 at 320 C and a nearly complete conversion could be achieved at 370 C. The mass ratio of AS to vanadium slag significantly affected the extraction of both vanadium and titanium, which increased with the increasing mass ratio until an 8:1 ratio was achieved, after which, the extraction decreased. A stratification phenomenon of the vanadium slag and ammonium bisulfate at high AS/slag mass ratios was observed, which could be responsible for the decreasing extraction. © 2018 Elsevier B.V. All rights reserved.
Keywords: Vanadium Titanium Vanadium slag Ammonium sulfate Roasting
1. Introduction Vanadium is an important strategic metal and is widely used in the iron and steel industry, as well as in non-ferrous alloys due to its excellent hardness, tensile strength, and corrosion resistance [1]. Vanadium accounts for only 0.02% of the crustal weight, which although is a higher abundance than that of copper, zinc, and nickel, and ranks 22nd in the known elements, it does not naturally occur in its pure state [2]. Research has confirmed that vanadium initially presents in igneous rocks and gathers in a water-insoluble state of V(III) [3]. Because the ion radii of V(III), Mn(III), Fe(III), and Ti(III) are close, it is quite common for these ions to form a polymetallic symbiotic ore. Vanadium-titanium magnetite ore is a typical polymetallic symbiotic ore that is primarily found in Russia, China, and South Africa. In China, vanadium slag, a by-product of vanadium-
* Corresponding author. E-mail address: [email protected] (C. Li). https://doi.org/10.1016/j.jallcom.2018.01.300 0925-8388/© 2018 Elsevier B.V. All rights reserved.
titanium magnetite in the converter steelmaking process, is a typical vanadium metallurgical raw material, which contributes to more than 40% of V2O5 production in the country [4]. In general, it is almost impossible to separate vanadium from vanadium slag in an unenhanced procedure because there is little vanadium in vanadium slag that could dissolve in water, alkali, or acid directly [5,6]. Further, vanadium primarily occurs in the very stable spinel phase in vanadium slag. Theoretically, it is necessary to recover vanadium from vanadium slag by transforming the lowvalence insoluble vanadium in the spinel phase into high-valent soluble vanadium [7e9]. The traditional commercial methods for vanadium extraction from vanadium slag are sodium roastingwater leaching and calcification roasting-acid leaching [10,11]. In the two methods, the vanadium slag is roasted with an additive, such as NaCl or CaO, above 850 C to decompose the spinel phase structure and vanadium extraction of about 75e80% is obtained [12]. Recently, several studies have been conducted to enhance vanadium extraction. Li et al. researched the process of extracting
G. Zhang et al. / Journal of Alloys and Compounds 742 (2018) 504e511
vanadium by calcification roasting and ammonium carbonate leaching and obtained 96% vanadium recovery [6]. Rashchi et al. revealed the effect of alkaline roasting and H2SO4 leaching on vanadium extraction from vanadium slag using surface response methodology [13]. Xie et al. investigated the oxidation behavior of the vanadium phase in vanadium slag using the sodium roasting process and achieved 90% vanadium extraction [14]. Although over 90% vanadium extraction could be obtained in these studies, a roasting temperature of at least 800 C was required, which is energy intensive. The sodium-roasting and calcification-roasting processes also involve the emission of harmful gases and high additive consumption [15]. In addition, both the sodium and calcification roasting processes seldom allow for the simultaneous extraction of titanium, a high-value-added metal associated in vanadium slag, since the titanium cannot be dissolved during vanadium extraction. Therefore, it is necessary to develop a new extraction route. The obvious advantages of the ammonium sulfate roastingleaching (ASRL) process are high efficiency, low energy consumption (roasting temperatures of only 300e400 C), and environmental friendliness (ammonium sulfate is a recyclable extractant), especially in dealing with low-grade symbiotic minerals [16,17]. Saleh et al. researched the technology of extracting zinc by the ASRL process and obtained a 95% zinc extraction rate at 350 C [18]. Highfield et al. investigated magnesium extraction from serpentine using the ammonium sulfate roasting process and determined that the silicate minerals could decomposed at 350 C [19]. Li et al. used ammonium sulfate to decompose low-grade nickel laterite at 400 C, where 90.8% nickel and 85.4% cobalt could be selectively extracted [20]. In this study, we proposed a novel ASRL process that can be used to simultaneously extract and recover vanadium and titanium from vanadium slag under mild conditions for comprehensively utilizing vanadium slag. In order to enhance the extraction, raw vanadium slag was melted and water quenched for activation, which could be easily realized in industry. The decomposition behavior and microstructure morphology of vanadium slag in the presence of ammonium sulfate at different roasting temperatures is investigated. Furthermore, the effect of the ammonium sulfate dosage on the extraction is discussed. The mineral composition of leaching residues is also characterized.
2. Experimental 2.1. Materials
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Fig. 1. XRD analysis of raw vanadium slag.
2.2. Procedure In the water quenching process, the raw vanadium slag was placed in a high-purity SiO2 crucible, which was positioned centrally and heated by MoSi2 rods in an electric furnace (laboratory customization). When heated to 1500 C in air atmosphere, the slag was dropped rapidly into a bucket located immediately below the hearth through a specially designed outlet and cooled by water in the bucket. After being crushed and milled, the water quenched vanadium slag was dried at 110 C for 12 h. In each roasting test, the vanadium slag sample was evenly mixed with (NH4)2SO4 (AS) at a predetermined mass ratio. The mixture was placed in a porcelain boat, heated at a rate of 10 C/min until 370 C, and then annealed for 90 min in an electric furnace (KSL-1200X, Heifei Kejing Materials Technology Co., Limited, Heifei, China). The roasted slag was then withdrawn and cooled in a desiccator to room temperature. The roasted samples were leached in 6 vol% H2SO4 at a liquid-tosolid mass ratio of 8:1 and 60 C for 1 h. The obtained slurry was run through a vacuum filter. The leaching solution and residues were collected and analyzed to determine the leaching ratio of both vanadium and titanium. The simultaneous extraction of vanadium and titanium from vanadium slag using ammonium sulfate roasting-leaching process was shown in Fig. 2. The ratio could be calculated by following equation (1):
a ¼ f1 ðm2 w2 Þ=ðm1 w1 Þg 100%
The vanadium slag used in this research was provided by Panzhihua Steel & Iron Co., Ltd, Sichuan province, China. The vanadium slag was crushed and milled to a thickness of 75 mm by a ball mill after drying at 110 C for 12 h. The chemical composition of the slag is shown in Table 1. The X-ray diffraction (XRD) patterns of vanadium slag are shown in Fig. 1. The XRD patterns indicate that FeV2O4 (Ref. code: 01-075-0317), Fe2TiO4 (Ref. code: 01-071-1141), FeMn2O4 (Ref. code: 01-075-0035), and Ca(Fe, Mg) (SiO3)2 (Ref. code: 00-024-0204) occur as the primary phase of the vanadium slag. (NH4)2SO4 and H2SO4 were of analytical grade.
(1)
where m1(g) is the mass of the vanadium slag used in the roasting procedure; w1(wt.%) is the content of vanadium or titanium in the vanadium slag; m2(g) is the mass of the leaching residue obtained from the leaching procedure; and w2(wt.%) is the content of vanadium or titanium in the leaching residue. 2.3. Characterization The XRD (DX-2007, Fangyuan Instrument Factory, China), with
Table 1 Chemical composition of the vanadium slag used in this study (wt./%). Composition
V2O5
TiO2
Fe2O3
MnO
SiO2
MgO
CaO
Al2O3
Others
Wt./%
17.52
13.10
36.73
10.00
14.91
2.34
2.26
2.20
0.93
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Fig. 2. Simultaneous extraction of vanadium and titanium from vanadium slag using ammonium sulfate roasting-leaching process.
Cu Ka radiation (l ¼ 0.154056 nm), was used to confirm the mineral phase of the solid samples under the condition of 1 /min from 10 to 75 . The surface morphologies of the solid samples were observed by scanning electron microscopy (SEM) (JSM-7500F, JEOL, Japan) at a 5 kV accelerating voltage. The element content of the roasted samples was detected by an energy dispersive X-ray spectrometer (EDS, IS250, Oxford, Japan). 3. Results and discussion 3.1. Thermal decomposition process of ammonium sulfate Fig. 3 shows the thermogravimetry-differential scanning calorimetry (TG-DSC) curves of pure AS from room temperature to 570 C. The experiment was conducted at a heating rate of 10 C/ min and N2 flow rate of 100 mL/min. Three obvious endothermic peaks were observed at
Fig. 3. TG-DSC curve of the AS.
approximately 360 C, 370 C, and 510 C, which could be assigned to the decompositions of AS, ammonium bisulfate, and ammonium pyrophosphate, respectively [21]. The three stage reactions could be expressed as follows: (NH4)2SO4(s)]NH4HSO4(l) þ NH3(g)[,
(2)
2NH4HSO4(l)](NH4)2S2O7(s) þ H2O(g),
(3)
(NH4)2S2O7(s)]2NH3(g)[ þ 2N2(g)[ þ 6SO2(g)[ þ 9H2O(g).
(4)
The experimental rate of lost weight for AS was 13.69%, which is consistent with the 12.87% theoretical value. Clearly, the intermediate product, ammonium bisulfate, is acidic due to ionization of HSO 4 , which plays a key role in mineral decomposition. Therefore, the control of the roasting temperature in a suitable range is very important for the decomposition of minerals to maximize the
Fig. 4. XRD analysis of water-quenched vanadium slag.
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recycling of AS. 3.2. Effect of water quenching on the vanadium slag Fig. 4 presents the XRD pattern of water-quenched vanadium slag. Although the slag had almost the same diffraction peaks as the raw vanadium slag, the peaks appeared to become a little weak and were wider than those of the raw vanadium slag. This was because the rapid water cooling process could lead to incomplete nucleation growth. Additionally, the characteristic peaks of the Ca(Fe, Mg)(SiO3)2 phase were also changed in the 13.47, 31.51, 32.43 , and 33.03 positions. Fig. 5(a) and (b) show the back-scatter electron (BSE) analysis of the raw vanadium slag and water-quenched vanadium slag, respectively. Owing to rapid cooling, the particles were smaller in the water-quenched vanadium slag than that in raw vanadium slag. Fig. 5 (c) and (d) present the EDS analysis of points 1 and 2 in the raw vanadium slag. It indicates that the white bright area (point 1) was enriched in the spinel phase, and the dark black area (point 2) was enriched in the olivine phase. 3.3. Effect of roasting temperature on conversion of vanadium slag Fig. 6 presents the XRD patterns of the water-quenched slags roasted with AS at different temperatures. At 270 C, diffraction peaks of both ammonium sulfate and vanadium slag appeared in the roasted sample; no new phases were observed, which indicates no decomposition of the slag. Significant decomposition of the slag occurred above 320 C. At 320 C, the original spinel phases in vanadium slag, such as FeV2O4, Fe2TiO3, and Fe2MnO4, initiated a transformation into (NH4)3V(SO4)3, (NH4)3Fe(SO4)3, (NH4)2Mn(SO4)2, and TiSO4. However, there still existed some characteristic peaks of the spinel phase and AS, which indicate that
507
the decomposition was not complete. When the temperature increased to 370 C, all the diffraction peaks of the original spinel phase and AS disappeared, demonstrating complete decomposition of the slag at this temperature. Clearly, 370 C was a suitable reaction temperature for simultaneous extraction of vanadium and titanium from the vanadium slag. In addition, it was noticed that various double salts were formed by AS with various metals present in the slag; i.e., V, Fe, and Mn remained in the same stoichiometry in the temperature range from 320 C to 370 C and no decomposition of these salts occurred. However, when the temperature was further increased to 420 C, all the double salts decomposed into the ones with a low molar ratio of NH4 to metal ions; some double salts decomposed to those with no ammonium ion. According to our previous study [16], notable decomposition of TiOSO4 into acidresistant TiO2 would start at temperatures over 420 C. Therefore, to simultaneously recover vanadium and titanium, a suitable roasting temperature should be controlled in the range of 370e400 C. The SEM images of roasted samples at various temperatures were shown in Fig. 7. The SEM results indicate that both the vanadium slag and ammonium sulfate still existed and no roasting reaction occurred at 270 C, which was in agreement with the XRD results. When the roasting temperature achieved 320 C, the roasted particles acquire surface roughness; this could result from the overflow of product gases, indicating that the roasting reaction initiated, which was in good agreement with the XRD results at 320 C. At 370 C, the roasted product particles had a more porous and loose surface, indicating further overflow of gas products. The results appear to suggest that the vanadium slag was completely converted, as demonstrated by the XRD analysis. When the roasting temperature was elevated to 420 C, the roasted particles become smaller and a slight fusion was observed.
Fig. 5. BSE-EDS analysis of the vanadium slag: (a) raw vanadium slag; (b) water-quenched vanadium slag; (c) EDS analysis of point 1; (d) EDS analysis of point 2.
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Fig. 6. XRD analysis of roasted samples at different temperatures: (a) 270 C; (b) 320 C; (c) 370 C; (d) 420 C.
3.4. Effect of ammonium sulfate dosage on the vanadium and titanium extraction The effect of the mass ratio of AS to vanadium slag, which ranged from 0 to 16:1, on the extraction of vanadium and titanium, from both the raw and water quenched vanadium slags, was investigated under otherwise identical conditions. The results are shown in Fig. 8. The results demonstrate that the extraction of both vanadium and titanium increased with an increasing AS-to-vanadium slag mass ratio for both the raw and water-quenched vanadium slag. In the absence of AS, the raw vanadium slag had low vanadium and titanium extractions (both 35%), which considerably increased to 54% and 42%, respectively, upon extraction of the water-quenched vanadium slag. The maximum for the vanadium and titanium extraction was obtained at a mass ratio of 8:1. The respective percentages were 75.60% and 65.45% for the raw vanadium slag, with a rapid increase to 91.44% and 77.43% for the water-quenched slag. Clearly, water quenching significantly increased the extraction by 16% for vanadium and 12% for titanium. When the mass ratio was greater than eight, the extraction gradually decreased; the reason for this was discussed later. Fig. 9 shows the evolution of the contents of vanadium and titanium in the leaching residue, which was obtained by dissolution of the roasted slags in 6% H2SO4, with the AS-to-vanadium slag mass ratio. In the absence of AS, the respective contents were 11% and
15% for the raw vanadium slag, which decreased to 7.0% and 12%, respectively, for the water-quenched vanadium slag. With increasing AS/slag mass ratio, the contents of vanadium and titanium gradually decreased, and the minimum was obtained at a mass ratio of 8:1 for both the raw and water-quenched vanadium slags. When the mass ratio increased beyond 8:1, the contents of vanadium and titanium increased. The trend was in good agreement with the results shown in Fig. 7. As shown in Figs. 7 and 8, the extraction of both vanadium and titanium decreased when the mass ratio of AS to slag became greater than 8:1. During the roasting experiment, a large amount of foam formed at high mass ratios. The foam was formed due to the gas products [NH3(g) and H2O(g)] passing through the viscous liquid intermediate product, ammonium bisulfate, the melting point of which was less than 150 C. The higher the mass ratio, the more the foam. A large difference in the density of the foam and vanadium slag particles led to stratification of the two reactants. The ammonium bisulfate floated in the upper layer of the reaction system, while the vanadium slag submerged into the lower layer, which deteriorated the extraction. The process mechanism was shown in Fig. 10. 3.5. Characterization of leaching residues Fig. 11 shows the XRD patterns of the leaching residues from both the raw and water-quenched vanadium slags roasted at the
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Fig. 7. SEM analysis of roasted samples at various temperatures: (a) 270 C; (b) 320 C; (c) 370 C; (d) 420 C.
phases in the water-quenched slag disappear after AS roasting followed by dilute H2SO4 leaching. The result was in good agreement with the high extraction of vanadium demonstrated in Fig. 7. Fig. 12 shows the image of leaching residue from the waterquenched vanadium slag. Compared with the vanadium slag particles shown in Fig. 5, which were smooth and compact, the leaching residue became irregular and porous. Clearly, the roasting and subsequent leaching completely destroy the original spinel structure.
4. Conclusion
Fig. 8. Effect of the mass ratio of AS/V-slag on vanadium and titanium extraction (roasting temperature, 370 C; roasting time, 60 min; leaching time, 60 min; leaching temperature, 60 C; sulfuric acid concentration, 6%).
AS-to-slag mass ratio of 8:1. The primary phases of the leaching residues from raw vanadium slag were CaFeSi2O6, Fe2TiO4, FeV2O4, and FeMn2O4; no crystal phases occurred in the leaching residue of water-quenched vanadium slag. Clearly, compared with the XRD patterns of the vanadium slags shown in Fig. 4, almost all the spinel
A novel environmentally friendly process, based on (NH4)2SO4 roasting and dilute H2SO4 leaching, to simultaneously extract vanadium and titanium from vanadium slag was proposed. The method of high-temperature water quenching pretreatment for the vanadium slag has been proven to be effective for vanadium and titanium separation. In detail, compared with the raw vanadium slag, the extraction rate of water-quenched vanadium and titanium increased by 16% and 12%, respectively. Furthermore, the optimized condition for the simultaneous extraction of vanadium and titanium was an AS-to-vanadium slag mass ratio of 4:1 and 370 C roasting, followed by leaching in a 6% H2SO4 solution. Meanwhile, the spinel phases in the vanadium slag, such as FeV2O4, Fe2TiO3, and Fe2MnO4, initiated conversion into (NH4)3V(SO4)3, (NH4)3Fe(SO4)3, (NH4)2Mn(SO4)2, and TiSO4 at 320 C, and a nearly complete transformation could be achieved at 370 C. The effect of the AS to vanadium slag mass ratio on the extraction of both vanadium and titanium was positive until 8:1. However, because of
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Fig. 9. Content of vanadium and titanium in the leaching residue.
Fig. 10. Stratification of the vanadium slag and ammonium bisulfate during the roasting process.
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Sichuan University Postdoctoral Research and Development Fund (NO. 2017SCU12017). References
Fig. 11. XRD analysis of leaching residues.
Fig. 12. BSE analysis of leaching residue from water-quenched vanadium slag.
the stratification of the vanadium slag and ammonium bisulfate at higher AS/slag mass ratios, the extraction decreased. Acknowledgements This work was financially supported by the National Key Research and Development Program (No. 2016YFB0600904) and
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