Efficient Phase Transformation of Î³-Al2O3 to

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Applied Chemistry

Efficient Phase Transformation of #-Al2O3 to #-Al2O3 in Spent Hydrodesulphurization Catalyst by Microwave Roasting Method Jialiang Zhang, Cheng Yang, Yongqiang Chen, and Chengyan Wang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b04621 • Publication Date (Web): 04 Jan 2019 Downloaded from http://pubs.acs.org on January 6, 2019

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Industrial & Engineering Chemistry Research

Efficient Phase Transformation of γ-Al2O3 to α-Al2O3 in Spent Hydrodesulphurization Catalyst by Microwave Roasting Method Jialiang Zhanga,b, Cheng Yanga, Yongqiang Chena,b, Chengyan Wanga,b,* a

School of Metallurgical and Ecological Engineering, University of Science and

Technology Beijing, Beijing 100083, China b

Beijing Key Laboratory of Rare and Precious Metals Green Recycling and

Extraction, University of Science and Technology Beijing, Beijing 100083, China * Corresponding author: Tel.: 861062332271; Fax: 861062333170 Email: [email protected] (C. Wang)

ABSTRACT In the preparation of hydrodesulphurization (HDS) catalyst, highly reactive γ-Al2O3 is used as a carrier, resulting in an undesirable high leaching of aluminum during the recycling of spent catalyst. In this research, microwave roasting was employed to transform γ-Al2O3 into more stable α-Al2O3 for decreasing Al leaching. The phase transformation was investigated by XRD, XPS, and FTIR, and the results show that the transformation to α-Al2O3 can be achieved at a lower temperature of 1000 °C and a much shorter time of 1 h, compared to the conventional roasting method. The effect of transformation temperature on the leaching of metals was then investigated. The leaching of Al significantly decreased in both alkaline and acid leaching, and moreover the leaching of Co and Ni was reinforced after the transformation of Al2O3. It is helpful to simplify the subsequent process of Al separation and increase the overall recovery rate of valuable metals.

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1. Introduction Hydrodesulphurization (HDS) catalysts are widely applied in the petroleum refining industry.1 After repeating catalytic processing for crude oil, the catalysts turn to be deactivated with the deposition of carbon and some metals such as V, Ni, etc.2, 3 The catalysts deactivate with time and eventually become hazardous wastes.4, 5 The production amount of spent HDS catalysts is about 120,000 tons (dry basis) every year.6 In another hand, these solid wastes generally contain 15–30% aluminum, 4– 12% molybdenum, 1–5% cobalt, 1–5% nickel and 1–5% vanadium, which make it economically feasible to recover these valuable metals from spent catalysts.7 Many meaningful researches are devoted to the recycling of spent HDS catalysts. The available methods can be divided into pyrometallurgical, hydrometallurgical and pyrohydrometallurgical combined processes.8-10 The state of metals in spent catalysts is usually a mixture of sulfide and oxide. As a result, the pyrohydrometallurgical method combining oxidation roasting with two-stage leaching has always been the most common method, in which the spent catalyst is roasted first in air to remove oil and transform metal sulfides into oxides. Subsequently, Mo and V are extracted from the roasted products through using alkaline solution as the leaching agent. Acid leaching is then followed to extract Co and Ni from the alkaline leaching residues.11-13 This process is simple and its required equipment is easily available, and the valuable metals can be selectively leached in two stages, which simplify the subsequent separation process. However, the carrier of HDS catalyst is γ-Al2O3 with a high activity,14 so the high content of Al is inevitable for it to be dissolved in the alkaline


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and acid leaching process, which leads to an increase in reagent consumption. What’s more, the precipitation of Al as Al(OH)3 through pH adjustment is the main approach to remove aluminum from the leachate of spent catalyst. However, a high amount of valuable metals are lost due to their co-precipitation of Al(OH)3.15, 16 Some scholars have demonstrated a solvent extraction process to separate Al and other metals in the leachate,17-20 but the industrial application of this method is restricted by the expensive extraction agent and complex operation. Therefore, reducing the leaching of aluminum becomes imperative and significant for the efficient recovery of valuable metals and the reduction of operating cost. The carrier of HDS catalyst, γ-Al2O3 which is called as transition alumina, is the metastable forms of aluminum oxide, while another common alumina polymorph, α-Al2O3, is much more stable and usually crystallized at high temperatures.21-23 So, if γ-Al2O3 can be transformed into α-Al2O3, the leaching of Al is expected to decrease and be beneficial to subsequent separation and purification process. Mechanical milling was frequently used to transform γ-Al2O3 into α-Al2O3.24, 25 However, it was necessary to spend a long time in obtaining high transformation efficiency. In addition, conventional heating method was also employed to achieve the transformation from γ-Al2O3 into α-Al2O3, but this process requires a high temperature of 1100 to 1200 °C and a long time of more than 5 h.26-28 It is worth noting that a mixture of aluminum nitrate and carbon black or urea is used as a raw material to synthesize α-Al2O3 by microwave heating and this process could be conducted at lower temperature and less time.29-31 Additionally, microwave heating



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has the benefits of more controllable and selective heating and higher heating rate over conventional heating, because microwave irradiation delivers the required energy instead of heating the entire system.32 Hence, in the present study, transforming from γ-Al2O3 of HDS catalyst into α-Al2O3 by microwave roasting was proposed and the effect of roasting temperature on transformation efficiency was investigated. Then, we explored the leaching behavior of Al and valuable metals in the processes of alkaline and acid leaching at different transformation temperatures. In addition, some characterization methods including XRD, XPS, FTIR and SEM were applied to investigate the properties of the initial spent catalyst and roasting products, particularly for the existing form of Al2O3.

2. Experimental 2.1. Materials The spent HDS catalyst used in this study was applied by a local petroleum-refining plant, and it was cylindrical with an average diameter of 1.2 mm and length of 7 mm, containing a large amount of residual oil supported on γ-Al2O3. The sample was dried at 100 °C for 12 h. Then, it was crushed and ground to 74–148 µm and thoroughly mixed for composition analysis and subsequent experiments. The composition of the initial spent catalyst is shown in Table 1. Table 1 Chemical composition of the initial spent catalyst Element

Mo

V

W

Ni

Co

Al

S

C

Si

Mass fraction (%)

5.99

1.06

0.32

3.32

1.72

24.8

7.62

23.0

0.16

2.2. Methods


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In a typical experimental run, 20.0 g of initial spent catalyst was placed in a quartz tube and then reacted in a microwave reactor (MW-HS-06, Kunming University of Science and Technology, China). An argon gas of 600 mL min−1 was firstly circulated through the quartz tube for 30 min before the roasting. Then the catalyst was gradually heated to a specified temperature (output power: 800W, frequency: 2450 MHz, heating rate: 35 °C min−1) and maintained for 1 h. After roasting, the roasted products were then cooled inside the furnace to ambient temperature under the protection of argon gas. Roasting temperature was investigated to determine the optimal transformation temperature of the carrier in spent catalyst. In the leaching experiment, the microwave roasted products were roasted in a muffle furnace at 500 °C under air atmosphere for 2 h to remove residual oil and make sulfides convert to oxides. After that, alkaline leaching was conducted in a 200 mL glass reactor with a magnetic agitation. A desired mass of roasted catalyst and NaOH solution of 3 mol L−1 were reacted in the reactor with an S/L ratio of 200 g L−1 at 90 °C for 3 h. After alkaline leaching, the contents of Mo, V and Al in the leachate were analyzed by ICP (Optima 7000 DV, Perkin Elmer instruments, US). Subsequently, the leaching residues and H2SO4 solution of 1.5 mol L−1 were reacted in the reactor with an S/L ratio of 200 g L−1 at 90 °C for 3 h. After acid leaching, the content of Ni, Co and Al in the filtered leachate was analyzed by ICP. During the leaching process, the samples in a glass reactor were heated in a water bath with magnetic agitation. The reaction temperature and stirring speed are controllable and stable in the leaching experiments.



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In this study, the leaching efficiency ηi can be calculated according to Eq. (1).

ηi 

ci  V  100% mi  ωi

(1)

where ci (g L−1) and V (L) are the concentration of element “i” and the volume of leachate, and mi (g) and ωi (%) are the mass of the spent catalyst and the content of element “i” in it, respectively. The oil in the initial catalyst can be removed simultaneously with the transformation of Al2O3. The removal rate was represented by the removal rate of carbon, and the removal rate of carbon ηc can be calculated according to Eq. (2).

ηc 

m0  ω0  mc  ωc  100% m0  ω0

(2)

where m0 (g) and mc (g) are the mass of the initial spent catalyst and roasted products, respectively, ω0 (%) and ωc (%) are the contents in them, respectively. 2.3. Characterization The carbon content and sulfur content of the samples before and after the roasting process were measured using a carbon-sulfur analyzer (EMIA-820V, Horiba, Japan). In order to study the phase transformation, the initial spent HDS catalyst and roasted products were examined using XRD (RINT-TTR3, RIGAKU, Japan), XPS (AXIS Ultra DLD, Kratos, Japan), and FTIR (Nicolet Nexus 410, US). Surface characterizations were performed by SEM (MLA250, FEI, US), and EDS (MLA250, FEI, US). The components of the collected oil were analyzed using GC-MS (QP2010, SHIMADZU, Japan).

3. Results and discussion


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3.1 Characterization for transformation efficiency from γ-Al2O3 into α-Al2O3 The spent HDS catalyst was roasted for 1 h at different temperatures by microwave roasting. Some characterization methods including XRD, XPS and FTIR were applied to study the phase transformation during the roasting process, particularly for Al2O3 transformation. Fig. 1 shows the XRD patterns of initial spent catalyst and roasting products. The characteristic peaks of 2θ of the spent HDS catalyst at 39.48°, 45.91°, and 66.95° were attributed to γ-Al2O3 (International Centre for Diffraction Data (ICDD) file number 75-0921). While in the XRD patterns of roasted catalyst at 700 °C and 900 °C (Fig. 1(b) and Fig. 1(c)), eight broad diffraction peaks corresponding to α-Al2O3 at 2θ = 25.60°, 35.15°, 37.78°, 43.36°, 52.56°, 57.51°, 66.52°, and 68.21° (ICDD file number 78-2427) appeared, indicating that a part of γ-Al2O3 was transformed into α-Al2O3. After roasting at 1000 °C (Fig. 1(d)), the XRD pattern shows that the peaks appearing at 2θ can be well assigned to α-Al2O3 and the peaks of γ-Al2O3 had basically disappeared, which indicates that γ-Al2O3 in the spent catalyst was basically transformed into α-Al2O3. As mentioned in the introduction, the temperature of the transformation of γ-Al2O3 into α-Al2O3 by conventional roasting was at least 1100–1200 °C for a long time. Compared with conventional roasting, microwave roasting can transform γ-Al2O3 into α-Al2O3 at a lower temperature and phase transformation time was significantly reduced. Thus, the method of microwave roasting is more efficient in energy utilization and time. When the temperature exceeded 1000 °C to 1100 °C (Fig. 1(e)), the existing form of support alumina remained basically unchanged. Additionally, as shown in Fig. 1, valuable



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metals in the spent catalyst were mainly presented in the form of sulfides and the diffraction peaks of some metal sulfides were more apparent with an increase in roasting temperature. The reason may be that a large amount of organic matters in the spent catalyst were removed and the crystallization degree of metal sulfides increased in the roasting process.

Fig. 1. XRD patterns of (a) the initial spent HDS catalyst and the products roasted at (b) 700 °C, (c) 900 °C, (d) 1000 °C, (e) 1100 °C for 1 h The XPS Al 2p spectra for the initial and roasted catalyst at various temperatures are presented in Fig. 2. The two particular binding energy positions 74.30 eV and 74.14 eV corresponded to γ-Al2O3 phase and α-Al2O3 phase, respectively.33,

34

The

relative content of aluminum element in different forms can be determined by the calculation of the areas of peaks for different substances in the XPS spectrum. Therefore, the calculated distribution of alumina form in different materials is also shown in Fig. 2. The aluminum element in the initial spent HDS catalyst was basically in the form of γ-Al2O3. The relative content of γ-Al2O3 decreased with increasing roasting temperature until it basically disappeared at 1000 °C, at which the relative contents of γ-Al2O3 and α-Al2O3 were 4.2% and 95.8%, respectively. These


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results indicate that γ-Al2O3 of the spent HDS catalyst can be efficiently transformed into α-Al2O3 by microwave roasting, which was consistent with the XRD results.

Fig. 2. The XPS Al 2p spectra and the calculated distribution of alumina form for the initial and roasted catalyst Fig. 3 shows the fourier transform-infrared spectrum for the initial spent catalyst and microwave roasted products at 1000 °C. As seen from Fig. 3, the broad bands of 830–870 cm−1 and 550–600 cm−1 were observed in the spectra of initial spent catalyst, and these two bands were the characteristic ones of γ-Al2O3.35-37 After microwave roasting at 1000 °C, the bands of γ-Al2O3 disappeared and three new bands of 453 cm−1, 602 cm−1 and 640 cm−1 appeared. According to the reference,35 these three bonds correspond to α-Al2O3. It indicates that γ-Al2O3 in the spent HDS catalyst was successfully transformed into α-Al2O3 at 1000 °C. In addition, after microwave roasting at 1000 °C, some bands which are evident in the initial spectra disappeared. Among them, bands of 3440 cm−1, 2955 cm−1 and 2925 cm−1 were assigned to the



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C-H vibration of aliphatic groups or aromatic rings, and the weaker absorption band at 1458 cm−1 and 1377 cm−1 were attributed to the C-H flexion vibrations of aliphatic groups.38,

39

It suggests that the deposited oil in the spent catalyst was efficiently

removed in the microwave roasting process.

Fig. 3. Fourier transform-infrared spectra of the initial and roasted spent catalyst (roasting temperature: 1000 °C) 3.2 Oil recovery As demonstrated by FTIR results, the oil was removed from the spent catalyst with the phase transformation to α-Al2O3. The oil deposited in spent HDS catalyst is harmful for the metal leaching in the hydrometallurgical process and can result in a decreased leaching of valuable metals. Oxidation roasting is a common method to remove the oil. However, it has a disadvantage that the temperature is easily out of control because of the rapid combustion of extremely flammable oil.40,

41

Additionally, due to the incomplete combustion of oil, much of toxic and harmful gases cause a serious environmental pollution. Thus, in the present study, microwave roasting under an inert atmosphere was adopted to recover the oil, so that the serious pollution of exhausted gases can be avoided. The removal rate of carbon at different


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temperatures is presented in Fig. 4 (the points at 500 °C, 600 °C and 700 °C in Fig. 4 were quoted from our previous study)42 and it shows that the carbon removal rate gradually increased with the increasing roasting temperature. When the roasting temperature was 1000 °C at which the carrier can be entirely transformed into α-Al2O3, the carbon removal rate was 86.7% and the weight loss was 31.1%, which indicates that the removal efficiency of oil is relatively high by microwave roasting. GC-MS analysis was used to analyze the composition of recovered oil and the results are presented in Fig. S1 and Table S1. The main components in the recovered oil via microwave roasting are aromatic and aliphatic compounds, and their contents are about 80.5% and 19.5%, respectively. Thus, the recovered oil can be used for the production of petrochemical products and as an energy source.

Fig. 4. Effect of roasting temperature on carbon removal rate (the points at 500 °C, 600 °C and 700 °C were quoted from our previous study)42 and photograph of the oil recovered by microwave roasting at 1000 °C 3.3. Leaching of metals from roasted spent catalyst A large proportion of the oil was removed and recovered during microwave roasting, and the obtained products were roasted in a muffle furnace under air



atmosphere to remove residual oil and transform sulfides into oxides. The amount of exhaust gas was much lower than that of the direct oxidation roasting process. Alkaline and acid leaching was then followed to extract Mo, V and Co, Ni from the roasted products, respectively. The effects of roasting temperature on leaching efficiency of metals are presented in Fig. 5 and Fig. 6. The main chemical compositions of the alkaline leachate and acid leachate are presented in Table 2. As shown in Fig. 5 and Table 2, after microwave roasting, the leaching of Al decreased gradually with increasing roasting temperature and whether microwave roasting was used or not, Mo and V can be efficiently leached during the alkaline leaching process. Compared with the results without microwave roasting, after microwave roasting at 1000 °C, the leaching efficiency of Al significantly decreased from 24.7% to 10.4%. Accordingly, the concentration of Al in alkaline leachate decreased from 18.2 g L−1 to 7.6 g L−1. In the acid leaching, 22.5% of Al was leached from the spent HDS catalyst unexperienced microwave roasting, but the leaching efficiency of Al decreased to 15.4% after microwave roasting at 1000 °C and the concentration of Al in acid leachate decreased from 22.5 g L−1 to 15.3 g L−1. Unexpectedly, the leaching rate increased from 81.3% to 95.1% for Co and 80.3% to 94.1% for Ni. The results show that the leaching of Al significantly decreased in both alkaline and acid leaching processes due to the successful transformation of γ-Al2O3 into more stable α-Al2O3. Moreover, microwave roasting had a reinforcing effect on the acid leaching of Co and Ni. The leachate with higher concentration of valuable metals and lower concentration of Al can be obtained, indicating the following


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purification could become easier and the overall recovery rate of valuable metals could be promoted. For the alkaline leachate, Al can be removed by adjusting pH with acid solution to precipitate Al(OH)3 and then Mo, V and W could be separated by solvent extraction or ion-exchange.9, 43 For the acid leachate, Al can also be removed by adjusting pH with sodium hydroxide solution to precipitate Al(OH)3 and then Co and Ni could be separated by solvent extraction, which is common in the industrial process.44, 45 After microwave roasting at 1000 °C, the main chemical compositions of the oxidation roasting products, alkaline leaching residues and acid leaching residues are presented in Table 3. It shows that the content of Al in the final leaching slag was 50.6% and the contents of valuable metals were reduced to a very low value. The main component of the final leaching residues was α-Al2O3 and the purity achieved above 90%. Therefore, according to the nature of α-Al2O3, such as high melting point, mechanical strength and hardness, the final leaching slag can be utilized to prepare some high value-added materials, such as refractory, abrasive or ceramic materials, etc.

Fig. 5. Effect of microwave roasting temperature on leaching efficiency of metals



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during alkaline leaching (NaOH concentration: 3 mol L−1, S/L ratio: 200 g L−1, temperature: 90 °C, time: 3 h)

Fig. 6. Effect of microwave roasting temperature on leaching efficiency of metals during acid leaching (H2SO4 concentration: 1.5 mol L−1, S/L ratio: 200 g L−1, temperature: 90 °C, time: 3 h) Table 2 Main chemical compositions of alkaline and acid leachates at different temperatures. Elemental contents (g L−1) Temperature (°C)

Alkaline leaching solution

Acid leaching solution

Al

Mo

V

Al

Co

Ni

Without microwave roasting

18.2

16.3

2.3

22.5

5.4

10.4

700

18.0

16.3

2.3

21.3

5.5

10.1

900

16.1

16.3

2.2

19.9

5.6

10.6

1000

7.6

16.5

2.2

15.3

6.3

12.1

1100

6.9

16.3

2.3

13.0

6.3

12.2

Table 3 Main chemical compositions of oxidation roasting products, alkaline leaching residues and acid leaching residues (microwave roasting temperature: 1000 °C)


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Materials Oxidizing roasting products Alkaline leaching residues Acid leaching residues

Element contents (%) Al

Mo

V

Co

Ni

38.0

8.2

1.5

2.5

4.7

434

0.3

0.5

2.8

5.2

50.6

0.3

0.2

0.1

0.2

SEM-EDS characterization was performed for the initial spent HDS catalyst, microwave roasted products and residues after alkaline and acid leaching (Fig. 7). As shown in Fig. 7(a), the morphology of sample before microwave roasting was regularly spherical and smooth. However, as shown in Fig. 7(d), the morphology of the roasted products was much rougher and more anomalous, and a lot of smaller particles appeared. Fig. 7(e) and Fig. 7(f) show that the leaching residues obtained under microwave roasting became visibly small and dispersive, while the change in leaching residues unexperienced microwave roasting was less apparent, as shown in (Fig. 7(b) and Fig. 7(c)). It indicates that the better erosion and dissolution of solids can be obtained during the leaching process after microwave roasting. The reason is that when microwave irradiation was used to treat the initial spent catalyst, the heterogeneity of this material led to different heating rates in different parts, resulting in a structural destruction of the roasted products. It increased the contact area between solution and roasted product and promoted the leaching efficiency of valuable metals. EDS elemental mappings show that both Mo and V in the spent catalyst were leached after alkaline leaching, and substantially Co and Ni were leached after acid leaching, which further confirmed the results that microwave



roasting could facilitate the alkaline and acid dissolution of valuable metals from spent catalyst.


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Fig. 7. SEM-EDS analysis for (a) initial spent catalyst; (b, c) the alkaline and acid leaching residues without microwave roasting; (d) the spent catalyst after microwave roasting; (e, f) the alkaline and acid leaching residues after microwave roasting

4. Conclusion The Al-based carrier of spent HDS catalyst was successfully transformed from γ-Al2O3 into α-Al2O3 by microwave roasting in this study. XRD and XPS experiments reveal that γ-Al2O3 of the spent HDS catalyst can be transformed into α-Al2O3 at 1000 °C for only 1 h, at which the relative contents of γ-Al2O3 and α-Al2O3 were 4.2% and 95.8%, respectively. In addition, the oil covered on the spent catalyst can be efficiently recovered along with the transformation process. The recovered oil can be used for the production of petrochemical products and as an energy source. Leaching experiments show that the leaching of Al significantly decreased after the transformation of Al2O3. The leaching efficiency of Al decreased to 10.4% and 15.4% during alkaline and acid leaching processes, respectively. Furthermore, the leaching efficiency of Co and Ni increased in the acid leaching. This reinforcing effect could be explained by SEM-EDS that roasted products were much rougher and more anomalous to obtain the better erosion and dissolution of solids during the leaching process after microwave roasting. The method of microwave roasting was found to be efficient and energy-saving to transform γ-Al2O3 into α-Al2O3 in spent HDS catalyst. It is helpful to simplify the subsequent Al-separation process and improve the overall recovery efficiency of valuable metals. Moreover, the final leaching residues with high α-Al2O3 purity can be utilized to prepare high value-added materials.


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Acknowledgements This work was supported by the National Natural Science Foundation of China (Nos. 51504022, 51834008, 51874040, U1702252) and the Fundamental Research Funds for the Central Universities (Nos. FRF-BD-18-010A, 230201606500078, FRF-TP-17-036A2). References (1) Akcil, A.; Vegliò, F.; Ferella, F.; Okudan, M. D.; Tuncuk, A. A review of metal recovery from spent petroleum catalysts and ash. Waste Manage. 2015, 45, 420-433. (2) Zhang, J.; Deng, Y.; Zhou, Q.; Qin, P.; Liu, Y.; Wang, C. Novel geochemistry-inspired method for the deep removal of vanadium from molybdate solution. J. Hazard. Mater. 2017, 331, 210-217. (3) Lai, Y. C.; Lee, W. J.; Huang, K. L.; Wu, C. M. Metal recovery from spent hydrodesulfurization catalysts using a combined acid-leaching and electrolysis process. J. Hazard. Mater. 2008, 154, 588-594. (4) Ruiz, V.; Meux, E.; Schneider, M.; Georgeaud, V. Hydrometallurgical treatment for valuable metals recovery from spent CoMo/Al2O3 catalyst. 2. Oxidative leaching of an unroasted catalyst using H2O2. Ind. Eng. Chem. Res. 2011, 50, 5307-5315. (5) Marafi, M.; Stanislaus, A. Waste catalyst utilization: extraction of valuable metals from spent hydroprocessing catalysts by ultrasonic-assisted leaching with acids. Ind. Eng. Chem. Res. 2011, 50, 9495-9501. (6) Dufresne, P. Hydroprocessing catalysts regeneration and recycling. Appl. Catal., A 2007, 322, 67-75. (7) Park, K. H.; Mohapatra, D.; Reddy, B. R. Selective recovery of molybdenum from spent HDS catalyst using oxidative soda ash leach/carbon adsorption method. J. Hazard. Mater. 2006, 138, 311-316. (8) Zeng, L.; Cheng, C. Y. A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation catalysts : Part I: Metallurgical processes. Hydrometallurgy 2009, 98, 1-9. (9) Zeng, L.; Cheng, C. Y. A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation catalysts : Part II: Separation and purification. Hydrometallurgy 2009, 98, 10-20. (10) Binnemans, K.; Jones, P. T.; Blanpain, B.; Gerven, T. V.; Yang, Y.; Walton, A.; Buchert, M. Recycling of rare earths: a critical review. J. Clean. Prod. 2013, 51, 1-22. (11) Alsheeha, H.; Marafi, M.; Raghavan, V.; Rana, M. S. Recycling and Recovery Routes for Spent Hydroprocessing Catalyst Waste. Ind. Eng. Chem. Res. 2013, 52, 12794-12801. (12) Sun, D. D.; Chang, L.; Tay, J. H.; Navratil, J. D.; Easton, C. Recovery and Marine Clay Stabilization of Heavy Metals Present in Spent Hydrotreating Catalysts. J. Environ. Eng. 2001, 127, 916-921. (13) Sun, D. D.; Tay, J. H.; Easton, C. Recovery and encapsulation of heavy metals on refinery spent hydrotreating catalyst. Water Sci. Technol. 2000, 42, 71-77.



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For Table of Contents Only


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For Table of Contents Only 530x269mm (300 x 300 DPI)



Fig. 1. XRD patterns of (a) the raw spent HDS catalyst and the products roasted at (b) 700 °C, (c) 900 °C, (d) 1000 °C, (e) 1100 °C for 1 h 221x176mm (300 x 300 DPI)


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Fig. 2. The XPS Al 2p spectra and the calculated distribution of alumina form for the raw and microwave roasted spent HDS catalyst 366x261mm (300 x 300 DPI)



Fig. 3. FTIR spectrum of the raw spent catalyst and the roasted products at 1000 °C 219x178mm (300 x 300 DPI)


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Fig. 4. Effect of roasting temperature on carbon removal rate (flow rate of argon gas: 600 mL min−1, time: 1 h) and photograph of the oil recovered by microwave roasting at 1000 °C 231x184mm (300 x 300 DPI)



Fig. 5. Effect of microwave roasting temperature on leaching efficiency of metals during alkaline leaching (NaOH concentration: 3 mol L−1, S/L ratio: 200 g L−1, temperature: 90 °C, time: 3 h) 259x176mm (300 x 300 DPI)


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Fig. 6. Effect of microwave roasting temperature on leaching efficiency of metals during acid leaching (H2SO4 concentration: 1.5 mol L−1, S/L ratio: 200 g L−1, temperature: 90 °C, time: 3 h) 257x175mm (300 x 300 DPI)



Fig. 7. SEM-EDS analysis: (a) the raw spent catalyst; (b, c) the alkaline and acid leaching residues without microwave roasting; (d) the spent catalyst after microwave roasting; (e, f) the alkaline and acid leaching residues after microwave roasting 167x273mm (300 x 300 DPI)


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Efficient Phase Transformation of Î³-Al2O3 to

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