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Investigations on the extraction of molybdenum and vanadium from ammonia leaching residue of spent catalyst
Int. J. Miner. Process. 79 (2006) 42 – 48 www.elsevier.com/locate/ijminpro
Investigations on the extraction of molybdenum and vanadium from ammonia leaching residue of spent catalyst Yun Chen *, Qiming Feng, Yanhai Shao, Guofan Zhang, Leming Ou, Yiping Lu School of Resource Processing and Bioengineering, Central South University, Changsha, 410083, PR China Received 14 August 2005; received in revised form 28 November 2005; accepted 28 November 2005 Available online 4 January 2006
Abstract Extraction of molybdenum and vanadium from ammonia leaching residue (main chemical composition: 2.05% Mo, 0.42% V, 65.6% Al2O3 and 10.7% SiO2) of spent catalyst was investigated by roasting the residue with soda carbonate, followed by hydrometallurgical treatment of the roasted products. In the roasting process, over 91.3% of molybdenum and 90.1% of vanadium could be extracted when a charge containing a sodium carbonate to spent catalyst ratio of 0.15 was roasted at 750 8C for 45 min and the roasted mass was leached with water (liquid to solid ratio of 2) at 80–90 8C for 15 min. After the purification of leach liquor, an extraction solvent consisting of 20 vol.% trialkylamine (N235, commercialized in China) and 10 vol.% secondary octyl alcohol (phase modifier) dissolved in sulfonated kerosene was used to extract molybdenum and vanadium in leach liquor. 10 wt.% ammonia water was used as stripping agent. Adding 30 g/l NH4NO3 to the stripping solution and adjusting the pH to 7–8.5, over 99% of vanadium can be crystallized as ammonium metavanadate. Over 98% of molybdenum can be crystallized as ammonium polymolybdate when pH is between 1.5 and 2.5 (pH is adjusted by HNO3). Ammonium metavanadate and ammonium polymolybdate were calcinated at 500–550 8C, the purity of MoO3 and V2O5 was 99.08% and 98.06% respectively. In the whole process, 88.2% of molybdenum and 87.1% of vanadium could be achieved. The proposed roasting, leaching and separation steps give a feasible alternative for the processing of ammonia leaching residue of spent catalyst and can be applied in the comprehensive utilization of low grade molybdenum ores. D 2005 Elsevier B.V. All rights reserved. Keywords: Roasting; Purification; Solvent extraction; Molybdenum; Vanadium; Spent catalyst
1. Introduction Molybdenum and vanadium have strategic and industrial importance due to their applications in many technological fields (Sutulov, 1979; Moskalyk and Alfantazi, 2003). However, with the ceaseless exploitation of resources in the world, the high grade ore is exhausted day by day, primary sources are presently
* Corresponding author. Tel./fax: +86 731 8830913. E-mail address: [email protected] (Y. Chen). 0301-7516/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.minpro.2005.11.009
insufficient to supply demand and secondary sources are being increasingly exploited. With the processing cost of low-grade ore becoming higher and higher, more and more countries pay more attention to the serious environmental problem. In order to alleviate insufficient domestic resources, and improve the environmental condition, many countries in the world pay much attention to the comprehensive utilization of the secondary resources. In Japan, recycling of the waste catalyst had been done since the 1950s, while the turnover of waste catalyst in the U.S.A. had already been up to 500 million dollars in 1996 (Liu, 2000).
Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
Petroleum refining industry mostly uses molybdenum-containing catalysts for desulphurization and mild hydrogenation process, trace amount of vanadium in petroleum can be adsorbed and concentrated on the catalyst (Kar, 2005). These catalysts have limited life cycles and, after utilization, are generated as spent catalyst (Kar et al., 2005). This kind of spent catalyst forms an important secondary source of many valuable metals. Spent hydro-refining catalyst mainly consists of 10–30% Mo, 0–12% V2O5, 0.5–6% NiO, 6–8% CaO, 8–12% S, 10–12% carbon and the balance is Al2O3 (Sun et al., 2001; Marafi and Stanislaus, 2003; Kar et al., 2005). Hence, it was desirable to develop a commercial hydrometallurgical process for the comprehensive utilization of spent catalyst. During the past decade considerable research was devoted to the processing of spent catalyst. A survey of literatures revealed the technology for recycling molybdenum from spent catalyst and other resources (Sun et al., 2001; Kar et al., 2005; Zhang et al., 1996; van den Berg et al., 2002). These processes include hypochlorite, electro-oxidation, nitric acid leaching, alkali leaching and ammonia leaching, but the molybdenum among the residue produced by these processes is 2–3 wt.%, and 0.5–1.0% vanadium (Marafi and Stanislaus, 2003; Sun et al., 2001; Saily et al., 1996), the solid residues containing high concentrations of heavy metals above environmentally acceptable level can be expected (Sun et al., 1998). Due to the comprehensive utilization of resources and the restriction from environmental protection, a novel process was developed to recover molybdenum and vanadium in ammonia leaching residue of spent catalyst. 2. Materials and methods 2.1. Materials The raw material used in this study is the ammonia leaching residue of spent catalyst, the particle size is between 0.040 and 0.074 mm. Table 1 presents the chemical composition analysis result of the waste material. It can be indicated that the valuable and harmful elements among residues are molybdenum and vanadium. It is not suitable for the recovery of alumina as the high content of SiO2.
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2.2. Methods The residues were mixed with sodium carbonate in a certain proportion and then the mixture was put in a furnace (the temperature accuracy of the furnace is F5 8C). It was roasted at a desired temperature, then dissolved in hot water, and filtered. In this process, molybdenum and vanadium were leached along with few parts of Al, Si, and P. The impurity of Si and P were removed by chemical precipitation with the addition of Mg (NO3)2 and ammonia. After the purification, the leach liquor was free of Al, Si and P, 20 vol.% trialkylamine was used to extract molybdenum and vanadium in leach liquor (pH 1.5– 2.5, O/A= 1:5), 10 wt.% ammonia water was used as stripping agent (O/A= 2:1). Ammonium metavanadate and ammonium polymolybdate were crystallized from the stripping solution by the addition of NH4NO3 and adjusting the pH to a suitable value. The purity of MoO3 and V2O5 was 99.08% and 98.06% respectively after calcination for 1 h at 500 8C. Fig. 1 is the recovering flow sheet of spent catalyst. 3. Results and discussion 3.1. Roasting 3.1.1. Effect of roasting temperature In this process, the roasting temperature was varied in the range of 450–1000 8C, using 20 wt.% sodium carbonate with 60 min of roasting. The recovery of molybdenum and vanadium vs. temperature is shown in Fig. 2. Over 96% of molybdenum and vanadium could be recovered when the temperature is above 900 8C. But at this temperature, more of alumina and SiO2 reacted with sodium carbonate, It was harmful to the later purification of leach liquor. Hence, an optimum temperature of 750 8C was chosen. 3.1.2. Addition of sodium carbonate The effect of sodium carbonate addition on the recovery of molybdenum and vanadium was studied for a period of 60 min at 750 8C. The addition of sodium carbonate varied from 2 to 30 wt.% and the results illustrated in Fig. 3. It can be indicated from
Table 1 Main chemical compositions of residues Constituents
Mo
V
Al2O3
SiO2
P2O5
As2O3
SO3
Fe2O3
NiO
CaO
H2 O
Others
Wt.%
2.05
0.42
61.95
10.28
3.58
0.11
3.62
2.16
3.22
1.05
5.42
6.14
44
Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
Residue of spent catalyst
Roasting 750ºC
Water leaching 80~90ºC Filtrate(discard) Leach liquor Ammonia water Mg(NO3)2 HNO3
Purification pH=10.1 precipitations purificated liquor
Solvent extraction
Waste water treatment
Raffinate Stripping Organic phase Stripping solution
30g/l NH4NO3
pH=8.2
Precipitation of NH4VO3
Ammonium metavanadate
HNO3 pH=2.05
Solution
Mother liquor
Calcinations 500ºC
Ammonium polymolybdate
V2O5 Calcinations 500ºC
MoO3
Fig. 1. Flow sheet for the recovery of Mo and V from ammonia leaching residue of spent catalyst.
Fig. 3 that at 15 wt.% of sodium carbonate, over 91% of molybdenum and vanadium can be recovered. Further increasing of sodium carbonate, there was no appreciable variation in the recovery of molybdenum and vanadium but more of alumina and SiO2 were leached. Thus, 15 wt.% sodium carbonate was chosen in the later experiment. 3.1.3. Effect of roasting time In order to study the role of reaction time on the recovery of molybdenum and vanadium, the reaction time was varied from 15 to 90 min, with an interval of 15 min, keeping the temperature and Na2CO3
addition constant. The experimental results are shown in Fig. 4. It is shown that roasting time of 45 min seems to be sufficient enough to recover about 91.3% of molybdenum and 90.1% of vanadium. Further increase in time does not affect the recovery of molybdenum and vanadium; on the contrary, it will lead to the more leaching of alumina and SiO2. Thus, the above results revealed that, on the basis of laboratory scale study, it is possible to recover 91.3% of molybdenum and 90.1% of vanadium at 750 8C with 15 wt.% sodium carbonate when roasting for a period of 45 min.
Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
45
100
100
90 80 molybdenum vanadium
70
Recovery/%
Recovery/%
80
60
40
molybdenum vanadium
60 50 40 30 20
20 conditions:time=60min, Na2CO3=20wt.%
0 400
0 500
600
700
800
900
condition: 750°C, 15wt% sodium carbonate
10 1000
0
10
20
30
40
50
60
70
80
90
100
Time/min
Temperature/°C
Fig. 2. Effect of temperature on the recovery of molybdenum and vanadium.
3.2. Water leaching and purification of leach liquor The roast was leached in a glass beaker with water on a heating plate at 80–90 8C for 15 min, at liquid/ solid ratio of 2 with magnetic stirring. The molybdenum and vanadium in leach liquor were analyzed and the leaching recoveries were calculated from the leach liquor. Under the above mentioned optimum conditions, the content of molybdenum and vanadium in filtrate can be down to 0.2 wt.% and 0.05 wt.% respectively. Due to the low grade of Mo and V in the materials, the concentration of Mo and V in leach liquor was poor (Mo: 10–13 g/l, V: 2–2.5 g/l), organic solvent extraction was chosen to concentrate Mo and V in solution. However, in the leaching process, part of alumina, SiO2, As and P was leached, As and P can
Fig. 4. Effect of roasting time on the recovery of molybdenum and vanadium.
react with molybdenum and vanadium in solution and formed many kinds of heteropolyacids (Enbo et al., 1995). It was harmful for the solvent extraction of Mo and V. Hence, the purification of leach liquor was necessary. 3.2.1. Effect of initial pH on the purification of leach liquor The impurity of Si, As and P were removed by chemical precipitation with the addition of Mg (NO3)2 and ammonia due to the low solubility of MgNH4PO4, MgNH4AsO4 and MgSiO3 (Stratful et al., 2001; Battistoni et al., 1997). According to our experience, the initial pH of solution and reaction time was very important in the precipitation of As and P. The effect of pH on the purification of leach liquor was illustrated in Fig. 5.
100 100 90 90 80 70
60
Removal/%
Recovery/%
80
molybdenum vanadium
70
50 40 30
P As
60 50 40
Condition:1.0wt% concentrated ammonia and
30 20
condition: 750°C, time=60min
0.8wt% Mg(NO3)2 stirring 1h at 50°C
20
10
Initial concentration: P=1.31g/l, As=0.06g/l
10 0
0
5
10
15
20
25
30
35
sodium carbonate addition/wt%
0 7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
pH
Fig. 3. Effect of sodium carbonate addition on the recovery of molybdenum and vanadium.
Fig. 5. Effect of initial pH on the purification of leach liquor.
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Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48 100
Under the suitable condition (addition of 0.8 wt.% Mg (NO3)2 and 1.0 wt.% concentrated ammoniacal liquor, adjusting pH to 10.0–10.5 and stirring 1 h at 50 8C, over 96% of Al, Si and P can be removed from the leach liquor. The loss rate of molybdenum and vanadium was less than 2%. The purification result of leach liquor was illustrated in Table 2.
90 80
Removal/%
70
P As
60 50
Condition:1.0wt% concentrated ammonia and
40 0.8wt% Mg(NO3)2 pH=10.1, 50°C
30
3.3. Solvent extraction of molybdenum and vanadium
Initial concentration: P=1.31g/l, As=0.06g/l
20 10 0
20
40
60
80
100
Time/min
Fig. 6. Effect of reaction time on the purification of leach liquor.
Obviously, with the decreasing of initial pH, the removal of P and As decreased; this can be explained by Eqs. (1) and (2): þ 2þ HPO2 Y MgNH4 PO4 A þ Hþ 4 þ NH4 þ Mg
ð1Þ
þ 2þ Y MgNH4 AsO4 A þ Hþ : HAsO2 4 þ NH4 þ Mg
ð2Þ With the forming of precipitations, hydrogen was released to the solution. Therefore, when the initial pH of solution was low (pH b 9), the removal was poor. At pH 10.1, 98.47% of P and 91.67% of As were precipitated from the solution. 3.2.2. Effect of reaction time on the purification of leach liquor The effect of reaction time on the removal rates of P and As was shown in Fig. 6. With the increasing of reaction time, there was a palpable effect on the precipitation of P and As. Due to the absence of foreign solid phases in this process, the precipitation mechanism is likely to be heterogeneous, enough reaction time was needed. It can be seen from Fig. 6 that 60 min of reaction time was suitable in the precipitation process.
A considerable research has been devoted to recovering molybdenum and vanadium from aqueous solution by solvent extraction with organic solutions of various extractants (Taich et al., 1986; Olazabal et al., 1992; Zhang et al., 1996). Amines were the most common extractants in the extraction of molybdenum and vanadium. According to the literatures and our past experiences, trialkylamine (N235, commercialized in China) was chosen as the extractants, the organic phase was made up of 20 vol.% N235, 10 vol.% secondary octyl alcohol (phase modifier) and 70 vol.% sulfonated kerosene, N235 was acidificated by 2 mol/ l HCl (volume ratio = 1:1) before using. A series of experiments were carried out to determine the optimum extraction conditions, the optimum operating conditions for extracting and stripping were presented in Table 3. Under the optimum conditions, the extraction rate of molybdenum and vanadium was no less than 99.9% by single stage extraction (O/A= 1:5), and the stripping rate of molybdenum and vanadium was above 99.8% by single stage stripping with 10 wt.% ammonia water (O/A= 2:1). In the process of extraction and stripping, no trouble in phase separation performance
Table 3 Recovery of molybdenum and vanadium from the leach liquor Parameter Extraction Extractant
Value
pH adjustment O/A ratio Temperature Initial pH Extraction rate
20 vol.% N235 + 10 vol.% secondary octyl alcohol + 70 vol.% sulfonated kerosene 50% HNO3 1:5 30 8C 2.15 Mo 99.8%, V 99.2%
Leach liquor (g/l) 2.35 11.89 4.4 3.8 1.31 0.06 After purification (g/l) 2.30 11.71 0.08 0.03 0.02 0.005 Removing rate (%) 2.13 0.67 98.18 99.21 98.47 91.67
Stripping Stripping agent O/A ratio Temperature Stripping ratio
10 wt.% ammonia water 2:1 30 8C Mo 99.83%, V 99.85%
Optimum conditions: 0.8 wt.% Mg(NO3)2 and 1.0 wt.% concentrated ammoniacal liquor, pH = 10.1, stirring 1 h at 50 8C.
The composition of leach liquor was listed in Table 2 (after purification), pH was adjusted to 2.15.
Table 2 Purification result of leach liquor Constituents
V
Mo
Al
Si
P
As
Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
occurs and the addition of secondary octyl alcohol could avoid the formation of a second organic phase and/or emulsion. 3.4. Production of MoO3 and V2O5 In order to get the product of MoO3 and V2O5 from the stripping solution, molybdenum and vanadium must be separated first. Due to the low solubility of ammonium metavanadate when pH is between 7.5 and 8.5 (Kelmers, 1961), ammonium metavanadate can be crystallized and precipitated from the solution firstly with the addition of NH4NO3. After the precipitation of ammonium metavanadate, ammonium polymolybdate was crystallized and precipitated at 50 8C when pH was adjusted to 2.0–2.5 by HNO3. A series of experiments were carried out to determine optimum operating conditions, the optimum conditions were listed in Table 4. After calcination at 500 8C for 1 h, the purity of MoO3 and V2O5 was 99.08% and 98.06% respectively. High purity of MoO3 can be obtained by the following process: ammonium polymolybdate dissolved in ammonia water, ammonium paramolybdate was crystallized and precipitated by evaporative crystallization, high purity of MoO3 (no less than 99.9%) can be obtained after calcination. The material balance of the whole process was listed in Table 5, the data came from a bench scale test under selected optimal processing conditions. In the whole process, the recovery of molybdenum and vanadium was 88.2% and 87.1%, and the content of molybdenum and vanadium among residues can be down to 0.2 wt.% and 0.05 wt.% respectively. The proposed roasting, leaching and separation steps give a feasible alternative for the processing of ammonia leaching residue of spent Table 4 Operating condition and the purity of product Constituent
V
Mo
Stripping solution (g/l) After precipitation of V (g/l) After precipitation of Mo (g/l) Precipitation of vanadium
22.81
118.63
0.03
118.32
Precipitation of molybdenum Purity of V2O5 Purity of MoO3
1.45 NH4NO3 30 g/l, pH = 8.2, 30 8C, stirring 60 min pH = 2.05, 50 8C, stirring 30 min 98.06% 99.08%
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Table 5 The material balance of the whole process Constituents
V
Leach liquor (g/l) Leaching rate (%) After purification (g/l) Raffinate (g/l) Extraction rate (%) Stripping solution (g/l) Stripping rate (%) After precipitation of V (g/l) Precipitation rate of V (%) After precipitation of Mo (g/l) Precipitation rate of Mo (%) Recovery of V and Mo in the whole process (%)
2.35 90.1 2.30
Mo 11.89 91.4 11.71
0.02 99.2 22.8
0.02 99.8 118.6
99.8 0.03
99.9 118.3
Al
Si
P
As
4.4
3.8
1.31
0.06
0.08
0.03
0.02
0.005
99.8 1.45 98.8 87.1
88.2
The data came from a bench scale test under the selected optimal processing conditions.
catalyst and can be applied in the comprehensive utilization of low grade molybdenum ores. 4. Conclusions An investigation was conducted to develop an approach to recover molybdenum and vanadium from ammonia leaching residue of spent catalyst. Based on results obtained from the current work, the following conclusions are made: a) Under selected conditions, i.e. roasting at 750 8C and addition of 15 wt.% sodium carbonate for 45 min, up to 91.3% of molybdenum and 90.1% of vanadium could be extracted, and the content of molybdenum and vanadium in filtrate can be down to 0.2 wt.% and 0.05 wt.% respectively. b) After the purification of leach liquor, solvent extraction was used to concentrate Mo and V in solution, the extraction rate of molybdenum and vanadium was no less than 99.9% by single stage extraction (O/A= 1:5), and the stripping rate of molybdenum and vanadium was above 99.8% by single stage stripping. c) Ammonium metavanadate and ammonium polymolybdate were crystallized from the stripping solution by the addition of NH4NO3 and adjusting the pH to a suitable value, the purity of MoO3 and V2O5 was 99.08% and 98.06% respectively after calcination for 1 h at 500 8C.
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Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
d) In the whole process, over 88.2% molybdenum and 87.1% vanadium could be recovered from the ammonia leaching residue of spent catalyst. The proposed roasting, leaching and separation steps give a feasible alternative for the processing of ammonia leaching residue of spent catalyst and can be applied in the comprehensive utilization of low grade molybdenum ores. References Battistoni, P., Fava, G., Pavan, P., Musacco, A., Cecchi, F., 1997. Phosphate removal in anaerobic liquors by struvite crystallization without addition of chemicals: preliminary results. Water Research 31, 2925 – 2929. Enbo, W., Jingyang, N., Lin, X., 1995. Study on thermal property of heteropolyacids with keggin structure. Acta Chimica Sinica 53, 757 – 764. Kar, B.B., 2005. Carbothermic reduction of hydro-refining spent catalyst to extract molybdenum. International Journal of Mineral Processing 75, 249 – 253. Kar, B.B., Murthy, B.V.R., Misra, V.N., 2005. Extraction of molybdenum from spent catalyst by salt-roasting. International Journal of Mineral Processing 76, 143 – 147. Kelmers, A.D., 1961. A portion of the system NH3–V2O5–H2O at 30 8C. Journal of Inorganic and Nuclear Chemistry 17, 168 – 173. Liu, H., 2000. Recovering of spent catalyst in the foreign country. Chinese Resource Comprehensive Utilization 12, 35 – 37. Marafi, M., Stanislaus, A., 2003. Options and processes for spent catalyst handling and utilization. Journal of Hazardous Materials, B 101, 123 – 132. Moskalyk, R.R., Alfantazi, A.M., 2003. Processing of vanadium: a review. Minerals Engineering 16, 793 – 805.
Olazabal, M.A., Orive, M.M., Fernandez, L.A., Madariaga, J.M., 1992. Selective extraction of vanadium (V) from solutions containing molybdenum (VI) by ammonium salts dissolved in toluene. Solvent Extraction and Ion Exchange 10, 623 – 635. Saily, A., Khurana, U., Yadav, S.K., Tandon, S.N., 1996. Thiophosphinic acids as selective extractants for molybdenum recovery from a low grade ore and spent catalysts. Hydrometallurgy 41, 99 – 105. Stratful, M.D., Scrimshaw, Lester, J.N., 2001. Conditions influencing the precipitation of magnesium ammonium phosphate. Water Research 35, 4191 – 4199. Sun, D.D., Li, X.Z., Brungs, M., Trimm, D., 1998. Encapsulation of heavy metals on spent fluid catalytic cracking catalyst. Water Science and Technology 38, 211 – 217. Sun, D.D., Tay, J.H., Cheong, H.K., Leung, D.L.K., Qian, G.R., 2001. Recovery of heavy metals and stabilization of spent hydrotreating catalyst using a glass–ceramic matrix. Journal of Hazardous Materials, B 87, 213 – 223. Sutulov, A., 1979. In: Sutulov, A. (Eds.), International Molybdenum Encyclopedia, 1778-1978, vol I—Resources and Production. Internet Publications, Santiago, Chile. Taich, S., Hiroshi, W., Hiroki, S., 1986. Liquid–liquid extraction of molybdenum(VI) from aqueous acid solutions by highmolecular weight amines. Solvent Extraction and Ion Exchange 4, 987 – 998. van den Berg, J.A.M., Yang, Y., Nauta, H.H.K., van Sandwijk, A., Reuter, M.A., 2002. Comprehensive processing of low grade sulphidic molybdenum ores. Minerals Engineering 15, 879 – 883. Zhang, P.W., Inoue, K., Yoshizuka, K., Tsuyama, H., 1996. Extraction and selective stripping of molybdenum(VI) and vanadium(IV) from sulfuric acid solution containing aluminum(III), cobalt(II), nickel(II) and iron(III) by LIX63 in Exxsol D80. Hydrometallurgy 41, 45 – 53.
Investigations on the extraction of molybdenum and vanadium from ammonia leaching residue of spent catalyst Yun Chen *, Qiming Feng, Yanhai Shao, Guofan Zhang, Leming Ou, Yiping Lu School of Resource Processing and Bioengineering, Central South University, Changsha, 410083, PR China Received 14 August 2005; received in revised form 28 November 2005; accepted 28 November 2005 Available online 4 January 2006
Abstract Extraction of molybdenum and vanadium from ammonia leaching residue (main chemical composition: 2.05% Mo, 0.42% V, 65.6% Al2O3 and 10.7% SiO2) of spent catalyst was investigated by roasting the residue with soda carbonate, followed by hydrometallurgical treatment of the roasted products. In the roasting process, over 91.3% of molybdenum and 90.1% of vanadium could be extracted when a charge containing a sodium carbonate to spent catalyst ratio of 0.15 was roasted at 750 8C for 45 min and the roasted mass was leached with water (liquid to solid ratio of 2) at 80–90 8C for 15 min. After the purification of leach liquor, an extraction solvent consisting of 20 vol.% trialkylamine (N235, commercialized in China) and 10 vol.% secondary octyl alcohol (phase modifier) dissolved in sulfonated kerosene was used to extract molybdenum and vanadium in leach liquor. 10 wt.% ammonia water was used as stripping agent. Adding 30 g/l NH4NO3 to the stripping solution and adjusting the pH to 7–8.5, over 99% of vanadium can be crystallized as ammonium metavanadate. Over 98% of molybdenum can be crystallized as ammonium polymolybdate when pH is between 1.5 and 2.5 (pH is adjusted by HNO3). Ammonium metavanadate and ammonium polymolybdate were calcinated at 500–550 8C, the purity of MoO3 and V2O5 was 99.08% and 98.06% respectively. In the whole process, 88.2% of molybdenum and 87.1% of vanadium could be achieved. The proposed roasting, leaching and separation steps give a feasible alternative for the processing of ammonia leaching residue of spent catalyst and can be applied in the comprehensive utilization of low grade molybdenum ores. D 2005 Elsevier B.V. All rights reserved. Keywords: Roasting; Purification; Solvent extraction; Molybdenum; Vanadium; Spent catalyst
1. Introduction Molybdenum and vanadium have strategic and industrial importance due to their applications in many technological fields (Sutulov, 1979; Moskalyk and Alfantazi, 2003). However, with the ceaseless exploitation of resources in the world, the high grade ore is exhausted day by day, primary sources are presently
* Corresponding author. Tel./fax: +86 731 8830913. E-mail address: [email protected] (Y. Chen). 0301-7516/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.minpro.2005.11.009
insufficient to supply demand and secondary sources are being increasingly exploited. With the processing cost of low-grade ore becoming higher and higher, more and more countries pay more attention to the serious environmental problem. In order to alleviate insufficient domestic resources, and improve the environmental condition, many countries in the world pay much attention to the comprehensive utilization of the secondary resources. In Japan, recycling of the waste catalyst had been done since the 1950s, while the turnover of waste catalyst in the U.S.A. had already been up to 500 million dollars in 1996 (Liu, 2000).
Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
Petroleum refining industry mostly uses molybdenum-containing catalysts for desulphurization and mild hydrogenation process, trace amount of vanadium in petroleum can be adsorbed and concentrated on the catalyst (Kar, 2005). These catalysts have limited life cycles and, after utilization, are generated as spent catalyst (Kar et al., 2005). This kind of spent catalyst forms an important secondary source of many valuable metals. Spent hydro-refining catalyst mainly consists of 10–30% Mo, 0–12% V2O5, 0.5–6% NiO, 6–8% CaO, 8–12% S, 10–12% carbon and the balance is Al2O3 (Sun et al., 2001; Marafi and Stanislaus, 2003; Kar et al., 2005). Hence, it was desirable to develop a commercial hydrometallurgical process for the comprehensive utilization of spent catalyst. During the past decade considerable research was devoted to the processing of spent catalyst. A survey of literatures revealed the technology for recycling molybdenum from spent catalyst and other resources (Sun et al., 2001; Kar et al., 2005; Zhang et al., 1996; van den Berg et al., 2002). These processes include hypochlorite, electro-oxidation, nitric acid leaching, alkali leaching and ammonia leaching, but the molybdenum among the residue produced by these processes is 2–3 wt.%, and 0.5–1.0% vanadium (Marafi and Stanislaus, 2003; Sun et al., 2001; Saily et al., 1996), the solid residues containing high concentrations of heavy metals above environmentally acceptable level can be expected (Sun et al., 1998). Due to the comprehensive utilization of resources and the restriction from environmental protection, a novel process was developed to recover molybdenum and vanadium in ammonia leaching residue of spent catalyst. 2. Materials and methods 2.1. Materials The raw material used in this study is the ammonia leaching residue of spent catalyst, the particle size is between 0.040 and 0.074 mm. Table 1 presents the chemical composition analysis result of the waste material. It can be indicated that the valuable and harmful elements among residues are molybdenum and vanadium. It is not suitable for the recovery of alumina as the high content of SiO2.
43
2.2. Methods The residues were mixed with sodium carbonate in a certain proportion and then the mixture was put in a furnace (the temperature accuracy of the furnace is F5 8C). It was roasted at a desired temperature, then dissolved in hot water, and filtered. In this process, molybdenum and vanadium were leached along with few parts of Al, Si, and P. The impurity of Si and P were removed by chemical precipitation with the addition of Mg (NO3)2 and ammonia. After the purification, the leach liquor was free of Al, Si and P, 20 vol.% trialkylamine was used to extract molybdenum and vanadium in leach liquor (pH 1.5– 2.5, O/A= 1:5), 10 wt.% ammonia water was used as stripping agent (O/A= 2:1). Ammonium metavanadate and ammonium polymolybdate were crystallized from the stripping solution by the addition of NH4NO3 and adjusting the pH to a suitable value. The purity of MoO3 and V2O5 was 99.08% and 98.06% respectively after calcination for 1 h at 500 8C. Fig. 1 is the recovering flow sheet of spent catalyst. 3. Results and discussion 3.1. Roasting 3.1.1. Effect of roasting temperature In this process, the roasting temperature was varied in the range of 450–1000 8C, using 20 wt.% sodium carbonate with 60 min of roasting. The recovery of molybdenum and vanadium vs. temperature is shown in Fig. 2. Over 96% of molybdenum and vanadium could be recovered when the temperature is above 900 8C. But at this temperature, more of alumina and SiO2 reacted with sodium carbonate, It was harmful to the later purification of leach liquor. Hence, an optimum temperature of 750 8C was chosen. 3.1.2. Addition of sodium carbonate The effect of sodium carbonate addition on the recovery of molybdenum and vanadium was studied for a period of 60 min at 750 8C. The addition of sodium carbonate varied from 2 to 30 wt.% and the results illustrated in Fig. 3. It can be indicated from
Table 1 Main chemical compositions of residues Constituents
Mo
V
Al2O3
SiO2
P2O5
As2O3
SO3
Fe2O3
NiO
CaO
H2 O
Others
Wt.%
2.05
0.42
61.95
10.28
3.58
0.11
3.62
2.16
3.22
1.05
5.42
6.14
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Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
Residue of spent catalyst
Roasting 750ºC
Water leaching 80~90ºC Filtrate(discard) Leach liquor Ammonia water Mg(NO3)2 HNO3
Purification pH=10.1 precipitations purificated liquor
Solvent extraction
Waste water treatment
Raffinate Stripping Organic phase Stripping solution
30g/l NH4NO3
pH=8.2
Precipitation of NH4VO3
Ammonium metavanadate
HNO3 pH=2.05
Solution
Mother liquor
Calcinations 500ºC
Ammonium polymolybdate
V2O5 Calcinations 500ºC
MoO3
Fig. 1. Flow sheet for the recovery of Mo and V from ammonia leaching residue of spent catalyst.
Fig. 3 that at 15 wt.% of sodium carbonate, over 91% of molybdenum and vanadium can be recovered. Further increasing of sodium carbonate, there was no appreciable variation in the recovery of molybdenum and vanadium but more of alumina and SiO2 were leached. Thus, 15 wt.% sodium carbonate was chosen in the later experiment. 3.1.3. Effect of roasting time In order to study the role of reaction time on the recovery of molybdenum and vanadium, the reaction time was varied from 15 to 90 min, with an interval of 15 min, keeping the temperature and Na2CO3
addition constant. The experimental results are shown in Fig. 4. It is shown that roasting time of 45 min seems to be sufficient enough to recover about 91.3% of molybdenum and 90.1% of vanadium. Further increase in time does not affect the recovery of molybdenum and vanadium; on the contrary, it will lead to the more leaching of alumina and SiO2. Thus, the above results revealed that, on the basis of laboratory scale study, it is possible to recover 91.3% of molybdenum and 90.1% of vanadium at 750 8C with 15 wt.% sodium carbonate when roasting for a period of 45 min.
Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
45
100
100
90 80 molybdenum vanadium
70
Recovery/%
Recovery/%
80
60
40
molybdenum vanadium
60 50 40 30 20
20 conditions:time=60min, Na2CO3=20wt.%
0 400
0 500
600
700
800
900
condition: 750°C, 15wt% sodium carbonate
10 1000
0
10
20
30
40
50
60
70
80
90
100
Time/min
Temperature/°C
Fig. 2. Effect of temperature on the recovery of molybdenum and vanadium.
3.2. Water leaching and purification of leach liquor The roast was leached in a glass beaker with water on a heating plate at 80–90 8C for 15 min, at liquid/ solid ratio of 2 with magnetic stirring. The molybdenum and vanadium in leach liquor were analyzed and the leaching recoveries were calculated from the leach liquor. Under the above mentioned optimum conditions, the content of molybdenum and vanadium in filtrate can be down to 0.2 wt.% and 0.05 wt.% respectively. Due to the low grade of Mo and V in the materials, the concentration of Mo and V in leach liquor was poor (Mo: 10–13 g/l, V: 2–2.5 g/l), organic solvent extraction was chosen to concentrate Mo and V in solution. However, in the leaching process, part of alumina, SiO2, As and P was leached, As and P can
Fig. 4. Effect of roasting time on the recovery of molybdenum and vanadium.
react with molybdenum and vanadium in solution and formed many kinds of heteropolyacids (Enbo et al., 1995). It was harmful for the solvent extraction of Mo and V. Hence, the purification of leach liquor was necessary. 3.2.1. Effect of initial pH on the purification of leach liquor The impurity of Si, As and P were removed by chemical precipitation with the addition of Mg (NO3)2 and ammonia due to the low solubility of MgNH4PO4, MgNH4AsO4 and MgSiO3 (Stratful et al., 2001; Battistoni et al., 1997). According to our experience, the initial pH of solution and reaction time was very important in the precipitation of As and P. The effect of pH on the purification of leach liquor was illustrated in Fig. 5.
100 100 90 90 80 70
60
Removal/%
Recovery/%
80
molybdenum vanadium
70
50 40 30
P As
60 50 40
Condition:1.0wt% concentrated ammonia and
30 20
condition: 750°C, time=60min
0.8wt% Mg(NO3)2 stirring 1h at 50°C
20
10
Initial concentration: P=1.31g/l, As=0.06g/l
10 0
0
5
10
15
20
25
30
35
sodium carbonate addition/wt%
0 7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
pH
Fig. 3. Effect of sodium carbonate addition on the recovery of molybdenum and vanadium.
Fig. 5. Effect of initial pH on the purification of leach liquor.
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Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48 100
Under the suitable condition (addition of 0.8 wt.% Mg (NO3)2 and 1.0 wt.% concentrated ammoniacal liquor, adjusting pH to 10.0–10.5 and stirring 1 h at 50 8C, over 96% of Al, Si and P can be removed from the leach liquor. The loss rate of molybdenum and vanadium was less than 2%. The purification result of leach liquor was illustrated in Table 2.
90 80
Removal/%
70
P As
60 50
Condition:1.0wt% concentrated ammonia and
40 0.8wt% Mg(NO3)2 pH=10.1, 50°C
30
3.3. Solvent extraction of molybdenum and vanadium
Initial concentration: P=1.31g/l, As=0.06g/l
20 10 0
20
40
60
80
100
Time/min
Fig. 6. Effect of reaction time on the purification of leach liquor.
Obviously, with the decreasing of initial pH, the removal of P and As decreased; this can be explained by Eqs. (1) and (2): þ 2þ HPO2 Y MgNH4 PO4 A þ Hþ 4 þ NH4 þ Mg
ð1Þ
þ 2þ Y MgNH4 AsO4 A þ Hþ : HAsO2 4 þ NH4 þ Mg
ð2Þ With the forming of precipitations, hydrogen was released to the solution. Therefore, when the initial pH of solution was low (pH b 9), the removal was poor. At pH 10.1, 98.47% of P and 91.67% of As were precipitated from the solution. 3.2.2. Effect of reaction time on the purification of leach liquor The effect of reaction time on the removal rates of P and As was shown in Fig. 6. With the increasing of reaction time, there was a palpable effect on the precipitation of P and As. Due to the absence of foreign solid phases in this process, the precipitation mechanism is likely to be heterogeneous, enough reaction time was needed. It can be seen from Fig. 6 that 60 min of reaction time was suitable in the precipitation process.
A considerable research has been devoted to recovering molybdenum and vanadium from aqueous solution by solvent extraction with organic solutions of various extractants (Taich et al., 1986; Olazabal et al., 1992; Zhang et al., 1996). Amines were the most common extractants in the extraction of molybdenum and vanadium. According to the literatures and our past experiences, trialkylamine (N235, commercialized in China) was chosen as the extractants, the organic phase was made up of 20 vol.% N235, 10 vol.% secondary octyl alcohol (phase modifier) and 70 vol.% sulfonated kerosene, N235 was acidificated by 2 mol/ l HCl (volume ratio = 1:1) before using. A series of experiments were carried out to determine the optimum extraction conditions, the optimum operating conditions for extracting and stripping were presented in Table 3. Under the optimum conditions, the extraction rate of molybdenum and vanadium was no less than 99.9% by single stage extraction (O/A= 1:5), and the stripping rate of molybdenum and vanadium was above 99.8% by single stage stripping with 10 wt.% ammonia water (O/A= 2:1). In the process of extraction and stripping, no trouble in phase separation performance
Table 3 Recovery of molybdenum and vanadium from the leach liquor Parameter Extraction Extractant
Value
pH adjustment O/A ratio Temperature Initial pH Extraction rate
20 vol.% N235 + 10 vol.% secondary octyl alcohol + 70 vol.% sulfonated kerosene 50% HNO3 1:5 30 8C 2.15 Mo 99.8%, V 99.2%
Leach liquor (g/l) 2.35 11.89 4.4 3.8 1.31 0.06 After purification (g/l) 2.30 11.71 0.08 0.03 0.02 0.005 Removing rate (%) 2.13 0.67 98.18 99.21 98.47 91.67
Stripping Stripping agent O/A ratio Temperature Stripping ratio
10 wt.% ammonia water 2:1 30 8C Mo 99.83%, V 99.85%
Optimum conditions: 0.8 wt.% Mg(NO3)2 and 1.0 wt.% concentrated ammoniacal liquor, pH = 10.1, stirring 1 h at 50 8C.
The composition of leach liquor was listed in Table 2 (after purification), pH was adjusted to 2.15.
Table 2 Purification result of leach liquor Constituents
V
Mo
Al
Si
P
As
Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
occurs and the addition of secondary octyl alcohol could avoid the formation of a second organic phase and/or emulsion. 3.4. Production of MoO3 and V2O5 In order to get the product of MoO3 and V2O5 from the stripping solution, molybdenum and vanadium must be separated first. Due to the low solubility of ammonium metavanadate when pH is between 7.5 and 8.5 (Kelmers, 1961), ammonium metavanadate can be crystallized and precipitated from the solution firstly with the addition of NH4NO3. After the precipitation of ammonium metavanadate, ammonium polymolybdate was crystallized and precipitated at 50 8C when pH was adjusted to 2.0–2.5 by HNO3. A series of experiments were carried out to determine optimum operating conditions, the optimum conditions were listed in Table 4. After calcination at 500 8C for 1 h, the purity of MoO3 and V2O5 was 99.08% and 98.06% respectively. High purity of MoO3 can be obtained by the following process: ammonium polymolybdate dissolved in ammonia water, ammonium paramolybdate was crystallized and precipitated by evaporative crystallization, high purity of MoO3 (no less than 99.9%) can be obtained after calcination. The material balance of the whole process was listed in Table 5, the data came from a bench scale test under selected optimal processing conditions. In the whole process, the recovery of molybdenum and vanadium was 88.2% and 87.1%, and the content of molybdenum and vanadium among residues can be down to 0.2 wt.% and 0.05 wt.% respectively. The proposed roasting, leaching and separation steps give a feasible alternative for the processing of ammonia leaching residue of spent Table 4 Operating condition and the purity of product Constituent
V
Mo
Stripping solution (g/l) After precipitation of V (g/l) After precipitation of Mo (g/l) Precipitation of vanadium
22.81
118.63
0.03
118.32
Precipitation of molybdenum Purity of V2O5 Purity of MoO3
1.45 NH4NO3 30 g/l, pH = 8.2, 30 8C, stirring 60 min pH = 2.05, 50 8C, stirring 30 min 98.06% 99.08%
47
Table 5 The material balance of the whole process Constituents
V
Leach liquor (g/l) Leaching rate (%) After purification (g/l) Raffinate (g/l) Extraction rate (%) Stripping solution (g/l) Stripping rate (%) After precipitation of V (g/l) Precipitation rate of V (%) After precipitation of Mo (g/l) Precipitation rate of Mo (%) Recovery of V and Mo in the whole process (%)
2.35 90.1 2.30
Mo 11.89 91.4 11.71
0.02 99.2 22.8
0.02 99.8 118.6
99.8 0.03
99.9 118.3
Al
Si
P
As
4.4
3.8
1.31
0.06
0.08
0.03
0.02
0.005
99.8 1.45 98.8 87.1
88.2
The data came from a bench scale test under the selected optimal processing conditions.
catalyst and can be applied in the comprehensive utilization of low grade molybdenum ores. 4. Conclusions An investigation was conducted to develop an approach to recover molybdenum and vanadium from ammonia leaching residue of spent catalyst. Based on results obtained from the current work, the following conclusions are made: a) Under selected conditions, i.e. roasting at 750 8C and addition of 15 wt.% sodium carbonate for 45 min, up to 91.3% of molybdenum and 90.1% of vanadium could be extracted, and the content of molybdenum and vanadium in filtrate can be down to 0.2 wt.% and 0.05 wt.% respectively. b) After the purification of leach liquor, solvent extraction was used to concentrate Mo and V in solution, the extraction rate of molybdenum and vanadium was no less than 99.9% by single stage extraction (O/A= 1:5), and the stripping rate of molybdenum and vanadium was above 99.8% by single stage stripping. c) Ammonium metavanadate and ammonium polymolybdate were crystallized from the stripping solution by the addition of NH4NO3 and adjusting the pH to a suitable value, the purity of MoO3 and V2O5 was 99.08% and 98.06% respectively after calcination for 1 h at 500 8C.
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Y. Chen et al. / Int. J. Miner. Process. 79 (2006) 42–48
d) In the whole process, over 88.2% molybdenum and 87.1% vanadium could be recovered from the ammonia leaching residue of spent catalyst. The proposed roasting, leaching and separation steps give a feasible alternative for the processing of ammonia leaching residue of spent catalyst and can be applied in the comprehensive utilization of low grade molybdenum ores. References Battistoni, P., Fava, G., Pavan, P., Musacco, A., Cecchi, F., 1997. Phosphate removal in anaerobic liquors by struvite crystallization without addition of chemicals: preliminary results. Water Research 31, 2925 – 2929. Enbo, W., Jingyang, N., Lin, X., 1995. Study on thermal property of heteropolyacids with keggin structure. Acta Chimica Sinica 53, 757 – 764. Kar, B.B., 2005. Carbothermic reduction of hydro-refining spent catalyst to extract molybdenum. International Journal of Mineral Processing 75, 249 – 253. Kar, B.B., Murthy, B.V.R., Misra, V.N., 2005. Extraction of molybdenum from spent catalyst by salt-roasting. International Journal of Mineral Processing 76, 143 – 147. Kelmers, A.D., 1961. A portion of the system NH3–V2O5–H2O at 30 8C. Journal of Inorganic and Nuclear Chemistry 17, 168 – 173. Liu, H., 2000. Recovering of spent catalyst in the foreign country. Chinese Resource Comprehensive Utilization 12, 35 – 37. Marafi, M., Stanislaus, A., 2003. Options and processes for spent catalyst handling and utilization. Journal of Hazardous Materials, B 101, 123 – 132. Moskalyk, R.R., Alfantazi, A.M., 2003. Processing of vanadium: a review. Minerals Engineering 16, 793 – 805.
Olazabal, M.A., Orive, M.M., Fernandez, L.A., Madariaga, J.M., 1992. Selective extraction of vanadium (V) from solutions containing molybdenum (VI) by ammonium salts dissolved in toluene. Solvent Extraction and Ion Exchange 10, 623 – 635. Saily, A., Khurana, U., Yadav, S.K., Tandon, S.N., 1996. Thiophosphinic acids as selective extractants for molybdenum recovery from a low grade ore and spent catalysts. Hydrometallurgy 41, 99 – 105. Stratful, M.D., Scrimshaw, Lester, J.N., 2001. Conditions influencing the precipitation of magnesium ammonium phosphate. Water Research 35, 4191 – 4199. Sun, D.D., Li, X.Z., Brungs, M., Trimm, D., 1998. Encapsulation of heavy metals on spent fluid catalytic cracking catalyst. Water Science and Technology 38, 211 – 217. Sun, D.D., Tay, J.H., Cheong, H.K., Leung, D.L.K., Qian, G.R., 2001. Recovery of heavy metals and stabilization of spent hydrotreating catalyst using a glass–ceramic matrix. Journal of Hazardous Materials, B 87, 213 – 223. Sutulov, A., 1979. In: Sutulov, A. (Eds.), International Molybdenum Encyclopedia, 1778-1978, vol I—Resources and Production. Internet Publications, Santiago, Chile. Taich, S., Hiroshi, W., Hiroki, S., 1986. Liquid–liquid extraction of molybdenum(VI) from aqueous acid solutions by highmolecular weight amines. Solvent Extraction and Ion Exchange 4, 987 – 998. van den Berg, J.A.M., Yang, Y., Nauta, H.H.K., van Sandwijk, A., Reuter, M.A., 2002. Comprehensive processing of low grade sulphidic molybdenum ores. Minerals Engineering 15, 879 – 883. Zhang, P.W., Inoue, K., Yoshizuka, K., Tsuyama, H., 1996. Extraction and selective stripping of molybdenum(VI) and vanadium(IV) from sulfuric acid solution containing aluminum(III), cobalt(II), nickel(II) and iron(III) by LIX63 in Exxsol D80. Hydrometallurgy 41, 45 – 53.