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A novel nanofiltration process for the recovery of vanadium from acid leach solution
Hydrometallurgy 142 (2014) 94–97
Contents lists available at ScienceDirect
Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Technical note
A novel nanofiltration process for the recovery of vanadium from acid leach solution Guanghao Shang, Guiqing Zhang, Congjie Gao, Weng Fu, Li Zeng ⁎ School of Metallurgy and Environment, Central South University, Changsha 410083, China Key laboratory of Hunan Province for Metallurgy and Material Processing of Rare Metals, Changsha 410083, Hunan, China
a r t i c l e
i n f o
Article history: Received 1 March 2013 Received in revised form 7 November 2013 Accepted 19 November 2013 Available online 9 December 2013 Keywords: Vanadium Stone coal Nanofiltration Recovery
a b s t r a c t The effects of pH, feed concentration and operation pressure on the recovery of vanadium from acid leach solution of stone coal using nanofiltration membrane technology were investigated. The rejection and permeate flux of vanadium with two kinds of membranes in nanofiltration process were also studied. After pre-treatment of leach solution to remove calcium by the addition of sodium carbonate, the vanadium in the final concentrated solution can be up to 30 g/L from 1.429 g/L in the feed under the optimum conditions of pH 6–6.5 and operation pressure of 2069 kPa at room temperature during nanofiltration process with the rejection of vanadium more than 95%. The final concentrated solution can be directly used to produce the V2O5 by traditional method, and the permeate stream can be recycled to leaching. The conceptual flow sheet for the extraction of vanadium from acid leach solution using nanofiltration membrane has been developed. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Stone coal is carbonaceous shale which contains vanadium with a grade normally around 0.13%–1.2% in terms of V2O5. In China, the gross reserve of vanadium in stone coal is 118 million tons, accounting for more than 87% of domestic reserve of vanadium (Bin, 2006; Qi, 1999). The methods on the recovery of vanadium from acid leach solution which normally contains 1–4 g/L V2O5 include precipitation, solvent extraction and ion exchange. These methods, to some degree, have their own problems: low recovery of vanadium with chemical precipitation, big investment with solvent extraction and large amount of waste water generation with ion exchange (Lu, 2002; Wang and Wang, 2012). The aim of this paper is to explore an environmentallyfriendly and highly-effective way to extract vanadium from acid leach solutions. As an important branch of membrane separation technology, nanofiltration was brought up from 1950s and developed from 1980s. It has been widely applied in many fields of chemical engineering. Nanofiltration is a novel membrane process which plays the function of separation, purification and concentration into one role without chemical reaction, phase transition and secondary pollution. There are two main features of nanofiltration membrane, one is 200–1000 of molecular weight cutoff, and the other is with a negative charge on the surface of membrane, which results in a certain rejection to inorganic electrolyte (Cséfalvay et al., 2009; Fievet et al., 2002; Gao, 2004; Ortega et al., 2008; Petersen, 1993; Rautenbach and Groschl, 1990; Wang, ⁎ Corresponding author at: School of Metallurgy and Environment, Central South University, Changsha 410083, China. E-mail address: [email protected] (L. Zeng). 0304-386X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.hydromet.2013.11.007
2003). The rejection order of nanofiltration membrane on cations and anions is listed as follows (Zhang, 2004): þ
þ
2þ
2þ
2þ
H bNa bCa bMg bCu bM
−
−
−
2−
2−
3þ
4−
NO3 bCl bOH bSO4 bCO3 bM
:
Therefore, with the short supply of energy, lack of water resources and strict environmental protection, nanofiltration membrane technology is becoming an important and promising means to the development of novel metallurgical processes with high efficiency, energy conservation and without pollution. This paper investigates the recovery of vanadium from acid leach solutions using nanofiltration membrane. The permeate stream was recycled to leaching and the final concentrated solution was used to precipitate vanadium and then produce V2O5.
2. Experimental 2.1. Materials The sulfuric acid leach solution of stone coal was obtained from Huaihua Shuangxi Vanadium Plant. The pH of reddish orange solution Table 1 Composition of the leach solution of stone coal. Element
V
SO2− 4
PO3− 4
Ca2+
Mg2+
Al3+
Concentration (g/L)
2.02
2.749
0.226
0.920
0.120
0.028
G. Shang et al. / Hydrometallurgy 142 (2014) 94–97
95
Table 2 Properties of DK and DL membranes. MWCO
Maximum work pressure (Mpa)
pH range
Rejection to MgSO4 (%)
Maximum work temperature (°C)
DK DL
150–300 150–300
4.14 4.14
2–11 2–11
98 96
50 50
was around 2–4. The composition of the solution is shown in Table 1. The concentration of vanadium is in terms of V2O5. It can be seen from Table 1 that the concentration of calcium and sulfate is relatively high, which may result in membrane fouling in nanofiltration process since the precipitation of calcium sulfate. Thus, it is necessary to pre-treat the feed. The calcium in the feed was precipitated by adding sodium carbonate and the solution was then filtrated followed by micro-filtrated. The resultant solution containing 1.429 g/L V2O5 was used as the feed in the nanofiltration experiment after pH adjustment. The nanofiltration membranes of DK and DL were purchased from GE-Osmonics company and the properties of two membranes are listed in Table 2. The two kinds of membranes were soaked in DI-water for 24 h and used to measure the water flux before use. After nanofiltration process, the membrane was rinsed with DI-water and used to measure water flux again. If the value of flux decreased much, 1.0% of Na2EDTA has to be used to wash the membranes under low pressure and high flow speed for 2 h. The washed membrane was then soaked in the solution of 1.0% Na2EDTA for 1 to 15 h, depending on the degree of contamination.
2.2. Methods The schematic diagram of nanofiltration testing device is shown in Fig. 1. The feed was pumped into two parallel cells equipped with nanofiltration membranes of 81.7 cm2 effective area each. During nanofiltration process, the concentrated solution was refluxed for cycling and sampled from reflux inlet of feed tank. The permeate stream was separately collected and sampled. The pressure was controlled by adjusting different valves. The permeate flux of membrane was determined by measuring the volume of permeate. Vanadium was titrated with ammonium ferrous sulfate.
2.3. Fundamental Fig. 2 shows the forms of vanadium(V) existing in an aqueous solution under different pHs and concentrations. It is noted that the nature of species formed depends on pH, oxidation state and concentration of the metal and ligands in the solution (Liao and Bo, 1985). As seen from Fig. 2, the vanadium(V) in the sulfuric acid leach solution (lgCv (total) = − 1.65, pH = 2–4) is mostly in the forms of 5− , V10O6− V10O26(OH)4− 2 , V10O27(OH) 28 . These species are multivalent anions with molecule weight all above 200, which could be rejected by nanofiltration membrane and crudely separated from the feed.
Fig. 2. Forms of vanadium(V) existing in aqueous solution (based on Baes and Mesmer, 1976).
3. Results and discussion 3.1. The effect of pH and operative pressure on rejection and permeate flux The rejection and permeate flux of vanadium with two kinds of membranes under different feed pH and operative pressure are listed in Figs. 3 and 4, respectively. Both permeate flux of vanadium increased with the increase in the pH range of 2.5–6.5, while the rejection of vanadium maintained 98% of DK membrane and 96% of DL membrane. Further increase of pH resulted in the decrease of permeate flux and especially the rejection of vanadium. This phenomenon can be explained by the change of vanadium species in an aqueous solution. As seen from Fig. 2, the species of V10O6− 28 is 3− when the pH increases to 6.5 gradually converted to V4O4− 12 and V3O9 above, corresponding to the decrease of molecule weight from 958 to 396 and 297, and the decrease of charge number, resulting in the decrease of rejection of vanadium. The effect of pH on permeate flux could be attributed to the isoelectric point in the pH range of 6–6.5 of two kinds of membranes since the maximum permeate flux is normally observed around the isoelectric point of nanofiltration membrane (Childress and Elimelech, 2000; Qin et al., 2004). Therefore, the optimum pH for concentrating vanadium using nanofiltration membrane was determined to be 6–6.5. It was also found that the permeate flux of both membranes significantly increased with the increase of operation pressure during the pH range tested. The large operation pressure also resulted in the large
Membrane flux(L·m-2·h-1)
Type
200 160
DK 1034kPa DK 1724kPa DL 1034kPa DL 1724kPa
DK 1379kPa DK 2069kPa DL 1379kPa DL 2069kPa
120 80 40 0 2.5
3.5
4.5
5.5
6.5
7.5
pH Fig. 1. The schematic diagram of nanofiltration testing device.
Fig. 3. The effect of pH and operation pressure on permeate flux of vanadium with two kinds of membranes.
96
G. Shang et al. / Hydrometallurgy 142 (2014) 94–97
100%
100%
90%
V rejection
V rejection
96% 92% 88% 84% 80% 2.5
DK 1034kPa DK 1724kPa DL 1034kPa DL 1724kPa
3.5
DK 1379kPa DK 2069kPa DL 1379kPa DL 2069kPa
4.5
5.5
DK
80%
DL
70%
6.5
60% 0
7.5
3
6
9
12
15
V concentration in concentrated liquid (g/L)
pH Fig. 4. The effect of pH and operation pressure on rejection of vanadium with two kinds of membranes.
rejection of vanadium. It is suggested that the operation pressure can be selected as high as possible in the tolerance range of membrane. The feed pH of 6–6.5 and operation pressure of 2069 kPa was therefore chosen in subsequent experiment.
3.2. The effect of vanadium concentration in concentrated solution on the process of nanofiltration The permeate flux of vanadium with both membranes was continuously measured and sampled at interval during the nanofiltration process using a feed of 1.429 g/L V2O5 at pH 6–6.5 and pressure of 2069 kPa. The results are shown in Figs. 5 and 6. As seen, the rejection and the permeate flux of vanadium with both membranes gradually decreased with the increase of vanadium concentration in concentrated solution. But the rejection of vanadium with both membranes maintained above 96% during the whole process. Compared with DK membrane, DL membrane has larger permeate flux but relatively slightly lower rejection. For example, when the vanadium concentration in concentrated solution increased from 1.429 g/L to 12 g/L, the permeate flux of vanadium with DL membrane gradually decreased from 130 L/(m 2 ·h) to 90 L/(m2·h) in comparison to that with DK membrane that sharply decreased from 100 L/(m2·h) to 20 L/(m2·h). Given consideration that the permeate stream can be recycled to leaching step, it is suggested that DL membrane is recommended to be applied in practice. The concentration of vanadium in final concentrated solution reached 30.86 g/L V2O5, which can be directly used to produce vanadium product. The ammonium salt was added into the concentrated solution to precipitate NH4VO3 at 40 °C and pH 8. After calcination of ammonium metavanadate at 550 °C for 1.5 h, the V2O5 with high purity meeting the standard specification was produced.
Fig. 6. The effect of V concentration in concentrated solution on the rejection.
3.3. Process flowsheet development A conceptual process flowsheet for the extraction of vanadium from acid leach solution of stone coal using nanofiltration membrane is shown in Fig. 7. After the removal of calcium, the leach solution is directly passed through nanofiltration membrane. The resultant concentrated solution containing around 30 g/L V 2O 5 can be directly used to produce the vanadium product using the traditional method. The permeate stream can be recycled to leaching step to further recover vanadium. The new process for the recovery of vanadium from the acid leach solution exhibits advantages of high recovery of vanadium, easy operation and without generation of waste water and waste slag.
4. Conclusions A novel nanofiltration process for the recovery of vanadium from acid leach solution of stone coal was proposed. The vanadium in leach solution can be effectively rejected by the nanofiltration membrane of DK and DL with the rejection more than 96% and the DL membrane is recommended to be applied in practice since larger permeate flux. The concentration of vanadium in final concentrated solution reached 30 g/L V2O5 from 1.429 g/L in feed under optimum condition of pH around 6–6.5 and operation pressure of 2069 kPa. The permeate stream can be recycled to leaching for totally high recovery of vanadium.
Leach solution of stone coal Na2CO3
Removal of Calcium Filtration
Membrane flux(L·m-2·h-1)
160
Nano-filtration DK
120
DL
Concentrated solution (CV2O5>30g/L) NH4Cl
80
Precipitation
Permeate stream Recycled to leaching
NH4VO3
40
Calcination 0 0
3
6
9
12
15
V2O5
V concentration in concentrated liquid (g/L) Fig. 5. The effect of V concentration in concentrated solution on the permeate flux.
Fig. 7. Conceptual process flowsheet of the extraction of vanadium from acid leach solution of stone coal using nanofiltration membrane.
G. Shang et al. / Hydrometallurgy 142 (2014) 94–97
References Baes, C.F., Mesmer, R.E., 1976. The hydrolysis of cations, Vol. 68. Wiley, New York. Bin, Z.Y., 2006. Progress of the research on extraction of vanadium pentoxide from stone coal and the market of the V2 O 5 . Hunan Nonferrous Met. 22, 16–20 (In Chinese). Childress, A.E., Elimelech, M., 2000. Relating nanofiltration membrane performance to membrane charge (electrokinetic) characteristics. Environ. Sci. Technol. 34, 3710. Cséfalvay, Edit, Pauer, Viktor, Mizsey, Peter, 2009. Recovery of copper from process waters by nanofiltration and reverse osmosis. Desalination 240, 132–142. Fievet, P., Labbez, C., Szymczyk, A., Vidonne, A., Foissy, A., Pagetti, J., 2002. Electrolyte transport through amphoteric nanofiltration membranes. Chem. Eng. Sci. 57, 2921–2931. Gao, C.J., 2004. Nanofiltration membrane and its application. Chin. J. Nonferrous Met. 14 (S1), 310–316. Liao, S.M., Bo, T.L., 1985. Foreign Vanadium Metallurgy, first ed. Metallurgical Industry Publishing House, Beijing.
97
Ortega, Lina M., Lebrun, Rémi, Blais, Jean-Francois, Hausler, Robert, 2008. Removal of metal ions from an acidic leachate solution by nanofiltration membranes. Desalination 227, 204–216. Lu, Z.L., 2002. The study and pilot plant test on the extraction of V2O5 from stone coal in acidic media (in Chinese). China Hydrometall. 21 (4), 175–183. Petersen, R.J., 1993. Composite reverse osmosis and nanofiltration membranes. J. Membr. Sci. 83 (81), 150. Qi, M.J., 1999. The extraction of vanadium from stone coal: present and prospective (in Chinese). China Hydrometall. 72, 1–10. Qin, J.J., Oo, Maung Htun, Lee, Hsiaowan, Coniglio, Bruno, 2004. Effect of feed pH and ion rejection under acidic conditions in NF process. J. Membr. Sci. 232, 153–159. Rautenbach, R., Groschl, A., 1990. Separation potential of nanofiltration membranes. Desalination 77, 73–84. Wang, X.L., 2003. The new development of nanofiltration membrane technology (in Chinese). J. Tianjin Inst. Urban Constr. 9 (2), 83–89. Wang, X.W., Wang, M.Y., 2012. State-of-art development of vanadium extraction from stone coal (in Chinese). Iron Steel Vanadium Titan. 33 (1), 8–14. Zhang, Q.X., 2004. Metallurgical Separation Science and Engineering, first ed. Science Press, Beijing 229–230 (In Chinese).
Contents lists available at ScienceDirect
Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Technical note
A novel nanofiltration process for the recovery of vanadium from acid leach solution Guanghao Shang, Guiqing Zhang, Congjie Gao, Weng Fu, Li Zeng ⁎ School of Metallurgy and Environment, Central South University, Changsha 410083, China Key laboratory of Hunan Province for Metallurgy and Material Processing of Rare Metals, Changsha 410083, Hunan, China
a r t i c l e
i n f o
Article history: Received 1 March 2013 Received in revised form 7 November 2013 Accepted 19 November 2013 Available online 9 December 2013 Keywords: Vanadium Stone coal Nanofiltration Recovery
a b s t r a c t The effects of pH, feed concentration and operation pressure on the recovery of vanadium from acid leach solution of stone coal using nanofiltration membrane technology were investigated. The rejection and permeate flux of vanadium with two kinds of membranes in nanofiltration process were also studied. After pre-treatment of leach solution to remove calcium by the addition of sodium carbonate, the vanadium in the final concentrated solution can be up to 30 g/L from 1.429 g/L in the feed under the optimum conditions of pH 6–6.5 and operation pressure of 2069 kPa at room temperature during nanofiltration process with the rejection of vanadium more than 95%. The final concentrated solution can be directly used to produce the V2O5 by traditional method, and the permeate stream can be recycled to leaching. The conceptual flow sheet for the extraction of vanadium from acid leach solution using nanofiltration membrane has been developed. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Stone coal is carbonaceous shale which contains vanadium with a grade normally around 0.13%–1.2% in terms of V2O5. In China, the gross reserve of vanadium in stone coal is 118 million tons, accounting for more than 87% of domestic reserve of vanadium (Bin, 2006; Qi, 1999). The methods on the recovery of vanadium from acid leach solution which normally contains 1–4 g/L V2O5 include precipitation, solvent extraction and ion exchange. These methods, to some degree, have their own problems: low recovery of vanadium with chemical precipitation, big investment with solvent extraction and large amount of waste water generation with ion exchange (Lu, 2002; Wang and Wang, 2012). The aim of this paper is to explore an environmentallyfriendly and highly-effective way to extract vanadium from acid leach solutions. As an important branch of membrane separation technology, nanofiltration was brought up from 1950s and developed from 1980s. It has been widely applied in many fields of chemical engineering. Nanofiltration is a novel membrane process which plays the function of separation, purification and concentration into one role without chemical reaction, phase transition and secondary pollution. There are two main features of nanofiltration membrane, one is 200–1000 of molecular weight cutoff, and the other is with a negative charge on the surface of membrane, which results in a certain rejection to inorganic electrolyte (Cséfalvay et al., 2009; Fievet et al., 2002; Gao, 2004; Ortega et al., 2008; Petersen, 1993; Rautenbach and Groschl, 1990; Wang, ⁎ Corresponding author at: School of Metallurgy and Environment, Central South University, Changsha 410083, China. E-mail address: [email protected] (L. Zeng). 0304-386X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.hydromet.2013.11.007
2003). The rejection order of nanofiltration membrane on cations and anions is listed as follows (Zhang, 2004): þ
þ
2þ
2þ
2þ
H bNa bCa bMg bCu bM
−
−
−
2−
2−
3þ
4−
NO3 bCl bOH bSO4 bCO3 bM
:
Therefore, with the short supply of energy, lack of water resources and strict environmental protection, nanofiltration membrane technology is becoming an important and promising means to the development of novel metallurgical processes with high efficiency, energy conservation and without pollution. This paper investigates the recovery of vanadium from acid leach solutions using nanofiltration membrane. The permeate stream was recycled to leaching and the final concentrated solution was used to precipitate vanadium and then produce V2O5.
2. Experimental 2.1. Materials The sulfuric acid leach solution of stone coal was obtained from Huaihua Shuangxi Vanadium Plant. The pH of reddish orange solution Table 1 Composition of the leach solution of stone coal. Element
V
SO2− 4
PO3− 4
Ca2+
Mg2+
Al3+
Concentration (g/L)
2.02
2.749
0.226
0.920
0.120
0.028
G. Shang et al. / Hydrometallurgy 142 (2014) 94–97
95
Table 2 Properties of DK and DL membranes. MWCO
Maximum work pressure (Mpa)
pH range
Rejection to MgSO4 (%)
Maximum work temperature (°C)
DK DL
150–300 150–300
4.14 4.14
2–11 2–11
98 96
50 50
was around 2–4. The composition of the solution is shown in Table 1. The concentration of vanadium is in terms of V2O5. It can be seen from Table 1 that the concentration of calcium and sulfate is relatively high, which may result in membrane fouling in nanofiltration process since the precipitation of calcium sulfate. Thus, it is necessary to pre-treat the feed. The calcium in the feed was precipitated by adding sodium carbonate and the solution was then filtrated followed by micro-filtrated. The resultant solution containing 1.429 g/L V2O5 was used as the feed in the nanofiltration experiment after pH adjustment. The nanofiltration membranes of DK and DL were purchased from GE-Osmonics company and the properties of two membranes are listed in Table 2. The two kinds of membranes were soaked in DI-water for 24 h and used to measure the water flux before use. After nanofiltration process, the membrane was rinsed with DI-water and used to measure water flux again. If the value of flux decreased much, 1.0% of Na2EDTA has to be used to wash the membranes under low pressure and high flow speed for 2 h. The washed membrane was then soaked in the solution of 1.0% Na2EDTA for 1 to 15 h, depending on the degree of contamination.
2.2. Methods The schematic diagram of nanofiltration testing device is shown in Fig. 1. The feed was pumped into two parallel cells equipped with nanofiltration membranes of 81.7 cm2 effective area each. During nanofiltration process, the concentrated solution was refluxed for cycling and sampled from reflux inlet of feed tank. The permeate stream was separately collected and sampled. The pressure was controlled by adjusting different valves. The permeate flux of membrane was determined by measuring the volume of permeate. Vanadium was titrated with ammonium ferrous sulfate.
2.3. Fundamental Fig. 2 shows the forms of vanadium(V) existing in an aqueous solution under different pHs and concentrations. It is noted that the nature of species formed depends on pH, oxidation state and concentration of the metal and ligands in the solution (Liao and Bo, 1985). As seen from Fig. 2, the vanadium(V) in the sulfuric acid leach solution (lgCv (total) = − 1.65, pH = 2–4) is mostly in the forms of 5− , V10O6− V10O26(OH)4− 2 , V10O27(OH) 28 . These species are multivalent anions with molecule weight all above 200, which could be rejected by nanofiltration membrane and crudely separated from the feed.
Fig. 2. Forms of vanadium(V) existing in aqueous solution (based on Baes and Mesmer, 1976).
3. Results and discussion 3.1. The effect of pH and operative pressure on rejection and permeate flux The rejection and permeate flux of vanadium with two kinds of membranes under different feed pH and operative pressure are listed in Figs. 3 and 4, respectively. Both permeate flux of vanadium increased with the increase in the pH range of 2.5–6.5, while the rejection of vanadium maintained 98% of DK membrane and 96% of DL membrane. Further increase of pH resulted in the decrease of permeate flux and especially the rejection of vanadium. This phenomenon can be explained by the change of vanadium species in an aqueous solution. As seen from Fig. 2, the species of V10O6− 28 is 3− when the pH increases to 6.5 gradually converted to V4O4− 12 and V3O9 above, corresponding to the decrease of molecule weight from 958 to 396 and 297, and the decrease of charge number, resulting in the decrease of rejection of vanadium. The effect of pH on permeate flux could be attributed to the isoelectric point in the pH range of 6–6.5 of two kinds of membranes since the maximum permeate flux is normally observed around the isoelectric point of nanofiltration membrane (Childress and Elimelech, 2000; Qin et al., 2004). Therefore, the optimum pH for concentrating vanadium using nanofiltration membrane was determined to be 6–6.5. It was also found that the permeate flux of both membranes significantly increased with the increase of operation pressure during the pH range tested. The large operation pressure also resulted in the large
Membrane flux(L·m-2·h-1)
Type
200 160
DK 1034kPa DK 1724kPa DL 1034kPa DL 1724kPa
DK 1379kPa DK 2069kPa DL 1379kPa DL 2069kPa
120 80 40 0 2.5
3.5
4.5
5.5
6.5
7.5
pH Fig. 1. The schematic diagram of nanofiltration testing device.
Fig. 3. The effect of pH and operation pressure on permeate flux of vanadium with two kinds of membranes.
96
G. Shang et al. / Hydrometallurgy 142 (2014) 94–97
100%
100%
90%
V rejection
V rejection
96% 92% 88% 84% 80% 2.5
DK 1034kPa DK 1724kPa DL 1034kPa DL 1724kPa
3.5
DK 1379kPa DK 2069kPa DL 1379kPa DL 2069kPa
4.5
5.5
DK
80%
DL
70%
6.5
60% 0
7.5
3
6
9
12
15
V concentration in concentrated liquid (g/L)
pH Fig. 4. The effect of pH and operation pressure on rejection of vanadium with two kinds of membranes.
rejection of vanadium. It is suggested that the operation pressure can be selected as high as possible in the tolerance range of membrane. The feed pH of 6–6.5 and operation pressure of 2069 kPa was therefore chosen in subsequent experiment.
3.2. The effect of vanadium concentration in concentrated solution on the process of nanofiltration The permeate flux of vanadium with both membranes was continuously measured and sampled at interval during the nanofiltration process using a feed of 1.429 g/L V2O5 at pH 6–6.5 and pressure of 2069 kPa. The results are shown in Figs. 5 and 6. As seen, the rejection and the permeate flux of vanadium with both membranes gradually decreased with the increase of vanadium concentration in concentrated solution. But the rejection of vanadium with both membranes maintained above 96% during the whole process. Compared with DK membrane, DL membrane has larger permeate flux but relatively slightly lower rejection. For example, when the vanadium concentration in concentrated solution increased from 1.429 g/L to 12 g/L, the permeate flux of vanadium with DL membrane gradually decreased from 130 L/(m 2 ·h) to 90 L/(m2·h) in comparison to that with DK membrane that sharply decreased from 100 L/(m2·h) to 20 L/(m2·h). Given consideration that the permeate stream can be recycled to leaching step, it is suggested that DL membrane is recommended to be applied in practice. The concentration of vanadium in final concentrated solution reached 30.86 g/L V2O5, which can be directly used to produce vanadium product. The ammonium salt was added into the concentrated solution to precipitate NH4VO3 at 40 °C and pH 8. After calcination of ammonium metavanadate at 550 °C for 1.5 h, the V2O5 with high purity meeting the standard specification was produced.
Fig. 6. The effect of V concentration in concentrated solution on the rejection.
3.3. Process flowsheet development A conceptual process flowsheet for the extraction of vanadium from acid leach solution of stone coal using nanofiltration membrane is shown in Fig. 7. After the removal of calcium, the leach solution is directly passed through nanofiltration membrane. The resultant concentrated solution containing around 30 g/L V 2O 5 can be directly used to produce the vanadium product using the traditional method. The permeate stream can be recycled to leaching step to further recover vanadium. The new process for the recovery of vanadium from the acid leach solution exhibits advantages of high recovery of vanadium, easy operation and without generation of waste water and waste slag.
4. Conclusions A novel nanofiltration process for the recovery of vanadium from acid leach solution of stone coal was proposed. The vanadium in leach solution can be effectively rejected by the nanofiltration membrane of DK and DL with the rejection more than 96% and the DL membrane is recommended to be applied in practice since larger permeate flux. The concentration of vanadium in final concentrated solution reached 30 g/L V2O5 from 1.429 g/L in feed under optimum condition of pH around 6–6.5 and operation pressure of 2069 kPa. The permeate stream can be recycled to leaching for totally high recovery of vanadium.
Leach solution of stone coal Na2CO3
Removal of Calcium Filtration
Membrane flux(L·m-2·h-1)
160
Nano-filtration DK
120
DL
Concentrated solution (CV2O5>30g/L) NH4Cl
80
Precipitation
Permeate stream Recycled to leaching
NH4VO3
40
Calcination 0 0
3
6
9
12
15
V2O5
V concentration in concentrated liquid (g/L) Fig. 5. The effect of V concentration in concentrated solution on the permeate flux.
Fig. 7. Conceptual process flowsheet of the extraction of vanadium from acid leach solution of stone coal using nanofiltration membrane.
G. Shang et al. / Hydrometallurgy 142 (2014) 94–97
References Baes, C.F., Mesmer, R.E., 1976. The hydrolysis of cations, Vol. 68. Wiley, New York. Bin, Z.Y., 2006. Progress of the research on extraction of vanadium pentoxide from stone coal and the market of the V2 O 5 . Hunan Nonferrous Met. 22, 16–20 (In Chinese). Childress, A.E., Elimelech, M., 2000. Relating nanofiltration membrane performance to membrane charge (electrokinetic) characteristics. Environ. Sci. Technol. 34, 3710. Cséfalvay, Edit, Pauer, Viktor, Mizsey, Peter, 2009. Recovery of copper from process waters by nanofiltration and reverse osmosis. Desalination 240, 132–142. Fievet, P., Labbez, C., Szymczyk, A., Vidonne, A., Foissy, A., Pagetti, J., 2002. Electrolyte transport through amphoteric nanofiltration membranes. Chem. Eng. Sci. 57, 2921–2931. Gao, C.J., 2004. Nanofiltration membrane and its application. Chin. J. Nonferrous Met. 14 (S1), 310–316. Liao, S.M., Bo, T.L., 1985. Foreign Vanadium Metallurgy, first ed. Metallurgical Industry Publishing House, Beijing.
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