Res Chem Intermed (2013) 39:1313–1321 DOI 10.1007/s11164-012-0687-6
Fatty amides synthesized from vegetable oil as extractant of molybdenum(VI) Emad A. Jaffar Al-Mulla • Nor Azowa Bt Ibrahim Kamyar Shameli • Mansor Bin Ahmad • Wan Md. Zin Wan Yunus
•
Received: 8 May 2012 / Accepted: 8 June 2012 / Published online: 27 June 2012 Ó Springer Science+Business Media B.V. 2012
Abstract In this study, fatty amides (FAs) synthesized from palm olein were used to extract and separate Mo(VI) from acidic media. Effects of various parameters upon the separation of Mo(VI) from Co(II), Ni(II), Al(III) and Mn(II), including extractant concentration, metal ion concentration, contact time, diluent, and acidity, were investigated. It was found that Mo(VI) was successfully separated from the above commonly associated metal ions by stripping from the loaded organic phase. Different acidic and alkaline solutions were used. Ammonium hydroxide solution was an optimal. Extraction of Mo(VI) into the organic phase involved the formation of 1:3 complexes. This work presents the development of a low-cost and environmentally friendly extractant to recycle and recover molybdenum. Keywords
Fatty amides Molybdenum(VI) Acidic media
Introduction Recently, molybdenum has received a lot of attention in industrial applications [1]. In many petrochemical processes, molybdenum is widely used as an effective catalyst. This metal should be recovered from primary and secondary sources due to
E. A. J. Al-Mulla (&) N. A. B. Ibrahim K. Shameli M. B. Ahmad Department of Chemistry, Faculty of Science, Universiti Putra Malaysia (43400) UPM, Serdang, Selangor, Malaysia e-mail:
[email protected] E. A. J. Al-Mulla Department of Chemistry, College of Science, University of Kufa, B.O. Box 21, An-Najaf, Iraq W. Md. Z. W. Yunus Department of Chemistry, Centre for Defence Foundation Studies, National Defence University of Malaysia, Sungai Besi Camp, 57000 Kuala Lumpur, Malaysia
123
1314
E. A. J. Al-Mulla et al.
its industrial demand. Attempts have been made to develop an effective separation process for recovering molybdenum from various matrices. Solvent extraction has been widely used in recycling valuable metals. In economic terms, it is important to choose more selective and effective extractants of valuable metals. Many studies have been carried out for the extraction of molybdenum using hydroxyoxime [2], thiophosphinic acid [3], and secondary amine [4] as extractants. Amines and amides with high molecular weight are common extractants for the separation of anionic metals [5–9]. Fatty amides with the general formula RCONH2, which have non-bonded lone pairs of electrons on the nitrogen and the oxygen of the amide group, are interesting ligands. These ligands will become a cationic reagent when the amide nitrogen groups are protonated in acidic solutions and hence have the potential for attracting metal anions. Although the coordination of amides and their derivatives ligands with several metal ions have been studied, our literature search shows that there is no information regarding the use of amides for the extraction of molybdenum in acidic media. The presence of long chain fatty acids (mainly C16 and C18) in palm olein suggests that fatty amides should be useful for the extraction of metal ions from aqueous solutions [10]. Recent study has involved not only the development of new reagents for specific metals but also the synthesis of the fatty amides (FAs) extractant as a simple and environmentally friendly process and using abundant raw materials.
Materials and methods Materials Ammonium molybdate was obtained from BDH Chemical (UK). Palm olein was from Ngo Chew Hong Oils Fats, Selangor, Malaysia. Standard solutions of metal ions were prepared by diluting the stock solutions from BDH Chemical. Metal ion concentrations were quantitatively determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using Perkin Elmer Plasma 1000 equipment (Massachusetts, USA). Lipozyme and urea were purchased through local suppliers from Novo Nordisk, Denmark, and Merck, Germany, respectively. Synthesis of fatty amides Fatty amides were synthesized by reacting 3.84 g of commercial palm olein in 20 mL of hexane as a solvent with 4.20 g of urea. The pH was adjusted to 7 by adding about 5 mL of 0.5 M NaOH. The reaction was carried out in the presence of lipase catalyst in a 100-mL stoppered flask. The mixture was incubated in a water shaker batch (125 rpm) at 40 °C for 36 h. Hot hexane was added to the reaction to dissolve the product. The organic phase was then separated from the water phase using a separation funnel. To obtain the solid fatty amides, the hexane fraction was cooled in a refrigerator at 5 °C for 5 h, filtered, and then reprecipitated by hexane.
123
Fatty amides synthesized from vegetable oil
1315
Scheme 1 Fatty amides synthesis from palm olein
The product was then dried in an oven at 50 °C. The preparation reaction is shown in the Scheme 1. The proposed mechanism of reaction was described by our previous report [9]. Characterization of FAs The presence of amide in FAs was also determined by FTIR spectra. FTIR spectra of the products were recorded by the FTIR spectrophotometer (Perkin Elmer FT-IRSpectrum BX, USA) using the KBr disc technique. Elemental analyzer (LECO CHNS-932) was used for quantitative analysis of nitrogen contents. The determination was carried out under N2 atmospheric conditions using sulfamethazine as the standard. Extraction procedure A known concentration of Mo(VI) solution was shaken with a toluene solution containing FAs (7.5 9 10-3 mol L-1) at an equal phase ratio (10 mL) in a mechanical shaker (Schwabach, Germany) for 30 min. After agitation, the solutions were allowed to stand for 10 min to complete phase separation. The aqueous phase was then separated and the aqueous phase concentration of Mo(VI) was determined by ICP-AES. Hydrochloric acid (HCl), nitric acid (HNO3) and sulfuric acid (H2SO4) of various concentrations were used to determine the effect of different acids and their concentration on the percentage extraction of Mo(VI). The extraction of HCl by FAs was studied by shaking FAs (7.5 9 10-3 mol L-1) in toluene solutions with aqueous solutions containing different concentrations of HCl. The aqueous phase was separated and the HCl concentration in the aqueous phase was determined with standard sodium hydroxide (NaOH) solution using phenolphthalein as an indicator.
Results and discussion Characterization of FAs Characteristic bands of palm olein were observed at 2,910, 2,852, and 1,747 cm-1 resulting from, C–H asymmetric stretching of CH2, C–H symmetric stretching of CH2, and C=O stretching of ester (glyceride), respectively [9, 11]. The fatty amides
123
1316
E. A. J. Al-Mulla et al.
Fig. 1 FTIR spectra of palm olein and FAs from palm olein
spectra showed absorption bands at 3,312, 1,624, and 1,045 cm-1 attributed to –NH2 group stretching, C=O stretching, and C–N stretching of amide, respectively. The disappearance of the peak at 1,747 cm-1 and the presence of the peaks at 3,312, 1,626, and 1,045 cm-1 indicate that fatty amides have been formed (Fig. 1) [9, 12]. The amount of amide produced was indicated by the nitrogen content of the dry product. This was determined by elemental analysis and found to be 5.02 %. The percentage conversion of palm olein into FAs was 96 %. Extraction of Mo(VI) The percentage extraction of Mo(VI) increases from 10-5 to 10-3 mol L-1 with the increase in acid concentration. Further increase in acid concentration decreases the percentage extraction (Table 1). H2MoO4 is the dominant kind of Mo(VI) in solution around pH 2 [13, 14]. The ratio of Mo:FAs is 1:3 as shown in the study of the effect of the extractant and metal ion concentration. The extraction of Mo(VI) from dilute acid media can be shown by equations 1 and 2. RCONH2 þ Hþ ! ½RCONH2 Hþ þ
þ
3½RCONH2 H þ H2 MoO4 ! ½RCONH2 3 H
HMoO 4
ð1Þ þ 3H
þ
ð2Þ
When the acid concentration is increased to 10-1 mol L-1 or higher, the percentage extraction of Mo(VI) decreases due to the presence of the dominant kind of MoO?2 2 at low pH [13]. This reduces the possibility of the protonated extractant to form complexes with the Mo(VI). The amide group will reduce the electrostatic attraction of the molybdenum anions. Therefore, the low percentage extraction was at 10-4 mol L-1 or less. A similar behavior was observed for extraction of Mo(VI) with fatty amides from HCl, H2SO4, and HNO3. However, quantitative extraction of
123
Fatty amides synthesized from vegetable oil Table 1 Percentage extraction of Mo(VI) from dual mixtures with Ni(II), Co(II), Al(III), and Mn(II)
Log [acid (mol/L)]
1317
Extraction (%) HCl
H2SO4
HNO3
-5
39
52
58
-4
41
59
57
-3
88
84
76
-2
84
83
77
-1
79
38
76
0
08
10
11
Fig. 2 Extraction of a HCl and b Mo(VI) with 7.5 9 10-3 mol L-1 FAs in toluene
Mo(VI) occurs over a wide range of HCl solution and over a narrow range of both HNO3 and H2SO4 solutions of acid concentration from 10-3 to 10-1 mol L-1. So, HCl was used in all the experiments for this study. The percentage extraction of HCl and Mo(VI) from different concentrations of HCl is shown in Fig. 2. By forming ion pair species [FAsH?Cl-], fatty amides can extract HCl into the organic phase due to the basic nature of nitrogen atoms of the amide group [6, 15]. It was found that the percentage extraction of Cl- was low, indicating that HCl had only a small effect on the Mo(VI) extraction. Contact time effect The proposed extraction mechanism of ion pair formation with the protonated extractant, i.e. extraction of Mo(VI) with fatty amide, takes place fast, with equilibrium being attained within 1–5 min.
123
1318
E. A. J. Al-Mulla et al.
Diluent effect A 7.5 9 10-3 mol L-1 solution of fatty amide in different diluents was used in order to choose the best organic diluent for the extraction of Mo(VI). Xylene, toluene, chloroform, and octanol as organic solvents were studied. It was found that the percentage extraction of Mo(VI) using chloroform and octanol as the diluent was 40 and 16 %, respectively, whereas this percentage was 75 and 96 % using xylene and toluene, respectively. The inductive effect of the hydrogen atom will increase due to the presence of chloroform or octanol with nitrogen atoms of the amide groups. This statement leads to the decrease in the basicity of the amide groups [16]. Therefore, the basicity of the nitrogen atoms in the extraction of Mo(VI) plays a crucial role. Extractant concentration effect Figure 3 shows the extraction of Mo(VI) using various concentrations of fatty amide in the range of (0.9–6.0) 9 10-3 mol L-1 to study the effect of the concentration on the extraction. It was found that the extraction of Mo(VI) increases when the concentration of fatty amide increases. A straight line was observed with a slope of 2.9 at a log–log plot of distribution ratio versus concentrations of fatty amide, indicating the participation of one molecule of Mo(VI) ion and three molecules of fatty amide.
Fig. 3 Effect of FAs concentration on extraction of Mo(VI) Mo(VI), 100 mg L-1 in 0.01 mol L-1 HCl; FAs (0.9–6.0) 9 10-3 mol L-1)
123
Fatty amides synthesized from vegetable oil
1319
Fig. 4 Extraction isotherm for extraction of Mo(VI) (Mo(VI) (0.3–10.0) 9 10-3 mol L-1 in 0.01 mol L-1 HCl; FAs, 7.5 9 10-3 mol L-1 Table 2 Stripping efficiency HCl (Mol L-1)
%EMo (%ENi)
EMo (%ECo)
10-1
94 (0.1)
91 (1)
94 (0.1)
91 (3)
10-2
92 (1)
96 (0.1)
93 (1)
96 (1)
10-3
91 (2)
90 (0.8)
89 (2)
93 (2)
-1
-3
Metal concentrations, 50 mg L ; extractant, 7.5 9 10
%EMo (%EAl)
-1
mol L
%EMo (%EMn)
FAs in toluene
Metal ion concentration effect Figure 4 illustrates the effect of metal ion concentration on the extraction of Mo(VI) in the range of (0.3–10.0) 9 10-3 mol L-1 using 7.5 9 10-3 mol L-1 fatty amide, suggesting that the increase in metal ion concentration does not affect the distribution ratio The results show that a 1:3 was the proposed extraction ratio for metal:extractant stoichiometry at maximum loading. Dual separation of Mo(VI) from Ni(II), Co(II), Al(III) and Mn(II) Table 2 shows the separation of Mo(VI) from dual mixtures including Mn(II), Co(II), Ni(II), or Al(III) in HCl. The method allows the extraction of about 90 % of Mo(VI) in the presence of Mn(II), Co(II), Ni(II), and Al(III), whereas the organic phase contains only 0.1–3 % of the other metals. Stripping reagent effect Table 3 shows the stripping of Mo(VI) from loaded fatty amide organic solutions using different alkaline and acidic solutions. It was found that the more efficient back extraction was observed using alkaline solutions. Table 4 shows the effect of
123
1320
E. A. J. Al-Mulla et al.
Table 3 Effect of alkaline solution concentration on stripping of Mo(VI)
Stripping agent
Extraction conditions: aqueous solution, 10 mL of Mo(VI) (100 mg L-1 in 0.01 mol L-1 HCl); organic phase, 10 mL of FAs (7.5 9 10-3 mol L-1 in toluene). Stripping condition: 10 mL of stripping agent Table 4 Extraction of Mo(VI) with 7.5 9 10-3 mol L-1 FAs in toluene as a function of acid concentration
HCl (2 mol L-1)
23
H2SO4 (2 mol L-1)
14
HNO3 (2 mol L-1)
10
NH4OH (0.01 mol L-1)
72
Na2CO3 (0.01 mol L-1)
42
NaOH (0.01 mol L-1)
59
Alkali
NH4OH
Na2CO3
Extraction conditions: aqueous solution, 10 mL of Mo(VI) (100 mg L-1 in 0.01 mol L-1 HCl); organic phase, 10 mL of FAs (7.5 9 10-3 mol L-1 in toluene). Stripping condition: 10 mL of stripping agent
Mo(VI) stripped (%)
NaOH
Conc. (mol L-1)
Mo(VI) stripped (%)
0.01
75
0.05
91
0.1
95
0.5
98
0.01
39
0.05
51
0.1
60
0.5
73
0.01
63
0.05
67
0.1
77
0.5
100
alkali concentration in the range of 0.01–0.5 mol L-1 on the percentage stripping of Mo(VI). In basic aqueous solution, the Mo(VI) ion exists in the form of MoO42[17, 18]. Thus, the most proposed stripping reaction can be assumed to be as shown in equation 3. ½RCONH2 3 Hþ HMoO 4 ðorgÞ þ 2OHðaqÞ !
3RCONH2ðorgÞ þ MoO2 4 ðaqÞ þ 2H2 O
ð3Þ
According to Equation (3), the high concentration of OH- in the stripping solution will be the facility to break up the complex of the molybdenum–amide, so the chance of the Mo(VI) ions forming complexes with the protonated extractant will decrease. The above results are in agreement with Sharifah et al. [19]
Conclusions Fatty amides (FAs) were successfully utilized as extractant for Mo(VI) ion extraction from acidic media. By the acid concentration, the extraction involves the formation of a 1:3 Mo(VI):FAs complex using toluene as the solvent. The results
123
Fatty amides synthesized from vegetable oil
1321
show that the extractant has a high selectivity of the extractant for Mo(VI) over Ni(II), Co(II), Mn(II), and Al(III). This study allows the drawing of the following conclusions: 1. 2. 3.
The synthesis of extractant is simple, eco-friendly, and economic. The study has involved the development of a method to recover Mo(VI) from acidic media using a mixture of fatty amides. The extraction of Mo(VI) from other metal ions is qualitative owing to the high selectivity with a fast rate of extraction.
Acknowledgments The authors would like to thank Universiti Putra Malaysia (UPM) for supporting this paper. All the technical staffs in the Department of Chemistry, Faculty of Science, University of Putra Malaysia are also acknowledged for their assistance.
References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
A. Saily, U. Khurana, S.K. Yadav, S.N. Tandon, Hydrometallurgy 41, 99 (1995) A.M. Sastre, F.J. Alguacil, Chem. Eng. J. 81, 109 (2001) K. Saberyan, M.M. Ghannadi, P. Ashtari, A.S. Keshavarz, Miner. Eng. 16, 391 (2003) G.N. Iatsenko, Palant, A.A. Dungan, Hydrometallurgy 55, 1 (2000) M. Bag, P. Chattopadhyay, S. Basu, Radioanal. Nucl. Chem. 290, 175 (2011) V.F. Travkin, Y.M. Glubokov, E.V. Mironova, V.V. Yakshin, Russ. J. Appl. Chem. 74, 1664 (2001) Z. Pouramini, A. Moradi, Res. Chem. Intermed. doi:10.1007/s11164-012-0556-3 (2012) (online first article) I. Szczepa˜nska, A. Borowiak-Resterna, M. Wi0 sniewski, Hydrometallurgy 68, 159 (2003) E.A.J. Al-Mulla, W.M.Z. Yunus, N.A. Ibrahim, M.Z. Abdul Rahman, J. Oleo Sci. 59, 59 (2010) E.A.J. Al-Mulla, W.M.Z. Yunus, N.A. Ibrahim, M.Z. Abdul Rahman, J. Oleo Sci. 59, 157 (2010) W.H. Hoidy, M.B. Ahmad, E.A.J. Al-Mulla, W.M.Z. Yunus, N.A. Ibrahim, J. Oleo Sci. 59, 229 (2010) W.H. Hoidy, M.B. Ahmad, E.A.J. Al-Mulla, W.M.Z. Yunus, N.A. Ibrahim, Oriental J. Chem. 26, 369 (2010) J. Marchese, F. Valenzuela, C. Basualto, A. Acosta, Hydrometallurgy 72, 309 (2004) C. Basualto, J. Marchese, F. Valenzuela, A. Acosta, Talanta 59, 999 (2003) R.K. Jha, K.K. Gupta, P.G. Kulkarni, P.B. Gurba, P. Janardan, R.D. Changarani, P.K. Dey, P.N. Pathak, V.K. Manchanda, Desalination 232, 225 (2008) M. Witt, H.-F. Gru¨tzmacher, Int. Mass Spectrom. 164, 93 (1997) F.R. Valenzuela, J.P. Andrade, J. Sapag, C. Tapia, C. Basualto, Miner. Eng. 8, 893 (1995) Y. Sato, F. Valenzuela, T. Tsuneyuki, K. Kondo, F. Nakashio, J. Chem. Eng. Jpn. 20, 317 (1987) M. Sharifah, W.M.Z. Yunus, M.J. Haron, M.Z.A. Rahman, J. Chem. Technol. Biotechnol. 83, 1565 (2008)
123