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Solvent extraction of Fe(III) from the chloride leach liquor of low grade iron ore tailings using Aliquat 336
Hydrometallurgy 108 (2011) 93–99
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Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
Solvent extraction of Fe(III) from the chloride leach liquor of low grade iron ore tailings using Aliquat 336 R.K. Mishra, P.C. Rout, K. Sarangi ⁎, K.C. Nathsarma Institute of Minerals and Materials Technology (CSIR), Bhubaneswar-751 013, India
a r t i c l e
i n f o
Article history: Received 7 January 2011 Received in revised form 1 March 2011 Accepted 5 March 2011 Available online 17 March 2011 Keywords: Iron Aliquat 336 Solvent extraction Stripping
a b s t r a c t Solvent extraction of iron (III) from the HCl leach liquor of low grade iron ore tailings was studied with Aliquat 336, a quaternary amine in kerosene. p-Nonyl phenol was used as the third phase modifier. The effect of different parameters such as equilibration time, HCl concentration, H+ concentration, Cl− concentration and extractant concentration on extraction of iron was studied. The effect of different diluents such as xylene, benzene, toluene, diphenyl ether, diethyl ether, cyclohexane, hexanol, cyclohexanol and butanol on extraction of iron was investigated. The effect of various salts such as NaCl, NaNO3, Na2SO4, NaOOCCH3, and Na3C6H5O7·2H2O in the feed solution within the concentrations of 0.5 to 2.5 M on extraction of iron was studied. It was observed that extraction of iron increased from 51.82 to 97.52% and from 5.81 to 97.19% with increase in HCl and extractant concentrations from 1.67 to 9.7 M and from 0.025 to 0.4 M, respectively. From the slope analysis study, the number of moles of H+, Cl− and Aliquat 336 associated with the extracted species was determined and the extracted species was found to be R3NCH3·FeCl4. The McCabe–Thiele plot for extraction of iron with 0.2 M Aliquat 336 illustrated 2-stages at 1:1 phase ratio and the loaded organic contained 0.338 M (18.8496 kg/m3) iron indicating 98.57% extraction. The stripping of iron from the loaded organic carried out with distilled water showed quantitative stripping in 3-stages at O:A ratio of 2:1. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Usually iron is economically recovered from high grade ores through the conventional flotation and pyrometallurgical routes, but it is not easy to recover iron from low grade iron ores or low grade iron ore tailings by the conventional method. Again, the presence of iron in acidic leach liquor is a common problem in most of the hydrometallurgical processing. Removal of iron from the acidic leach liquors is usually carried out via precipitation and solvent extraction techniques. The present paper deals with the solvent extraction of iron from the hydrochloric acid leach liquors of low grade iron ore tailings with Aliquat 336 in kerosene. Literature on solvent extraction of Fe(III) with Aliquat 336 is scanty; however, a variety of other extractants such as D2EHPA, PC88A, Cyanex 272, Cyanex 301, Cyanex 302, Cyanex 923, TBP, TOPO, TOA, Alamine 336, LIX 860 and LIX 984 have been used for the purpose. In extraction of iron(III) from an acidic sulphate solution by didecylamine sulphate in benzene at 25 °C (Baes, 1955), the effect of the concentrations of acid, Fe(III), extractant and sodium sulphate was studied to show the extraction of monomeric and dimeric forms of the hydrolyzed complex, FeOHSO4. The simultaneous extraction of micro and macro amounts of In, Fe, Ga, Cd, Co and Zn from HCl medium
⁎ Corresponding author. Tel.: + 91 6742581635; fax: + 91 6742581637. E-mail address: [email protected] (K. Sarangi). 0304-386X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2011.03.003
using Tri-n-octylamine (TOA) and Aliquat 336 in benzene (Bargeev et al., 1978) showed a decrease in extraction of microelements in presence of the extractable of macroelements. All other conditions being equal, the suppression of extraction was greater for metals whose extracted haloacid complexes were dissociated more in the organic phase. The suppression of extraction was more for unicharged anionic complexes than the doubly charged anions. With TOA the extracted complexes were TOAHMCl4 for Fe and Ga, TOAH(TOAHCl) InCl4 for In, and (TOAH)2MCl4 for Zn, Cd and Co; with Aliquat 336 the extracted complexes were R4NMCl4 for Fe, Ga and In, and (R4N)2MCl4 for Zn, Cd and Co, where ‘M’ is the metal ion. In extraction of Fe(III) from HCl medium with Tri-n-octylamine in benzene, xylene, toluene, chloroform, carbon tetrachloride and cyclohexane (Miroslav et al., 1978), the study of chemical analysis, viscosity and IR measurements of the organic phase concluded the formation of cyclic polymer complexes of structures having the ratio of TOA:HCl:FeCl3 as 2:2:1 in extractions carried out at low acid concentrations which changed to 1:1:1 for extractions carried out at higher acid concentrations. Extraction of iron(III) from a HCl solution was carried out with D2EHPA, PC 88A and Cyanex 272 and their mixtures in kerosene (Sandhibigraha et al., 1996) in which extraction of the metal ion increased with increasing concentrations of HCl and for extraction of a mole of metal ion 3 moles each of HCl and extractant were required. The decrease and increase in extraction of iron in presence of Na2SO4, NaNO3, NaCl and NaSCN was due to the salting-in and salting-out effects, respectively. In the study of synergism, Cyanex 272 was the
R.K. Mishra et al. / Hydrometallurgy 108 (2011) 93–99
best but D2EHPA was the least synergist. Solvent extraction of iron(III) from 1 M FeCl3 solution using TBP, MIBK and their mixtures in kerosene (Reddy and Sarma, 1996) increased with the concentrations of HCl and extractants, and the extracted species was HFeCl4.3Solvent. Synergism was observed in the mixture of extractants. Iron was extracted with the mixture of 70% TBP and 30% MIBK in 3-stages at O:A ratio of 3:2 and the loaded organic was stripped with distilled water in 2-stages at O:A ratio of 4:5. A rapid method for separation of Fe(III) and Al(III) from a sulphate solution was developed using Cyanex 302 in chloroform (Ajgaonkar and Dhadke, 1997) in which iron was extracted with 0.005 M extractant at pH 2.0–2.5 followed by extraction of Al with 0.01 M extractant at pH 3.0–4.0. Both loaded organic phases were stripped with 1.0 and 2.0 M HCl. The extraction of iron(III) from the HCl leach liquor of ilmenite bearing Fe(III), Ti(IV), Cr(VI) and V(V) was investigated with Cyanex 923 in xylene (Saji et al., 1998). The extraction of metal ions increased with increasing concentrations of HCl and the extractant. The extracted species was HFeCl4.2Cyanex 923. Stripping of the Fe–LO decreased with increasing HCl concentrations but was finally carried out with 0.4 M HCl in 2-stages at O:A ratio of 1:3. The extraction of iron(III) from a chloride solution bearing 1 M iron(III) and 2 M HCl was carried out with a mixture of 70% TBP and 30% MIBK in kerosene (Saji and Reddy, 2001). The extracted species was HFeCl4.2Solvent. Iron from the feed was extracted in 2-stages at O:A ratio of 2:1 and the loaded organic was stripped with distilled water in 3-stages at O:A ratio of 2:3. The extraction of iron(III) from a concentrated acid chloride solution was carried out with MIBK, TBP, D2EHPA and their mixtures in benzene (Sahu and Das, 2000) in which the mixture D2EHPA-TBP showed better synergism than D2EHPAMIBK. The stripping of Fe from the loaded organic increased with HCl up to 120 g/L after which it decreased with further increase in HCl due to back-extraction of the chloro-complex(es) formed in the strip solution. The order of stripping of the extracted complex was: D2EHPA N D2EHPA-MIBK N D2EHPA-TBP. Liquid–liquid extraction of iron and titanium from the ilmenite sulphate leach liquor was carried out with D2EHPA in dodecane (Silva et al., 2008) followed by selective stripping of iron from the organic phase with 4.5 pH H2SO4 and stripping of Ti from the Fe-free organic with an aqueous fluoride solution at pH 4.5. Solvent extraction of iron(III) from the spent FeCl3 etching solution bearing 114.8 Fe(III), 29.2 Fe(II), 312.3 total chloride and 4.8 Ni in g/L (Lee and Lee, 2005) was carried out with 1.0 M Alamine 336 in toluene in 2-stages at O/A ratio of 7 leading to 99% extraction and stripping of iron from the organic phase using 0.1 N HCl at O/A ratio of 10 was 94%. Stripping of iron from the organic phase increased with temperature (25–60 °C) and was endothermic. The extraction of Fe(III) was carried out with TBP in kerosene and the generated data were used for the extraction of iron from the simulated waste chloride titania liquor (Thomas et al., 2004) bearing Mg(II), Al(III), Ti(IV), V(V), Cr(III) and Mn(II) including the effect of HCl and TBP on extraction of iron. The extraction and stripping isotherms were constructed and analysed. The Fe(III) loaded TBP thus underwent precipitation stripping with NaOH to obtain plate like hematite powder. 2. Experimental 2.1. Chemicals and reagents Aliquat 336 (a mixture of tri-octyl/decyl ammonium chloride of average molecular weight 442 g/mol) was supplied by Cognis Inc., USA and was used as such without any purification. Distilled kerosene (b.p 180–240 °C) was used as the diluent and 30% v/v p-nonyl phenol was used as the phase modifier. All other chemicals used were of analytical reagent grade supplied by BDH/Merck, India. The low grade iron ore collected from Minerals Matrics Limited (MML), India was beneficiated at Institute of Minerals and Materials
Technology (CSIR), Bhubaneswar. After beneficiation, the tailings contained 13.375% Fe, 0.8% Al2O3 and 76.8% SiO2. Other metals such as Cu, Ni, Co, Mg, Mn and Pb present were in traces. After leaching of the iron ore tailings with 10.962 N HCl for 6 h, the leach liquor contained 0.685 M (38.2475 kg/m3) Fe and 6.356 M free HCl along with 0.657 kg/m3 Al and 0.0189 kg/m3 Si. Other metals present in leach liquor were 1.35 g/m3 Cu, 1.78 g/m3 Ni, 1.63 g/m3 Co, 173.12 g/m3 Mg, 14.28 g/m3 Mn and zero Pb. This leach liquor was used to recover the iron values using the solvent extraction technique. 2.2. Methods All the experiments were carried out at room temperature (30 ± 1 °C). Equal volumes (10 cm3) of the aqueous phase bearing iron and free HCl and the organic phase containing the extractant, diluent and modifier were taken in a separatory funnel and equilibrated manually for 5 min. After phase disengagement, the raffinate was separated and analysed to record the equilibrium concentrations of iron and free acid. For construction of McCabe–Thiele plots for extraction and stripping, the O:A ratio of phases was varied within 1:5 to 5:1, while keeping the total volume phases constant. The analysis of iron was carried out volumetrically by the standard SnCl2 reduction–K2Cr2O7 titration method and the solutions bearing very low concentrations of Fe(III) was analysed by the Perkin Elmer Model AA 200 Atomic Absorption Spectrophotometer (AAS) after suitable dilutions with 1 M HCl. The concentration of iron in the organic phase was calculated from the difference of concentrations between the aqueous phase before and after extraction. The organic phase was filtered through the 1PS phase separating paper and a suitable aliquot of it was stripped and analysed. 3. Results and discussions 3.1. Effect of HCl concentration The effect of HCl concentration within the range of 1.67 to 9.77 M with a constant iron concentration of 0.342 M (19.124 kg/m3) in the feed solution on extraction of Fe(III) was studied. The extractions were carried out with 0.2 M Aliquat 336 and 15% p-nonyl phenol in kerosene at 1:1 phase ratio, in which the extraction of iron increased from 51.82 to 97.52% (Fig. 1). In another set of experiment, the effect of H+ ion concentration within a small range of 3.178 to 4.178 M in the solution, in presence of a constant Cl− concentration of 4.178 M achieved by the addition of NaCl, on extraction of Fe(III) was studied with 0.2 M Aliquat 336 at 1:1 phase ratio. The experimental data plotted in Fig. 2 illustrated an increase in iron extraction from 65.37 to
100
%Fe extraction
94
80
60
40
0
2
4
6
8
10
[HCl], M Fig. 1. Effect of [HCl] on extraction of Fe(III).
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67.5
82 80
% Fe extraction
%Fe extraction
67.0
66.5
66.0
65.5
65.0
95
78
y = 8.9333x + 30.003 2
R = 0.9864
76 74 72
3
3.5
4
70 4.6
4.5
4.8
5
5.2
5.4
5.6
5.8
[Cl-], M
+
[H ], M
Fig. 4. Effect of [Cl−] on extraction of Fe(III).
Fig. 2. Effect of [H+] on extraction of Fe(III).
67.29% with increase in H+ concentration from 3.178 to 3.778 M, but with further increase in H+ concentration, the extraction decreased to 66.01%. The plot of log D vs. log [H+] in Fig. 3 is a straight line with a slope of 0.48 indicating zero association of HCl with the extracted species.
3.4. Mechanism for extraction of iron with Aliquat 336 Extraction of iron from the HCl medium with the quaternary amine (Aliquat 336) can be expressed as follows: FeAq + 4ClAq + R3 NCH3 ClOrg ⇔R3 NCH3 : FeCl4Org + Cl
3þ
3.2. Effect of Cl− concentration The effect of chloride ion concentration within 4.696 to 5.596 M in the solution in presence of a constant H+ ion concentration of 5.596 M on extraction of Fe(III) was studied with 0.2 M Aliquat 336 in kerosene and the experimental data as plotted in Fig. 4 illustrate an increase in iron extraction from 72.26 to 80.44% with increase in chloride concentration. The plot of log D vs. log [Cl−] in Fig. 5 is a straight line with slope value of 3.02. This indicates the association of 3 mol of Cl− ion with the extraction of a mole of metal ion into the organic phase. 3.3. Effect of extractant concentration on Fe(III) extraction
ð1Þ
The equilibrium constant, Kext can be given as: Kext = ¼
½R3 NCH3 : FeCl4 Org ½Cl ½Fe3þ Aq ½Cl 4Aq ½R3 NCH3 ClOrg
ð2Þ
½R3 NCH3 : FeCl4 Org ½Fe3þ Aq ½Cl 3Aq ½R3 NCH3 ClOrg
or Kext =
The effect of Aliquat 336 concentration within 0.025–0.4 M on the extraction of iron from the aqueous solution bearing 0.342 M (19.124 kg/m3) Fe and 9.269 M HCl was studied. The experimental data plotted in Fig. 6 illustrate a linear increase in extraction of iron from 8.94 to 97.19% with increase in extractant concentration. The plot of log D vs log [extractant] for extraction of iron as shown in Fig. 7 illustrates the slope of 1.09 which indicates the association of a mole of the extractant for extraction of a mole of metal ion with the extracted complex.
D ½Cl 3Aq ½R3 NCH3 ClOrg
where D =
ð3Þ
½R3 NCH3 : FeCl4 Org ½Fe3 + Aq
Taking logarithm for the Eq. 3 and rearranging
log D = log Kext + 3log½Cl Aq + log½R3 NCH3 ClOrg
ð4Þ
From the slope analysis study obtained above, the above extraction mechanism is confirmed.
0.32 0.65 0.31
y = 0.4887x + 0.0314 R2 = 0.9975
0.55
y = 3.0159x - 1.65 R2 = 0.9849
log D
log D
0.3
0.29
0.45 0.28
0.27 0.48
0.5
0.52
0.54
0.56
+
log [H ], M Fig. 3. Plot of log D vs. log [H+].
0.58
0.6
0.35 0.675
0.7
0.725
log[Cl-], M
Fig. 5. Plot of log D vs. log [Cl−].
0.75
R.K. Mishra et al. / Hydrometallurgy 108 (2011) 93–99
100
100
80
80
% Iron Extraction
% Fe(III) extraction
96
60
40
20
Cyclohexane Xylene Benzene Toluene Diphenyl ether Diethyl ether Hexanol Butanol Cyclohexanol Kerosene
60
40
20 0
2
4
6
8
10
[HCl], M 0
0
0.1
0.2
0.3
0.4
Fig. 8. Effect of diluents on extraction of Fe(III) at various [HCl].
0.5
[Aliquat 336], M diluents. As expected from the dielectric constant value of kerosene (2.0), extraction with this kerosene would have been the least. Since kerosene contains both aromatics and aliphatics, extraction with kerosene has come in between.
Fig. 6. Effect of [Aliquat 336] on extraction of Fe(III).
3.5. Effect of diluents The effect of different aromatic and aliphatic diluents such as benzene, toluene, xylene, diphenylether, butanol, hexanol, diethyllether, cyclohexane and cyclohexanol on extraction of Fe(III) was studied at different HCl concentrations within 1.667 to 9.768 M using 0.15 M Aliquat 336. The experimental data for extraction of iron with different diluents is shown in Fig. 8. It was observed that the percentage extraction of iron with the aliphatic diluents except cyclohexane was higher than the aromatic diluents. The percentage extraction of iron from 1.667 to 9.768 M HCl varied from 79 to 79.92% and from 99.1 to 99.42% in aromatic and aliphatic diluents, respectively. At the same acid concentration, the percentage extraction of iron was 97.52% in kerosene. The extraction efficiency of Aliquat 336 in presence of different diluents is in the order: cyclohexane b xylene b benzene b toluene b diphenyl ether b diethyl ether b hexanol b butanol b cyclohexanol. The dielectric constants of the diluents are given in Table 1. It was observed that the percentage extraction of iron increased with increasing dielectric constant of the diluents but it would have been the reverse (Thomas et al., 2004). This reverse behaviour during extraction may be due to the high polar HCl medium and extraction of the anionic species FeCl− 4 by Aliquat 336. As has been observed, the extraction efficiency in presence of kerosene is higher than the aromatic diluents but lower than the aliphatic 0.2
log D
-0.2
3.6. Effect of salts To study the effect of various salts such as NaCl, Na2SO4, NaNO3, CH3COONa and Na3C6H5O7.2H2O (Trisodium citrate dihydrate) on the extraction of Fe(III) from the chloride solution, extractions were carried out with 0.1 M Aliquat 336 in kerosene at equal phase ratio. The concentrations of all the salts in the solution were varied within the range 0.5 to 2.5 M other than the trisodium citrate dehydrate whose concentration was varied within 0.5 to 2.0 M. The percentage Fe(III) extraction increased with increasing concentrations of NaCl, Na2SO4, NaNO3 and Na3C6H5O7.2H2O (Fig. 9) other than CH3COONa where quantum of extraction remained nearly constant. The percentage extraction of iron in presence of the salts was in the order: NaCl N Na2SO4 N NaNO3 N Na3C6H5O7·2H2O. 3.7. Extraction isotherm for iron To recover iron from the solution containing 0.342 M (19.124 kg/m3) Fe, the solution was equilibrated with 0.2 M Aliquat 336 in kerosene at O: A ratios within 1:5 to 5:1 while keeping the total volume of phases constant. After phase disengagement, the aqueous and organic phases were analysed for metal concentrations. The McCabe–Thiele plot in Fig. 10 illustrated 2-stages of extraction at an equal phase ratio for quantitative recovery of iron. To confirm this, a 2-stage counter-current simulation study with 0.2 M Aliquat 336 at 1:1 phase ratio was carried out in which the raffinates and the loaded organic were analysed for iron concentrations. The loaded organic contained 0.338 M (18.8496 kg/m3) iron resulting in 98.57% extraction. The second stage raffinate contained
Table 1 Dielectric constant of diluents.
-0.6 y = 1.0859x + 0.6991 R 2 = 0.9869
-1
-1.4 -2
-1.6
-1.2
-0.8
-0.4
log[Aliquat 336], M Fig. 7. Plot of log D vs. log [Aliquat 336].
0
Sl. no.
Diluents
Dielectric constant
1 2 3 4 5 6 7 8 9 10
Kerosene Cyclohexane, 25 °C Xylene, 20 °C Benzene, 25 °C Toluene, 25 °C Diphenyl ether, 20 °C Di-ethyl ether, 20 °C Hexanol, 25 °C Cyclohexanol, 25 °C 1-Butanol, 25 °C
2.0 2.015 2.27 2.274 2.379 3.726 4.2666 13.3 15 17.8
% Fe(III) extraction
R.K. Mishra et al. / Hydrometallurgy 108 (2011) 93–99
85
50
80
40
30
Na2SO4 NaCl NaNO3 CH3COONa.3H2O Na3C6H5O7.2H2O
75
97
20
70 O:A ratio 2:1, 3-stages
10 65
0
0.5
1
1.5
2
2.5
3
[Salt], M
0
0
5
10
15
20
[Fe]Org, kg/m3
Fig. 9. Effect of [salt] on extraction of Fe(III) with Aliquat 336.
0.273 mg/m3 Fe along with 0.657 kg/m3 Al, 0.0189 kg/m3 Si, 1.35 g/m3 Cu, 1.78 g/m3 Ni, 1.63 g/m3 Co, 173.12 g/m3 Mg, 14.28 g/m3 Mn indicating zero co-extraction of Al, Si, Cu, Ni, Co, Mg and Mn. 3.8. Stripping isotherm of iron loaded Aliquat 336 The loaded organic phase containing 0.338 M (18.8496 kg/m3) iron was stripped with distilled water. To find out the required number of stages and the O:A ratio for stripping, the stripping studies were carried out at O:A ratios within 1:5 to 5:1, while keeping the total volume of phases constant. The McCabe–Thiele plot in Fig. 11 predicted 3-stages of stripping at O:A ratio of 2:1. To confirm the prediction, a 3-stage counter-current stripping study was carried out using the iron loaded organic and distilled water. The third stage spent organic and the strip solution contained 4.48 mg/m3 and 0.651 M (36.3728 kg/m3) iron indicating 99.98% stripping.
Fig. 11. Stripping of Fe loaded Aliquat 336 with distilled water.
The ln kext values for Fe extraction with Aliquat 336 were calculated using Eq. 4 and were plotted against 1/T in Fig. 13. The plot is a straight line with slope and intercept values of − 2.344 and 12.209, respectively. Assuming that H is constant over the temperature range investigated, the enthalpy changes ΔH and the entropy changes ΔS were calculated from the slope and the intercept values of Fig. 13 and were found to be 19.489 kJ/mol and 101.511 J∙mol–1∙K–1, respectively. The free energy change (ΔG) was calculated from the relationship as given in Eq. 6: ΔG = −RT ln kext :
ð6Þ
The values of ΔH, ΔG and ΔS obtained for Fe extraction are given in Table 2. The enthalpy change (ΔH) value is positive for this iron extraction study indicating the extraction process is endothermic.
3.9. Effect of temperature 3.10. IR spectra of Aliquat 336 and Fe-loaded Aliquat 336 The effect of temperature on extraction of iron was studied in the range of 283 to 323 K. The concentration of extractant and A:O ratio was kept constant at 0.2 M and 1:1, respectively. The percentage extraction of iron increased from 39.57 to 64.12 with an increase of temperature from 283 to 323 K and the distribution coefficient (D) values increased from 0.655 to 1.787 (Fig. 12). The Gibbs–Helmholtz equation for enthalpy and entropy change can be written as: ln k = −
ΔH ΔS + RT R
ð5Þ
The FTIR absorption spectra of Aliquat 336, metal loaded Aliquat 336 and of Aliquat 336 after stripping were recorded to know the interaction between the extractant and the metal ion. The spectra of extractants and their complexes with iron are shown in Fig. 14 and the peaks obtained in different spectra are given in Table 3. The ―C―H symmetric and asymmetric deformation vibrations and stretching vibrations for pure and Fe-bonded Aliquat 336 as shown in the Table 3 are identical. The wide absorption band at 3413.4 and 3205.1 for Fe–Aliquat 336 and Aliquat 336, respectively are may be due to the stretching vibration of ―OH of soluble water in Aliquat 2
70 25
60
15
10 O:A ratio 1:1, 2-stages
1.5
D
% Extraction
20
50 % Extn D
1
40
5
0
0
5
10
15
20
25
[Fe]Aq, kg/m3 Fig.10. Extraction isotherm for extraction of Fe(III) using Aliquat 336 in kerosene.
30 280
290
300
310
320
0.5 330
Temperature, K Fig. 12. Effect of temperature on % extraction of iron.
98
R.K. Mishra et al. / Hydrometallurgy 108 (2011) 93–99
5.5
Table 3 Characteristic IR spectral bond positions for Aliquat 336 and Fe–Aliquat 336 Fe in cm− 1. Corresponding bond
Fe–Aliquat 336
Aliquat 336
―C―N sv ―C―N sv ―C―H sdv ―N―CH3 adv ―C―H sv ―C―H sv ―C―H sv ―O―H sv
829.3 1180.2 1259.3 1376.9 1461.8 2858.0 2925.5 2956.3 3413.4
831.1 – 1267.02 1373.8 1461.8 2858.0 2925.5 2958.3 3205.1
ln Kext.
5.0
4.5
4.0
3.5 3.0
y = -2.3441x + 12.209 R 2 = 0.9985
sdv: symmetric deformation vibration; adv: asymmetric deformation vibration; sv: stretching vibration.
3.2
3.4
3.6
1000/T, K
336 (Nayl, 2010). The peak at 1461.8 cm− 1 which is the characteristic peak for quaternary amine due to (CH3)N+ is also observed in both spectra. But the peak at 1267.02 cm− 1 due to ―C―N stretching vibration for Aliquat 336 is shifted to 1259.3 cm− 1 for Fe loaded Aliquat 336 indicating the possibility of bonding between Fe and Aliquat 336. The spectrum of spent Aliquat 336 after stripping (Fig. 14) is identical to that of pure Aliquat 336 which confirmed the complete stripping of iron from the loaded Aliquat 336.
following conclusions were drawn from the study. The extraction of iron increased from 51.82 to 97.52% and from 8.94 to 97.19% with an increase in HCl and extractant concentrations from 1.67 to 9.7 M and 0.025 to 0.4 M, respectively. There was no extraction of other metal ions into the organic phase other than Fe(III). The plots of log D vs. log [H+], log D vs. log Cl− and log D vs. [Aliquat 336] were straight lines with slope values of 0.48, 3.02 and 1.09 indicating the association of zero mol of HCl, three mol of chloride and one mole of extractant with the extracted complex for which the extracted species is determined to be R3NCH3·FeCl4. The percentage extraction of iron with Aliquat 336 in different diluents increased in the order: cyclohexane b xylene b benzene b toluene b diphenyl ether b diethyl ether b hexanol b butanol b cyclohexanol. The percentage extraction of iron in presence of different salts was in the order: NaCl N Na2SO4 NaNO3 N Na3C6H5O7·2H2O. The presence of CH3COONa in the solution within the range of concentrations had no effect on the extraction of iron. Quantitative extraction of iron was obtained in 2-counter-current stages at equal phase ratio and the loaded organic contained 0.338 M (18.8496 kg/m3) iron indicating 98.57% extraction. The stripping isotherm for the loaded organic with distilled water showed quantitative stripping in 3-stages at O:A ratio of 2:1. The third stage spent organic and the strip solution contained 4.48 mg/m3 and 0.651 M (36.3728 kg/m3) iron. The stripping of the Fe loaded Aliquat 336 was quantitative. The enthalpy and entropy change (ΔH and ΔS) values for Fe extraction were found to be 19.489 kJ/mol and 101.511 J∙mol− 1∙K− 1, respectively.
4. Conclusion
Acknowledgements
The extraction of iron from the HCl leach liquor of the low grade iron ore tailings was carried out with Aliquat 336 in kerosene and the
The authors are thankful to Dr. T. Subbaiah, HOD, Hydro & Electrometallurgy Department for encouragement and Prof. B.K. Mishra, Director, IMMT, Bhubaneswar for kind permission to publish this paper. The authors are also thankful to the Council of Scientific & Industrial Research, New Delhi, India for the financial support.
Fig. 13. Effect of temperature on Kext.
Table 2 Thermodynamic parameters for extraction of iron with Aliquat 336. Temperature, K
ΔG, kJ/mol
ΔH, kJ/mol
ΔS, J∙mol∙K
283 288 293 298 303 308 313 318 323
− 9.279 − 9.705 − 10.210 − 10.760 − 11.327 − 11.781 − 12.294 − 12.782 − 13.287
19.489
101.511
References
Fig. 14. IR Spectra for Aliquat 336 and Fe loaded Aliquat 336.
Ajgaonkar, H.S., Dhadke, P.M., 1997. Solvent extraction separation of iron(III) and aluminium(III) from other elements with Cyanex 302. Talanta 44, 563–570. Baes Jr., C.F., 1955. The extraction of iron(III) from acidic sulphate solution by didecylamine sulphate in benzene. U.S. Atomic Energy Commission. ORNL-1930. Bargeev, V.V., Fischer, C., Yudushkina, L.M., Zolotov, Yu.A., 1978. Mutual influence of metals in the extraction of their chloride complexes with Tri-n-octylamine and Aliquat 336 in benzene. Journal of Inorganic and Nuclear Chemistry 40, 553–557. Lee, M.S., Lee, K.J., 2005. Separation of iron and nickel from a spent FeCl3 etching solution by solvent extraction. Hydrometallurgy 80, 163–169. Miroslav, M., Jana, S., Miroslav, C., Jiri, C., 1978. Effect of the solvent on the extraction of iron(III)chloride by tri-n-octylamine. Chemicky Prumysl 28 (1), 16–23. Nayl, A.A., 2010. Extraction and separation of Co(II) and Ni(II) from acidic sulfate solutions using Aliquat 336. Journal of Hazardous Materials 173, 23–230. Reddy, B.R., Sarma, P.V.R.B., 1996. Extraction of iron(III) at macro-level concentrations using TBP, MIBK and their mixtures. Hydrometallurgy 43, 299–306. Sahu, K.K., Das, R.P., 2000. Mixed solvent systems for the extraction and stripping of iron(III) from concentrated acid chloride solutions. Metallurgical and Materials Transactions B 31B, 1169–1174.
R.K. Mishra et al. / Hydrometallurgy 108 (2011) 93–99 Saji, J., Prasada Rao, T., Iyer, C.S.P., Reddy, M.L.P., 1998. Extraction of iron(III) from acidic chloride solutions by Cyanex 923. Hydrometallurgy 49, 289–296. Saji, J., Reddy, M.L.P., 2001. Liquid–liquid extraction and separation of iron(III) from titania wastes using TBP-MIBK mixed solvent system. Hydrometallurgy 61, 81–87. Sandhibigraha, A., Sarma, P.V.R.B., Chakravortty, V., 1996. Solvent extraction of iron (III) from aqueous hydrochloric acid solutions using D2EHPA, PC 88A and Cyanex 272 and their mixtures. Scandinavian Journal of Metallurgy 25, 135–140.
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Silva, Glauco Correa da, Silva, Jose Waldemar, Cunha, Dias da, Dweck, Jo, Afonso, Julio Carlos, 2008. Liquid–liquid extraction (LLE) of iron and titanium by bis-(2-ethylhexyl) phosphoric acid (D2EHPA). Minerals Engineering 21, 416–419. Thomas, Jesty, Surender, G.D., Reddy, M.L.P., 2004. Preparation of hematite powders with plate-like morphology from titania wastes by solvent extraction followed by precipitation stripping and hydrothermal synthesis. Separation Science and Technology 39, 1695–1715.
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Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
Solvent extraction of Fe(III) from the chloride leach liquor of low grade iron ore tailings using Aliquat 336 R.K. Mishra, P.C. Rout, K. Sarangi ⁎, K.C. Nathsarma Institute of Minerals and Materials Technology (CSIR), Bhubaneswar-751 013, India
a r t i c l e
i n f o
Article history: Received 7 January 2011 Received in revised form 1 March 2011 Accepted 5 March 2011 Available online 17 March 2011 Keywords: Iron Aliquat 336 Solvent extraction Stripping
a b s t r a c t Solvent extraction of iron (III) from the HCl leach liquor of low grade iron ore tailings was studied with Aliquat 336, a quaternary amine in kerosene. p-Nonyl phenol was used as the third phase modifier. The effect of different parameters such as equilibration time, HCl concentration, H+ concentration, Cl− concentration and extractant concentration on extraction of iron was studied. The effect of different diluents such as xylene, benzene, toluene, diphenyl ether, diethyl ether, cyclohexane, hexanol, cyclohexanol and butanol on extraction of iron was investigated. The effect of various salts such as NaCl, NaNO3, Na2SO4, NaOOCCH3, and Na3C6H5O7·2H2O in the feed solution within the concentrations of 0.5 to 2.5 M on extraction of iron was studied. It was observed that extraction of iron increased from 51.82 to 97.52% and from 5.81 to 97.19% with increase in HCl and extractant concentrations from 1.67 to 9.7 M and from 0.025 to 0.4 M, respectively. From the slope analysis study, the number of moles of H+, Cl− and Aliquat 336 associated with the extracted species was determined and the extracted species was found to be R3NCH3·FeCl4. The McCabe–Thiele plot for extraction of iron with 0.2 M Aliquat 336 illustrated 2-stages at 1:1 phase ratio and the loaded organic contained 0.338 M (18.8496 kg/m3) iron indicating 98.57% extraction. The stripping of iron from the loaded organic carried out with distilled water showed quantitative stripping in 3-stages at O:A ratio of 2:1. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Usually iron is economically recovered from high grade ores through the conventional flotation and pyrometallurgical routes, but it is not easy to recover iron from low grade iron ores or low grade iron ore tailings by the conventional method. Again, the presence of iron in acidic leach liquor is a common problem in most of the hydrometallurgical processing. Removal of iron from the acidic leach liquors is usually carried out via precipitation and solvent extraction techniques. The present paper deals with the solvent extraction of iron from the hydrochloric acid leach liquors of low grade iron ore tailings with Aliquat 336 in kerosene. Literature on solvent extraction of Fe(III) with Aliquat 336 is scanty; however, a variety of other extractants such as D2EHPA, PC88A, Cyanex 272, Cyanex 301, Cyanex 302, Cyanex 923, TBP, TOPO, TOA, Alamine 336, LIX 860 and LIX 984 have been used for the purpose. In extraction of iron(III) from an acidic sulphate solution by didecylamine sulphate in benzene at 25 °C (Baes, 1955), the effect of the concentrations of acid, Fe(III), extractant and sodium sulphate was studied to show the extraction of monomeric and dimeric forms of the hydrolyzed complex, FeOHSO4. The simultaneous extraction of micro and macro amounts of In, Fe, Ga, Cd, Co and Zn from HCl medium
⁎ Corresponding author. Tel.: + 91 6742581635; fax: + 91 6742581637. E-mail address: [email protected] (K. Sarangi). 0304-386X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2011.03.003
using Tri-n-octylamine (TOA) and Aliquat 336 in benzene (Bargeev et al., 1978) showed a decrease in extraction of microelements in presence of the extractable of macroelements. All other conditions being equal, the suppression of extraction was greater for metals whose extracted haloacid complexes were dissociated more in the organic phase. The suppression of extraction was more for unicharged anionic complexes than the doubly charged anions. With TOA the extracted complexes were TOAHMCl4 for Fe and Ga, TOAH(TOAHCl) InCl4 for In, and (TOAH)2MCl4 for Zn, Cd and Co; with Aliquat 336 the extracted complexes were R4NMCl4 for Fe, Ga and In, and (R4N)2MCl4 for Zn, Cd and Co, where ‘M’ is the metal ion. In extraction of Fe(III) from HCl medium with Tri-n-octylamine in benzene, xylene, toluene, chloroform, carbon tetrachloride and cyclohexane (Miroslav et al., 1978), the study of chemical analysis, viscosity and IR measurements of the organic phase concluded the formation of cyclic polymer complexes of structures having the ratio of TOA:HCl:FeCl3 as 2:2:1 in extractions carried out at low acid concentrations which changed to 1:1:1 for extractions carried out at higher acid concentrations. Extraction of iron(III) from a HCl solution was carried out with D2EHPA, PC 88A and Cyanex 272 and their mixtures in kerosene (Sandhibigraha et al., 1996) in which extraction of the metal ion increased with increasing concentrations of HCl and for extraction of a mole of metal ion 3 moles each of HCl and extractant were required. The decrease and increase in extraction of iron in presence of Na2SO4, NaNO3, NaCl and NaSCN was due to the salting-in and salting-out effects, respectively. In the study of synergism, Cyanex 272 was the
R.K. Mishra et al. / Hydrometallurgy 108 (2011) 93–99
best but D2EHPA was the least synergist. Solvent extraction of iron(III) from 1 M FeCl3 solution using TBP, MIBK and their mixtures in kerosene (Reddy and Sarma, 1996) increased with the concentrations of HCl and extractants, and the extracted species was HFeCl4.3Solvent. Synergism was observed in the mixture of extractants. Iron was extracted with the mixture of 70% TBP and 30% MIBK in 3-stages at O:A ratio of 3:2 and the loaded organic was stripped with distilled water in 2-stages at O:A ratio of 4:5. A rapid method for separation of Fe(III) and Al(III) from a sulphate solution was developed using Cyanex 302 in chloroform (Ajgaonkar and Dhadke, 1997) in which iron was extracted with 0.005 M extractant at pH 2.0–2.5 followed by extraction of Al with 0.01 M extractant at pH 3.0–4.0. Both loaded organic phases were stripped with 1.0 and 2.0 M HCl. The extraction of iron(III) from the HCl leach liquor of ilmenite bearing Fe(III), Ti(IV), Cr(VI) and V(V) was investigated with Cyanex 923 in xylene (Saji et al., 1998). The extraction of metal ions increased with increasing concentrations of HCl and the extractant. The extracted species was HFeCl4.2Cyanex 923. Stripping of the Fe–LO decreased with increasing HCl concentrations but was finally carried out with 0.4 M HCl in 2-stages at O:A ratio of 1:3. The extraction of iron(III) from a chloride solution bearing 1 M iron(III) and 2 M HCl was carried out with a mixture of 70% TBP and 30% MIBK in kerosene (Saji and Reddy, 2001). The extracted species was HFeCl4.2Solvent. Iron from the feed was extracted in 2-stages at O:A ratio of 2:1 and the loaded organic was stripped with distilled water in 3-stages at O:A ratio of 2:3. The extraction of iron(III) from a concentrated acid chloride solution was carried out with MIBK, TBP, D2EHPA and their mixtures in benzene (Sahu and Das, 2000) in which the mixture D2EHPA-TBP showed better synergism than D2EHPAMIBK. The stripping of Fe from the loaded organic increased with HCl up to 120 g/L after which it decreased with further increase in HCl due to back-extraction of the chloro-complex(es) formed in the strip solution. The order of stripping of the extracted complex was: D2EHPA N D2EHPA-MIBK N D2EHPA-TBP. Liquid–liquid extraction of iron and titanium from the ilmenite sulphate leach liquor was carried out with D2EHPA in dodecane (Silva et al., 2008) followed by selective stripping of iron from the organic phase with 4.5 pH H2SO4 and stripping of Ti from the Fe-free organic with an aqueous fluoride solution at pH 4.5. Solvent extraction of iron(III) from the spent FeCl3 etching solution bearing 114.8 Fe(III), 29.2 Fe(II), 312.3 total chloride and 4.8 Ni in g/L (Lee and Lee, 2005) was carried out with 1.0 M Alamine 336 in toluene in 2-stages at O/A ratio of 7 leading to 99% extraction and stripping of iron from the organic phase using 0.1 N HCl at O/A ratio of 10 was 94%. Stripping of iron from the organic phase increased with temperature (25–60 °C) and was endothermic. The extraction of Fe(III) was carried out with TBP in kerosene and the generated data were used for the extraction of iron from the simulated waste chloride titania liquor (Thomas et al., 2004) bearing Mg(II), Al(III), Ti(IV), V(V), Cr(III) and Mn(II) including the effect of HCl and TBP on extraction of iron. The extraction and stripping isotherms were constructed and analysed. The Fe(III) loaded TBP thus underwent precipitation stripping with NaOH to obtain plate like hematite powder. 2. Experimental 2.1. Chemicals and reagents Aliquat 336 (a mixture of tri-octyl/decyl ammonium chloride of average molecular weight 442 g/mol) was supplied by Cognis Inc., USA and was used as such without any purification. Distilled kerosene (b.p 180–240 °C) was used as the diluent and 30% v/v p-nonyl phenol was used as the phase modifier. All other chemicals used were of analytical reagent grade supplied by BDH/Merck, India. The low grade iron ore collected from Minerals Matrics Limited (MML), India was beneficiated at Institute of Minerals and Materials
Technology (CSIR), Bhubaneswar. After beneficiation, the tailings contained 13.375% Fe, 0.8% Al2O3 and 76.8% SiO2. Other metals such as Cu, Ni, Co, Mg, Mn and Pb present were in traces. After leaching of the iron ore tailings with 10.962 N HCl for 6 h, the leach liquor contained 0.685 M (38.2475 kg/m3) Fe and 6.356 M free HCl along with 0.657 kg/m3 Al and 0.0189 kg/m3 Si. Other metals present in leach liquor were 1.35 g/m3 Cu, 1.78 g/m3 Ni, 1.63 g/m3 Co, 173.12 g/m3 Mg, 14.28 g/m3 Mn and zero Pb. This leach liquor was used to recover the iron values using the solvent extraction technique. 2.2. Methods All the experiments were carried out at room temperature (30 ± 1 °C). Equal volumes (10 cm3) of the aqueous phase bearing iron and free HCl and the organic phase containing the extractant, diluent and modifier were taken in a separatory funnel and equilibrated manually for 5 min. After phase disengagement, the raffinate was separated and analysed to record the equilibrium concentrations of iron and free acid. For construction of McCabe–Thiele plots for extraction and stripping, the O:A ratio of phases was varied within 1:5 to 5:1, while keeping the total volume phases constant. The analysis of iron was carried out volumetrically by the standard SnCl2 reduction–K2Cr2O7 titration method and the solutions bearing very low concentrations of Fe(III) was analysed by the Perkin Elmer Model AA 200 Atomic Absorption Spectrophotometer (AAS) after suitable dilutions with 1 M HCl. The concentration of iron in the organic phase was calculated from the difference of concentrations between the aqueous phase before and after extraction. The organic phase was filtered through the 1PS phase separating paper and a suitable aliquot of it was stripped and analysed. 3. Results and discussions 3.1. Effect of HCl concentration The effect of HCl concentration within the range of 1.67 to 9.77 M with a constant iron concentration of 0.342 M (19.124 kg/m3) in the feed solution on extraction of Fe(III) was studied. The extractions were carried out with 0.2 M Aliquat 336 and 15% p-nonyl phenol in kerosene at 1:1 phase ratio, in which the extraction of iron increased from 51.82 to 97.52% (Fig. 1). In another set of experiment, the effect of H+ ion concentration within a small range of 3.178 to 4.178 M in the solution, in presence of a constant Cl− concentration of 4.178 M achieved by the addition of NaCl, on extraction of Fe(III) was studied with 0.2 M Aliquat 336 at 1:1 phase ratio. The experimental data plotted in Fig. 2 illustrated an increase in iron extraction from 65.37 to
100
%Fe extraction
94
80
60
40
0
2
4
6
8
10
[HCl], M Fig. 1. Effect of [HCl] on extraction of Fe(III).
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67.5
82 80
% Fe extraction
%Fe extraction
67.0
66.5
66.0
65.5
65.0
95
78
y = 8.9333x + 30.003 2
R = 0.9864
76 74 72
3
3.5
4
70 4.6
4.5
4.8
5
5.2
5.4
5.6
5.8
[Cl-], M
+
[H ], M
Fig. 4. Effect of [Cl−] on extraction of Fe(III).
Fig. 2. Effect of [H+] on extraction of Fe(III).
67.29% with increase in H+ concentration from 3.178 to 3.778 M, but with further increase in H+ concentration, the extraction decreased to 66.01%. The plot of log D vs. log [H+] in Fig. 3 is a straight line with a slope of 0.48 indicating zero association of HCl with the extracted species.
3.4. Mechanism for extraction of iron with Aliquat 336 Extraction of iron from the HCl medium with the quaternary amine (Aliquat 336) can be expressed as follows: FeAq + 4ClAq + R3 NCH3 ClOrg ⇔R3 NCH3 : FeCl4Org + Cl
3þ
3.2. Effect of Cl− concentration The effect of chloride ion concentration within 4.696 to 5.596 M in the solution in presence of a constant H+ ion concentration of 5.596 M on extraction of Fe(III) was studied with 0.2 M Aliquat 336 in kerosene and the experimental data as plotted in Fig. 4 illustrate an increase in iron extraction from 72.26 to 80.44% with increase in chloride concentration. The plot of log D vs. log [Cl−] in Fig. 5 is a straight line with slope value of 3.02. This indicates the association of 3 mol of Cl− ion with the extraction of a mole of metal ion into the organic phase. 3.3. Effect of extractant concentration on Fe(III) extraction
ð1Þ
The equilibrium constant, Kext can be given as: Kext = ¼
½R3 NCH3 : FeCl4 Org ½Cl ½Fe3þ Aq ½Cl 4Aq ½R3 NCH3 ClOrg
ð2Þ
½R3 NCH3 : FeCl4 Org ½Fe3þ Aq ½Cl 3Aq ½R3 NCH3 ClOrg
or Kext =
The effect of Aliquat 336 concentration within 0.025–0.4 M on the extraction of iron from the aqueous solution bearing 0.342 M (19.124 kg/m3) Fe and 9.269 M HCl was studied. The experimental data plotted in Fig. 6 illustrate a linear increase in extraction of iron from 8.94 to 97.19% with increase in extractant concentration. The plot of log D vs log [extractant] for extraction of iron as shown in Fig. 7 illustrates the slope of 1.09 which indicates the association of a mole of the extractant for extraction of a mole of metal ion with the extracted complex.
D ½Cl 3Aq ½R3 NCH3 ClOrg
where D =
ð3Þ
½R3 NCH3 : FeCl4 Org ½Fe3 + Aq
Taking logarithm for the Eq. 3 and rearranging
log D = log Kext + 3log½Cl Aq + log½R3 NCH3 ClOrg
ð4Þ
From the slope analysis study obtained above, the above extraction mechanism is confirmed.
0.32 0.65 0.31
y = 0.4887x + 0.0314 R2 = 0.9975
0.55
y = 3.0159x - 1.65 R2 = 0.9849
log D
log D
0.3
0.29
0.45 0.28
0.27 0.48
0.5
0.52
0.54
0.56
+
log [H ], M Fig. 3. Plot of log D vs. log [H+].
0.58
0.6
0.35 0.675
0.7
0.725
log[Cl-], M
Fig. 5. Plot of log D vs. log [Cl−].
0.75
R.K. Mishra et al. / Hydrometallurgy 108 (2011) 93–99
100
100
80
80
% Iron Extraction
% Fe(III) extraction
96
60
40
20
Cyclohexane Xylene Benzene Toluene Diphenyl ether Diethyl ether Hexanol Butanol Cyclohexanol Kerosene
60
40
20 0
2
4
6
8
10
[HCl], M 0
0
0.1
0.2
0.3
0.4
Fig. 8. Effect of diluents on extraction of Fe(III) at various [HCl].
0.5
[Aliquat 336], M diluents. As expected from the dielectric constant value of kerosene (2.0), extraction with this kerosene would have been the least. Since kerosene contains both aromatics and aliphatics, extraction with kerosene has come in between.
Fig. 6. Effect of [Aliquat 336] on extraction of Fe(III).
3.5. Effect of diluents The effect of different aromatic and aliphatic diluents such as benzene, toluene, xylene, diphenylether, butanol, hexanol, diethyllether, cyclohexane and cyclohexanol on extraction of Fe(III) was studied at different HCl concentrations within 1.667 to 9.768 M using 0.15 M Aliquat 336. The experimental data for extraction of iron with different diluents is shown in Fig. 8. It was observed that the percentage extraction of iron with the aliphatic diluents except cyclohexane was higher than the aromatic diluents. The percentage extraction of iron from 1.667 to 9.768 M HCl varied from 79 to 79.92% and from 99.1 to 99.42% in aromatic and aliphatic diluents, respectively. At the same acid concentration, the percentage extraction of iron was 97.52% in kerosene. The extraction efficiency of Aliquat 336 in presence of different diluents is in the order: cyclohexane b xylene b benzene b toluene b diphenyl ether b diethyl ether b hexanol b butanol b cyclohexanol. The dielectric constants of the diluents are given in Table 1. It was observed that the percentage extraction of iron increased with increasing dielectric constant of the diluents but it would have been the reverse (Thomas et al., 2004). This reverse behaviour during extraction may be due to the high polar HCl medium and extraction of the anionic species FeCl− 4 by Aliquat 336. As has been observed, the extraction efficiency in presence of kerosene is higher than the aromatic diluents but lower than the aliphatic 0.2
log D
-0.2
3.6. Effect of salts To study the effect of various salts such as NaCl, Na2SO4, NaNO3, CH3COONa and Na3C6H5O7.2H2O (Trisodium citrate dihydrate) on the extraction of Fe(III) from the chloride solution, extractions were carried out with 0.1 M Aliquat 336 in kerosene at equal phase ratio. The concentrations of all the salts in the solution were varied within the range 0.5 to 2.5 M other than the trisodium citrate dehydrate whose concentration was varied within 0.5 to 2.0 M. The percentage Fe(III) extraction increased with increasing concentrations of NaCl, Na2SO4, NaNO3 and Na3C6H5O7.2H2O (Fig. 9) other than CH3COONa where quantum of extraction remained nearly constant. The percentage extraction of iron in presence of the salts was in the order: NaCl N Na2SO4 N NaNO3 N Na3C6H5O7·2H2O. 3.7. Extraction isotherm for iron To recover iron from the solution containing 0.342 M (19.124 kg/m3) Fe, the solution was equilibrated with 0.2 M Aliquat 336 in kerosene at O: A ratios within 1:5 to 5:1 while keeping the total volume of phases constant. After phase disengagement, the aqueous and organic phases were analysed for metal concentrations. The McCabe–Thiele plot in Fig. 10 illustrated 2-stages of extraction at an equal phase ratio for quantitative recovery of iron. To confirm this, a 2-stage counter-current simulation study with 0.2 M Aliquat 336 at 1:1 phase ratio was carried out in which the raffinates and the loaded organic were analysed for iron concentrations. The loaded organic contained 0.338 M (18.8496 kg/m3) iron resulting in 98.57% extraction. The second stage raffinate contained
Table 1 Dielectric constant of diluents.
-0.6 y = 1.0859x + 0.6991 R 2 = 0.9869
-1
-1.4 -2
-1.6
-1.2
-0.8
-0.4
log[Aliquat 336], M Fig. 7. Plot of log D vs. log [Aliquat 336].
0
Sl. no.
Diluents
Dielectric constant
1 2 3 4 5 6 7 8 9 10
Kerosene Cyclohexane, 25 °C Xylene, 20 °C Benzene, 25 °C Toluene, 25 °C Diphenyl ether, 20 °C Di-ethyl ether, 20 °C Hexanol, 25 °C Cyclohexanol, 25 °C 1-Butanol, 25 °C
2.0 2.015 2.27 2.274 2.379 3.726 4.2666 13.3 15 17.8
% Fe(III) extraction
R.K. Mishra et al. / Hydrometallurgy 108 (2011) 93–99
85
50
80
40
30
Na2SO4 NaCl NaNO3 CH3COONa.3H2O Na3C6H5O7.2H2O
75
97
20
70 O:A ratio 2:1, 3-stages
10 65
0
0.5
1
1.5
2
2.5
3
[Salt], M
0
0
5
10
15
20
[Fe]Org, kg/m3
Fig. 9. Effect of [salt] on extraction of Fe(III) with Aliquat 336.
0.273 mg/m3 Fe along with 0.657 kg/m3 Al, 0.0189 kg/m3 Si, 1.35 g/m3 Cu, 1.78 g/m3 Ni, 1.63 g/m3 Co, 173.12 g/m3 Mg, 14.28 g/m3 Mn indicating zero co-extraction of Al, Si, Cu, Ni, Co, Mg and Mn. 3.8. Stripping isotherm of iron loaded Aliquat 336 The loaded organic phase containing 0.338 M (18.8496 kg/m3) iron was stripped with distilled water. To find out the required number of stages and the O:A ratio for stripping, the stripping studies were carried out at O:A ratios within 1:5 to 5:1, while keeping the total volume of phases constant. The McCabe–Thiele plot in Fig. 11 predicted 3-stages of stripping at O:A ratio of 2:1. To confirm the prediction, a 3-stage counter-current stripping study was carried out using the iron loaded organic and distilled water. The third stage spent organic and the strip solution contained 4.48 mg/m3 and 0.651 M (36.3728 kg/m3) iron indicating 99.98% stripping.
Fig. 11. Stripping of Fe loaded Aliquat 336 with distilled water.
The ln kext values for Fe extraction with Aliquat 336 were calculated using Eq. 4 and were plotted against 1/T in Fig. 13. The plot is a straight line with slope and intercept values of − 2.344 and 12.209, respectively. Assuming that H is constant over the temperature range investigated, the enthalpy changes ΔH and the entropy changes ΔS were calculated from the slope and the intercept values of Fig. 13 and were found to be 19.489 kJ/mol and 101.511 J∙mol–1∙K–1, respectively. The free energy change (ΔG) was calculated from the relationship as given in Eq. 6: ΔG = −RT ln kext :
ð6Þ
The values of ΔH, ΔG and ΔS obtained for Fe extraction are given in Table 2. The enthalpy change (ΔH) value is positive for this iron extraction study indicating the extraction process is endothermic.
3.9. Effect of temperature 3.10. IR spectra of Aliquat 336 and Fe-loaded Aliquat 336 The effect of temperature on extraction of iron was studied in the range of 283 to 323 K. The concentration of extractant and A:O ratio was kept constant at 0.2 M and 1:1, respectively. The percentage extraction of iron increased from 39.57 to 64.12 with an increase of temperature from 283 to 323 K and the distribution coefficient (D) values increased from 0.655 to 1.787 (Fig. 12). The Gibbs–Helmholtz equation for enthalpy and entropy change can be written as: ln k = −
ΔH ΔS + RT R
ð5Þ
The FTIR absorption spectra of Aliquat 336, metal loaded Aliquat 336 and of Aliquat 336 after stripping were recorded to know the interaction between the extractant and the metal ion. The spectra of extractants and their complexes with iron are shown in Fig. 14 and the peaks obtained in different spectra are given in Table 3. The ―C―H symmetric and asymmetric deformation vibrations and stretching vibrations for pure and Fe-bonded Aliquat 336 as shown in the Table 3 are identical. The wide absorption band at 3413.4 and 3205.1 for Fe–Aliquat 336 and Aliquat 336, respectively are may be due to the stretching vibration of ―OH of soluble water in Aliquat 2
70 25
60
15
10 O:A ratio 1:1, 2-stages
1.5
D
% Extraction
20
50 % Extn D
1
40
5
0
0
5
10
15
20
25
[Fe]Aq, kg/m3 Fig.10. Extraction isotherm for extraction of Fe(III) using Aliquat 336 in kerosene.
30 280
290
300
310
320
0.5 330
Temperature, K Fig. 12. Effect of temperature on % extraction of iron.
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R.K. Mishra et al. / Hydrometallurgy 108 (2011) 93–99
5.5
Table 3 Characteristic IR spectral bond positions for Aliquat 336 and Fe–Aliquat 336 Fe in cm− 1. Corresponding bond
Fe–Aliquat 336
Aliquat 336
―C―N sv ―C―N sv ―C―H sdv ―N―CH3 adv ―C―H sv ―C―H sv ―C―H sv ―O―H sv
829.3 1180.2 1259.3 1376.9 1461.8 2858.0 2925.5 2956.3 3413.4
831.1 – 1267.02 1373.8 1461.8 2858.0 2925.5 2958.3 3205.1
ln Kext.
5.0
4.5
4.0
3.5 3.0
y = -2.3441x + 12.209 R 2 = 0.9985
sdv: symmetric deformation vibration; adv: asymmetric deformation vibration; sv: stretching vibration.
3.2
3.4
3.6
1000/T, K
336 (Nayl, 2010). The peak at 1461.8 cm− 1 which is the characteristic peak for quaternary amine due to (CH3)N+ is also observed in both spectra. But the peak at 1267.02 cm− 1 due to ―C―N stretching vibration for Aliquat 336 is shifted to 1259.3 cm− 1 for Fe loaded Aliquat 336 indicating the possibility of bonding between Fe and Aliquat 336. The spectrum of spent Aliquat 336 after stripping (Fig. 14) is identical to that of pure Aliquat 336 which confirmed the complete stripping of iron from the loaded Aliquat 336.
following conclusions were drawn from the study. The extraction of iron increased from 51.82 to 97.52% and from 8.94 to 97.19% with an increase in HCl and extractant concentrations from 1.67 to 9.7 M and 0.025 to 0.4 M, respectively. There was no extraction of other metal ions into the organic phase other than Fe(III). The plots of log D vs. log [H+], log D vs. log Cl− and log D vs. [Aliquat 336] were straight lines with slope values of 0.48, 3.02 and 1.09 indicating the association of zero mol of HCl, three mol of chloride and one mole of extractant with the extracted complex for which the extracted species is determined to be R3NCH3·FeCl4. The percentage extraction of iron with Aliquat 336 in different diluents increased in the order: cyclohexane b xylene b benzene b toluene b diphenyl ether b diethyl ether b hexanol b butanol b cyclohexanol. The percentage extraction of iron in presence of different salts was in the order: NaCl N Na2SO4 NaNO3 N Na3C6H5O7·2H2O. The presence of CH3COONa in the solution within the range of concentrations had no effect on the extraction of iron. Quantitative extraction of iron was obtained in 2-counter-current stages at equal phase ratio and the loaded organic contained 0.338 M (18.8496 kg/m3) iron indicating 98.57% extraction. The stripping isotherm for the loaded organic with distilled water showed quantitative stripping in 3-stages at O:A ratio of 2:1. The third stage spent organic and the strip solution contained 4.48 mg/m3 and 0.651 M (36.3728 kg/m3) iron. The stripping of the Fe loaded Aliquat 336 was quantitative. The enthalpy and entropy change (ΔH and ΔS) values for Fe extraction were found to be 19.489 kJ/mol and 101.511 J∙mol− 1∙K− 1, respectively.
4. Conclusion
Acknowledgements
The extraction of iron from the HCl leach liquor of the low grade iron ore tailings was carried out with Aliquat 336 in kerosene and the
The authors are thankful to Dr. T. Subbaiah, HOD, Hydro & Electrometallurgy Department for encouragement and Prof. B.K. Mishra, Director, IMMT, Bhubaneswar for kind permission to publish this paper. The authors are also thankful to the Council of Scientific & Industrial Research, New Delhi, India for the financial support.
Fig. 13. Effect of temperature on Kext.
Table 2 Thermodynamic parameters for extraction of iron with Aliquat 336. Temperature, K
ΔG, kJ/mol
ΔH, kJ/mol
ΔS, J∙mol∙K
283 288 293 298 303 308 313 318 323
− 9.279 − 9.705 − 10.210 − 10.760 − 11.327 − 11.781 − 12.294 − 12.782 − 13.287
19.489
101.511
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Fig. 14. IR Spectra for Aliquat 336 and Fe loaded Aliquat 336.
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