Studies on the Solvent Extraction of Iron by Tri-n-Octyl amine
A.V.L.N.S.H. Hariharan1, Ch. Sudhakar1, and B. Venkateswara Rao2
1Department of Chemistry, GIT, GITAM University. Visakhapatnam – 530 045, India.
2Department of Engineering Chemistry, Andhra University. Visakhapatnam – 530 045, India.
*Corresponding Author E-mail: ahharan@gmail.com
ABSTRACT:
The extraction of Iron (III) from hydrochloric, sulphuric, nitric and perchloric acid solutions with Tri-n-octylamine (TOA) in benzene has been studied. The extractions from hydrochloric acid solutions are nearly quantitative and are partial from the remaining acid solutions. The optimum conditions for extraction were established from the study of the effect of several variables like concentration of amine, metal ion, acidity, foreign ions etc. Attempts are also made to strip iron from the organic phase with 1.0M H2SO4.The extracted species are identified. The method has been applied for the recovery and determination of iron in food as well as natural samples.
KEYWORDS: Solvent extraction -iron (III) - Mineral acid- Tri-n- Octyl amine [TOA]
Iron is the most important element of the human body and also plays vital role in oxygen transport through Haem. Solvent extraction of iron (III) from aqueous hydrochloric1-4 sulphuric5,6 , citric7 , perchloric8 and other9 acid solutions has been reported by earlier workers by different extractants. Most of these studies are concerned with the extraction of iron especially from hydrochloric acid media. It is also studied that the free amine cannot extract iron (III) from aqueous acid solutions. The object of the present study aims at the extraction of iron (III) by Tri-n-octyl amine (TOA) from hydrochloric, sulphuric, perchloric and nitric acid solutions and to establish the nature of the extracted species. In the present work determination of iron (III) has been attempted and was successfully applied for the analysis of iron in vegetables and natural samples.
EXPERIMENTAL:
A stock solution of 0.5 M TOA (Mol. Wt.353.67 g/mol) in chloroform was prepared and diluted appropriately to get the required concentration. Ferric chloride (E. Merck) (Mol.Wt.270.3 g/mol) was used for preparing iron(III) solution (0.45M) and was standardized using standard potassium dichromate solution volumetrically. Double distilled water was use throughout the studies. All other chemicals used were of Anala R grade and are purified by standard methods.
IRON (III) EXTRACTION:
Procedure
An aliquat (20ml) of iron (III) of appropriate concentration and mineral acid were by equilibrated equal volume of TOA in benzene (0.05M) pre-equilibrated with 0.1M mineral acid. The solution was shaken for 5 minutes. The two phases were allowed to settle and were separated. Iron(III) from the organic phase was stripped with 20ml of 1.0M H2SO4 and was estimated spectrophotometrically10 by measuring the absorption of Fe(III)–thiocyanate complex at 480nm, using Shimadzu UV-Visible Spectrophotometer type UV-260. The equilibrium iron (III) concentration in the organic phase was determined by taking the difference in the initial and the equilibrium iron (III) concentrations in the aqueous phase.
RESULTS AND DISCUSSION:
The results obtained on the variation of distribution ratio as a function of aqueous phase concentration of mineral acid (HCl, H2SO4, HNO3 and HClO4) are presented in Table-1. In the case of hydrochloric and sulphuric acid solutions the extraction of iron (III) by TOA in benzene as a function of acidity, the distribution ratio (Kd) increased with increasing the concentration of the acid up to 6.0 M and remained constant up to 8.0 M acidity. The extractions are nearly quantitative from both the acid solutions (Table 1). The distribution ratio increased with increase in acid concentration up to 7.0 M acidity in case of nitric and perchloric acid solutions.
Table – 1: Percentage Extraction of Iron (III) by TOA from mineral acid solutions
[Fe (III)] = 1.0 x 10-3 M [TOA] = 5.0 x 10-2 M
|
H2SO4 |
HNO3 |
HClO4 |
||
|
Molarity(M) |
%Extraction |
%Extraction |
%Extraction |
%Extraction |
|
0.5 |
76.38 |
68.4 |
89.27 |
89.27 |
|
1 |
88.54 |
71.35 |
89.98 |
90.7 |
|
1.5 |
93.92 |
74.94 |
90.7 |
91.77 |
|
2 |
98.2 |
76.38 |
91.42 |
91.77 |
|
2.5 |
98.93 |
93.2 |
91.54 |
92.49 |
|
3 |
99.23 |
93.56 |
91.77 |
92.49 |
|
4 |
99.3 |
94.6 |
93.2 |
93.2 |
|
4.5 |
99.38 |
94.6 |
93.34 |
93.55 |
|
5 |
99.5 |
94.99 |
93.56 |
94.63 |
|
5.5 |
99.6 |
95.7 |
94.59 |
94.63 |
|
6 |
99.8 |
95.7 |
94.63 |
94.63 |
|
7 |
99.8 |
95.7 |
94.99 |
95.7 |
|
8 |
99.8 |
95.7 |
94.99 |
95.7 |
COMPOSITION OF THE EXTRACTED SPECIES:
In the extraction isotherm method11 the limiting ratio of the metal to TOA was found to be unity (1 mole of TOA=1 mole of Fe(III)) with all the acid systems. Effect of TOA concentration on the extraction has been studied using the distribution ratio method12. The log-log plots of Kd Vs. TOA from acid solutions gave straight lines. With hydrochloric perchloric and nitric acid solutions the log-log plot gave straight line of unit slope(Fig-1). On the other hand, the slope analysis of the distribution data in sulphuric acid solutions indicates that the solvation number is two .
ABSORPTION SPECTRA:
The individual Iron (III) extracted species with TOA was studied in U.V. region13. The absorption spectra from sulphuric acid media exhibits absorption band at 295 and 355 nm . These two are the absorption characteristics of Fe(OH) and hydroxyl – group bridging species Fe(OH)2 Fe respectively, and the appearance of new peak at 305 nm corresponds to the complexes FeSO4+ and Fe(SO4)-2.
The observed iron: TOA molar ratio of unity from solutions (by distribution ratio method) could be explained as arising from the extraction of iron (III) by the following ion-exchange mechanism. According to Smulek , the extracted species in hydrochloric acid is FeCl4- which associates with one amine cation to form an ion – pair.
From hydrochloric and nitric acid solutions:
TOAHCl + Fe3++ 4Cl- ó [TOAH+ FeCl4-] org + Cl-
TOAHNO3 + Fe3++ 4NO3 ó [TOAH +Fe NO3 4-] org + NO3–
TOAHClO4 + Fe3++ 4ClO4- ó [ TOAH+ Fe (ClO4)4-] org + NO3 –
From sulphuric acid solutions:
2(TOA)2 SO4+ 2Fe3++ 2SO42-+ 2H2O(aq)ó[(TOAH)2SO4.FeOH(SO4)2]2 org + 2H+
On the basis of the proposed mechanism for the extraction of iron (III), the dependence of the distribution ratio on the nature of the mineral acid.
EFFECT OF STRIPPING AGENTS:
After extraction, iron (III) was stripped with 20ml reagents of various concentrations (0.1 – 2.0 M) of ACOH, H2SO4 and NaOH solutions.. It was observed that 1.0 M H2SO4 alone is a good stripping agent. However in no case the acid strips out all the iron (III) in a single extraction. 99.8% iron (III) could be recovered from organic phase by making contact three times with equal volumes of 1.0 M H2SO4.
VARIATION OF DILUENTS
Besides benzene various diluents used in the present study are benzene, xylene, toluene, carbon tetra chloride, n-hexane, n-heptane, cyclohexane, nitrobenzene, dichloro methane which are of wide verities in their chemical nature and dielectric constant. Maximum extraction efficiency was achieved with chloroform as diluent (Table-2). Hence the same diluent was used in all these studies. With, n-hexane, n-heptane, dichloromethane and nitrobenzene low % extraction was noticed (70 to 80%).
Table-2 : Effect of Diluents on Extraction
[Fe (III)] = 1.0 x 10-3 M [TOA]= 5.0 x 10-2 M
(From HCl medium)
|
Diluent |
Dielectric constant |
% extraction |
|
Benzene |
2.28 |
90.7 |
|
CHCl3 |
4.81 |
98.2 |
|
CCl4 |
2.23 |
96.5 |
|
Cyclo hexane |
2 |
83.3 |
|
n-Hexane |
1.89 |
80.5 |
|
n-heptane |
1.92 |
79.7 |
|
Nitrobenzene |
34.82 |
69.2 |
|
Toulene |
2.43 |
81.8 |
|
Xylene |
2.56 |
85.8 |
Analysis of iron in various samples
The validity of the method of extraction for recovery of iron has been tested by analyzing food and vegetable samples. The samples were weighed accurately and finely powdered in a mortar. A known amount of the powdered sample was dissolved in 2.5 M HCl. The mixture was shaken well for about 15 min. and then filtered by Whatman filter paper No. 40. The first portion of filtrate was discarded. The clear solution obtained was made up to 100ml. From this stock solution, an aliquot of the solutions was extracted with benzene solutions of TOA as described by the earlier procedure. The results obtained for different samples are presented in Table-3
Table – 3: Estimation of iron in food and vegetable samples
|
Sample |
Iron present (%) |
Iron found % by extraction |
% recovery |
|
Green gram |
4.05 |
3.92 |
97.53 |
|
Raw rice |
30.0 |
28.67 |
95.66 |
|
Spinach |
20.0 |
18.68 |
93.40 |
|
Soya beans |
20.0 |
19.32 |
96.66 |
|
Baked potatoes |
39.0 |
38.16 |
97.85 |
CONCLUSIONS:
The developed method was applied to the extraction separation and determination of iron in food and vegetable samples. The average % recovery of iron was found to be 96.22 % and the determination can be achieved efficiently in minimum amount of time.
ACKNOWLEDGEMENTS:
Thanks are due to Dr. V. Muralidhara Rao, Retd. Professor, School of Chemistry, Andhra University, Visakhapatnam for his valuable suggestions. Thanks are also due to Principal, GIT and Management of GITAM University for providing necessary facilities to carry out these investigations..
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Received on 02.01.2012 Modified on 29.01.2012
Accepted on 12.02.2012 © AJRC All right reserved
Asian J. Research Chem. 5(2): February 2012; Page 312-314