ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2008, том 63, № 3, с. 237-241
^=ОРИГИНАЛЬНЫЕ СТАТЬИ =
УДК 543
EXTRACTION OF MOLYBDENUM(V) AS ITS FERRON COMPLEX WITH TRIOCTYLAMINE IN CHLOROFORM FROM SULPHURIC ACID MEDIUM © 2008 r. A. K. Bishnoi*, R. Dass, R. G. Sharma**
*Department of Industrial Chemistry, Guru Nanak Khalsa College, Yamuna Nagar -135001, Haryana, India **Department of Chemistry, N. A. S. College Meerut-250001, India Received 13.06.2006
A simple, rapid and highly selective method for the separation of molybdenum from a large number of elements of analytical importance has been developed. The method is based on the extraction of Mo(V)-ferron (7-iodo-8-hydroxyquinoline-5-sulphonic acid) complex into trioctylamine-chloroform in sulphuric acid medium using ascorbic acid as reductant. Many elements such as Re(VII), W(VI), U(VI), Th(IV), Cr(III, VI), V(V), Ce(IV), Ru(III), Co(II), Ni(II), Mn(II), Fe(II, III), Cd(II), Mg(II), Cu(II), Al(III), Zn(II), Pb(II), Ag(I), and As(V) are not extracted under the conditions proposed and thus molybdenum can be easily separated without any interference. Sulphate, chloride, nitrate, phosphate and oxalate anions have no effect on the extraction of molybdenum. However, zirconium and palladium interfere seriously. The ratio of Mo : ferron : TOA in the extracted species is found to be 1 : 1 : 3 by Job's method of continuous variations. This value has been further confirmed by mole-ratio method.
In most methods of separation of molybdenum, both in pentavalent and hexavalent state, this element is extracted into chloroform as its 8-hydroxyquinoline and 2-methyl-8-hydroxyquinoline chelates. 8-Mercapto-quinoline [1a], oxine [1b] and some derivatives [1c, 28] have also been used for the extraction of molybdenum. However, all of these methods [1-8] have been mostly employed for the extraction separation and spectrophotometric determination of molybdenum in micro amounts only. In addition, these methods also suffer from several common interferences and thus have serious limitations in their practical application to various natural, synthetic and technical samples. Therefore, the separation of molybdenum from many elements is a matter of prime concern.
Earlier, ferron is introduced as an analytical reagent for the colorimetric determination of iron(III) in aqueous phase and later on it is also recommended for the extraction spectrophotometry determination of vanadi-um(V) [9]. It forms water soluble complexes with a large number of analytically important metal ions, but only a few of these ions are extracted into different organic solvents at low pH. Taking this advantage into account, the reagent has been used for extractive separation of molybdenum.
In the present work, a new, highly rapid and selective method for the separation of molybdenum from rhenium, tungsten, chromium, uranium, vanadium, iron, cobalt, nickel and several other analytically important elements is proposed. The method is based on the
extraction of molybdenum(V)-ferron complex with tri-octylamine in chloroform from sulphuric acid medium.
EXPERIMENTAL
Reagents and solutions. A stock solution of molybdenum (5 mg/mL) is prepared by dissolving an accurately weighed amount of sodium molybdate dihydrate (Thomas Baker, A.R.) in deionised water and standardized by the oxine method. Working solutions are obtained by suitable dilutions of the stock solution.
Solutions of other diverse metal ions are prepared by dissolving their commonly available salts (A.R.) in deionised water or dilute acids and are standardized by conventional methods. Lower concentrations at appropriate levels are obtained by suitable dilutions.
1% (w/v) Ferron (7-iodo-8-hydroxyquinoline-5-sul-phonic acid) (Riedel, A.R.) solution is prepared in 1 : 1 water-acetone mixture.
5 M Sulphuric acid solution is prepared by suitable dilution of 17.8 M H2SO4 (Qualigens, SQ, density 1.84 g/mL).
Ascorbic acid (Thomas Baker, A.R.) is dissolved in deionized water to give 5% (w/v) solution.
0.2% (v/v) Trioctylamine (Fluka, extrapure >99%) solution is prepared in chloroform.
Instrument. An Elico SL 164 UV-VIS double beam spectrophotometer with 10 mm matched cells was used for absorbance measurements and spectral studies.
Table 1. Analysis of molybdenum samples by the proposed method
Sr. No. Composition of sample Mo found**/mg
Matrix* Mo added/mg
1 U(5), Ru(2.5), Re(0.1) 5.0 5.24
2 W(3), V(3), Pb(1) 4.5 4.53
3 W(5), U(2.5), Ag(1) 15.0 14.97
4 [Fe(7), Cu(0.1), Ni(0.9), Cr(1.9)]*** 0.1 0.09
5 [Fe(2.2), Cu(0.0128)]*** 3.0 3.05
6 [Fe(0.3), Ni(2.5), Cr(5), Co(2.5), Al(0.6), Ti(0.6)]*** 1.5 1.45
7 BCS(406/1) 1 00%***** 0.992 ± 0.011%****
8 BCS(261/1) 0 11%***** 0.104 ± 0.008%****
9 BCS(219/4) 0.58%***** 0.575 ± 0.005%****
10 Reverberatory Flue Dust 1.0 0.98 ± 0.12****
11 Well water 0.1 0.11 ± 0.038****
12 Canal Water 0.2 0.20 ± 0.034****
13 Industrial Effluent 2.0 2.1 ± 0.04****
* Number in brackets indicates mg amounts of elements in the aliquot for analysis. ** Average of triplicate analyses. *** Sample number 4, 5 and 6 are analogous to stainless U, ferromolybdenum and nimonic 80, respectively. **** Mean ± standard deviation (n = 7). ***** Certified Mo content.
Samples. Synthetic samples: Synthetic samples are prepared by mixing molybdenum solution with solutions of other diverse metal ions in suitable proportions to get the desired composition as shown in Table 1.
Steel: Steel samples (0.1 g) is dissolved as mentioned earlier [10] and molybdenum is separated and determined by the proposed method using suitable ali-quots. 100 mg of ascorbic acid and 100 mg sodium fluoride were added in each case.
Reverberatory flue dust: Reverberatory flue dust sample (0.1 g) from copper manufacture, containing no molybdenum, is mixed with a solution of known molybdenum content and brought into solution as reported earlier [10]. Molybdenum is separated and determined by the proposed method in a suitable aliquot, after adding 100 mg thiourea in each case.
Industrial effluent: A solution of known molybdenum content (2 mg) is mixed with the industrial effluent sample (1 L) collected from the main outlet of effluents of metal industries located in twin cities-Yamuna Na-gar and Jagadhari. To a 10 mL aliquot of the sample solution, 1 mL of hydrogen peroxide (20 volumes) and 2 mL of aqueous ammonia are added. The resulting solution is then boiled and evaporated to dryness. The resulting mass is leached with 5 mL of 2 M H2SO4 and subjected to Mo determination by the proposed procedure.
Canal water: To a 100 mL water sample taken from the Western Yamuna Canal at Yamuna Nagar site, a known amount of molybdenum (0.2 mg), 1 mL of hydrogen peroxide (20 volumes) and 2 mL of aqueous ammonia are added. The contents are then boiled and evaporated to dryness. The residue is dissolved in 2 M
H2SO4 and the final volume is raised to 100 mL. An aliquot (3 mL) is subjected to the analysis by the proposed method.
Well water: To a 100 mL aliquout of well water, a known amount of molybdenum (0.1 mg) is added and brought into solution following the earlier reported [11] procedure. Taking 5 mL aliquot of the solution, molybdenum is extracted and subjected to the determination by the proposed procedure.
Procedure for extraction, separation and determination. Formation and extraction of Mo(V)-ferron complex, to a 5 mL sample solution containing molybdenum up to 2 mg and/or other diverse metal ions taken in a 100 mL separatory funnel, 2 mL of 5 M H2SO4, 100 mg ascorbic acid, and 2.5 mL of 1.0% (w/v) ferron solution are added. The final volume is made to 10 mL with deionised water. The contents of the funnel are mixed well and allowed to stand for a minute. The coloured species are then extracted with 10 mL of 0.2% (v/v) tri-octylamine in chloroform for 2 minutes and the two layers are allowed to separate. The extract is drawn off into another 100 mL separatory funnel.
When molybdenum concentration exceeds 0.25 mg/mL for quantitative recovery of metal ion, the raffinate is shaken twice separately, with 10 mL solvent phase, each time for 2 min.
Back-extraction of molybdenum. The aqueous phase is discarded and the combined organic phase (if more than one extraction is performed) is shaken vigorously by contacting it twice for 2 min with equal volume of water adjusted to alkaline reaction with sodium hydroxide. To the combined back-extract, 4-5 drops of
Table 2. Effect of various parameters on the absorbance of Mo(V)-ferron complex
H2SO4* (M) 0 0.25 0.5-1.25 1.5 2.0
Mo-extraction (%) 0.0 70 99.2 95 89.2
1% (w/v) ferron** (mL) 0.2 0.5 1.0 1.25 1.5-2.5
Mo-extraction (%) 60 80 90 95 99.2
Equilibration time*** (s) 15 30 60 75 90-300
Mo-extraction (%) 45 70 95 98 99.2
Mo**** (mg/mL) 0.005 0.05 0.25 0.4 0.6
Mo-extraction (%) 100 100 100 99.2 85
* Mo, 2 mg; 1% (w/v) ferron solution, 2 mL; ascorbic acid, 100 mg; aqueous volume = solvent volume = 10 mL; equilibration time, 120 s. ** acidity, 1 M H2SO4; other conditions are kept to be same as in (*) except variation in ferron concentration. *** 1% (w/v) ferron solution, 2.5 mL; other conditions are kept to be same as in (**) except variation in equilibration time. **** Equilibration time, 120 s; other conditions are kept to be same as in (***) except variation in the amount of molybdenum.
30% H2O2 are added, then the solution is boiled for 23 min. The solution is then adjusted to acidic reaction by adding H2SO4 and boiled off to remove the excess of H2O2. The solution thus obtained is standardised by suitable methods [12]. The effect of anions on the extraction of molybdenum is studied by adding known amounts of their usually available sodium salts (A.R.).
Determination of the element. Molybdenum in mg amounts is determined gravimetrically by the oxine method [12] or cerimetry [12] and in the case of ^g amounts it is determined colorimetrically by the thiocy-anate-pyrogallol method [13]. Other elements are determined by the conve
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