Extractive separation of group IVB elements: Analysis of alloy samples

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Pergamon

EXTRACTIVE

Talanta, Vol.42, No. 4, pp. 635-639, 1995 Copyright@ 1995ElsevierScienceLtd Printed in Great Britain. All rights reserved 0039-9140/95$9.50+ 0,00

0039-9140(95)01466-7

SEPARATION ANALYSIS

OF

OF

GROUP

ALLOY

IVB ELEMENTS:

SAMPLES

S. M. KAKADEand V. M. SHINDE* Analytical Laboratory, Department of Chemistry, The Institute of Science, 15, Madam Cama Road, Bombay 400 032, India (Received 15 July 1994. Revised 31 October 1994. Accepted 1 November 1994)

Summary--Amethod is proposed for the extraction and mutual separation of quadrivalent titanium, zirconium and hafnium from hydrochloricacid using triphenylphosphine oxide dissolved in toluene as an extractant. The optimum conditions for the extraction and separation have been evaluated from critical study of acid concentration, extractant concentration, period of equilibration and effect of diluent. The effect of foreign ions on the extraction and determination is also discussed. The probable compositionof the extracted species has been deduced from logD-logC plots. The method affords mutual separation of titanium, zirconium and hafnium and is applicable to the analysis of alloy samples,

Titanium, zirconium and hafnium have in- controlling of temperature ~°'~6'~9 and coextraccreased rapidly in commercial importance. Tita- tions. L3'~5In our laboratory we have explored the nium and its alloys are useful in defence utility of triphenylphosphine oxide for separapplications, particularly in aircraft, missiles ation of group elements such as gallium, indium and in rocketry. Zirconium is used in nuclear and thallium 2~ and vanadium, niobium and tantalum. 22 An extension of this study showed reactors as a structural and container material. It also finds use in a variety of alloy steels and that triphenylphosphine oxide dissolved in toluwhen added to niobium, forms a superconduct- ene can also be used for extraction and ing alloy. Hafnium is used as a control material separation of group IVB elements, namely titain water cooled nuclear reactors and rectifiers nium(IV), zirconium(IV) and hafnium(IV). The and hence a method is desired for separation proposed method has the following advantages: and determination of these metal ions. 1. Extraction time is in seconds. Several oxygen containing solvents such as 2. Extraction is possible both at trace and dibutyl hydrogen phosphate, ~ bis-(2-ethylmacrolevel. hexyl)phosphate, 2'3 tri-n-butyl phosphate ~7 trib3. Extraction occurs in single step and recovutylphosphine oxide, 8 tri-isoamylphosphate, 9'~° eries of elements are >99.0%. trioctylphosphine oxide, 1~ mesityl oxide, 12 4. Provides mutual separation of titanium, 2,mercaptopyridine-1-0xide, ~3dioctyl methylene zirconium and hafnium. diphosphate, ~4 2-ethylhexyl dihydrogen phos5. Method is applicable to the analysis of phate, ~5 petroleum sulphoxide, ~6 N,N-diethyl alloy samples. carbamoylphosphate and N,N-diethyl car6. Method is reproducible and accurate. bamoyl methylene phosphate, ~7 4-benzoyl-3methyl-l-phenyl pyrazolin-5-0ne ~s and tetraphenyl imidodiphosphate, ~9 have been used for Apparatus extraction studies of quadrivalent titanium, zirThe absorbance and pH measurements were conium and hafnium. The methods using high taken on spectronic 20-D (Milton Roy and Co.) molecular weight amines are also critically dis- and Control Dynamics digital pH meter with cussed in earlier communication. 2° The existing combined glass electrode. ICP-AES was carried methods have limitations such as longer extrac- out using a Plasmalab 8440 Labtam instrument. tion period, 1'5"7"1°'1L'14"16"17"19 u s e of salting out agents, 3"~2'~s incomplete extraction, 6"s9 critical Reagents and chemicals The stock solutions of titanium(IV), zirconium(IV) and hafnium(IV) were prepared by dis*Author to whom correspondence should be addressed.

EXPERIMENTAL

635

636

S. M. KAKADEand V. M. SHINDE Table 1. Optimum extraction conditions for titanium(IV), zirconium(IV) and hafnium(IV)

Metal ion Titanium(IV) (5-15/~g) Zirconium(IV) (1-10/Jg) Hafnium(IV) (1-I0/tg)

Acid concentration/ total volume 9.0M HC1/10 ml 7.0M HCI/10 ml 3.5-5.0M HC1/10 ml

Organic phase 2 × 5 ml of 6.5% TPPO in toluene 5 ml of 6.0% TPPO in toluene 5 ml of 3.5% TPPO in toluene

solving l g potassium titanyl oxalate (together with 2 g of ammonium sulphate in 25 ml concentrated sulphuric acid), 0.1 g zirconium nitrate (in 25 ml concentrated nitric acid) and 0.45 g hafnium dioxide (Koch-light) (in 9 ml of 48% hydrofluoric acid and l ml concentrated sulphuric acid), respectively, and diluting to 250 ml with distilled water. The solutions were standardized by known methods23-25and diluted as required. Triphenylphosphine oxide (TPPO) (Fluka grade) dissolved in toluene was used for extraction and separation of titanium(IV), zirconium(IV) and hafnium(IV). All other chemicals used were of analytical reagent grade.

General extraction procedure for titanium(IV), zirconium(IV) and hafnium(IV)

Extraction period (sec)

Stripping solution

Determination procedure

60

2 x 5 ml water 2 x 5 ml water 2 x 5 ml water

Spectrophotometry using H20226 Spectrophotometry using Alizarin Red S as reagent26 Spectrophotometry using Xylenol Orange 26

50 35

RESULTS AND DISCUSSION

Variation in the concentration of acid (HCI/HBr) and TPPO (using toluene as the diluent) show that the quantitative extraction of titanium(IV) occurs from 9.0M HCI solution with 6.5% TPPO, whereas extraction of zirconiurn(IV) is quantitative with 6.0% TPPO from 7.0M HCI solution (Figs 1 and 2). Hafnium(IV), extraction is quantitative from 3.5 to 5.0M HC1 with 3.5% TPPO. Titanium(IV), zirconium(IV) and hafnium(IV) showed no extraction from hydrobromic acid solution. The suitability of several solvents such as benzene, toluene, xylene, carbon tetrachloride and chloroform for the extraction of titanium(IV), zirconium(IV) and hafnium(IV) using the proposed method was investigated. It was found that TPPO dissolved in toluene or benzene gives quantitative extraction of titanium(IV), zirconium(IV) and hafnium(IV). In all other diluents extraction was incomplete. Variation of the shaking period showed that the minimum extraction periods for titanium(IV), zirconium(IV) and hafnium(IV) are 60, 50 and 35 sec, respectively. Prolonged shaking leads to emulsion and hinders phase separation.

To an aliquot of a solution containing microgram amounts of metal ions, hydrochloric acid was added to give the desired molarity in a total volume of l0 ml (the optimum extraction conditions are reported in Table I). The solution was transferred into a separating funnel and extracted with TPPO dissolved in toluene for the required shaking time. After removing the aqueous layer, the metal ions were stripped from the organic layer with two 5 ml portions C B A of water and subsequently determined spectrophotometrically. For titanium(IV), 2 ml of 3% hydrogen per80o x i d e 26 solution were added; made up to the mark with water and the absorbance measured 0 at 410 nm using water as blank. For zirconium(IV), l ml of 1% gum arabic solution, 5 ml of ~ 40 0.05% aqueous solution of Alizarin Red S26 m were added and diluted up to the mark with 2O 0.1M hydrochloric acid and the absorbance d measured at 520 nm using reagent blank as l I I I I reference. For hafnium(IV), 2 ml of 1% ascorbic 2 4 6 8 10 acid and 2 ml of 0.05% aqueous solution of Concentration of HCI, M Xylenol Orange 26 were added and diluted up to Fig. 1. Extraction hehaviour of." Ti(IV), curve A; Zr(IV), the mark with water and the absorbance curve B; and Hf(IV), curve C all as a function of HCI measured at 530 nm using reagent blank pre- concentration with 6.5, 6.0 and 3.5% TPPO in toluene, pared analogously. respectively.

Extractive separation of Group IVB elements

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[TPPO] % Fig. 2. Extraction behaviour of Ti(IV), curve A; Zr(IV), curve B; and Hf(IV), curve C all as a function of TPPO concentration of 9.0, 7.0 and 3.5M HCI concentrations, respectively.

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0.6

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Log of TPPO concentration, % Fig. 3. Plot of the log of the distribution ratio vs log of the TPPO concentration at 9.0, 7.0 and 3.5M HCI concentrations for Ti(IV) (A), Zr(IV) (B) and Hf(IV) (C), respectively.

hafnium(IV)] which are further soivated by TPPO. The probable mechanism of solvation is MC14" 2 H 2 0 + 2 T P P O

Nature of extracted species The nature o f the extracted species was established using l o g D - l o g C plots. A plot o f log o f distribution ratio vs. log o f T P P O concentration for titanium(IV), zirconium(IV) and hafnium (IV) at 9.0, 7.0 and 3.5M HCi concentration, respectively, gave slopes o f 2.3, 2.2 and 2.4, respectively (Fig. 3) indicating a metal to T P P O ratio o f 1:2. Since the extraction o f titanium(IV), zirconium(IV) and hafnium(IV) are done at reasonably high H C I concentrations, we expect formation o f tetrachloro species such as MCI 4 [M is titanium(IV), zirconium(IV) or

MC14" 2 T P P O + 2 H 2 0 . T P P O , being more basic, supplants the water molecules and renders the species hydrophobic. A MC14 type o f species was proposed by earlier workers also, for instance Hf(NO3) 4 • 2TBP 27 and Z r C I 4 . 2 T O P O 2s. At low H C I concentration, however, there is a possibility o f species such as ZrOC12" 2 T P P O or HfOCI2" 2TPPO.

Effect of foreign ions Various cations and anions were investigated in an interference study on the extraction and

Table 2. Diverse ion effect Tolerance limit, (#g)* Titanium(IV) None 50 In(III), V(V) 100 Ga(III), Te(IV) 200 Au(III), TI(III), Fe(III),? Nb(V), W(VI) 500 Hg(II), Ni(ll), Sn(II), Ta(V), Mo(VI), F , -

-

s2o~ , PO~

1000 1500

Cu(II), Mn(lI), Pd(II), Cd(II), Cr(VI), tartrate, thiourea, oxalate Bi(lIl), Ru(II1), Th(1V)

2000

Zn(lI), AI(III), Se(IV), citrate, EDTA

3000

Ce(IV)

Zirconium(IV) Ga(III), V(V) -In(III) TI(III), Fe(IIl),t Te(IV), Nb(V), W(VI) Hg(II), Ni(II), Sn(II) Au(IIl), Mo(VI), $20 ~-

-

-Ga(III), V(V) In(liD, TI(III), Fe(III),t Te(IV), W(VI) Ni(II), Au(III), Nb(V)

Se(IV), Ta(V), F-, PO~-

Hg(II), Sn(II), Ta(V), Mo(VI), F-, $20 ~-

Pd(II), Cr(VI), thiourea, oxalate Zn(II), Mn(II), Bi(III), Ru(Ill), AI(III), Th(IV), citrate, tartrate, EDTA Ce(IV), Cd(II)

Se(IV), thiourea, PO43

*Maximum allowable amounts of foreign ions to create _+1% error. tIron(III) is masked with 500 #g of EDTA. TAL 42/4,--J

Hafnium(IV) -

Cu(ll), Mn(II), Pd(lI), Ru(lII), Th(IV), Cr(VI), EDTA, oxalate Zn(ll), Ce(IV), Cd(II), Bi(lll), AI(III), tartrate, F-

S. M. KAKADEand V. M. SHINDE

638

Ti(IV), 5-15 p,g; Zr(IV), 5-10 p,g; Hf(IV), 5-10 p,g 3.5 M HCI in a total of 10 mL. Extract for 35 sec with 5 mL of 3.5% TPPO in toluene.

1

Organic phase, (HI)

Aqueous phase, (Ti, Zr)

Strip with 2x5 mL of water and determine spectrophotometrically with xylenol orange 26 or with ICP-AES

Evaporate the aqueous phase to incipient dryness, dissolve the residue in distilled water and add sufficient HCI to make its concentration 7.0 M in a total volume of 10 mL. Then extract for 50 see with 5 mL of 6.0% TPPO in toluene.

I Organic phase, (Zr) Aqueous phase, (Ti) Strip with 2x5 mL of water and Estimate spectrophotometrically with H20226 or with ICP-AES determine spectrophotometrically with Alizarin Red S 26 or with ICP-AES Fig. 4. Flow chart for the mutual separation of Ti(IV), Zr(IV) and Hf(IV) in synthetic mixtures.

determination of titanium(IV), zirconium(IV) and hafnium(IV) by the recommended procedure. The tolerance limit was set at the amount required to cause + 1% error in metal recovery. The results are reported in Table 2.

Mutual separation of titanium(IV), zirconium(IV) and hafnium(IV) Titanium(IV), zirconium(IV) and hafnium(IV) were separated from a ternary mixture by the scheme shown in Fig. 4. The recoveries of titanium, zirconium and hafnium were > 99.0% (Table 3).

Application to the analysis of alloys The proposed method was applied to the separation and determination of titanium(IV), zirconium(IV) and hafnium(IV) in alloys such as Ce-Zn-Zr (BCS 307) (0.125 g alloy dissolved in 2 ml concentrated hydrochloric acid and diluted to 25 ml with distilled water), sillimanite (BCS 309) (0.025 g alloy dissolved in 4 ml of aqua regia, evaporated, filtered and diluted to 25 ml with distilled water) and 6% Zn-AI (BCS

300/1) (0.1 g alloy dissolved in 2 ml concentrated hydrochloric acid and diluted to 25 ml with distilled water). We could not procure samples containing hafnium, hence a known amount of hafnium was added to alloy solutions and the procedure was followed for its recovery. The analysis show that the procedure is applicable to alloys which contain all three metals. The recoveries of zirconium and hafnium in Ce-Zn-Zr (Zr, 0.56%; Fe, 0.0021%; Mn, 0.006%; Zn, 2.08%; Cu, 0.005%; Ni, 0.001%; total rare earth 2.84% + 1 mg Hf); that of titanium and hafnium in sillimanite (SiO2, 34.1%; Fe203, 1.51% ; CaO, 0.22%; Na20, 0.34%; A1203, 61.1%; TiO2, 1.92%; MgO, 0.17%; K20, 0 . 4 6 % + 1 mg Hf) alloy and recoveries of titanium, zirconium and hafnium in Zn-A1 alloy (Ti, 0.09%; Fe, 0.24%; Mg, 2.74%; Zr, 0.18%; Cu, 1.27%; Cr, 0.13%; Si, 0.014%; Mn, 0.33%; Zn, 5.83% + l mg Hf) are better than 99%. The recoveries of titanium, zirconium and hafnium were confirmed by ICP-AES before and after extraction.

Table 3. Determination of titanium, zirconium and hafnium in ternary mixtures Analysis no. l 2 3

Mixture (#g)

Recovery (%)

Ti, 10; Zr, 5; HI', 5 Ti, 5; Zr, 10; Hf, 5 Ti, 15; Zr, 5; Hf, 10

Ti, 99.7; Zr, 99.2; Hf, 99.0 Ti, 99.2; Zr, 99.7; Hf, 99.0 Ti, 99.7; Zr, 99.0; Hf, 99.5

*Average of six determinations

Coefficient of variation (%) Ti, 0.52; Zr, 0.63; HI', l.l Ti, 1.14; Zr, 0.38; Hf, 1.1 Ti, 0.46; Zr, 0.62; Hf, 0.85

Extractive separation of Group IVB elements

Acknowledgement--The authors thank the Council of Scientific and Industrial Research (CSIR), New Delhi for financing the project.

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