Duam(

Sa

b

a

ARRA

KUSPBE

1

tppcaoa

1d

Spectrochimica Acta Part A 91 (2012) 222– 227

Contents lists available at SciVerse ScienceDirect

Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

j our na l ho me p age: www.elsev ier .com/ locate /saa

evelopment of an extractive spectrophotometric method for estimation ofranium in ore leach solutions using 2-ethylhexyl phosphoniccid-mono-2-ethylhexyl ester (PC88A) and tri-n-octyl phosphine oxide (TOPO)ixture as extractant and 2-(5-bromo-2-pyridylozo)-5-diethyl aminophenol

Br-PADAP) as chromophore

ujoy Biswasa, P.N. Pathakb,∗, S.B. Roya

Uranium Extraction Division, Bhabha Atomic Research Centre, Mumbai 400 085, IndiaRadiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India

r t i c l e i n f o

rticle history:eceived 31 October 2011eceived in revised form 1 February 2012ccepted 2 February 2012

eywords:raniumpectrophotometryC88Ar-PADAPxtraction

a b s t r a c t

An extractive spectrophotometric analytical method has been developed for the determination ofuranium in ore leach solution. This technique is based on the selective extraction of uranium from mul-tielement system using a synergistic mixture of 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester(PC88A) and tri-n-octyl phosphine oxide (TOPO) in cyclohexane and color development from the organicphase aliquot using 2-(5-Bromo-2-pyridylazo)-5-diethyl aminophenol (Br-PADAP) as chromogenicreagent. The absorption maximum (�max) for UO2

2+–Br-PADAP complex in organic phase samples,in 64% (v/v) ethanol containing buffer solution (pH 7.8) and 1,2-cyclohexylenedinitrilotetraaceticacid (CyDTA) complexing agent, has been found to be at 576 nm (molar extinction coefficient, ε:36,750 ± 240 L mol−1 cm−1). Effects of various parameters like stability of complex, ethanol volume, orematrix, interfering ions etc. on the determination of uranium have also been evaluated. Absorbance mea-surements as a function of time showed that colored complex is stable up to >24 h. Presence of increasedamount of ethanol in colored solution suppresses the absorption of a standard UO2

2+–Br-PADAP solution.Analyses of synthetic standard as well as ore leach a solution show that for 10 determination relativestandard deviation (RSD) is <2%. The accuracy of the developed method has been checked by determining

uranium using standard addition method and was found to be accurate with a 98–105% recovery rate.The developed method has been applied for the analysis of a number of uranium samples generatedfrom uranium ore leach solutions and results were compared with standard methods like inductivelycoupled plasma emission spectrometry (ICPAES). The determined values of uranium concentrations bythese methods are within ±2%. This method can be used to determine 2.5–250 �g mL−1 uranium in oreleach solutions with high accuracy and precision.

. Introduction

Uranium is an important element in the actinides series dueo its wide applications in nuclear industry as a nuclear fuel. Therimary source of uranium is naturally occurring uranium oreresent in the earth crust. The recovery of uranium from ore isarried out via two step process viz. (a) acid, alkali or bio leaching,

nd (b) separation from the ore leach solution [1–7]. Monitoringf uranium concentration in ore leach solution is an importantspect for its effective and efficient recovery. A large number of

∗ Corresponding author. Tel.: +91 22 25594089; fax: +91 22 25505151.E-mail address: ppathak@barc.gov.in (P.N. Pathak).

386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved.oi:10.1016/j.saa.2012.02.005

© 2012 Elsevier B.V. All rights reserved.

analytical techniques have been used for the determination ofuranium in a wide variety of samples such as environmental,seawater, process streams, effluent/waste streams, ores and oreleach solutions. The increasing availability of power full instru-mentals techniques such as neutron activation analysis (NAA),energy dispersive X-ray fluorescence (EDXRF), inductively cou-pled plasma emission spectrometry (ICPAES), inductively coupledplasma emission mass spectrometry (ICP-MS) has enabled the anal-ysis of complex mixtures with high accuracy and precision [8–13].However, these advanced techniques require sophisticated, high

value instruments (including nuclear reactors). On the other hand,the low cost techniques (such as spectrophotometry) cannot beused successfully without prior chemical separations due to spec-tral interference of rare earths and transition elements [14,15].

S. Biswas et al. / Spectrochimica Acta Part A 91 (2012) 222– 227 223

Table 1Typical composition of an ore leach solution analyzed by ICPAES technique.

Elément Concentration, �g mL−1

U 193.9Al 1214.6B 2.1Ce 43.7Cr 19.8Co 1.6Dy 4.6Er 2.1Eu 0.6Fe 330.4Gd 5.1Mg 1017.1Mn 3440.9Ni 6.0Sm 6.7

Nepocasmcrtei(Bdoa

tse(bmn(mstcmbcowmri5lqbon

650625600575550525500475450

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Ab

so

rban

ce

Wavelength, nm

Blank

U(VI)-Br-PADAP

0.05 g of Br-PADAP chromophore was dissolved in 100 mL abso-lute ethanol.

evertheless, the association of spectrophotometric techniquesmploying chelating agents and chemometric methods, such asartial least squares (PLS), multivariate calibration procedures,ffers outstanding advantages for the analysis of complex matri-es [16,17]. In this context, 2-(5-bromo-2-pyridylozo)-5-diethylminophenol (Br-PADAP) as chelating agent has been exten-ively used for the spectrophotometric analysis of U(VI) in variousatrices [18,19]. It is observed that Br-PADAP has been used to

omplex a variety of metal ions including cobalt, zinc, copper,are-earths and U(VI). Das et al. demonstrated the determina-ion of trace amounts of U(VI) in nitric acid medium by selectivextraction of U(VI) from a mixture of U(VI), Pu(IV), Fe(III), Th(IV)n to organic phase comprising of tri-n-octyl phosphine oxideTOPO)/cyclohexane and simultaneous color development usingr-PADAP [20]. Suresh et al. developed an analytical method for theetermination of trace amount of U(VI) in presence of large excessf Th(VI) in nitric acid medium using excess amount of complexinggents [21].

In the present paper, a modified method has been developed forhe measurement of trace amounts of U(VI) present in ore leacholutions containing a large number of other metal ions viz. rarearths, transition elements (Fe, Mn, Ni, Cr, etc.) in sulphate mediumTable 1). In view of non selective nature of Br-PADAP, U(VI) haseen selectively extracted from ore leach solution in to organicedium containing a synergistic mixture of 2-ethylhexyl phospho-

ic acid-mono-2-ethylhexyl ester and tri-n-octyl phosphine oxidePC88A + TOPO) in cyclohexane and simultaneously color develop-

ent in organic medium using Br-PADAP in presence of a bufferolution at pH 7.8. NaF and ascorbic acid were used as additive inhe aqueous phase for masking of extraction of other elements. Theomplexation of Br-PADAP with U(VI) is pH dependent and is opti-um at ∼8. Several common laboratory buffers such as phosphate,

orate and N-cyclohexyl-3-aminopropanesulfonic acid (CAPS) areapable of maintaining the pH within the acceptable range. Becausef limited water solubility of Br-PADAP, stock solution of Br-PADAPas prepared in absolute ethanol prior to addition to the reactionixture. After addition of Br-PADAP, color development is very

apid in the presence of sufficient amount of U(VI). This resultsn a bathochromic shift of the absorbance maxima from 444 nm to76 nm (Fig. 1). The wavelength shift can be detected with a visible-

ight spectrophotometer. PC88A in combination with TOPO showsuantitative extraction of uranium from 1 M HNO3. Conditions haveeen optimized for extraction and spectrophotometric estimationf uranium in ore leach solution containing 2.5–250 �g mL−1 ura-ium.

Fig. 1. Absorption spectra of U(VI)–Br-PADAP complexes in 0.1 M PC88A + 0.05 MTOPO/cyclohexane medium.

2. Experimental

2.1. Reagents

PC88A (Daihachi Chemical Industry Co. Ltd. Japan, 95% pure),TOPO (E-Merck) and cyclohexane (E-Merck), ascorbic acid (B.D.H,A.R Grade) were used without further purification. Nuclear gradepure U3O8 was obtained from uranium extraction division, BARC,India. 1,2-Cyclohexylenedinitrilotetraacetic acid (CyDTA), sodiumfluoride (NaF), sulphosalicylic acid (SSA), triethanolamine (TEA)was procured from SIGMA, USA. The chromogenic reagent 2-(5-bromo-2-pyridylazo-5-diethylaminophenol) (Br-PADAP) waspurchased from Fluka, Germany. All other reagents used in theexperiment were of A.R. grade.

2.2. Preparation of standard uranyl sulphate solution

Nuclear grade pure U3O8 was first dissolved in 6–8 M HNO3 bywarming and then fumed with sulphuric acid to convert in to sul-phate medium. The volume of the solution was made up to 100 mLby H2SO4 in such a way that the free acidity of the solution became2 M and uranium concentration 1000 �g mL−1. The standard solu-tions of various concentrations were prepared with proper dilution.

2.3. Preparation of complexing solution

To 40 mL of redistilled water, 1.25 g of CyDTA, 0.25 g NaF and3.25 g of SSA were dissolved. The pH of the solution was adjustedto 7.8 using NaOH solution and the final volume was made up to100 mL.

2.4. Buffer solution

To 80 mL of redistilled water 14.2 mL of TEA was dissolved andpH of this solution was adjusted to 7.8 by adding concentratedHClO4. The solution was left to stand overnight and pH of the solu-tion again readjusted to 7.8. The solution was further diluted to100 mL using double distilled water.

2.5. Br-PADAP solution (0.05%, w/v)

224 S. Biswas et al. / Spectrochimica Acta Part A 91 (2012) 222– 227

Table 2Color stability of U(VI)–Br-PADAP complex, �max: 576 nm.

U-STD, �g mL−1 Absorbance

10 min 4 h 24 h

10 0.025 0.026 0.02520 0.076 0.076 0.07530 0.098 0.098 0.09950 0.174 0.175 0.174

100 0.366 0.368 0.367

2

d

2

fPialmolmFll

2

t5wlacoistabos

3

3

0aa3ccuPc

250200150100500

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Ab

so

rban

ce

[U], µg mL-1

Slope : 0.00386 ± 3.47 x 10-5 , R: 0.9998

extraction of Fe(III) present in aqueous samples by reducing to Fe(II)state. Similarly, the acidity of the aqueous phase was maintained1 M by adding HNO3 to prevent extraction of transition metal aswell as rare earth elements from aqueous phase to organic phase

Table 3Interferences test for different metal ions for the ability to complex with Br-PADAP.

Do not complex Complex but can be masked Complex, not masked

Li Co UCs CdTa NiNa PbMg ZnCe FeCr CuW ThKCaMoRb

200 0.759 0.759 0.761250 0.958 0.953 0.971

.6. Mixture of PC88A and TOPO solution (0.1 M + 0.05 M)

6.31 g of PC88A and 1.93 g of TOPO were accurately weighed andissolved in 100 mL cyclohexane.

.7. Spectrophotometers

A Unicam UV 500 UV–visible spectrophotometer was usedor the absorbance measurement of the colored sample (U–Br-ADAP) solutions. Jobinyvon Emission, ICPAES (Model No JY 328))nstrument was used to determine the concentrations of uraniumnd other trace impurities. The uranium concentrations in oreeach solutions were determined either by Br-PADAP or by ICPAES

ethod (as per requirements) with the relative standard deviationf ±2–5% [18]. The detection limit (3�) of the ICPAES instrument foranthanides and non-transition elements: <0.2 ppb, transition ele-

ents: <1 ppb and rare earths elements: <3 ppb (for pure solution).or real solutions containing a number of elements, the detectionimit was 100 ppb. Table 1 shows the composition of a typical oreeach solution.

.8. Recommended procedure

The sample aliquot was taken in 20 mL 1 M HNO3 in an extrac-ion vial. To this following reagents were added carefully 2 mL of% (w/v) ascorbic acid, 5 mL of 2% NaF (w/v) and the equilibratedith 5 mL organic phase for 10 min (sufficient for achieving equi-

ibrium conditions) in 50 mL standard vial. After equilibration, thequeous phase was discarded. For color development to 1 mL ofomplexing solution in a 25 mL standard flask, 2 mL of extractedrganic phase was taken. Other reagents were added in the follow-ng orders; 4 mL Br-PADAP solution, 1 mL buffer, 16 mL ethanol. Theolution was finally diluted to 25 mL by distilled water. The solu-ions were kept for 10 min to allow complete color developmentnd then absorbance was measured at 576 nm against a reagentlank. The calibration curve was drawn by taking average valuef five similar measurements (different samples) of each standardolution.

. Results and discussion

.1. Effect of time on color stability

Fig. 1 shows the absorption of U(VI)–Br-PADAP complex in.1 M PC88A + 0.05 M TOPO/cyclohexane synergistic mixture (useds extractant) and which reveals that absorption maximum appearst 576 nm. The molar extension coefficient (ε) at �max = 576 nm is6,750 ± 240 L mol−1 cm−1 in the presence of 64% ethanol in theolored sample solution. The color stability of U(VI)–Br-PADAP

omplex was monitored as a function of time, which was extendedp to several hours. It was observed that the color of U(VI)–Br-ADAP complex is stable up to >24 h (Table 2). Fig. 2 shows thealibration plot for the determination of U(VI) in sulphuric acid

Fig. 2. Calibration plot of determination of U(VI) in sulphate medium using Br-PADAP in 0.1 M PC88A + 0.05 M TOPO/cyclohexane organic medium.

medium. It is observed that the calibration curve is linear up to250 �g mL−1 U(VI) of sample solution and obeyed the followingequation:

y = m · x + c (1)

where ‘m’ is the slope (3.86(±0.35) × 10−4) of the calibration curve,‘c’ is the constant (−0.00549 ± 0.00448), y and x are the variables,respectively. The colored complex obeys Beer’s law in the rangeof 2.5–250 �g mL−1 sample solution. A number of metal ions caninterfere in the color development of U(VI)–Br-PADAP complexleading to error in absorbance measurement (Table 3). Therefore,the solvent extraction step is introduced for selective separationof uranium in to 0.1 M PC88A + 0.05 M TOPO/cyclohexane fromthe aqueous medium prior to color development in the organicphase by Br-PADAP reagent in the presence of complexing agentand buffer of pH 7.8. The reaction between Br-PADAP and U(VI) ispH sensitive and the main function of buffer solution is to main-tain constant pH (7–8) to allow stable color development usingthe organic extracts containing uranium. It helps in the quanti-tative determination of U(VI) present in sample solutions. It isimportant to mention that ascorbic acid is added to prevent the

BaAgGdAl

S. Biswas et al. / Spectrochimica Acta Part A 91 (2012) 222– 227 225

250200150100500

0.0

0.2

0.4

0.6

0.8

1.0

1.2A

bso

rban

ce

[U], µg mL-1

64%

56%

F0

dNmcCtctOitip

U

3

oiesaitPps3ofi

3

bc1t(

Table 4Recovery study of the analytical technique on the basis of added/found concentra-tion of uranium standards.

[U]added, �g mL−1 [U]found, �g mL−1 % Recovery ± % Difference

19.4 ± 10 19.4 ± 10.5 105.0 +5.0019.4 ± 20 19.4 ± 19.4 97.2 −2.8519.4 ± 30 19.4 ± 31.6 105.3 +5.3319.4 ± 50 19.4 ± 51.6 103.1 +3.10

|t| = X̄1 − X̄2

s√

(1/n1) + (1/n2)(3)

Table 5Effect of various ions on the determination of U(VI) concentration in ore leach solu-tion; [U(VI)]: 200 �g mL−1.

Ions Amount (�g) Error (%)

Al 1214 <1Ce 44 <2Cr 20 <2Fe 3330 <5Mg 1017 <2Mn 3440 <2Y 15 <2Zr 500 <1

ig. 3. Effect of ethanol content in absorbance of U(VI)–Br-PADAP complexes in.1 M PC88A + 0.05 M TOPO/cyclohexane medium.

uring selective extraction of uranium using synergistic mixture.aF present in the aqueous phase acts as masking agent for ele-ents like Al(III), Fe(III), and Th(IV) etc. by forming most stable

omplexes in the aqueous phase. Thus, the complexing agentsyDTA and NaF suppress the extraction of impurities extracted ino the organic phase along with uranium. The stoichiometry of theolored complex has been determined by Job’s method as 1:1 withhe chemical formula [U Br PAPAP]+ [20]. At pH 7–8, both F− andH− ion could be coanions forming complex with [U Br PAPAP]+

on. However, F− ion has been proposed as the coanion in view ofhe reduced stability of [U Br PAPAP]+ in the presence of OH−

on [18]. The chemical reaction between Br-PADAP and uranium inresence of F-anions can be written as:

O22+ + F− + H Br PADAP → UO2FBr PADAP + H+ (2)

.2. Optimization of ethanol concentration

Ethanol plays an important role in this method. The solubilityf Br-PADAP as well as U(VI)–Br-PADAP complex in aqueous phases very poor, and may offer to phase separation and the addition ofthanol increases the solubility of U(VI)–Br-PADAP complex in theample solutions. Thus, ethanol is act as a phase modifier. There was

decrease in aqueous solubility of U(VI)–Br-PADAP complex lead-ng to phase separation for ethanol (v/v) content < 56%. However,here was a decrease in the absorbance values (∼23%) of U(VI)–Br-ADAP complex in the sample solutions with increased ethanolroportions from 56% to 64%; and correspondingly the molar exten-ion coefficient (ε) decreased from 47,886 ± 450 L mol−1 cm−1 to6,750 ± 240 L mol−1 cm−1 at �max = 576 nm (Fig. 3). Based on thisbservation, the ethanol concentration was maintained as 64% forurther studies. This helped in avoiding the phase separation byncreasing solubility of U(VI)–Br-PADAP complexes.

.3. Accuracy of the analytical method

The accuracy of the developed analytical method was testedy standard addition method. Uranium standards of various con-entrations were added to actual ore leach solution containing

9.4 �g mL−1 U(VI) and a large number of other elements as impuri-ies. The recoveries of the added standards were within 101.5 ± 3.5%Table 4).

19.4 ± 100 19.4 ± 100.3 100.3 +0.2619.4 ± 200 19.4 ± 201.6 100.8 +0.77

3.4. Effect of other ions

Table 5 shows the tolerable limits of different impurities ionsin the presence of 200 �g mL−1 of U(VI) in ore leach solution. Theextraction and interference of transition metal ions and rare earthsare less due to presence of F− as well as ascorbic acid. The mainrole of F− is to mask metal ions like Al(III), Zr(IV), Fe(III), La(III),where as the role of ascorbic acid is to reduce the oxidation stateof Fe(III)–Fe(II) to prevent its extraction in to the organic phase.It is observed that the presence of Th(IV) decrease the tolerancelimit. The probable reason for low tolerance limit of Th(IV) wasthe presence of insufficient amount of F− in the aqueous phase aswell as in the organic phase. On the other hand, ascorbic acid can-not mask it due to its stable +4 oxidation states. Hence, Th(IV) ionsget extracted in the organic phase along with U(VI) which reducethe signal of U(VI) to >10%. However, Th(IV) content in uraniumore leach solution is generally in the range of <10 �g mL−1 [22].Our studies suggest that the presence of thorium in this concentra-tion rage in leach solutions will not have any positive bias on themeasured uranium concentration.

3.5. Precision of the developed method

The precision of the methods was evaluated by analyzing stan-dard uranium and ore leach solutions 10 times under identicalconditions and it was found to be <2% at 50 �g mL−1 U (Table 6).Thus, the overall accuracy and precision is better than 2%.

3.6. t and F tests

For better comparison of proposed method with the existingmethod such as ICPAES, t and F-tests were carried out employinga ore leach solution containing 51.630 �g mL−1 uranium solutionin sulphuric acid medium for total number of analysis n = 10. Thevalue of absolute t was calculated using following equation [23]:

Mo 500 <2Th 200 <10

Number of measurement for single sample is 3 (n = 3).

226 S. Biswas et al. / Spectrochimica Acta Part A 91 (2012) 222– 227

Table 6Analysis of uranium standard and a typical ore leach solution for the evaluation ofrelative standard deviation of the methods.

S.N. [U]stand., �g mL−1 [U]ore leach., �g mL−1

1 51.29 51.552 48.19 51.553 50.26 52.854 48.96 51.815 48.96 50.786 48.94 52.077 48.94 50.528 51.04 53.379 51.55 51.0410 51.81 50.78

Average 49.82 51.63

r

wfarf

s

muTcvfSpatcmo

3

mwn

Tta

Table 8Evaluation of detection limit of the method for measurement of uranium in ore-leachsolution.

S.N. Absorbance (�max: 576 nm) [U], �g mL−1

1 0.006 1.62 0.005 1.33 −0.002 −0.54 0.01 2.65 0.002 0.56 −0.002 −0.57 0.003 0.88 0.001 0.39 0.002 0.510 0.004 1.04

Average 0.003 0.75

Detection limit = 2.5 �g mL−1.

Table 9Comparison of extraction spectrometric and ICPAES analysis of some typical oreleach solutions.

Ore leach samples [U], �g mL−1

Br-PADAP ICPAES ± % Difference

1 2.76 2.56 +0.202 3.88 4.20 −0.323 7.70 7.60 +0.104 19.46 19.40 +0.065 51.63 50.40 +1.23

rsd 1.6% 0.58%

sd: relative standard deviation.

here X̄1 and X̄2 are the average value of uranium evaluatedrom ICPAES and Br-PADAP methods, s is the pooled variance; n1nd n2 are the number of data point taken for the two methodsespectively. The value of pooled variance ‘s’ was calculated by theollowing equation:

2 = (n1 − 1)s21 + (n2 − 1)s2

2n1 + n2 − 2

(4)

where, s21 and s2

2 are the variance of ICPAES and Br-PADAPethod, respectively. Table 7 shows the results of determination of

ranium ore leach solution using ICPAES and Br-PADAP methods.he absolute value of t was found to be 0.53 where as the tabulatedritical value of t at 95% confidence limit for degrees of freedom

= 9 is 2.262 [23]. This exceeds the calculated value of 0.53; there-ore there is no difference between the means of results obtained.imilarly, the F-test of the two methods was carried out to com-are the precision of the above two methods. The F value of thebove two methods was calculated by dividing larger variance tohe smaller variance and its value was found as 1.965. The tabulatedritical value of F at 95% confidence limit is 3.184 which means theethod proposed for extractive spectrophotometric determination

f uranium using Br-PADAP is precious, convents and acceptable.

.7. Evaluation of detection limit

The detection limit of the above method was investigated byeasuring absorbance of the blank solution several times (n = 10)ithout adding any sample aliquot. The average value of ura-ium concentration in the blank solution was 0.75 �g mL−1. The

able 7 and F-test comparison of means from two (ICPAES and Br-PADAP) methods using

single ore leach solution.

Sample no. Experimental results Squares of deviations

ICP Method Br-PADAPmethod

ICP method Br-PADAPmethod

1 50.925 51.550 0.260100 0.0132252 52.171 51.550 0.541696 0.0132253 51.394 52.850 0.001681 2.0022254 52.392 51.810 0.915849 0.1406255 52.347 50.780 0.831744 0.4290256 50.625 52.070 0.656100 0.4032257 51.229 50.520 0.042436 0.8372258 51.635 53.370 0.040000 3.7442259 50.581 51.040 0.729316 0.15602510 51.050 50.780 0.148225 0.429025

Sum 514.349 516.320 4.167147 8.1680551.435 51.630 0.462 0.908Mean Variance

6 194.20 193.90 +0.30

Number of measurement for single sample is 3 (n = 3).

detection limit of the proposed analytical method was calculatedas three times of the standard deviation of uranium concentrationin the blank solution. Thus, the detection limit of this method wasdetermined to be ≥2.5 �g mL−1 (Table 8).

3.8. Application of the developed method to real samples

The proposed method was applied successfully for the determi-nation of uranium in ore leach solutions containing a large numberof other impurities (Table 9). It was observed that the results arevery close to the reported value using ICPAES technique and themethod can be helpful for the monitoring of uranium during oreleaching in front-end of fuel cycle. The main advantages of theproposed method over ICPAES technique are its simplicity, accu-racy and higher analytical range (2.5–250 �g mL−1). However, thismethod has relatively lower tolerance limit of Th.

4. Conclusions

The proposed method provides a simple, very sensitive andlow cost spectrophotometric procedure for determination of ura-nium in ore leach solutions. The solvent extraction step employing0.1 M PC88A + 0.05 M TOPO/cyclohexane was used to recover ura-nium selectively in organic phase. Br-PADAP, CyDTA as well asbuffer were used for development of intense color for spectropho-tometric measurement of uranium. Addition of NaF, ascorbic acidbefore the extraction step reduces the interference from transitionas well as lanthanide/actinide elements. The optimum concentra-tion of ethanol was determined as 64% to increase the solubilityof Br-PADAP in the aqueous phase. The tolerance limit of Th(IV) isrelatively low as compared to other elements due to strong com-plex formation of Th(IV) with synergistic mixture during solvent

extraction step. The method could be applied for the determinationof uranium in ore leach solution in the range of 2.5–250 �g mL−1

with the precision of <2%. A comparison of developed method and

ica Act

sl

R

[

[

[[

[

[[[[[

[

S. Biswas et al. / Spectrochim

tandard ICPAES method indicate that the former method is simple,ow cost and faster than the later.

eferences

[1] Uranium and uranium compounds, Encyclopedia of Chemical Technology, 3rded., vol. 23, 1983, p. 514.

[2] J.A. Brierley, C.L. Brierley, Hydrometallurgy 59 (2001) 233–239.[3] R.G. McCready, W.D. Gould, Bioleaching of uranium, in: H.L. Ehrlich, C.L. Brierley

(Eds.), Microbial Mineral Recovery, McGraw-Hill, New York, 1990, p. 107.[4] H.M. Lizama, M.J. Fairweather, Z. Dai, T.D. Allegretto, Hydrometallurgy 69

(2003) 109–116.[5] K.L. Narayana, K.M. Swamy, K.S. Rao, J.S. Murty, Miner. Process. Extr. Metall.

Rev. 16 (1997) 239–259.[6] K.M. Swamy, L.B. Sukla, K.L. Narayana, R.N. Kar, V.V. Panchanadikar, Ultrason.

Sonochem. 2 (1995) S5–S9.[7] T. Tekin, D. Tekin, M. Bayramoglu, Ultrason. Sonochem. 8 (4) (2001) 373–377.[8] A. El-Taher, Appl. Radiat. Isot. 68 (2010) 1189–1192.[9] A. El-Taher, A. Nossair, A.H. Azzam, K-L. Kratz, A.S. Abdel-Halim, J. Environ. Prot.

Eng. 29 (2004) 19–30.

[

[[

a Part A 91 (2012) 222– 227 227

10] M. Afzal, J. Hanif, M. Saleem, I. Hanif, R. Ahmed, J. Radioanal. Nucl. Chem. 152(1991) 251–259.

11] P. Shrivastav, S.K. Menon, Y.K. Agrawal, J. Radioanal. Nucl. Chem. 250 (2001)459–464.

12] M.C. Freitas, C.S. Hipólito, J. Radioanal. Nucl. Chem. 271 (2007) 179–183.13] O. Fujino, S. Umetani, E. Uenoa, K. Shigeta, T. Matsuda, Anal. Chim. Acta 420

(2000) 65–71.14] P.A. Greene, C.L. Copper, D.E. Berv, J.D. Ramsey, G.E. Collins, Talanta 66 (2005)

961–966.15] M. Aziz, Sh G. Beheir, K. Shakir, J. Radioanal. Nucl. Chem. 172 (1993) 319–327.16] S. Ku, N. Obarski, Z. Marczenko, Anal. Sci. 8 (1992) 213–218.17] Ali Niazi, J. Braz. Chem. Soc. 17 (2006) 1020–1026.18] D.A. Johnson, T.M. Florence, Anal. Chim. Acta 53 (1971) 73–79.19] S.K. Singh, S.K. Misra, S.S. Pandit, K.J. Parikh, S.C. Tripathi, J. Radioanal. Nucl.

Chem. 280 (2009) 33–39.20] S.K. Das, C.S. Kedari, S.C. Tripathi, J. Radioanal. Nucl. Chem. 280 (2010) 675–681.

21] A. Suresh, D.K. Patre, T.G. Srinivasan, P.R. Vasudeva Rao, Spectrochim. Acta A

58 (2002) 341–347.22] R. Ko, M.R. Weiler, Anal. Chem. 34 (1962) 85–87.23] T.J. Farrant, Practical Statistics for the Analytical Scientist, A Bench Guide, The

Royal Society of Chemistry, U.K, 1997, pp. 15–16.