Indian Journal of Chemical Technology Vol. 10, September 2003, pp. 531-538

Articles

Membrane based U(VI) transport across supported liquid membrane from aqueous acidic media

S R Sawanta, J V Sonawanea, A K Yenugopalana, P K Dey", Ani! Kumara* & J N Mathurb

"PREFRE Plant, Nuclear Recycle Group, BARC, Tarapur 401 502, India

bRadiochemistry Division, BARC, Trombay, Mumbai 400 085, India

Received 23 May 2002; revised received 4 Apri/2003; accepted 28 April 2003

Carrier-facilitated transport of U(VI) from dilute acidic nitrate solutions has been examined across a flat sheet supported liquid membrane (FSSLM) and hollow fiber supported liquid membrane (HFSLM) deploying Cyanex 272 (Cy 272) as the novel carrier. Using FSSLM system, the apparent rate constant (K0 bs) increased with increasing carrier concentration and became nearly constant above 0.2 M Cy 272, thereafter decreased slightly at 0.4 M Cy 272. Accurel polypropylene thin film support coded as 2E-PP and dodecane as the membrane solvent were invariably used. Among the several reagents tested, oxalic acid (0.9 M) served as the most efficient strippant for U(VI) across Cy 272-FSSLM as well as HFSLM systems. Application of this simple method has been extended for the removal of uranium from phosphate waste, which is generated in analytical laboratory of fuel reprocessing plant. In addition, transport of uranium was accomplished in presence of plutonium, americium and fission product contaminants from aqueous acidic media. ·

Reprocessing of spent nuclear fuels produces large vol umes of medium-level radioactive liquid wastes, which are normally concentrated by distillation. It will be of interest to recover all the long-lived radio nuclides (e.g. 137Cs, 90Sr, actinides, etc.), which will result in a better management of the radioactive wastes. The feasibility of decontaminating this concentrate by application of liquid membranes has been reported 1•

With supported liquid membranes (SLMs) using flat sheet (FS) or hollow fiber (HF) configurations, separation can be achieved based on continuous and simultaneous processes of selective extraction and back-extraction occurring on both sides of macroporous polymer film/lumen contammg a suitable ligand2

.3 . Several FSSLM systems have been extensively studied for their ability to separate and concentrate metal ions of strategic importance and actinides from radioactive waste streams4

-6

. Organo­phosphorus compounds containing the phosphoryl group (P=O) have been widely used as analytical extractants. Cyanex 272 [bis(2,4,4-trimethyl-pentyl)­phosphinic acid] has been commercially available for over a decade.'·8.

Cy 272 has shown great versatility in the extraction and separation of lanthanide and actinide metals9

•10

.

*For correspondence (E-mail: dranil@bom3.vsnl.net.in; Fax: +91-02525-282 158)

The extraction of Sc(III), Th(IV), Fe(III) and Lu(lll ) with Cy 272 from sulphuric acid or hydrochloric ac id solutions has also been reported 11

'12

• Akiba et a/. 1~ investigated the carrier-mediated transport of U(V l) across a FSSLM with trioctyl phosphine oxide (TOPO) stripped into a carbonate-receiving phase as U02(C03h-4. Shukla et a/. 14 determined the influence of nitric acid concentration in the feed solution, TBP concentration in the kerosene membrane, the stripping agent and the temperature on the uranyl flux. The LM study was accomplished with Au(lll) 15

, Ag(I) 16 and Cu(II) 17 using FSSLM which shows the impregnation method of polymeric membrane as done in this study. Few experiments dealing with uranium preconcen­tration were carried out in recirculation mode using hollow fibre supported liquid membrane (HFSLM) 18

'19

In the present investigation, studies were carried out for the removal of U(VI) from nitric acid as well as from phosphate bearing wastes. The factors which influence the mass transfer performance of FSSLM such as type of carrier, properties of membrane liquid. carrier concentration, feed acidity, nature and optimum concentration of the strippant in receiving phase etc. have been evaluated in detail. Also the transport of uranium was examined in presence of plutonium, amenctum and fission product contaminants from aqueous acidic media. Application

Articles

of this simple method has been extended for the removal of uranium in presence of plutonium from phosphate waste, which is generated in analytical laboratory of fuel reprocessing plant.

Experimental Procedure Cy 272 supplied by Cytec Industries, Inc. was used

1 ' ithout further purification. The determination of Cy 272 purity (87 .3%) and impurity characterization I ave been described earlier20

.

All the chemicals were of analytical reagent grade. 2'·'u tracer was purified as described elsewhere21

•

Radiochemical purity of the tracer was ascertained by alpha spectrometry . Accurel polypropylene thin flat sheet type hydrophobic microporous polymeric membrar.es, (Enka, 2E PP, FRG) were used throughout this study. The membrane films were soaked in Cy 272/dodecane soiutions for about 24 h.

Permeation measurements with FSSLM-dodecane solutions containing different concentrations of Cy 272 were used as carrier in FSSLM after equilibrating them wi th HN03 solutions of the required molarity. Single-stage FSSLM measurements were carried out with a two compartment permeation cell (2.8 cm3

each) in which a source phase aqueous solution was separated from the aqueous receivi ng phase by a porous support impregnated with Cy 272 having an effective membrane area of 1.13 cm2

. The source and receiving solutions were mechanically stirred at room temperature to minimise concentrahon polarization conditions at the membrane interfaces and in the bulk of the solutions. The variation of U concentration with time in the feed or stripping solutions were done by periodically assaying 233U tracer using alpha sci ntillation counter. The apparent rate constant, Kobs

(s-1) is defined as:

... (1)

where [ UJr.1 and [ UJr.o denote the concentration of uranium at time (t) and the initial concentration , respectively and t is the time elapsed in seconds. HFSLM was operated in recirculating mode. The impregnation of module was done by passing organic extractant solution at low flow rate through lumen side. The organic extractant was passed for l h in order to ensure uniform and complete impregnation of the hollow fiber membrane. The feed and strip solutions were circulated through the module by means of calibrated peristaltic pumps. The permeation of uranium through the HFSLM was followed by

532

Indian J. Chem. Technol.. September 2003

periodically sampling and assaying the feed and/or strip solution. The K obs was calculated using Eq. ( I ).

which assumes that there is insignificant change in concentration of 233 U in one pass of solution in recirculation mode. The overall membrane area (A) was calculated.from the equation:

A=2nrNL .. . (2)

where r is the internal radius of the hollow fiber, N is the number of fibers and L i~ the length. The efficiency of the strippants in FSSLM experiments was determined by taking 2.8 mL of different strippant solutions such as acetic ac id, sodi um carbonate, thiourea, EDT A and oxalic ac id between 0.3 to 1.0 M of each in the receiving compartment at the beginning of the experiment.

Liquid-liquid distribution ratio measurements-equal volumes (1 mL) of 233 U tracer in nitric acid of desired molarity and respective Cy 272 dissolved in suitabl e diluent were pipetted into a 15 mL glass stoppered tube and mechanically stirred for about ha lf an hour at room temperature (25°C). This time was sufficient to attain the equilibrium. After settling for about 30 min . aliquots from both the phases were withdrawn for assay. The distribution ratio (DM) of uranium is defined as the ratio of uranium concentration in the organic phase to that in the aqueous phase. With the knowledge of the value of DM, aqueous phase volume V w and the organic phase volume V0 , percentage extraction (%£) was calculated as,

... (3)

For the backextraction studies, aliquots from the loaded organic phase were drawn and subsequentl y backextracted for about 10 min with the same volume of the strippant.

Results and Discussion

Liquid-liquid extraction For the effective separation of metal ions using

carrier-facilitated transport, it is essential to know the extraction behaviour of the extractant to be used as a carrier. At 0.01, 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0. 7.0, 8.0 and 10.0 M nitric acid, the D values are 135.1' 1 0.3, 1.1' 0.5, 0.6, 0.8, 1.1 ' 1.3, 1.4, 1.5, 1.6 and 0.8 respectively under the experimental conditions (Volume ratio (org/aq): I , extractant: 0.01 M Cy 272, diluent:dodecane, aqueous phase:

Sawant et al.: Membrane based U(VI) transport across supported liquid membrane Articles

Table !-Apparent rate constants (Kobs) of U(Vl) across FSSLM using Cy 272 as a functi on of nitric acid concentration and carrier concentration

In itial feed concentration Strippant

Varying HN03 concentration,

HN03 (M)

0.01 0.1 0.5 1.0 2.0 3.0 4.0 5.0 6.0 7.0

(keeping 0.2 M Cy 272) Kobsx l0-5

, % Uranium s- 1 permeation

12.6 6.7 7.2 6.9 8.3 13.0 14.1 9.1 8.6 7.7

after 6 h 98 .0 97.2 96.5 95.5 94.5 94.2 89.3 85.7 79.7 74.5

0.5 mg dm-3 at varying HN03 concentration). The contaminants, which generally accompany U such as "

7c '06R d '44C 1· 'bi d · s, u an e, were neg 1g1 y extracte under the present experimental conditions. The equilibria for the extraction of U(VI) at low and high acidities22 can be written as:

... (4)

at low acidities, and

U02<al2+ + 2N03 -(a) + 2(H2A2)(ol <=> U02 (N03h.2(H2 A2)(ol .. . (5)

at higher acidities.

Effect of nitric acid concentration on uranium transport

The transport of U(VI) as a function of HN03 concentration (0.0 1 to 7.0 M) through the FSSLM was studied. Fig. 1 gives the plot of ln(C/C0 ) versus time for the permeation of U(VI) at different nitric acid concentrations. The results are reported in Table 1 as K obs· The transport of U(VI) from the feed to the strip solution, though decreased with increasing acidity , but was higher between 0.01 to 4.0 M HN03 and lower between 5.0 to 7.0 M HN03. Similar trend was also observed in the liquid-liquid extraction studies of the above system. It can be seen that by lowering the acidity from 6.0 M HN03 to pH 2, the permeation increased from around 80 to - 98% while using 0.2 M Cy 272/dodecane. The maximum U recovery (> 95 %) after 5 h and maximum K obs

: 5.0 mg dm-3U : 0.9 M oxalic acid in 0.3 M HN03

Varying carrier concentration (keeping

Cone. of Cy 272

(M) 0.01

O.G25 0.05 0. 1 0.2 0.4

- 3.5

-3

-2.5 ~

0 -2 (.) ...... (.) :£-1.5

-1

-0.5

0 0

4 .0M HN03) Kobsx i0-5

,

s-1

5.1 6.9 8.5 10.9 14.0 10.4

.O.OIMHN03

•tMHN03

.2M HNOJ

03MHN03

D4MHH03

eSMHN03

A6MHH03

07MHNOJ

D t g • • 4

• • •

100

% Uranium permeation

after 6 h 61.8 82.4 85.6 86.7 89.3 79.4

D

c ' § • 4 • • m

200

Time, min

D

i D ~

• lJ. • 0

... ... t • •

300 400

Fig. !- Influence of the nitri c acid concentration on penneabili 1y of U(VI) versus time U(VI): 5 mg/L. Carrier concentration: 0.2 M Cy 272/dodecane.

32.0x l0-5 s-' at 4.0 M HN03 and 28 .5x l0-5 s- ' at 0.0 I M HN03 after about 1 h of the transport process were recorded. For further studies, 4.0 M HN03 was selected as the feed condition, since the nitric acid concentration in the fuel reprocessing waste ranges between 2.0 to 4 .0 M .

Effect of cyanex 272 concentration on uranium transport

As seen in Table 1, a maximum value of Knb, 14.0x 10-5 s-' was obtained with the membrane prepared by impregnating wi th 0.2 M Cy 272/dodecane. Fig. 2 gives the plot of ln(C/C0 ) versus time for the permeation of U(VI) at different carrier concentration and it shows the dependence of U(V l)

533

Articles

-3.5

-3

-2.5

J -2 d' £ -1.5

-1

-o.s

0

0

•o.OIMCY2n ·

• 0.025 M CY 2n

~0.05MCY2n

AO.IMCYm

00.2 MCY272

•o.4MCY 212

0

0

• 1 • • •

100

0

0

tl

t I •

• 200

Time, min

0

A

.A.

• •

300

0

• • .A.

• •

400

Fig. 2-Influence of the carrier concentration on permeabi lity of U(YI) versus time. U(VI): 5 mg/L. Feed acidity : 4 M HN03 , Stripping solution: 0.9 M oxalic acid in 0.3M HN03.

permeability on the concentration of Cy 272 in the membrane phase. As a typical characteristics, a supported liquid membrane with no carrier present results in no transport of feed phase cations. It is obvious that the transport of U(VI) in such a system should be a function of both carrier concentration in the LM phase and diffusion coefficient, since the transfer of U(VI)-Cy 272 complex through the membrane is considered to be diffusive in nature. It is reported 19 that the extraction of U(VI) from nitric acid solution increases gradually with increasing concentration of Cy 272 in dodecane. However, a slight decrease in the permeability is noticed with increase in Cy 272 concentration in the liquid membrane beyond 0.2 ~il. This behaviour probably occurs because of the viscosity which is higher at 0.4 M Cy 272 as compared to that at the lower concentrations of Cy 272 in the membrane phase. Thus, the diffusion coefficient in the membrane decreases with an increase in the viscosity of the diluent, which probably could be explained by the S k E

. . . 23 to es- mstem equation .

D = KTj 6nrrJ ... (6)

where K, T, r and fJ denote the Boltzmann constant, the absolute temperature, the molecular radius of the metal complex and the viscosity of the organic phase, respectively. The trend can also be seen in Fig. 2, since the transport rate increases up to 0.2 M Cy 272 a!ld then decreases at 0.4 M Cy 272. Babcock et at?4

attributed the main cause of this behaviour to be due to the concentration gradient of the metal complex, the viscosity of the organic phase and hindered

534

Indian J. Chern. Techno!.. September 2003

Table 2-Effect of strippants on pertraction of U(V I) across FSSLM

Ini tial feed concentration Feed acidity Carrier concentration Time elapsed

Strippant used

H2C204* (0.3 M)

H2C204*(0.5 M)

H2C204*(0.9 M)

Thiourea( 1.0 M)

(NH4hC03 (0.5 M)

EDTA (0.5 M)

Na2C03 (0.5 M)

CH3COOH (I M)

: 5.0 mg dm-3 U :4 M HN03 : 0.2 M Cy 272/dodecane :6 h

Apparent rate o/o Recovery constant, of U (VI).

Kobsx i0-5 s-1 after 6 h

7.6 45.4

8.1 78.9

14. 1 89.3

0.9 5.2

3.7 27 .1

0.9 7.9

1.6 16.7

1.0 6.7

* Oxalic acid solutions prepared in 0.3 M HN03

diffusion of the metal complex and the tortuosity of the pores of the membrane.

Effect of strippant on permeation behaviour of uranium

The permeation of UOt+ ion across the Cy 272/dodecane membrane is mainly dependent upon the nature and type of the strippant used on the receiving side of the membrane. Several aqueous complexing agents such as oxalic acid, sodium carbonate, ammonium carbonate, EDT A, thiourea and acetic acid were used for this purpose. Of these, 0.9 M oxalic acid in 0.3 M HN03 proved to be the most efficient (Table 2), with this the maximum Koh'

14.lxlo-5 s- ' was obtained (after 6 h). Fig. 3 gives the plot of ln(C/C0 ) versus time for the permeation of U(VI) using different strippants. Thiourea, acetic acid and EDT A proved to be poor strippants as the urani um recovery never exceeded 10%. Similarly, sodi um carbonate and ammonium carbonate have resulted in 17% and 27% recovery of uranium in the stripping phase.

Influence of diluents on permeability of U(Vl) Both the permeability and selectivity involved in

the transport of permeants by organic membrane carriers are greatly influenced by the nature of the organic solvent. Izatt et a/.25 suggested that membrane stability versus rapid transport is the major choice to be made in choosing a membrane solvent. FSSLM performance is primarily dependen t on the intrinsic membrane solvent, and properties such as viscosity,

Sawant et al.: Membrane based U(Vl) transport across supported liquid membrane Articles

-3.5

-3 • 0.3M Oulc ecld • o.SM o .. 1c ldd .. 4 D.9M Oxalc edd

-2.5 • 1M Thioure• .. AO.SM (NH4)2C03 .. • J -2 • ()' .. •

£ -1 .5 ' • .. -1

.. • • • • • • II. -0.5 t II.

• ! 0

0 100 200 300 400

Time.mln

Fig. 3- Effect of stripping reagents on permeability of U(Vl) versus time U(Vl) : 5 mg/L. Carrier concentration : 0.2 M Cy 272 /dodecane, Feed acidity : 4 M HN03 , Time elapsed: 6 h.

volatility, surface tension, water solubility, etc. Shukla et al.26 concluded that in determining the efficiency of the membrane medium, polarity of the solvent is the most decisive factor. Kumar et al.18 have reported that aliphatic diluents are promising in HFSLM studies. To assess the influence of several commonly available aliphatic and aromatic diluents on the permeation of U(VI) , its transport with Cy 272 in various diluents was studied. After 6 h of permeation the Kobsx l0-5 are 13.1, 2.2, 13 .8, 10.5, 10.7, 11.6, 11.7 and 14.1 and the% recovery of U(VI) are 31.3 , 14.9, 98.0, 75 .0, 85 .8, 80.9, 76.6 and 89.3 for diluents benzene, carbon tetrachloride, a -dichlorobenzene, xylene, solvesso-100, Shell sol D-70 (SSD-70) , Shell soi-2046(SS-2046) and dodecane respectively. The experimental conditions for all the systems were kept same. Fig. 4 gives the plot of ln(C/Co) versus time for the permeation of U(Vf) using different diluents .

After 6 h of permeation carbon tetrachloride gave poor permeability as compared to diluent like dodecane, and the diluents S.S .D.-70, solvesso-100 and S.S.-2046 show better results than benzene (Fig 4). However, after 2, 3 and 4 h the permeation while using benzene diluent was found to be highest. The dielectric constant seems to have no correlation with the permeability of U(VI) . Although recovery of U(VI) is highest in o-dichloro benzene, it was not preferred for use since aromatic diluents and/or chloro substituted diluents are not preferred while working with highly radioactive solutions. Most of the studies were carried out with dodecane which is the next best diluent.

-3.5

-3

-2.5

;J -2 (}' £ -1 .5

- 1

-0.5

0 0

• CCL4

a s.s.o.-70 ASofvon10-tOO 6X-0-e S.S. 2048 0 0--OOodocono

i ' ' •

' ..

• • 100

8 0 i •

0 0 il 0 • • • .. a • . A

! .. ..

• • • • 200 300 400

Time, min

Fig. 4--Effect of different diluents on permeabilit y o f U( Vl) with Cy 272 versus time. U(Vl): 5 mg!L. Feed acidity: 4 M HNO_, . Carrier concentration: 0.2 M Cy 272/dodecane, Stripping so lution: 0.9 M oxalic acid in 0 .3 M HN03.

Stability of the support and leachability of the carrier from FSSLM

Under the optimum conditions, the stability of the polymeric solid thin film support, Accurel 2E-PP, was tested for uranium permeation. Each time the feed and the product solutions were replaced with fresh solution. At the end of the experiments even after 24 h of continuous use, this carrier did not leak out of the membrane phase. Danesi and Rickert27 have repo rted that the probable causes of FSSLM instability and progressive wettability of the support pores are induced by a lowering of the interfacial tensi on. The chemical resistance of polypropylene membrane against dodecane was periodically tested over a peri od of 15 days dipped in 0 .2 M carrier solution . At the end of each run , the polypropylene film support was washed and stored in dodecane.

On the first day after the time elapse of I. 3 and 6 h, Kobsx l0-5 s_t values were 6.8 , 7.1 , 6 .7 respecti ve ly and recovery of U after 6 h being 95.3%. On the sixth day after the elapse of 125, 14 7 and 150 h. Kobsx i0-5 s-1 values were 9.3, 8.2 and 8.4 respecti ve ly and recovery of U after 6 h being 95.2%. On the ] tenth day after the elapse of 241 , 243 and 246 h Kobsx l0-5 s- 1 values were 9.4, 8.3 and 8.5 respecti ve ly and recovery of U after 6 h being 91 .1 %. On the fifteenth day after elapse of 361, 363 and 366 h. Kobsx l0-5 s-1 values were 7.6, 7.2 and 6.1 respec ti ve ly and recovery of U after 6 h being 89.27o . The polypropylene membrane supports are seen to possess adequate stability in Cy 272/dodecane even after long use and also they can be regenerated for reuse.

535

Articles Indian J. Chern. Techno!.. September 2003

Table 3-Removal of U(VI) from si mulated titrimetric waste using FSSLM

:6 h Permeation Time Composition of waste : U: 1-5 g dm-3 in presence of

sulphate and phosphate Strippant : 0.9 M oxalic acid in 0.3 M HN03

Expt. No. Source phase u Pu

(g dm- 3 ) (mg dm- 3)

I 2.0

2 2.0 74

3 2.0 43

Selectivity and permeation of fission products across FSSLM

The selecti vi ty of FSSLM for U(VI) was determined towards the fission product contaminants. S(U, F.P.), expressed by the ratio of the permeability as,

S(U, F.P.) = P u(v t/Pwr > = In( Cu(VI). /Cu(VI).o)/ln( CF.P .. /CF.P. o) ... (7)

The process effluent spiked with U(VI), Pu(IV) and Am(l ll ) and fission products 106Ru, 137Cs, 125Sb and 144Ce in 3M HN03 were tested for permeation of U(V I) by using Cy 272. The activity" in source phase are l.Ob, 5.0\ 5.2d, 57.2, 2513.2, 23.3, 46.0, and in the receiving phase are 0 .9b, 0. 1 C. 0 .8d, 1.9, 93.4, 1.2, 2.6 and percentage permeation after 6 h are 94.2, 1.8, 1.5, 4. 1, 3.9, 5.2, 5 .7 for actinides such as 233 U, Pu(IV) and Am(III) and fission products 106Ru, 137Cs, 125Sb, 144Ce respectively. Here, the superscript alphabets represent a: activity of fission products (estimated by multichannel analyser using a High purity Germanium detector), b: concentration in g dm-3

, c: concentration in mg dm-3 and d: x 10-2 mg dm-3

.

It is evident from the above data that problematic f.. . d . to6R t37C 12sSb d tss ton pro uct contammants u, s, an 144Ce were poorly permeated (< 10%) whereas more than 94% of U(VI) could be recovered across single stage FSSLM from 3 M HN03 employing 0.2 M Cy 272 as the carrier and 0.9 M oxalic acid as the strippant.

Recovery of uranium from simulated titrimetric waste

A FSSLM method for the removal of uranium from phosphate bearing laboratory waste generated by Davies and Gray titrimetric method was standardized. Such a waste generally contains 1-5 g dm-3 of U, 1-5

536

Receiving phase % Recovery of U, U Pu after 6 h

(g dm-3 ) (mg dm-3 )

1.72 86

1.75

1.70

7.0

3.9

88

85

mg dm-3 of Pu in the presence of macro concentrations of the anions so/ - and Po/ -. Uptake of U(VI) from phosphate bearing analy tical waste was relatively poor while using Cy 272/dodecane, but it cou ld be substantially improved by addition of 0.5 mL of 10M HN03 per 10 mL of the waste. Loaded U(V I) could be readily stripped with 0.9 M oxalic ac id in 0.3 M HN03. The recovery of U(Vl) was - 86% (Table 3).

Uranium transport through HFSLM After obtaining data on FSSLM behav iour, whi ch is

rather a prerequisite for carryingout the work with hollow fiber configuration, further experiments were performed using the HFSLM module. HFSLM mode was operated for the transport of U(V I) from aqueous feed nitrate solution using Cy 272 as a carrier.

The characteristics of the HFSLM mod ul e al1(i hollow fiber membrane used in present study are given as: internal surface area: 134 em~; fiber 1.0.:2.5 mm; fiber 0 .0 .:2 .8 mm ; fiber wall thickness : 150 J.lm ; fiber length : 17 em; porosi ty: 70%; number of fibers: 10; pore size: 0.1 J.lm and material: polypropylene.

The optimum hydrodynamic conditions for the module used herein were identified by studying the uranium permeability as a function of flow rate of the feed solution (lumense inside). The experimen ts were performed at two-flow rates i.e. 50 and 150 mL/min. The data presented in Table 4 indicate that K"h' increased from 7.7x l0-4 to 18.4x !0-4 s- ' by increasing flow rate from 50 to 150 mL/min and permeation from 60 to 80%. More than 80% of uranium from nitric acid solution could be transported th rough 0 .2 M Cy 272 into 0.9 M oxalic acid (in 0.3 M HNO, ) strippant in about 6 h. Balance amount of uranium could only be transported after usi ng fresh strippant.

Sawant et al.: Membrane based U(VI) transport across supported liquid membrane Articles

Table 4--Transport of U(VI) from nitric acid medium using HFSLM

Initi al feed concentration

Source phase acidity

Carrier

Receiving phase

Temperature

Feed volume

Stripping phase volume

Time, h

2

3

4

5

6

: 5.0 mg dm-3 U(VI)

:4 M HN03

: 0.2 M Cy 272 in dodecane

: 0.9 M oxalic acid in 0.3 M HN03

: 25°C

: 3 L : 200 mL

Apparent rate constant Kobsx l0-4, s- 1

Flow rate, mUmin 50 150

7.7 18.4

6.8 16.1

6.3 14.1

5.8 10.4

5.2 9.3

4.4 7.7

Life time and radUztion stability of the polypropylene fiber

A long time experiment was designed to test the lifetime of the fiber. Once impregnated, the HFSLM module was used for 24 h. At the end of this cycle the fiber was washed with dodecane, dried and reimpregnated with fresh liquid membrane solution. After the reimpregnation, the system recovered the initial permeability level and a stable operation was possible for 10 days. Similar performance of the fibers has been reported earlier15

• The radiation stability of the polypropylene fiber has already been studied and it was observed that no deterioration of the fiber took place at - 2 Mrads dose for almost 200 h 28 .

Conclusions The hexavalent uranium cation could be

transported against its concentration gradient from 4 M HN03 solutions using 0.2 M Cyanex 272/dodecane as the carrier and 0.9 M oxalic acid in 0.3 M HN03 as a strippant. Application of this method has been successfully extended to the recovery of U(VI) from phosphate bearing waste generated in laboratory. - 86% of U(VI) removal could be obtained from laboratory waste in presence of fission product contaminants. Further, the batch mode, hollow fiber supported liquid membrane technique was operated. More than 80% of U(VI) was recovered from 0.2 M Cy 272 from nitric acid medium in a single run. HFSLM will be of great

importance in terms of finding out the applicability in continuous mode.

Acknowledgements The authors wish to thank Shri. N. K. Bansal.

Associate Director (0), Nuclear Recycle Group and Shri. R. D. Changrani, Chief Superintendent. PREFRE plant Tarapur for their keen interest in thi s work.

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(1989) 58.

2 Noble R D & Way J D in Liquid membranes: Theorv and Applications (American Chemical Society, Washington. DC), 1, 1987, Ill.

3 Izatt R M, Live( G C, Bruening R L, Bradshaw J S. Lamb J D & Christensen J, J Pure Appl Chem, 58 ( 1986) 1453.

4 Danesi P R, Chiarizia R & Rickert R G, J Phys Chem , 87 (1983) 4708.

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6 (a) Dozol J F, Casas J & Sastre A M, Sep Sci Techno/ . 28 ( 1993) 2007. (b) Shukla J P, Kumar A, Singh R K & Iyer R H, Separation of Radiotoxic Actinides from Reprocessing Waste with Liquid Membranes, American Chemical Society Symposium Series titled Chemical Separation with Liquid Membranes edited by Bartsch R A & Way J D, Vol. No. 642. Chapter 27 (American Chemical Society, Washington, DC).

7 Cytec Industries, Inc, Cyanex 272, Cyanex 302, Cyanex 30 I. Technical Brochures (West Paterson, New Jersey).

8 Rickelton W A & Boyle R I, Sep Sci Techno/, 23 ( 1988) 1227.

9 Li K & Freiser H, Solvent Extr Ion Exch, 4 ( 1986) 739.

10 Kamatsu Y & Freiser H, Anal Chim Acta, 227 (1989) 397.

11 Wang C & Li D Q, Solvent Extr !on Exch, 3 (1994) 615.

12 Li D Q, MaG X, Zhang X F, Zhano X L, Xue L Z & Zhi Z H, Proc International Solvent Extr Conf (I SEC 93), I ( 1993) 384.

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