Sudan Academv of Science (sAs) Atomic Energy Researches Coordination Council Extraction andPurification of Yellow Cake A Dissertation Submitted in Partial Fulfillment of the Requirement for DiplomaDegree in NuclearScience (Chemistry) By Elshafeea Hassan Yousif (B.Sc.) Supervisor: Dr. Adam Khatir Sam J January 2006 -' Sudan Academy of Science (SAS) Atomic Energy Researches Coordination Council Extraction and Purification of Yellow Cake A Dissertation Submitted in Partial Fulfillment of the Requirement for Diploma Degree in Nuclear Science (Chemistry) By Elshafeea Hassan Yousif (B.Sc.) Supervisor: Dr. Adam Khatir Sam January 2006 I
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Sudan Academv of Science(sAs)
Atomic Energy ResearchesCoordination Council
Extraction and Purification ofYellow Cake
A Dissertation Submitted in Partial Fulfillment of theRequirement for Diploma Degree in Nuclear Science
(Chemistry)
ByElshafeea Hassan Yousif
(B.Sc.)
Supervisor:Dr. Adam Khatir Sam
J
January 2006
-'
Sudan Academy of Science(SAS)
Atomic Energy ResearchesCoordination Council
Extraction and Purification ofYellow Cake
A Dissertation Submitted in Partial Fulfillment of theRequirement for Diploma Degree in Nuclear Science
(Chemistry)
ByElshafeea Hassan Yousif
(B.Sc.)
Supervisor:Dr. Adam Khatir Sam
January 2006
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ACKNOWLEDGMENT
I would l ike to thank honorable supervisor D.Adarn Khatir Sanr fcrr his
contitiuous support and guidance, support. and valuable instructions from
which I have benefi ted nruch in executing this rvork.
And also I would l ike to thank every one who aided me in this rvork.
Elshafeea Hassan Yousif(High Diplorna Student)
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••••~III-.
ACKNO\VLEDGMENT
I would like to thank honorable sllpervisor D.Adam Khatir Sam for his
continuous support and guidance, support and valuable instructions from
which I have benefited much in executing this work.
And also I would like to thank everyone who aided me in this work.
Elshafeea Hassan Yousif(High Diploma Student)
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ABSTRACT
' l ' l t is disscrtat ion has rcvicrved curre nt studies on productiorr and
puri l icat ion ol 'yel lorv cake l ionr uranium ores by both aci<J ancl alkal ine
leaclr ing processcs. l t cotnprises three chapters, the f i rst one r jeal wit |
uranium minerals, uraniunr deposits, geology of uranium and uranium
isott lpes. ' l 'hc
secottd clrapter covers nrining and mil l ing methods,
uraniurn leaclt i r tg chernistry, precipitat ion, and puri f icat ion of uraniunr
cotlccntrate by solvent extractiotr and possible impurities that contmonlyt
interl'ered rvith yellorv cake. "t'he last chapter presented ongoing literature
review.
{II
~-.,
•••••••••••••••
~: ~
I
ABSTRACT
This dissertation has reviewed current studies on production and
purification of yellow cake from llranium ores by both acid and alkaline
leaching processes. It comprises three chapters, the first one deal with
uranium minerals, uranium deposits, geology of uranium and uranium
isotopes. The second chapter covers mining and milling methods,
uranium leaching chemistry, precipitation, and purification of uranium
concentrate by solvent extraction and possible impurities that commonly,
interfered with yellow cake. The last chapter presented ongoing literature
1 I" r-e 132 j. , t219 Rn" 'II,~fl nrJls]21S Po 39 s .••.
Z 130 211 Pb It· 1 .:.. t·~.H") m 215 At 'f"
·L22 rTl;~~Bj~_ °2\ ::: -.I~-r,Boxed values 126
1 0.5 s Lead-207 is thefor half·llfe are '1.8 rn 207 Pb' I stable end roductfor mUltiple 124 I .L..J_..L _L -_.r..-__ J
d&f.i\y paths 8081 82 8384 85 86 87 88 8990 9192 9394HgTI Pb Si Po At AnFr Ra Ac Th Pa UNpPu
~2:.J5U Se~s
O 232Th Series
0:>38. U Senes
O "'1/.... N S .penes
The Uranium·235Decay Series
•••••..••••IIIIII•..•••••
CHAPTER TWO
NUCLEAR FUEL CYCLE
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•,•••••..11
••III
III
••••.'•
CHAPTER TWO
NUCLEAR FUEL CYCLE
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t
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NUCLEAR FUBL CYCLB
2.1 Uraniurn nr i r r ing:
Mining is f l rst step in truclcar fLrel cycle and i t carr ied out depending on
the orc depth and environrnental condit ions, through either open pit or
underground rnining. - l 'he Fig (2.1) shorvs the diagram of General ized
process for uraniunr extraction.
Open pit minirrg operat iorts, can be appl ied to sedimentary and vein type
ore bodies. And i t used for near surlace deposits. Open pit mining is
preferred to under.ground operation because a high productivity beller ore
recovery, easier delvatering and safer mining can have greater
environmental impact than underground rnining. Underground mining
used lbr depths from 50-200 m or more and the selected method and
loading operation depend on the type of the ore. Safety is very important
from radiation hazarrj come lrom direct radiation. dust and radon2.
2.2 Uraniur t rn t i l l ing:
The second step of nuclear fuel cycle is rni l l ing. This step involves
crushing and grinding operation to produce a sized or suitable for aciql or
alkaline leaching.
2.3 Uranium Leaching:
Leaching is an important step in the processing of uranium ore. The
leaching process controls the following2:
a) The proportion of uranium solubilized from the ore
b) The quantities of reagent, which are major operating cost, required to
maintain suitable leaching condit ion.
c) The concentrat ion of impuri t ies in leach solut ion.
d) The grinding requirenrents.
12
NUCLEAR FUEL CYCLE
2.2 Uranium milling:
The second step of nuclear fuel cycle is milling. This step involves
crushing and grinding operation to produce a sized or suitable for aci9 or
alkaline leaching.
2.3 Uranium Leaching:
Leaching is an important step in the processing of uranium ore. The
leaching process controls the following2:
a) The proportion of uranium solubilized from the ore
b) The quantities of reagent, which are major operating cost, required to
maintain suitable leaching condition.
c) The concentration of impurities in leach solution.
d) The grinding requirements.
2.1 Uranium mining:
Mining is first step in nuclear fuel cycle and it carried out depending on
the ore depth and environmental conditions, through either open pit or
underground mining. The Fig (2.1) shows the diagram of Generalized
process for uranium extraction.
Open pit mining operations, can be applied to sedimentary and vein type
ore bodies. And it used for near surface deposits. Open pit mining is
preferred to under ground operation because a high productivity beller ore,recovery, easier dewatering and safer mining can have greater
environmental impact than underground mining. Underground mmmg
used for depths from 50-200 m or more and the selected method and
loading operation depend on the type of the ore. Safety is very important
from radiation hazard come from direct radiation, dust and radon2•
111111JI-
•••••••••t.
••••IIIIII•••L _
12
lIIItIIilt
I
*
IIilI
I
lfrttIIt
Uraniurn ores are treated by either acid or alkal ine reagents t 'u. A lot of
f'actors tnust be considerccl to select acitl or alkaline reagent such as
carbotratc contertt to ore, el ' f ic iency of uranium extract ion rvater usage,
energy cottsutnption, prclduct qual i ty requirenrents and errvironrnental
considerat ion. Although acid leach is used in majori ty of uraniunr nr i l ls,
alkal irre lcaching has nurrrber of funclanrental advantages these a.e t .
a) ' l ' l te
solut ion is r t tore specif ic for uraniunr minerals, leaving most of
thc gangue unattacked.
b) Uranium cah be directly precipitated lrom leach liquor.
, c) ' i lre carbonate solution can be easily regenerated,
'I 'hcse characteristics also lead to a number of disadvantages that
include the fol lowing:
a. Fine grinding is required to expose the uraniunr minerals.
b. Some gangue minerals (such as calciurn sulphate and pyrite) can
react with alkaline reagent resulting in high consumption.
c. ' l 'he more relractory uraniunr minerals are not dissolved under
alkal ine condit ions. rAfter selection of reagent, there are five-leaching systems2:
l. Agitation leaching (acid and alkaline)
2. Pressure leaching (acid and alkaline)
3. Strong acid pugging and curing (acid)
4. Heap leaching (acid)
5. lnsitu leaching (nrainly alkal ine)
The choice of technique depends on the above lactors.
2.3,1 Acid leach cl ternistry ' of urart iurn'fhere are two valency states in rvhich uranium occurs naturally,
hexavalent forrn the oxide of rvhich is UOr. and tetravalent from.
the
tl-re
13
IIIII
•••--
I.-..
Uranium ores are treated by either acid or alkaline reagents 2,6. A lot of
factors must be considered to select acid or alkaline reagent such as
carbonate content to ore, efficiency of uranium extraction \vater usage,
energy consumption, product quality requirements and environmental
consideration. Although acid leach is used in majority of uranium mills,
alkaline leaching has number of fundamental advantages these are 2:
a) The solution is more specific for uranium minerals, leaving most of
the gangue unattacked.
b) Uranium cah be directly precipitated from leach liquor.
c) The carbonate solution can be easily regenerated,
These characteristics also lead to a number of disadvantages that
include the following:
a. Fine grinding is required to expose the uranium minerals.
b. Some gangue minerals (such as calcium sulphate and pyrite) can
react with alkaline reagent resulting in high consumption.
c. The more refractory uranium minerals are not dissolved under
alkaline conditions.
After selection of reagent, there are five-leaching systems2:
1. Agitation leaching (acid and alkaline)
2. Pressure leaching (acid and alkaline)
3. Strong acid pugging and curing (acid)
4. Heap leaching (acid)
5. Insitu leaching (mainly alkaline)
The choice of technique depends on the above factors.
2.3.1 Acid leach chemistry of uranium
There are two valency states in which urat1lum occurs naturally, the
hexavalent form the oxide of which is U03, and tetravalent from, the
13
. . ' ,
;
ttttItttt+
L
tI
ttttttt
L .--,nr
oxide ol ' ,uvhiclr is Uoz. rn i lexavalent fornr uraniurn goes cl i rect ly i ' toso lu t ion:
-+ UOz' . -+ l lzo ( l )
after oxidat ion to l lexavalent as shorvn.
UO, + 211'' l 'hc tctravalent goes into solutiorr
UO2 + UOrtt + 2e' (2)
This oxidat ion ca4 be achievecl by ferr ic ion in the leach solut ion as sivenby this equation
UO, + 2Fer* -r Uor* + 2Fe2n (3)
To maintain the dissolution of Uoz the Fer* must be renewed bysubsequent oxidaiion of Fe2* formed in eq.(3). tf manganese dioxide isused as the oxidant, the fol lowing react ions take place.
2Fe2'+ Mnoz + 4H* -) 2Fe3, + Mn2' + 2]lzo
2Fe2r +l/3clor + 2Fl '-+ Fer* + l/3cl-+ Huo
2Fe2* +HzSos + zH* -+ 2Fel* + HzSoa+ Hzo
(4)
(s){.
(6)The consumption of acid required to achieve the equivalent oxidation offerrous is reduced by s0%. tf sodium chlorate or caro,s acid are usedinstead of pyrolusite in the above eq.(5) (6).
By using sulphuric acid in presence of an oxiclizing agent which providesleach oxidation reduction potentials of 400-500 mV relative to saturatedcalonlcl electrode, being present in hexavalance form as uranyl ion thisreact ion occurs:
Uort' + 2soq2- -+ LJo2(so4)2-
UO2 (SO4)r ' -+ SO. t - -+ UO2(SO4)34-
The uranyl sulphate anion cotnplexes are species, rvhich are extracted bysolvent. Unfortunately the oxidizing sulphuric acid leach, rvhich is o{ten
(7)
(8)
l 4
oxide of which is U02. In Hexavalent form uranium goes directly into
solution:
The tetravalent goes into solution after oxidation to Hexavalent as shown.
U02~ UO/+ + 2e- (2)
This oxidation car} be achieved by ferric ion in the leach solution as given
by this equation
U02+ 2FeJ +~ UO/ + 2Fe2+ (3)
To maintain the dissolution of U02 the Fe3+ must be renewed by
subsequent oxidation of Fe2+ formed in eq.(3). If manganese dioxide is
used as the oxidant, the following reactions take place.
2Fe2++ Mn02 + 4H+ ~ 2FeJ++ Mn2
+ + 2H20 (4)
2Fe2++ 1/3CIOJ + 2H+ ~ Fe3++ 1/3Cr + H20 (5)
+2Fe
2+ +H2SOs + 2H+ ~ 2Fe3
+ + H2S04+ H20 (6)
The consumption of acid required to achieve the equivalent oxidation of
ferrous is reduced by 500/0. If sodium chlorate or caro's acid are used
instead ofpyrolusite in the above eq.(5) (6).
By using sulphuric acid in presence of an oxidizing agent which provides
leach oxidation reduction potentials of 400-500 mY relative to saturated
calomel electrode, being present in hexavalance form as uranyl ion this
reaction occurs:
UO/f
+ 2S0/- ~ U02(S04)2- (7)
U02 (S04)/-+ S04 2- ~ U02(S04)/- (8)
The uranyl sulphate anion complexes are species, which are extracted by
solvent. Unfortunately the oxidizing sulphuric acid leach, which is often
14
In addition sulphuric acid dissociates in water as follow:
IlttIItilil
1
tilililIItIttilI
carr ied out at tentperature of 40-80 oC is aggressive and non-select ive
result ing in ntatry other species besides uranium being leachedr. l -hese
prcscnt problcrns in uraniunr solvent extract ion. Sorne of the rnost
important species involved arer:
Soluble si l ica
I ungsten
Antimony
Arsenic
Molybdenurn
Vanadium'l' itaniurn
Zirconiunr
I'hosphate
si(oFr)4 sio2
(Woo)t '
( sbo4 ) r-
( AsO3)r'
(MoOa)2'
(vo'')(t' i03)2-
(ZrO)2'
( Poo ) ' -
HzSOo -+ HSO4- + H* k : 4x 10-r
HSO+--+ H* + SO+2- k: I .27x10'2
Chloride (Cl-) and nitrate (NO:-) anions may be present in the leach
l iquorr .
2.3,2 Alkal ine leach cherrr istry of uraniurn
The rcagent used in alkaline leach is carbonate and bicarbonate (sodium
carbonate - sodiurn bicarbonate). In solution the uranyl ion forms stable
complex with carbonate ion, thus.
UOrt' + 2(Cor)2- -+ [Uoz (COr)r]' ' (9)
Uort* + 3(Co:)2- -) [Uoz (Co:)r]o- (10)
For reaction (1) id alkaline process, the hydrogen ion is supplied by
bicarbonate, with inust be present for this purpose.
l 515
For reaction (1) iri alkaline process, the hydrogen ion is supplied by,
bicarbonate, with must be present for this purpose.
(9)
(l0)
[UOz(C03hf[UOz(C03)3t
Soluble silica Si(OH)4 SiOz,
(W04) z·Tungsten
Antimony ( Sb04 )3.
Arsenic ( As03)3.
Molybdenum (Mo04/'
Vanadium (V03')
Titanium (Ti03{
Zirconium (Zr03)2-
Phosphate ( P04 ) 3-
UOzz+ + 2(C03)z- --)
UOZ2
+ + 3(C03)2- --)
2.3.2 Alkaline leach chemistry of uranium
The reagent used in alkaline leach is carbonate and bicarbonate (sodium
carbonate - sodium bicarbonate). In solution the uranyl ion forms stable
complex with carbonate ion, thus.
In addition sulphuric acid dissociates in water as follow:
H2S04 --) HS04. + H+ k = 4x 10.1
HS04' --) H+ + solo k = 1.27x10.2
Chloride (Cr) and nitrate (NO)") anions may be present in the leach
I" Ilquor .
carried out at temperature of 40-80 QC is aggressive and non-selective
resulting in many other species besides uranium being leached!" These
present problems in uranium solvent extraction. Some of the most
important species involved are l:
••••••
IlIl
UO, + l l2O2
UO., + (( 'Or)r
-) UOr
+ 2( | I( 'Or ) ' +
( l l )
[UO2(CO,) , ] ' - + I l rO (12)
2.4 l tur i f icat ion ' |
A nunrber ol ' rrrethods dcpending upon type of solut ion can accomplish
thc puri f icat ion of the clar i l led leading solut ion. The variables include2:
a. Concentrat ion of Uraniunr.
b. ' i l re
arrrount and concentrat ion of i rnpuri t ies.
c. '[ 'he desired final purity of tl ie uraniunr product.
The lcading so lu t ion conrpos i t ion rv i l l essent ia l ly be dependent upon the
nrirrerlkrgy of the ore, attd leadirrg nrediurn. '[ 'hus.
a number of
puri f icat ion cornbinations nray be appl icable, For example, the
alternative can include the follorving, depending upon the feed solution
analysis and grade of procluct demanded2:
l. direct precipitation from alkaline and some acid liquors
2. lon exchange, elution and precipitation.
3. Solvent extract ion, str ipping and precipitat ion.
4. Ion exchange fol lorved by solvent extract iort .
2.5 Solvertt Extract iort
The rccovery of uraniurrt f i 'ortr orcs by using solvent extract ion since
1955 rvi th the use of diethyl hcxylphosphericacid (DEI-IPA) the (DAPE,X
process) attd since 1957 secondary or part icular ly the tert iary amines (the
AMEX process) lras bcen polrular extractions. A conrnron organic
phosphate tri-rr-butyl phosphate (TBP) is rvidely used for separating
Uranium (VI) fronr co-existirrg elernents in a nitric acid medium. 'fhe
Fig.(2.2) shows the flclw sheet of purification by solvent extraction 2'6.
'fhe distribution coefficient is considerably large over an acid range from
pH 3-6 M nitr ic acid.
l 6
puri tication combinations may be applicable.
16
(I I )
[U02(CO:dJ( + H20 (12)
For example, the1.
alternative can include the following, depending upon the feed solution
analysis and grade of product demamled2:
1. direct precipitation from alkaline and some acid liquors
2. Ion exchange, elution and precipitation.
3. Solvent extraction, stripping and precipitation.
4. Ion exchange followed by solvent extraction.
The recovery of uranium from ores by uSll1g solvent extraction slI1ce
1955 with the use of diethyl hexylphosphericacid (DEHPA) the (DAPEX
process) and since 1957 secondary or particularly the tertiary amines (the
AMEX process) has been popular extractions. A common organic
phosphate tri-n-butyl phosphate (TBP) is widely used for separating
Uranium (VI) from co-existing elements in a nitric acid medium. The
Fig.(2.2) shows the -flow sheet of purification by solvent extraction 2,6.
The distribution coefficient is considerably large over an acid range from
pH 3-6 M nitric acid.
2.5 Solvent Extraction
b. The amount and concentration of impurities.
c. The desired final purity of the uranium product.
The leading solution composition will essentially be dependent upon the
mineralogy of the ore, and leading medium. Thus, a number of
A number of methods depending upon type of solution can accomplish
the purification of the clm-ilied leading solution. The variables include2:
a. Concentration of Uranium.
2.4 Purit1cation t
••••-.
III*
tIIIIIIIIIIIt
The advantage of, ( ' t 'BP) is non-volat i l i ty (boi l ing point 289 "C) alcl i ts
stabi l i ty with c<lncentrated nitr ic acid. The disadvantage of i t , i ron,
thoriurn and protact inium are co-extracted rvi th uranium in nitr ic acid, so
if there are olte of tlrent tnust be separatecl prior to extracting uranium.
The extract ion of Uor2+ by (TBp) from sl ight ly acicl rnedium can,be
described as:
Uo2t*(oor+zNo3 rool
* 2TBo,ou .* Uo2No3)z .2TBP,"' (13)
Due to the large alkyl groups of TBp (cr2t{27o4p) the complex
conrpounds are readily soluble in organic solvents (e.g. kerosene). The
distr ibut ion coeff ic ient for the TBP extract iorr is siven as6:
D_
The appl icat ion of the lorv o[ nrass act ion to equation ( l 3) gives
D_[nq[, lrn\ (16)
From equation ( 16) i t can be seen that
increases with decreasing nitrate content.
luo,(rvo,) r.zra r,",)( l4 )
L, luo, (N o,) r.zrn rr.,, l^=6 (ls)
Where, K is the. equilibrium constant. Thus the distribution coefficient
finally becomcs;
K
t7
the distribution coeffiaient
17
(14)
(15)
( 16)
D=
From equation (16) it can be seen that the distribution coeffioient
increases with decreasing nitrate content.
Where, K is the, equilibrium constant. Thus the distribution coefficient
3. E1-Hazek,-N.T.; EI-Sayed,-M.S: Direct ural11um extraction
from dihydrate and hcmi-dihydrate wet process phosphoric
acids by liquid emulsion membrane. J. Radioanalytical-a~ld
Nuclear-Chemistry V. 257(2), 347-352 (2003)
4. Internet web site www.uic.com
I 0.Zi I 'bcrnran,-8. Ya. ; [ ;ed.rov,-yu.S. ; Arkhipov,-S.A. ; BI azheva,-I .v.;clekov,-R.G: Extract io. of Ua' ancl U6* uricler co.cl i t ionsof tlre second orgarric phase fbrrnation J. Rartiokhi,rit,o.. v. 43(2) lss- | se (2001 1.
I I .Cao,- l I .1 ' . ; Le, -Q. ' l ' . ; D inh, -M. ' l ' . ; 1 'han,_V.L. ; Le,_K.D:Ura.ium leaching a.d recovery frorn sandstone ores of NongSon Badirr (viet Nanr) lnternational symposiurn on theuranium productio. cycle and the environment, vienna (2000).
l2.Fyodorov,-G.V: Uraniunr production and the environment inKazakhstan (Report); r. The uranium productio' cycle and theenvrronment. Proceedings 571 l9l_l9g (2002).
I 3 .Faiza l , -R; FIa ln i , -L .N. ; Budi , -S. ; sugeng,-w. ;sus i lan ingtyas:
Rirang uranium ore processing using base methocl rvi thprrril ication of uraniurn hydroxitle fi-onr rar.e earths . FiftltScictrtiJic Presentotiotr otr Nucleqr Fttel C),cle: Nuclear FuelElements Developnre.t centre, National Atomic EnergyAgency 332 102- 108 (2000).
l4.wisnubroto,-D.-S: Uranium extraction from sulfuric acidsolution, National Atomi Energy Agency, serpong Indonesia(2r2) 6-12 (1997\.
l5.Awwad,-N.s: Equi l ibr ium and kinet ic studies on the extract ionof uranium (vl) l roln nitr ic acid medium into tr i -phenylphosphi 'e oxide using a single drop column technique.J. Nucleur-science.s-urtd-Appticat iorts, v. 36 (3),151-160
(2003)
l6.Mohanrnred,-A.-A.; Eltayeb,-M.-A.-H: uraniurn extract ionfrom uro area phosphate ore, Nuba mountains, Sudan .6,h Arabconlerence on peaceful uses of atonric energy cairo (Egypt)(2003) . '
79
IO.zil'bcnnan,-B. Ya.; Fcdorov,-Yu.S.; Arkhipov,-S.A.; Blazheva,I.V.;Glekov,-R.G: Extraction of U4
+ and UG+ under conditions
of the second organic phase formation J. Radiokhimiya., V. 43(2) 155-159(2001).
I I.Cao,-H.T.; Le,-Q.T.; Dinh,-M.T.; 1'han,-V.L.; Le,-K.D:
Uranium leaching and recovery from sandstone ores of Nong
Son Basin (Viet Nam) International symposium on the
uranium production cycle and the environment, Vienna (2000).
12.Fyodorov,-G.V: Uranium production and the environment in
Kazakhstan (Report); K. The uranium production cycle and the
environment. Proceedings 571 191-198 (2002).
13.Faizal,-R; Hafni,-L.N.; Budi,-S.; Sugeng,-W.;Susilaningtyas:Rirang uranium ore processing using base method with
purification of uranium hydroxide from rare earths . Fifth
Scientific Presentation on Nuclear Fuel Cycle: Nuclear FuelI
Elements Development Centre, National Atomic Energy
Agency 332 102-108 (2000).
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solution, National Atomi Energy Agency, Serpong Indonesia
(212) 6-12 (1997).
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of uranium (VI) from nitric acid medium into tri
phenyl phosphine oxide using a single drop column technique.1. Nuclcar-Scicnccs-and-Applications, V. 36 (3) ,151-160