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Solvent extraction separations with bpha. applications to the microanalysis of niobium and zirconium in uranium
Analylica Chimica Acta El~cvicr PuLlistling Cot~,pany,Arr~slcrdar~~ I’rintcdin Ttw Nctbcrtands
SOLVENT EXTRACTION THE MICROANALYSIS
0. A. VLTA,
W. h. .l,lSVII3<
‘12clruicul Division,. CLenricul J$xr (U.S..4 .) (Rcccivcd
Dcccmlxr
gth.
87
SEPARATIONS WITH BPHA. APPLICATIONS OF NIOBIUM AND ZIRCONIUM IN URANIUM*
AND
15.
.-I tanlysis
TO
LITTEl~Al., Departnrcut,
Goodyccrr .~lto~nic
Corporution,
I’ikcton.
Ohio
rgG7)
N-Bcnzoyl-N-phenylhydroxylaminc (BPHA), a cupferron analog, is used extensively as an organic precipitant’ and solvent extractant since it reacts with sevcral metals to form stable chelates that are soluble in organic solvents. BPHA, however, is superior to cupferron because it exhibits good thermal and chemical stability, and it forms chelates with several metals in concentrated acids. In strong acids, BPHA becomes more selective and reacts only with some transition elements. Conscquently, the solvent extraction from uranium of 52 elements with BPHA-chloroformhydrochloric acid was thoroughly investigated; particular emphasis was devoted to extraction of easily hydrolyzed transition metals. ALIMARIN ANI) PETRUKHINS investigated the extraction of the benzoylphenylhydroxaminates of niobium, tantalum, titanium, vanadium, and zirconium from strong sulfuric acid. NABLVANETSd found that extraction of easily hydrolyzed elements at PH so is often suppressed by formation of polymeric or colloidal particles; therefore, extraction from concentrated acids is desirable. LYLE AND SHENDRIKARG investigatedextraction of antimony and tin from strong hydrochloric acid or perchloric acid with BPHA. RYAN~ extracted vanadium from strong hydrochloric acid with BPHA. During the development of calorimetric procedures for vanadium and titanium in uranium’, it was found that the extraction of their BPHA chelates from hydrochloric acid was superior to sulfuric acid. Studies of the extraction characteristics of niobium, tantalum, and zirconium with the BPHA-chloroform-hydrochloric acid systems, therefore, were extended to include a total of 52 elements. From these studies, a method was developed for the quantitative separation of hafnium, niobium, tantalum, titanium, vanadium, and zirconium from uranium. After the elements have been separated, they can be determined by chemical or instrumental methods. ESPERlMENTAL
A preliminary survey was made of extraction characteristics of elements in Croups I through VIII, the rare earths, and the actinides with the BPHA-chloroformhydrochloric acid system. Extraction efficiencies of the elements, grouped into 3 categories, are shown in Fig. I. + Prcscnted in part at the Tenth Confcrencc Gatlinburg. Tennessee, September 27-29, Ig66.
on Analytical
Chemistry
Anal.
in Nuclear
Ciritn.
Acta,
Technology,
42 (1968)
87-94
0. A. VITA,
88
W. A. LEVIER,
E. LLTTERAL
For the extraction studies, a sulfate residue of 0.5 or I mg of each element was dissolved in 25 ml of hydrochloric acid of the desired normality, and the solution was transferred to a separatory funnel, Twenty-five ml of 0.5% BYHA in chloroform was added to the funnel, and the two solutions were contacted for 15 min. After a fi-min phase separation, the organic extract and aqueous raffinate were drained into separate
Fig. I. SoIvcnt extraction
of clcmcnts
with EWWA-chloroform-hydrochloric
acid.
platinum dishes and evaporated to dryness. The residues were digested with nitric andsulfuric acids, and fumed to dryness, The residues were ignited at 5oo” for 20 min, and the oxides were analyzed for their metal contents by atomic absorption, colorimetric, or radiometric methods. Whenever possible, raf f inates or extracts were analyzed directly. Matrixeffects of raffinatesanalyzed directlyby atomicabsorption procedures@ were controlled by analyzing portions of the standard solutions along with the reacted solutions, Colorimetry was used extensively for analyses of oxides dissolved in acids or fused with potassium pyrosulfate. For the chloroform extracts of titanium and vanadium, the evaporation step was omitted and the colors were measured directlye, Radiometric methods were applied for the actinides, ruthenium, tantalum and te~~lnetiuln‘ Both organic extracts and aqueous raffinates were analyzed directly after appropriate treatment. EXTRACTION
STUDIES
Contact time affects extraction of many metals, especially those that hydrolyze easily. Nearly all the elements that could be extracted reached equilibrium after a. 5-min contact period. Nb and Ta were exceptions and required a Io-min contact period to reach equilibrium. For this study, however, test solutions were contacted for 15 min to insure that equilibrium conditions had been reached. Sotzttion
age
Solution age adversely affects extractions of several elements because some hydrolyze to form chemically inert polymeric or colloidal species and others change
SOLVENT
EXTRACTIOE:
WITH
BPHA
%I
valence. When freshly prepared IO N hydrochloric acid solutions of niobium or tantalum were allowed to stand for 48 h, extraction efficiency decreased markedly from 99% to 93% for niobium and to 84% for tantalum. Chromium and vanadium are partially reduced in strong hydrochloric acid; consequently, they are extracted incompletely from aged solutions. Other elements studied were not affected by solution age because of their stability in strong hydrochloric acid. However, all aliquots of stock solutions were fumed with sulfuric acid immediately before the extraction procedure. That this treatment was sufficient to produce chemically active species was verified by extraction studies with niobium and tantalum. Effects of solution age also were ohserved in color development of easily hydrolyzed metal ions with chromogenic reagents, and the sulfuric acid pretreatment was used before calorimetric analyses for these elements. Valence state Valence state affects the extraction characteristics of some elements with BPHA-chloroform-hydrochloric acid system. In general, BPHA reacts with elements only in their highest valence state to form extractable chelates, but only those elements which yield stable ions of more than one valence in hydrochloric acid were studied. In most c‘ases, oxidation-reduction potentials of BPHAcontrolled the valence state of the element, BPHA reduces strong oxidizing ions such as chromate and permanganate, and oxidizes others like Fe s+. The effects of valence were studied for the extraction of antimony, chromium, iron, manganese, molybdenum, neptunium, plutonium, technetium, tin, vanadium, and uranium. Only antimony was extracted at more than one valence, and its extraction characteristics are shown in Fig. 7.
The distribution of BPHA between chloroform and hydrochlaric acid phases is shown in Fig. 2. The solubility of the reagent in the aqueous phase increases as the
=Oo
1
3
Fig. z. Distribution
HCLG of BPHA
7
9
11
between chloroform
and HCl
phases.
hydrochloric acid concentration is increased. This higher concentration of the BPHA in the aqueous phase favors chelate formation and stabilizes the metal ions in the hydrochloric acid. Stabilization could explain the higher extraction efficiencies observed for the transition metals of Groups IV, V, and VI-B. Am2.
G&z.
Ada,
42 (1968) 87-94
0.
90
A..
VITA, w. A. I.IwIl31~, E. LITTERAL
Hydroclrloric acid concentration The effect of hydrochloric acid concentration on the extraction of metals with the BPHA-chloroform system was evaluated for concentrations of hydrochloric acid ranging from r to xx N. A single Ifi-min contact was used. Extraction characteristics of Group IV-33 elements (titanium, zirconium, and hafnium) arc shown in Fig. 3. Chloro-complex formation could explain the observed minima for hafnium and zirconium extraction at 5 N hydrochloric acid. Extraction characteristics for Group V-B elements (vanadium, niobium, and tantalum) are illustrated in Fig;. 4, Vanadium(IV) is not extracted from hydrochloric thus vanadium must be oxidized to vanadium(V) imacid at any concentration; mediately before extraction to ensure complete separation. At the tantalum extraction minima, precipitates developed at lower acid concentrations and were observed at the phase interface. Formation of stable chloro-complexes in 3 N anil 7 N hydrochloric acid could account for the observed extraction minima. Figure 5 shows the extraction characteristics of Group VI-B elements (chromium, molybdenum, and tungsten), Chromiurn(II1) is not extracted from I to II N hydrochloric acid, and reduction of Cr(V1) to Cr(IfI) in strong hydrochloric acid causes
Fig. 3, Extraction
of group IV-B clcmcnts.
Pin. L Extraction of LZOUD V-B cIiUm{IV) : x10 cxtmct&n. _
clcments.
Fig. 5, Extraction - -; chromium(II1)
of Group VI-B clcments. : no extraction.
Fig. G. Extraction
of group VII-B
elements.
Titanium
-;
Vanadium
hnfnium -;
Chromium(W) Mn --;
1% --,
niobium -
--;
-;
zirconium --;
- -.
tzmtnlum
molybdcnum(V1)
-
-;
- -;
vana-
tungsten
SOLVENT
EXTRACTION
WITH
9x
BPHA
the sharp decrease in Cr(VI) extraction efficiency with increasing hydrochloric acid concentration. For tungsten, a slight extraction peak is observed at 5 N hydrochloric acid. In milligram quantities, tungsten partially precipitated in the extraction system if the hydrochloric acid concentration w‘as below 7 N. Extraction of the Group Vff-B elements (manganese and technetium) is shown in Fig. 6. Manganese(D) extraction is negligible from I through II N hydrochloric acid with only I: to 2% extracted. Manganese(VII) as permanganate was quickly reduced in the 13PHA-&loroform-WC1 extraction system; consequently, no extraction was observed. For technetium, 8 peak extraction efficiency of 700/Owas observed from 6.5 N hydrochloric acid. The valency state of technetium during the extraction was not determined although tecl~netiunl{VII) was initially introduced into the cxtraction system. Technetium probably is extracted in a reduced form, but a reason for the vast differences between the extraction of manganese and technetium is not evident. Figure 7 shows the extraction of the Group IV-A and V-A elements (antimony and tin). About 90% of antimony(II1) is extracted from I N hydrochloric acid, but extraction efficiencies decrease as the acid concentration increases, A complex formation between antimony and BPHA apparently does not occur in strong hydrochloric acid. Tin( IV) extraction (- 93 “4 from I N HCl) is similar to that of antimony(II1). The extraction efficiency decreased sharply to ncfiligible values in 7 through XI N hydrochloric acid.
100 QO-
80
.
I I I I 1 I I 1 \ \
70,
HCI (N)
Fig. 7. Extraction of woup and Pb: no cxtrcrction. Fig. 8. Extraction
XV-A
of group VIII
and V-A
clcmcnts.
clcments., Fc -;
Co -
Sb(III) -;
--;
Sb(V)
- -;
Sn(IV)
-
-;
Bi
Ni - -.
Extraction of the Group VIII elements (iron, cobalt, and nickel) is shown in Fig:, 8. Only iron(II1) is si@ficantly extracted, and its extraction occurs only at low concentrations of acid. The actinides (thorium, uranium, neptunium, and plutonium) in any valence state, are not extracted into BPHA-chloroform from I through II N hydrochloric acid. Distribution ratios were approximately 10 -6 for uranium and x0-4 for neptunium and plutonium for a single extraction, These values represent significant decontamination factors, and the extraction system probably can be used for radiochemical separations. Awx~. China. Acta,
42
(1968) 87-94
0, A. WTA,
42
W. A. LEVfER,
E. LITTERAL
Ry means of this extraction system, it was possible to clevelop a procedure for scparatin~niol~i~in~ tantalum, titanium, andzirconium from uranium*.Two established colorimctric procedures for niobium *O.lr and zirconiumrz were evaluated and applier1 to the microanalysis of these separated elements. Interferences in b:)th calorimetric methods include only those elements which arc extracted along with niobium and zirconium. Tantalum interfcrcs more seriously than reported, but a ratio of I :3 (tantalum to niobium) can he tolerated. Hafnium interferes with the analysis of zirconium, but a ratio of I : 5 (hafnium to zirconium) can be tolerated.
Beckman fj-cm cells.
Model
DU spcctrophotomcter
or equivalent,
co:nplcte
with I- and
Reageltts
All chemicals were reagent grade. 13estzoyl~~leny~~~~~y~~y~~~~i~2~, o&& ~w~~~ ~~ast~i~a~~ Uup~h CJle~~z~ca~s No. 7297). Dissolve 5 g of BPHA in 1.0 1 of chloroform. Arsenazo III, o.r% {w/v) (J. T. Bakcv CJ~cnticaZ Cowzfuzwy No. B-577). Dissolve IOO mg in IOO ml of water, made basic with 0.5 ml ~1 so)/ sodium carbonate. q-(2-Pyvidytazo)resorci~zot, o.r% (w[v) (E&wan Ovgawic Clmnicals No. 5706). Dissolve IOO mg in TOO ml of methanol.
Dissolve x.0-5.0 g of uranium sample with S N nitric acid in a zoo-ml platinum dish. Add IO ml of concentrated sulfuric acicl and xo tnl of concentrated hydrofluoric acid, and thoroughly mix the contents. Fume to dryness to expel nitrate and fluoride ions. Dissolve the residue with 30 ml of ro N hydrochloric acid, and transfer the solution to a separatory funnel using IO N hydrochloric acid as a rinse. Add 20 ml of o-50/O I3PHA-chloroform solution to the separatory funnel. Stopper the funnel ancl shake it for IO min. Allow the phases to separate for 5 min, and drain the chloroform layer into a second xzg-ml separatory funnel. Repeat the extraction with 15 ml of BPHA solution, shaking the funnel for 5 min, and combine the two extracts. Wash the extract twice for 30 set with 25 ml of IO N hydrochloric acid. Drain the extract into a platinum crucible and evaporate to dryness. Add 2 ml of 5 N nitric acid to the residue, and evaporate it to dryness over a water bath. Repeat the nitric acid step twice with concentrated nitric acid. Ignite the residue at Goo” for 15 min. Niobizcnz. Dissolve the residue with I ml of concentrated hydrofluoric acid and x ml of cont. sulfuric acid. Add 80 mg of potassium pyrosulfate to the solution, and fume to dryness, Dissolve the residue with IO ml of 0.05 M ammonium tartrate, and transfer the solution to a so-ml volumetric flask. Rinse the dish with 38.5 ml of I N hydrochloric acid, and add the rinsings to the flask. Add 0.5 ml of 0.025 M EDTA to the solution, and mix the contents of the flask. Add I ml of 0.x:/, +(2-pyridylazo)resorcinol solution to the flask, dilute to volume with water, stopper, and shake, After I h, measure the optical density of the solution in S-cm cells at 540 nm against a blank AwZ. C&m. Ada,
42
(1968) 87-94
SOLVENT
EXTRACTION
WITH
BPHA
93
“.“* reagents. Determine the niobium content from a calibration prepared with the sami_ curve established with uranium standards. Zirconizcm. Dissolve the residue with I ml of concentrated hydrofluoric acid and 2 ml of concentrated sulfuric acid. Fume to approximately 0.x ml. Dilute the solution with IO ml of concentrated hydrochloric acid, ancl transfer it to a so-ml valumetric flask, Rinse the dish with IO N hydrochloric acid, and after adding the rinsings to the flask, dilute the solution to about 45 ml with IO N hydrochloric acid and 4 ml of 0.1% arsenazo III. Dilute to volume with IO N hydrochloric acid, stopper, and shake. Measure the optical density of the solution in x-cm cells at 665 nm against a blank prepared with the same reagents. Determine the zirconium content from a calibration curve established with uranium standards. ofwmaiwt siandavds Uranium oxides spiked with niobium and zirconium at two levels (2.0 ,ug and xao ,@ were analyzed by the procedure. At the 2.0~pg level, analyses were made on separate extracts, and at the IOO-pg level, both niobium and zirconium were analyzed on the same extract. Results of standard analyses are shown in Table I. Analysis
TABLE
I
ANALYSES -P--.wL_ a.0 ~4s FOWld
FOR
7riobircua
_I_ 1.0
NIOUIUhI
AND
x00 pg GoDitrnr
x00
Fowad
Found
Fo wd --
“-._--_1.8 2.1
2.1
2.0
2.X
I.7
I.8
-
L.K,/dct I.O&
18% x.8%
--
pg zirconium
a.0 116 ziuconirrtn
2.0
Bhs
2IRCONlU.M IN URANIUM ___.....
L.E./dct 30% 13ias 5.of14.5~f
93.3
98.7
=04
97-s
93.3 96.0 99.5
99.9 99.3 97.6 93.3 98.8
100
98.5 IO1
90.G
I*.E./d&fc).O~~
Bias
-1.8&3.X0/,
L.E./dctfg.ry~ Bias - x.gf1.8%
SUMMARY
A detailed study of the benzoylphenylhydroxylamine (BI?HA)-chloroformhydrochloric acid solvent extraction system with 52 elements is described with emphasis placed on extraction of the easily hydrolyzed transition metals from strong hydrochloric acid. Prom this study, a separation procedure for hafnium, niobium, tantalum, titanium, vanadium, and zirconium from uranium was developed, and procedures are given for the microanalysis of niobium and zirconium in uranium. Niobium and zirconium are separated from uranium by extraction into BPHA-chloroform from ION HCl. The separated elements are then measured calorimetrically as the niobium-4-(z-pyridylazo)resorcinol and zirconium-arsenazo III complexes. The limit of detection is I pgfg U. Anal. Chitn. Ada,
42 (xgG8) 87-94
0.
94
A.
VITA,
W.
A. LEVIER,
E. LITTERAL
Unc 4tudc d&ail& cst effect&c sur I’extraction dans un solvant du systdme ~~cn~oylpl~~nyll~ydroxylamine (APIA)-chlorofor~n~-acide c~~lorlly~rique avcc 52 (sl& ments, spdcialement sur l’cxtraction de m&aux de transition facilement hydrolysabtes en milieu acide chlorhydriquc concentrC. On propose une sCparation de l’hafnium, du niobium, clu tantale, du titanc, du vanadium et du zirconium d’avec l’uranium, et un microdosage du niobium et du zirconium dans l’uranium. Niobium et zirconium sont &par& d’avec l’uranium par extraction au moyen du m&lange BPHA-chloroforme en milieu HCl IO N. Les 6ldments &par& sont ensuite do&s colorimbtriquement sous forme de complexes niobiuin-4-(z-pyridyla~o) r&orcinol et zirconium-arsen~L~o III. La limitc de dtttcction est de I pg/g U. ZtJSRMMI?NFASSUNG
Es wird ftir 52 Elemente die Fltissigextraktion mit Benzoylphenylhydroxylamin (BPHA) in Chloroform aus salzsauren LGsungen untersucht; dabei wird die Extraktion der leicht hydrolisierbaren ubergangsmetalle aus starker SalzGiure besondcrs berticksichtigt. Aus dicsen Untersuchungen wurde ein Verfahren zur Abtrennung von Hafnium, Niob, Tantal, Titan, Vanadin und Zirkonium van Uran entwickelt. IIIaneben wird tine Methodc ftir die Mikroanalyse von Niob und Zirkonium in Uran angegeben. Dazu werden Niob und Zirkonium mit BPHA aus IO N HCl vom Uran abgetrennt und anschliessend das Niob mit 2-Pyridylazoresorcinol und das Zirkonium mit Arsenazo III kolorimetrisch bestimmt. Die Nachweisgrenzc betrllgt I ,q,@ U. RBFERENCIZS 1 s. c. s1~ow%, .fwlysl, 75 (x950) 27. a 0. I-I. MORRISON AND I-I.FRILISIIR,SoZvml Now Yorlc, 1957, p. 171-172.
ExtmcLimr
i?r Amdyficul
CI&cmislry.John Wiley,
3 I. 1'.ALIhbuzIN AND 0. M. PETRUICI~IIN,.dndyfical Chemistry rg6a, Elscvicr, New York, X&3, p. 152-153. .I 13. I. NAUIVANETS, Rzrssiarl ./. Itrwg, Clumist., 7, 12 (IgG2) 1428. J S. J. LYLIZ AND A. D. SHENDRIKAR, An&. Chim Acta, 3G (xgGG) 280, 6 D. 35. RYAN. Aqalyst. 85 (rg60)jjGg. 7 0. A. VITA, L. 1%.MULLINS, JR. AND C. F. TRIVISONNO, I’Jrc Colovim+ic ~ficroclcte-mri?Jutdon
t.-#*Titatk.m~ ad Vanadimtt ha Urmtirrm Cor~r~o~r~~ctswith We~~zoylphet~yllrydrosylat~ti~~e, GAT-T1085.1963. 8 0. A. VITA, The Separation ad Microamzlysis of Niobiunr, Tawtalzrva, Tiiaairim, Va28adirrm, Zircouiurn: R&Vicatiou to Ura#iunr Co~tr~o~c~trZs.GAT-524, rgGG. I) Tmz PERKIN-ELMER CORPORATION, Analytical Met/rods fov Atomic Atsovption Spcctroplrotowctry, Norwalk, Connecticut, 19G4. IO R. BELCHISR. T, V. XASIAICRISIINA AND T. S. WEST, Tcdavta, IO (1963) 1013. II S.V. ELINSON, L. 'I'. PO~EBINA AND A. T. RISZOVA,~. A~ml.Chcr~z.USSR, 1s (xg6,t) 1078. 12 S. 33.SAVVIN, J. Anal. CJlenl. USSR (E+rglisJr trawzi.) I r7 (1gG2) 776. Aual.
Ckim.
Acta,
42 (rg68) 87-94
SOLVENT EXTRACTION THE MICROANALYSIS
0. A. VLTA,
W. h. .l,lSVII3<
‘12clruicul Division,. CLenricul J$xr (U.S..4 .) (Rcccivcd
Dcccmlxr
gth.
87
SEPARATIONS WITH BPHA. APPLICATIONS OF NIOBIUM AND ZIRCONIUM IN URANIUM*
AND
15.
.-I tanlysis
TO
LITTEl~Al., Departnrcut,
Goodyccrr .~lto~nic
Corporution,
I’ikcton.
Ohio
rgG7)
N-Bcnzoyl-N-phenylhydroxylaminc (BPHA), a cupferron analog, is used extensively as an organic precipitant’ and solvent extractant since it reacts with sevcral metals to form stable chelates that are soluble in organic solvents. BPHA, however, is superior to cupferron because it exhibits good thermal and chemical stability, and it forms chelates with several metals in concentrated acids. In strong acids, BPHA becomes more selective and reacts only with some transition elements. Conscquently, the solvent extraction from uranium of 52 elements with BPHA-chloroformhydrochloric acid was thoroughly investigated; particular emphasis was devoted to extraction of easily hydrolyzed transition metals. ALIMARIN ANI) PETRUKHINS investigated the extraction of the benzoylphenylhydroxaminates of niobium, tantalum, titanium, vanadium, and zirconium from strong sulfuric acid. NABLVANETSd found that extraction of easily hydrolyzed elements at PH so is often suppressed by formation of polymeric or colloidal particles; therefore, extraction from concentrated acids is desirable. LYLE AND SHENDRIKARG investigatedextraction of antimony and tin from strong hydrochloric acid or perchloric acid with BPHA. RYAN~ extracted vanadium from strong hydrochloric acid with BPHA. During the development of calorimetric procedures for vanadium and titanium in uranium’, it was found that the extraction of their BPHA chelates from hydrochloric acid was superior to sulfuric acid. Studies of the extraction characteristics of niobium, tantalum, and zirconium with the BPHA-chloroform-hydrochloric acid systems, therefore, were extended to include a total of 52 elements. From these studies, a method was developed for the quantitative separation of hafnium, niobium, tantalum, titanium, vanadium, and zirconium from uranium. After the elements have been separated, they can be determined by chemical or instrumental methods. ESPERlMENTAL
A preliminary survey was made of extraction characteristics of elements in Croups I through VIII, the rare earths, and the actinides with the BPHA-chloroformhydrochloric acid system. Extraction efficiencies of the elements, grouped into 3 categories, are shown in Fig. I. + Prcscnted in part at the Tenth Confcrencc Gatlinburg. Tennessee, September 27-29, Ig66.
on Analytical
Chemistry
Anal.
in Nuclear
Ciritn.
Acta,
Technology,
42 (1968)
87-94
0. A. VITA,
88
W. A. LEVIER,
E. LLTTERAL
For the extraction studies, a sulfate residue of 0.5 or I mg of each element was dissolved in 25 ml of hydrochloric acid of the desired normality, and the solution was transferred to a separatory funnel, Twenty-five ml of 0.5% BYHA in chloroform was added to the funnel, and the two solutions were contacted for 15 min. After a fi-min phase separation, the organic extract and aqueous raffinate were drained into separate
Fig. I. SoIvcnt extraction
of clcmcnts
with EWWA-chloroform-hydrochloric
acid.
platinum dishes and evaporated to dryness. The residues were digested with nitric andsulfuric acids, and fumed to dryness, The residues were ignited at 5oo” for 20 min, and the oxides were analyzed for their metal contents by atomic absorption, colorimetric, or radiometric methods. Whenever possible, raf f inates or extracts were analyzed directly. Matrixeffects of raffinatesanalyzed directlyby atomicabsorption procedures@ were controlled by analyzing portions of the standard solutions along with the reacted solutions, Colorimetry was used extensively for analyses of oxides dissolved in acids or fused with potassium pyrosulfate. For the chloroform extracts of titanium and vanadium, the evaporation step was omitted and the colors were measured directlye, Radiometric methods were applied for the actinides, ruthenium, tantalum and te~~lnetiuln‘ Both organic extracts and aqueous raffinates were analyzed directly after appropriate treatment. EXTRACTION
STUDIES
Contact time affects extraction of many metals, especially those that hydrolyze easily. Nearly all the elements that could be extracted reached equilibrium after a. 5-min contact period. Nb and Ta were exceptions and required a Io-min contact period to reach equilibrium. For this study, however, test solutions were contacted for 15 min to insure that equilibrium conditions had been reached. Sotzttion
age
Solution age adversely affects extractions of several elements because some hydrolyze to form chemically inert polymeric or colloidal species and others change
SOLVENT
EXTRACTIOE:
WITH
BPHA
%I
valence. When freshly prepared IO N hydrochloric acid solutions of niobium or tantalum were allowed to stand for 48 h, extraction efficiency decreased markedly from 99% to 93% for niobium and to 84% for tantalum. Chromium and vanadium are partially reduced in strong hydrochloric acid; consequently, they are extracted incompletely from aged solutions. Other elements studied were not affected by solution age because of their stability in strong hydrochloric acid. However, all aliquots of stock solutions were fumed with sulfuric acid immediately before the extraction procedure. That this treatment was sufficient to produce chemically active species was verified by extraction studies with niobium and tantalum. Effects of solution age also were ohserved in color development of easily hydrolyzed metal ions with chromogenic reagents, and the sulfuric acid pretreatment was used before calorimetric analyses for these elements. Valence state Valence state affects the extraction characteristics of some elements with BPHA-chloroform-hydrochloric acid system. In general, BPHA reacts with elements only in their highest valence state to form extractable chelates, but only those elements which yield stable ions of more than one valence in hydrochloric acid were studied. In most c‘ases, oxidation-reduction potentials of BPHAcontrolled the valence state of the element, BPHA reduces strong oxidizing ions such as chromate and permanganate, and oxidizes others like Fe s+. The effects of valence were studied for the extraction of antimony, chromium, iron, manganese, molybdenum, neptunium, plutonium, technetium, tin, vanadium, and uranium. Only antimony was extracted at more than one valence, and its extraction characteristics are shown in Fig. 7.
The distribution of BPHA between chloroform and hydrochlaric acid phases is shown in Fig. 2. The solubility of the reagent in the aqueous phase increases as the
=Oo
1
3
Fig. z. Distribution
HCLG of BPHA
7
9
11
between chloroform
and HCl
phases.
hydrochloric acid concentration is increased. This higher concentration of the BPHA in the aqueous phase favors chelate formation and stabilizes the metal ions in the hydrochloric acid. Stabilization could explain the higher extraction efficiencies observed for the transition metals of Groups IV, V, and VI-B. Am2.
G&z.
Ada,
42 (1968) 87-94
0.
90
A..
VITA, w. A. I.IwIl31~, E. LITTERAL
Hydroclrloric acid concentration The effect of hydrochloric acid concentration on the extraction of metals with the BPHA-chloroform system was evaluated for concentrations of hydrochloric acid ranging from r to xx N. A single Ifi-min contact was used. Extraction characteristics of Group IV-33 elements (titanium, zirconium, and hafnium) arc shown in Fig. 3. Chloro-complex formation could explain the observed minima for hafnium and zirconium extraction at 5 N hydrochloric acid. Extraction characteristics for Group V-B elements (vanadium, niobium, and tantalum) are illustrated in Fig;. 4, Vanadium(IV) is not extracted from hydrochloric thus vanadium must be oxidized to vanadium(V) imacid at any concentration; mediately before extraction to ensure complete separation. At the tantalum extraction minima, precipitates developed at lower acid concentrations and were observed at the phase interface. Formation of stable chloro-complexes in 3 N anil 7 N hydrochloric acid could account for the observed extraction minima. Figure 5 shows the extraction characteristics of Group VI-B elements (chromium, molybdenum, and tungsten), Chromiurn(II1) is not extracted from I to II N hydrochloric acid, and reduction of Cr(V1) to Cr(IfI) in strong hydrochloric acid causes
Fig. 3, Extraction
of group IV-B clcmcnts.
Pin. L Extraction of LZOUD V-B cIiUm{IV) : x10 cxtmct&n. _
clcments.
Fig. 5, Extraction - -; chromium(II1)
of Group VI-B clcments. : no extraction.
Fig. G. Extraction
of group VII-B
elements.
Titanium
-;
Vanadium
hnfnium -;
Chromium(W) Mn --;
1% --,
niobium -
--;
-;
zirconium --;
- -.
tzmtnlum
molybdcnum(V1)
-
-;
- -;
vana-
tungsten
SOLVENT
EXTRACTION
WITH
9x
BPHA
the sharp decrease in Cr(VI) extraction efficiency with increasing hydrochloric acid concentration. For tungsten, a slight extraction peak is observed at 5 N hydrochloric acid. In milligram quantities, tungsten partially precipitated in the extraction system if the hydrochloric acid concentration w‘as below 7 N. Extraction of the Group Vff-B elements (manganese and technetium) is shown in Fig. 6. Manganese(D) extraction is negligible from I through II N hydrochloric acid with only I: to 2% extracted. Manganese(VII) as permanganate was quickly reduced in the 13PHA-&loroform-WC1 extraction system; consequently, no extraction was observed. For technetium, 8 peak extraction efficiency of 700/Owas observed from 6.5 N hydrochloric acid. The valency state of technetium during the extraction was not determined although tecl~netiunl{VII) was initially introduced into the cxtraction system. Technetium probably is extracted in a reduced form, but a reason for the vast differences between the extraction of manganese and technetium is not evident. Figure 7 shows the extraction of the Group IV-A and V-A elements (antimony and tin). About 90% of antimony(II1) is extracted from I N hydrochloric acid, but extraction efficiencies decrease as the acid concentration increases, A complex formation between antimony and BPHA apparently does not occur in strong hydrochloric acid. Tin( IV) extraction (- 93 “4 from I N HCl) is similar to that of antimony(II1). The extraction efficiency decreased sharply to ncfiligible values in 7 through XI N hydrochloric acid.
100 QO-
80
.
I I I I 1 I I 1 \ \
70,
HCI (N)
Fig. 7. Extraction of woup and Pb: no cxtrcrction. Fig. 8. Extraction
XV-A
of group VIII
and V-A
clcmcnts.
clcments., Fc -;
Co -
Sb(III) -;
--;
Sb(V)
- -;
Sn(IV)
-
-;
Bi
Ni - -.
Extraction of the Group VIII elements (iron, cobalt, and nickel) is shown in Fig:, 8. Only iron(II1) is si@ficantly extracted, and its extraction occurs only at low concentrations of acid. The actinides (thorium, uranium, neptunium, and plutonium) in any valence state, are not extracted into BPHA-chloroform from I through II N hydrochloric acid. Distribution ratios were approximately 10 -6 for uranium and x0-4 for neptunium and plutonium for a single extraction, These values represent significant decontamination factors, and the extraction system probably can be used for radiochemical separations. Awx~. China. Acta,
42
(1968) 87-94
0, A. WTA,
42
W. A. LEVfER,
E. LITTERAL
Ry means of this extraction system, it was possible to clevelop a procedure for scparatin~niol~i~in~ tantalum, titanium, andzirconium from uranium*.Two established colorimctric procedures for niobium *O.lr and zirconiumrz were evaluated and applier1 to the microanalysis of these separated elements. Interferences in b:)th calorimetric methods include only those elements which arc extracted along with niobium and zirconium. Tantalum interfcrcs more seriously than reported, but a ratio of I :3 (tantalum to niobium) can he tolerated. Hafnium interferes with the analysis of zirconium, but a ratio of I : 5 (hafnium to zirconium) can be tolerated.
Beckman fj-cm cells.
Model
DU spcctrophotomcter
or equivalent,
co:nplcte
with I- and
Reageltts
All chemicals were reagent grade. 13estzoyl~~leny~~~~~y~~y~~~~i~2~, o&& ~w~~~ ~~ast~i~a~~ Uup~h CJle~~z~ca~s No. 7297). Dissolve 5 g of BPHA in 1.0 1 of chloroform. Arsenazo III, o.r% {w/v) (J. T. Bakcv CJ~cnticaZ Cowzfuzwy No. B-577). Dissolve IOO mg in IOO ml of water, made basic with 0.5 ml ~1 so)/ sodium carbonate. q-(2-Pyvidytazo)resorci~zot, o.r% (w[v) (E&wan Ovgawic Clmnicals No. 5706). Dissolve IOO mg in TOO ml of methanol.
Dissolve x.0-5.0 g of uranium sample with S N nitric acid in a zoo-ml platinum dish. Add IO ml of concentrated sulfuric acicl and xo tnl of concentrated hydrofluoric acid, and thoroughly mix the contents. Fume to dryness to expel nitrate and fluoride ions. Dissolve the residue with 30 ml of ro N hydrochloric acid, and transfer the solution to a separatory funnel using IO N hydrochloric acid as a rinse. Add 20 ml of o-50/O I3PHA-chloroform solution to the separatory funnel. Stopper the funnel ancl shake it for IO min. Allow the phases to separate for 5 min, and drain the chloroform layer into a second xzg-ml separatory funnel. Repeat the extraction with 15 ml of BPHA solution, shaking the funnel for 5 min, and combine the two extracts. Wash the extract twice for 30 set with 25 ml of IO N hydrochloric acid. Drain the extract into a platinum crucible and evaporate to dryness. Add 2 ml of 5 N nitric acid to the residue, and evaporate it to dryness over a water bath. Repeat the nitric acid step twice with concentrated nitric acid. Ignite the residue at Goo” for 15 min. Niobizcnz. Dissolve the residue with I ml of concentrated hydrofluoric acid and x ml of cont. sulfuric acid. Add 80 mg of potassium pyrosulfate to the solution, and fume to dryness, Dissolve the residue with IO ml of 0.05 M ammonium tartrate, and transfer the solution to a so-ml volumetric flask. Rinse the dish with 38.5 ml of I N hydrochloric acid, and add the rinsings to the flask. Add 0.5 ml of 0.025 M EDTA to the solution, and mix the contents of the flask. Add I ml of 0.x:/, +(2-pyridylazo)resorcinol solution to the flask, dilute to volume with water, stopper, and shake, After I h, measure the optical density of the solution in S-cm cells at 540 nm against a blank AwZ. C&m. Ada,
42
(1968) 87-94
SOLVENT
EXTRACTION
WITH
BPHA
93
“.“* reagents. Determine the niobium content from a calibration prepared with the sami_ curve established with uranium standards. Zirconizcm. Dissolve the residue with I ml of concentrated hydrofluoric acid and 2 ml of concentrated sulfuric acid. Fume to approximately 0.x ml. Dilute the solution with IO ml of concentrated hydrochloric acid, ancl transfer it to a so-ml valumetric flask, Rinse the dish with IO N hydrochloric acid, and after adding the rinsings to the flask, dilute the solution to about 45 ml with IO N hydrochloric acid and 4 ml of 0.1% arsenazo III. Dilute to volume with IO N hydrochloric acid, stopper, and shake. Measure the optical density of the solution in x-cm cells at 665 nm against a blank prepared with the same reagents. Determine the zirconium content from a calibration curve established with uranium standards. ofwmaiwt siandavds Uranium oxides spiked with niobium and zirconium at two levels (2.0 ,ug and xao ,@ were analyzed by the procedure. At the 2.0~pg level, analyses were made on separate extracts, and at the IOO-pg level, both niobium and zirconium were analyzed on the same extract. Results of standard analyses are shown in Table I. Analysis
TABLE
I
ANALYSES -P--.wL_ a.0 ~4s FOWld
FOR
7riobircua
_I_ 1.0
NIOUIUhI
AND
x00 pg GoDitrnr
x00
Fowad
Found
Fo wd --
“-._--_1.8 2.1
2.1
2.0
2.X
I.7
I.8
-
L.K,/dct I.O&
18% x.8%
--
pg zirconium
a.0 116 ziuconirrtn
2.0
Bhs
2IRCONlU.M IN URANIUM ___.....
L.E./dct 30% 13ias 5.of14.5~f
93.3
98.7
=04
97-s
93.3 96.0 99.5
99.9 99.3 97.6 93.3 98.8
100
98.5 IO1
90.G
I*.E./d&fc).O~~
Bias
-1.8&3.X0/,
L.E./dctfg.ry~ Bias - x.gf1.8%
SUMMARY
A detailed study of the benzoylphenylhydroxylamine (BI?HA)-chloroformhydrochloric acid solvent extraction system with 52 elements is described with emphasis placed on extraction of the easily hydrolyzed transition metals from strong hydrochloric acid. Prom this study, a separation procedure for hafnium, niobium, tantalum, titanium, vanadium, and zirconium from uranium was developed, and procedures are given for the microanalysis of niobium and zirconium in uranium. Niobium and zirconium are separated from uranium by extraction into BPHA-chloroform from ION HCl. The separated elements are then measured calorimetrically as the niobium-4-(z-pyridylazo)resorcinol and zirconium-arsenazo III complexes. The limit of detection is I pgfg U. Anal. Chitn. Ada,
42 (xgG8) 87-94
0.
94
A.
VITA,
W.
A. LEVIER,
E. LITTERAL
Unc 4tudc d&ail& cst effect&c sur I’extraction dans un solvant du systdme ~~cn~oylpl~~nyll~ydroxylamine (APIA)-chlorofor~n~-acide c~~lorlly~rique avcc 52 (sl& ments, spdcialement sur l’cxtraction de m&aux de transition facilement hydrolysabtes en milieu acide chlorhydriquc concentrC. On propose une sCparation de l’hafnium, du niobium, clu tantale, du titanc, du vanadium et du zirconium d’avec l’uranium, et un microdosage du niobium et du zirconium dans l’uranium. Niobium et zirconium sont &par& d’avec l’uranium par extraction au moyen du m&lange BPHA-chloroforme en milieu HCl IO N. Les 6ldments &par& sont ensuite do&s colorimbtriquement sous forme de complexes niobiuin-4-(z-pyridyla~o) r&orcinol et zirconium-arsen~L~o III. La limitc de dtttcction est de I pg/g U. ZtJSRMMI?NFASSUNG
Es wird ftir 52 Elemente die Fltissigextraktion mit Benzoylphenylhydroxylamin (BPHA) in Chloroform aus salzsauren LGsungen untersucht; dabei wird die Extraktion der leicht hydrolisierbaren ubergangsmetalle aus starker SalzGiure besondcrs berticksichtigt. Aus dicsen Untersuchungen wurde ein Verfahren zur Abtrennung von Hafnium, Niob, Tantal, Titan, Vanadin und Zirkonium van Uran entwickelt. IIIaneben wird tine Methodc ftir die Mikroanalyse von Niob und Zirkonium in Uran angegeben. Dazu werden Niob und Zirkonium mit BPHA aus IO N HCl vom Uran abgetrennt und anschliessend das Niob mit 2-Pyridylazoresorcinol und das Zirkonium mit Arsenazo III kolorimetrisch bestimmt. Die Nachweisgrenzc betrllgt I ,q,@ U. RBFERENCIZS 1 s. c. s1~ow%, .fwlysl, 75 (x950) 27. a 0. I-I. MORRISON AND I-I.FRILISIIR,SoZvml Now Yorlc, 1957, p. 171-172.
ExtmcLimr
i?r Amdyficul
CI&cmislry.John Wiley,
3 I. 1'.ALIhbuzIN AND 0. M. PETRUICI~IIN,.dndyfical Chemistry rg6a, Elscvicr, New York, X&3, p. 152-153. .I 13. I. NAUIVANETS, Rzrssiarl ./. Itrwg, Clumist., 7, 12 (IgG2) 1428. J S. J. LYLIZ AND A. D. SHENDRIKAR, An&. Chim Acta, 3G (xgGG) 280, 6 D. 35. RYAN. Aqalyst. 85 (rg60)jjGg. 7 0. A. VITA, L. 1%.MULLINS, JR. AND C. F. TRIVISONNO, I’Jrc Colovim+ic ~ficroclcte-mri?Jutdon
t.-#*Titatk.m~ ad Vanadimtt ha Urmtirrm Cor~r~o~r~~ctswith We~~zoylphet~yllrydrosylat~ti~~e, GAT-T1085.1963. 8 0. A. VITA, The Separation ad Microamzlysis of Niobiunr, Tawtalzrva, Tiiaairim, Va28adirrm, Zircouiurn: R&Vicatiou to Ura#iunr Co~tr~o~c~trZs.GAT-524, rgGG. I) Tmz PERKIN-ELMER CORPORATION, Analytical Met/rods fov Atomic Atsovption Spcctroplrotowctry, Norwalk, Connecticut, 19G4. IO R. BELCHISR. T, V. XASIAICRISIINA AND T. S. WEST, Tcdavta, IO (1963) 1013. II S.V. ELINSON, L. 'I'. PO~EBINA AND A. T. RISZOVA,~. A~ml.Chcr~z.USSR, 1s (xg6,t) 1078. 12 S. 33.SAVVIN, J. Anal. CJlenl. USSR (E+rglisJr trawzi.) I r7 (1gG2) 776. Aual.
Ckim.
Acta,
42 (rg68) 87-94