U(IV) – U(VI) hydrolytic precipitate

INORG.

NUCL.

CHEM.

LETTERS

U(iV)

Vol. 6,

- U(VI)

651-655,

pp.

HYDROLY21C

1970.

Pergamon

~e~ (Prague),

Printed

in Great Britain

PRECIPITATE

V4clav BAR:~[ Institute of Czechoslovak

N u c l e a r Research

Press.

Acad.

Sci.,

Czechoslovakia

¢Received 10 April 1970~

Samples

vere prepared by an a.~monia precipitation

chloride

or perchlorate

trations

of U 4+ and UO 2+ ions,

hydr~ted

cations were proved using absorption

2he same concentrations lytically

sed as its U(VI)

percentage

(PMR)

were measured. air because

,',ere sensitive

U(IV) ll~ sus~ension gates),

state

infrared

U 4+ as a

the precipitate

in

in a sar~p!e was expres In addition

to chemical

(IR) and proton m~gnetic

spectra as vcell as magnetic

the samples,

spectroscopy.

ions were again found ana-

content.

All operations

concen-

of which as

polarographically,

U valence

(see the Table),

resonance

content,

of these

from Utota l) after dissolving

an acid. The apparent

various

individualities

(UO~ + was determined

difference

analysis

solut~.on.~ containing

of

susceptibility

were perfor:ae:] in absence

especially

of

those with a low U(VI)

to oxidation.

PRECIPITATE it is gelatinous,

after Qrying f i~ely devi~ed,

~nensJon~- o~" cryst~llites, 20-40 o; tlEe ~iffraction

obtained

easily ~'~It(;rab:~e~ (aggresl.~ays lig~,t green. from X-~ray analysis,

pattern agrees

of UO 2 but a fe,~ additional

esoentislly

li:~es were observed 651

Diare

~ith that

indicating

652

U(IV) - U (VI) HYDROLYTIC F R E C I P I ' [ A T h

Vol. 6, No. 7

THE TABLE

Results of Chemical Analysis of Basic Samples

total weight 7(VI) decrease .'ontent ~U02+ x by ignition, % 0 50 i00 d

85.1 80.2-87.2 87.0

ADU e

87.7

14.9 12.8-19.9 13.0 12.3

~NH3

0.02 0.5 .... 2 .i

(H20)total %

3.1a, b 12.3-19.3

~3

(H20)tota I

U02+ x

0.003 0.i

e o e e o

@ . e l m

10.2

0.39

0.54 b, c 2.2-3.7 2.37 1.84

a - difference between experimental weight decrease and theoretical decrease for U(OH)4; b - calculated from the total weight decrease without correction for NH 3 content; c - H20/U(OH)4; d - obtained from U(OH) 4 by air oxidation; e - smmoni~n diurarmte.

a little lowered symmetry (caused e.g. by other coordination of uranium atoms in centers of unit cube faces in contrast to those in the corners, i.e. a crystallographic nonequivalency of U atoms). Accord~n~ to the IR spectrum, the sample contains a small amount of molecular water as a moisture only (eee the Table) which is removed by drying the sample under siccative at room temperature. Also the PMR spectra confirm presence of merely hydroxyl groups in the precipitate, thus its appropriate formula being[U(OH)4] n. IR spectrum in the U-O (below 600 cm -1) as well as O-H (above 3000 cm -1) stretching frequency regions of the initial sample is rather unresolved and can be influenced by drying. Three well resolved and doubled bands near 900, 1050 and 1125 cm -1 can be assigned to the OH deformation v~brations, indlcsting probably

Vol. 6, No. 7

U(IV) -U(VI) HYDROLYTIC PRECIPITATE

the presence

of two slightly different

bonds, perhaps ~s consequence

653

types of hydrogen

of crystallographic

nonequ~-

valency of the OH groups.

PRECIPITATE OF U(V), i.e. ~'61TH 50 $ U(Vl) It is a well filterable, olet shade)

black (sfter drying with a vi-

compoumd ~'ith the cr,ystallite

80 ~; its structure

is analogous

of about

to that cited above,

a little different lattice parameter. spectra,

dimensions

According

with

to the IR

it contains molecular water and uranyl-like particles

with terminal oxygens,

U0~ (their anatisymmetric

stretch

is observed at 892 cm-l), From these spectra two well resolved, undoubled OH d e f e c a t i o n characteristic.

v~bratJons at 1045 and 1090 cm -I are

The appropriate

[Jo2oH. = 2o] with

formula,

therefore,

is

equal to 2-3.

U(VI) PRECIPITATE From uranyl solutions an am~monium diursnate formed under conditions

used for preparation

(ADU) was

of the other

samples;

it differs in colour and poor filtersbility.

contains

the

NH 4 group as a new component

it is not a member of the genetic compounds.

therefore,

series of the above cited

Because of it, U(0H) 4 was full~ oxidized in air

to a U03.2H20 phase

(see the Table)

turally as well ~s spectroscopically phases,

(I) and,

It

known till now. Crystal!ite

, which differs struc(IR) from all U03.21{20 size increased during

the oxi,.~ation to about 400 ~; spontaneity could be considered as an indication

of that cbap4ze

that the resulting

taline state may be rather close to a thermodynamically equilibrium one.

crys-

654

LI(IV) -U(VI) HYDROLYTIC P R E C I P I T A T E

Vol. 6, No. 7

PRECIPITATE Wl.TH. OTHER.. U(VI) CONTENTS Colour of the state

(2).

U(VI),

sample

Ligl~t g r e e n

dark green

one up t o a b o u t

content

plete

10 - 90 % U ( V I )

leaJs

(with

less

blackening

a violet

an intense

their IR spectra.

valence

a b o u t 2~

increase

of

wl~ich i s

com-

sha~le ne:~r 50 %). is dirtily

full S, oxidized one brightly yelow.

The pre-

contain a uranyl-like

par-

band, shifting itself linearly

lower energies ~ith decreasing U(VI)

content,

to

appears in

This band, with decreasirt~ intensity,

observed down to about ]Oh U(VI). Generally, prove the existence of the non-oxygenated in compounds with lower oxygenated

its

that

(about 95% U(~I))

cipitates with 50 to 100,% U(¢I) ticle, UO~+;

for

5 %; f u r t ~ e r

to g r a d u a l

Almost oxidized precipitate yellow-green,

characteri.~tic

sample contains

t h e U(VI) for

is

that 50% U(V!)

(ursnyl-like)

the IR spectra

form of uranimn

content,

form in the region 5 0 -

Within both these regions,

can be

further specification

an.d the i0@,~5 U(VI). in behaviour

of the uranit~n as a central atom takes place. Paramagnetism rature, gel

of the U(OH) 4 powder,

dried at room tempe-

is a little lower t~lan that of the suspended U(OII)4

(3). Oxidation in air causes at first a remarkable

linear paramagnetism

decrease

and

to the value of 5g,% U(VI),

further oxidation leads again to linear but much slower decrease. These results terms of presence

can be preliminarily

of three chemic~l

and 100% of U(Vi) or U(IV), themselves

interpreted

individua

U(V) and U(VI))

in

(with O, 50

which combine

additively.

CONCLUS] Oils Within solid hydroxo

colaplexea sn interaction

of the

Vol. 6, No. 7

U(IV) -U(VI) HYDROLYTIC PRECIPITATE

655

U 4+ and U0~~ + ions takes place, even though before precipitation these ions provably exist in solution in simple hydrated forms. The U(V) hydroxo complex seems to be a dimer with both uranium atoms chemically equiw~lent. Individual~ty of the hydroxo complexes in the solid phose is disappearing in greater of lesser extent the crystal l~ttice being a form of a macromolecule with averaged ( i n ~ y s i c a l follows e.g. from the IR spectra. Similar

sense) bonds as it

~3(UO~ +) versus %U(Vi) shift in the ~3(UO~+)

shift waa observe~ in the IR

sgectrs of uranates (i.e. st the invariable hez~velent state) in relstion to the cation content, sodium ~4'5) as well as ammonium (1)

REFERENCES i. W.I. Stuart and. T.L., Whateley, J.Inorg.Nucl. Cbem.31,1639(1969). 2. J.J.Katz and E.Rabinowitch, The Chemistry of Uranium, McGraw Hill Book Co., New York 1951, p. 281. 3. V.Bsran and O.Voto~ek, Collection Czech.Chem. Commun.33, 4379(1969). 4. V.Baran ~n~ M.Tympl, Z.anorg.allg.Chem. 347, 175(1966). 5. V.Bar~n, Coordin.Chem. Revs., in Press.