On production of cerium dioxide

Article abstract of DOI:10.1023/A:1020941817972

The possibility of obtaining cerium dioxide by recovery of Ce(IV) phosphate from acid nitrate solutions with subsequent conversion of Ce(IV) phosphate to Ce(III) oxalate was studied.

Full text of DOI:10.1023/A:1020941817972

Russian Journal of Applied Chemistry, Vol. 75, No. 8, 2002, pp. 1357 1359. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 8, 2002,
pp. 1384 1386.
Original Russian Text Copyright
2002 by Lebedev, Rudenko.
BRIEF
COMMUNICATIONS
On Production of Cerium Dioxide
V. N. Lebedev and A. V. Rudenko
Tananaev Institute of Chemistry and Technology of Rare Elements and Minerals, Kola Scientific Center,
Russian Academy of Sciences, Apatity, Russia
Received March 11, 2002
Abstract The possibility of obtaining cerium dioxide by recovery of Ce(IV) phosphate from acid nitrate
solutions with subsequent conversion of Ce(IV) phosphate to Ce(III) oxalate was studied.
Cerium is the most widespread and demanded re- tained by addition of one mole of PO34 per one mole
presentative of rare-earth elements (REE). Its content
of CeO2, which corresponds to precipitation of basic
in most of the concentrates being refined exceeds phosphate CeOHPO4. This precipitate was filtered off,
50 wt %. As a rule, Ce(III) is isolated from an REE
mixture through its oxidation to Ce(IV) and subse-
quent separation by extraction or precipitation with
account of differences in the pH of precipitation of
mixture components [1, 2].
washed by repulping in 1 N HNO3 at a solid-to-liq-
uid phase ratio (s : l) of 1 : 3 and treated with oxalic
acid in 1.5 N HNO3 at 80 C for 1 h (s : l = 1 : 3). The
conversion to the oxalate occurs by the following re-
action:
It is impossible to completely separate cerium(IV)
from other REEs by precipitation techniques owing
to the close pH values of their precipitation and the
considerable adsorptivity of the resulting precipitates.
Purer cerium compounds can be obtained by precipi-
tation of Ce(IV) phosphate, which is precipitated at
higher acidity than triply charged REEs. Processes of
this kind have been proposed for recovery of cerium
from monazite [3] and a phosphate concentrate from
apatite [4]. A drawback of the phosphate procedure
is the complexity of phosphorus(V) removal.
2Ce(OH)PO4 nH2O(s) + 4H2C2O4(l)
Ce2(C2O4)3 10H2O(s) + 2H3PO4 + 2H2O + 2CO2.
Precipitated oxalates were isolated, washed with
1 N HNO3, and calcined at 900 C. The impurities in
cerium dioxide were determined by X-ray fluorescent
analysis. The results of the experiments are presented
in the table.
As a rule, 75 90% concentrates are produced by
single-stage precipitation of Ce(IV) hydroxide, car-
bonate, or basic nitrate [3]. Cerium samples obtained
by precipitation of Ce(IV) phosphate are significantly
A procedure for processing REE phosphates, based
on their conversion to oxalates, has been proposed
earlier [5, 6]. Its applicability to the production of
cerium dioxide was assessed in the present study.
Composition of cerium dioxide obtained by recovery of
CeOHPO4
EXPERIMENTAL
Recovery
Impurity content, wt %
conditions
Cerium was oxidized in an acid nitrate medium on
a platinum anode. A solution prepared from loparite
was used for oxidation. It contained 300 g l 1 of Ln2O3
Re-
HNO3,
pulp- La2O3 Pr6O11 Nd2O3 Sm2O3 P2O5
ing
M
1
and 164 g l of Ce2O3. After the oxidation the solu-
1
tion contained Ce(IV) in the form of CeO2 (42 g l ).
2
2
3
3
1
2
1
2
2.2
0.6
1.2
0.12
nd*
0.1
The cerium(IV) content in solutions was determined
by titration with Mohr’s salt (NH4)2Fe(SO4)2. Ceri-
um(IV) phosphate was precipitated from 2 3 N HNO3
solution by addition of ammonium hydrophosphate
(NH4)2HPO4. Almost complete precipitation was at-
0.78
1.86
0.66
0.34
0.52
0.26
0.58
1.12
0.58
0.11
nd*
*
Not determined.
1070-4272/02/7508-1357 $27.00 2002 MAIK Nauka/Interperiodica

1358
LEBEDEV, RUDENKO
purer and can be used in various fields of technology.
A required purity of cerium phosphate can be achieved
by its reprecipitation, which can be used for recovery
of cerium(IV) from acid solutions after its electrolytic
oxidation, since the precipitation procedures involve
solution neutralization. At the same time, the extrac-
tion recovery entails a considerable loss of the extrac-
tant because of its decomposition by Ce(IV), which is
a strong oxidizing agent, and by hydrogen peroxide
used for the reextraction.
It was found that oxalates obtained from Ce(IV)
phosphate differ from those prepared by conversion
of Ce(III) orthophosphate in their thermal behavior.
Samples of Ce(III) oxalates were synthesized under
similar conditions. The content of P2O5 in the samples
under study was not greater than 0.1%. Although both
kinds of oxalate samples have identical X-ray diffrac-
tion patterns (Fig. 1a) and thermogravimetric charac-
teristics (Fig. 2), the oxalate obtained from Ce(IV)
phosphate is converted to bright yellow cerium diox-
ide under heating at 250 C for 3 h, whereas the oxa-
late obtained from Ce(III) phosphate only loses water
and becomes X-ray-amorphous (Fig. 1b) under the
same conditions. It is converted to dioxide only at
410 C [7], and cerium(III) oxide is shown to form
at 370 C [8].
Low-temperature forms of cerium dioxide are like-
ly to be of practical importance, e.g., in catalysis
[9, 10]. On the whole, the technology of cerium di-
oxide production with preliminary recovery of Ce(IV)
phosphate is well applicable, because phosphate ions
and most of oxalic acid can be recycled. Naturally,
treatment of bulk precipitates of Ce(IV) phosphate
presents difficulty, but advantages of the method are
also obvious.
Fig. 1. X-ray diffraction patterns of oxalate samples ob-
tained by conversion of (1) Ce(IV) and (2) Ce(III) phos-
phates. Sample: (a) initial and (b) after heat treatment
at 250 C for 3 h.
CONCLUSION
It was shown that cerium dioxide can be produced
through preliminary recovery of Ce(IV) phosphate
from acid nitrate solutions and its subsequent conver-
sion to Ce(III) oxalate.
Differences in thermal behavior between cerium
oxalates obtained by conversion of Ce(IV) and Ce(III)
phosphates were found. In the first case, the product
decomposes at low temperature (250 C) to form CeO2.
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ples obtained by conversion of (1) Ce(IV) and (2) Ce(III)
phosphates. (T) Temperature.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 8 2002

ON PRODUCTION OF CERIUM DIOXIDE
1359
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