Determination of lanthanides (La, Ce, Nd, Sm) and other elements in metallic gallium by instrumental neutron activation analysis

Article abstract of DOI:10.1016/S0925-8388(02)00301-8

This paper reports the analytical results of lanthanides and other elements in pure elemental gallium. The analyses were performed by instrumental neutron activation analysis (INAA) at the nuclear reactor IEA-R1, IPEN, S?o Paulo. INAA has the advantage of being a multi-elemental and non-destructive analytical method. After irradiation, the samples were set aside for some days before running high resolution gamma spectrometry with a hyper-pure Ge detector. Gallium was recovered from the Bayer process alkaline leach solution, named by local aluminum industry as 'weak soda', (spent liquor) with a concentration of about 150 mg l^-1. As a first step, gallium was recovered from the 'weak soda' and enriched using a complexing ion-exchanger of the polyamidoxime type specially synthesized in the country for this purpose. After washing the column with water and then with pure sodium hydroxide to remove the interstitial 'spent liquor', gallium was eluted from the resin. The eluted gallium solution was made to 4 mol l^-1 in NaOH and subject to electrolysis. The metal was then collected from the electrodes and given a final purification step by dilute inorganic acid stripping. The most representative lanthanide elements found and analyzed in the metallic gallium were La, Ce, Nd and Sm. One of the most recent samples exhibited the following results: (μg g^-1) La (16.1), Ce (15.5), Nd (11.8) and Sm (3.6). Besides the lanthanides, the following elements were also analyzed: U, Cr, Fe, Co, Zn, Mo, Se, Sb and Ba. The results showed that the metal obtained is highly pure. The purity can be enhanced by stripping the metallic gallium with a dilute mineral acid.

Full text of DOI:10.1016/S0925-8388(02)00301-8

Journal of Alloys and Compounds 344 (2002) 36–39
L
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Determination of lanthanides (La, Ce, Nd, Sm) and other elements in
metallic gallium by instrumental neutron activation analysis
a ,
b
b
b
a
*
˜
A.M.G. Figueiredo , W. Avristcher , E.A. Masini , S.C Diniz , A. Abrao
a
Instituto de Pesquisas Energ e´ ticas e Nucleares, Tr. R. 400, Cidade Universit a´ ria, Caixa Postal 11049, 05422-970 S a˜ o Paulo, Brazil
b
Projeto G a´ lio, Escola Polit e´ cnica, Universidade de S. Paulo, Av. Prof. Mello Moraes 2373, Cidade Universit a´ ria, 05508-900 S a˜ o Paulo, Brazil
Abstract
This paper reports the analytical results of lanthanides and other elements in pure elemental gallium. The analyses were performed by
instrumental neutron activation analysis (INAA) at the nuclear reactor IEA-R1, IPEN, S a˜ o Paulo. INAA has the advantage of being a
multi-elemental and non-destructive analytical method. After irradiation, the samples were set aside for some days before running high
resolution gamma spectrometry with a hyper-pure Ge detector. Gallium was recovered from the Bayer process alkaline leach solution,
2
1
named by local aluminum industry as ‘weak soda’, (spent liquor) with a concentration of about 150 mg l . As a first step, gallium was
recovered from the ‘weak soda’ and enriched using a complexing ion-exchanger of the polyamidoxime type specially synthesized in the
country for this purpose. After washing the column with water and then with pure sodium hydroxide to remove the interstitial ‘spent
2
1
liquor’, gallium was eluted from the resin. The eluted gallium solution was made to 4 mol l in NaOH and subject to electrolysis. The
metal was then collected from the electrodes and given a final purification step by dilute inorganic acid stripping. The most representative
lanthanide elements found and analyzed in the metallic gallium were La, Ce, Nd and Sm. One of the most recent samples exhibited the
2
1
following results: (mg g ) La (16.1), Ce (15.5), Nd (11.8) and Sm (3.6). Besides the lanthanides, the following elements were also
analyzed: U, Cr, Fe, Co, Zn, Mo, Se, Sb and Ba. The results showed that the metal obtained is highly pure. The purity can be enhanced by
stripping the metallic gallium with a dilute mineral acid.

2002 Elsevier Science B.V. All rights reserved.
Keywords: Rare earths; Metallic gallium; Instrumental neutron activation analysis
1
. Introduction
solid-state lasers, especially in telecommunication systems
with optical fibers. Gallium arsenide is also a promising
material for solar cells and for computer memories.
Ab initio experiments [1] in the Mining Department of
Escola Polit e´ cnica, S a˜ o Paulo State University, laboratory
started with Kelex-100, but for practical reasons the
solvent extraction was postponed in favour of a solid
ion-exchange process.
In this paper, the possibility of using instrumental
neutron activation analysis for the determination of some
impurities in highly pure metal gallium was examined. The
well known accuracy and sensitivity of NAA has made it a
reference technique. This analytical technique offers ad-
vantages over other analytical methods in that it is multi-
elemental and non-destructive, eliminating the ‘blank’ of
the analysis.
Primary sources of gallium are scarce; all of its pro-
duction comes from secondary sources, such as the
aluminum industry. Gallium follows the aluminum in its
bauxite ores whose content is from 20 to 80 ppm. In the
Bayer process about 70% of the gallium is leached from
the bauxite and follows the aluminum into the caustic soda
solution, the remaining 30% being disposed with the red
mud. Gallium accumulates in the Bayer liquor due to
several recyclings, reaching a concentration of 100–200
2
1
mg l
.
Gallium is a vital material in the semiconductor indus-
try. It is mainly used in the form of arsenide and
phosphide, GaAs and GaP, respectively. Analog integrated
circuits have been the largest end-use application for
gallium in wireless communication systems. Gallium is
also used in the manufacture of light-emitting diodes, in
Neutron activation analysis has been applied to de-
termine several elements, including the rare earths, viz. Ce,
La, Nd, Sm, and Ba, Co, Cr, Fe, Mo, Se, Sb, U and Zn as
well in high-purity elemental gallium. The alkaline solu-
tion containing gallium as gallate in sodium hydroxide
*
Corresponding author.
E-mail address: grafigue@curiango.ipen.br (A.M.G. Figueiredo).
0
925-8388/02/$ – see front matter
 2002 Elsevier Science B.V. All rights reserved.
PII: S0925-8388(02)00301-8

A.M.G. Figueiredo et al. / Journal of Alloys and Compounds 344 (2002) 36–39
37
Table 2
before the electrolysis was also analyzed by instrumental
Typical composition of a spent Brazilian Bayer liquor
neutron activation analysis. In this paper the non-destruc-
tive activation analysis was used. All the elements depicted
in Tables 4–7 were analyzed via instrumental neutron
activation analysis.
Compound
Concentration
2
1
(
g l
160.0
0.15
80.0
)
NaOH
Ga
Al O
2
3
Organic matter
2
. From bauxites to metallic gallium
(
as humic acids)
8.0
1.220
0.14
0.265
,0.001
0.01
2
3
Density (g cm
)
2
.1. Brazilian bauxites and their Bayer liquors
Brazil has an important alumina and aluminum industry
V
Mo
Zn
Fe
due to its large bauxite deposits. A review of Brazilian
bauxite deposits made by Carvalho et al. [2] presented the
principal characteristics of these deposits.
2.2. Recovery of gallium from the spent liquor
Most of our work was done with liquors which origi-
nated from Companhia Brasileira de Alum ´ı nio–CBA,
located at Cidade Alum ´ı nio, S a˜ o Paulo. The alumina mills
process bauxites from Po c¸ os de Caldas and Cataguazes,
Minas Gerais, mines. In these processes most of the
vanadium and rare earths go to the red mud and the Bayer
liquor is poor in vanadium and rare earths but rich in
gallium.
Atomic absorption spectroscopy, fluorescence X-ray,
emission spectroscopy and conventional wet chemical
analyses were applied to analyze major and minor con-
stituents of the bauxite ore and liquor used for Brazilian
industrial production of aluminum. The major constituents
in bauxite are aluminum, iron, silicon, titanium and
organic matter (humic acids). Minor assayed elements of
interest, especially concerning the Bayer liquor, are gal-
lium, vanadium, molybdenum, copper, zinc and rare earth
elements. Ion exchange chromatography with chelating
resins and solvent extraction were used as the main
processes for the separation chemistry.
The process comprises the use of a chelating home-
made ion-exchange resin [1,5]. This resin contains amidox-
ime groups [3], which form chelate bonds to gallium [4].
After extracting gallium from the alkaline liquor with the
mentioned resin, the column is rinsed with pure sodium
hydroxide to remove the interstitial solution. The resin
exhibited great selectivity in relation to gallium. Vanadium
and molybdenum, also present in the liquor, were not
absorbed by the chelating resin. The selectivity for gallium
over aluminum is excellent, only traces of aluminum and
no vanadium plus molybdenum were coabsorbed.
Gallium is finally eluted with a dilute alkaline solution.
The eluted solution is then treated to separate the ultimate
traces of organic matter (humic and fulvic acids). The
eluted solution is acidified to a final pH 1.8–2.0, at room
temperature, and after aging for a period of no less than 2
h, the humic acids were separated by filtration. This
solution is refined by percolation through a macroporous
copolymer (XAD-16ீ). From this solution gallium is
concentrated via ion-exchange and precipitation and a final
alkali treatment before it is sent to the electrodeposition.
This is done, after adding some EDTA.
Table 1 presents the average chemical composition of
the Bayer liquors produced industrially by three Brazilian
mills.
After the production of the alumina, the CBA’s spent
Bayer liquors have the average chemical composition
depicted in Table 2. This material is being worked on at
the Mining Department of Escola Polit e´ cnica, S a˜ o Paulo
State University, for the preparation of metallic gallium.
2.3. Reduction to metallic gallium
Metallic gallium is currently produced by electrolytic
process. For many years the electrolytic process depended
on the fact that mercury forms an amalgam with gallium
from which the gallium may be extracted with a caustic
soda solution. The gallium amalgam can be produced
either directly or indirectly. The gallium is deposited
directly onto the mercury cathode; using the appropriate
conditions of temperature, agitation and current density, an
amalgam is formed. In another process, sodium amalgam
is used to reduce the gallium present in the Bayer liquor,
directly. This gives an amalgam from which the gallium is
removed by treatment with caustic alkali and the mercury
is then used again to produce sodium amalgam, i.e. the
mercury circulates in a closed system.
Table 1
Average chemical composition of Bayer liquors from three Brazilian
alumina mills
2
1
Metal
Concentration (mg l
Mill 1
)
Mill 2
Mill 3
8.04
0.48
1.50
10.5
115
Fe
Cu
Cd
Ni
V
9.09
0.53
1.35
9.60
128
10.6
0.96
1.65
12.5
142
84
Mo
Ga
18
55.8
,200
107
149
The environmental problems associated with mercury

3
8
A.M.G. Figueiredo et al. / Journal of Alloys and Compounds 344 (2002) 36–39
Table 3
further discourage the use of electrolytic gallium amalgam
processes. The Brazilian process uses no mercury. It is a
clean technique and does not damage the environment.
Radioisotopes used and their main nuclear characteristics
Element
Radioisotope
Half-life
days)
Energy
(keV)
(
1
1
6
5
31
41
0
2
.4. Electrowinning of gallium
Ba
Ce
Co
Cr
Fe
La
Ba
Ce
Co
11.5
32.5
5.24
27.8
45.1
496.3
145.4
1332.2
320.0
1098.6
328.6
1595.4
140.6
91.4
Gallium is produced by electro-deposition from an
1
Cr
alkaline solution. The electrolysis is conducted in the
presence of very small amounts of aluminum as the main
impurity and minor amounts of other elements like iron,
molybdenum, chromium, zinc, cobalt, and rare earth
elements. The final concentration of sodium hydroxide was
as high as 4 M.
Gallium is recovered by electrolysis using an anode
made from a metal which ideally does not introduce
undesirable impurities in the alkaline gallate solution under
the conditions of gallium electrolytic deposition. The
cathode is also made of a metal. Several metals have been
tested in our laboratory. Final choice has, until now, not
been made.
59
Fe
40
1
La
47.27 h
9
1
9
Mo
Nd
Mo
66 h
11.1
47
Nd
5
31.0
136.0
64.7
75
Se
Sb
Se
119.8
2
1
1
1
2
22
Sb
Sb
Sm
Np
2.70
60.2
47.1 h
2.35
245
564.2
1691.0
103.2
277.5
1115.4
24
53
39
Sm
U
Zn
65
Zn
Table 4
Trace elements in the sodium gallate before electrodeposition of Ga
errors associated with the results are one standard deviation considering
counting statistics)
(
3
. Determination of impurities in metallic gallium by
neutron activation analyses
Element
Concentration
2
1
(mg l )
Fifty to 100 mg of the samples (except batch [28 after
acid scrubbing, which weighed about 500 mg) were
accurately weighed in polyethylene bags. The elemental
synthetic standards of the analyzed elements were prepared
La
Ce
Nd
Sm
Ba
Cr
Fe
Mo
U
18.160.2
65.260.8
6462
13.860.2
1948696
4.660.8
41.860.4
2768
by pipetting convenient aliquots of standard solutions
2
(
SPEX) onto 1-cm pieces of Whatman No. 40 filter paper.
The standards were sealed in polyethylene bags.
The synthetic standards were validated by irradiation
with the geological reference materials BE-N (IWG-GIT)
and NIST SRM 2704 Buffalo River Sediment, which have
certified and recommended values for the elements ana-
lysed, giving results within 95% confidence limits.
Samples and standards were irradiated for 8 h at a
21562
61562
Zn
In Table 4 are the results of some elements determined
directly in a representative gallate solution just before the
electrowinning of gallium. All elements were determined
by non-destructive instrumental analysis (INAA).
1
2
22 21
thermal neutron flux of 10 n cm
s
at the IEA-R1m
nuclear reactor of IPEN. The measurements of the induced
gamma-ray activity were carried out in a GX20190 hy-
perpure Ge detector (Canberra). The multi-channel ana-
lyzer was a 8192 plug-in-card in a PC computer. The
resolution (FWHM) of the system was 1.90 keV for the
Table 5 depicts the analyses of two experiments where
Table 5
Two analyzed gallium samples obtained by electrolysis where the
electrodes suffered corrosion (errors associated to the results are one
standard deviation considering counting statistics)
21
6
0
1
332 keV gamma-ray of Co. Countings were performed
about 10 days after irradiation and the distance between
samples and detector was 10 cm. Counting times varied
from 1 to 10 h. The gamma-ray spectra were processed by
using the VISPECT software, which locates peak positions
and calculates the energies and net areas. There was no
correction for gamma-ray self attenuation by the gallium,
since this contribution was considered small in relation to
the errors due to counting statistics, and in only one case
the weight of the sample was 500 mg. The radioisotopes
used to determine the analyzed elements and their main
nuclear characteristics are shown in Table 3.
Element
Concentration (mg g
)
Batch [8
Batch [10
Ce
Co
Cr
0.1260.03
0.3260.01
23.160.2
12365
0.8260.04
1.260.2
,0.2
1.7560.05
1.9660.03
39.160.3
37069
2.5160.07
10.960.5
0.5260.07
0.3860.01
7361
Fe
La
Mo
Nd
Sm
Zn
,0.01
37.560.7

A.M.G. Figueiredo et al. / Journal of Alloys and Compounds 344 (2002) 36–39
39
Table 6
from a gallium-containing sodium aluminate solution
circulating in the Bayer process is briefly described here.
The process comprises subjecting an alkali aluminate
solution containing dissolved gallium from bauxite to a
percolation operation into a complexing ion-exchanger.
Gallium is preferably adsorbed from the aluminate solution
and, after scrubbing the resin with appropriate solution, it
is eluted. Finally, gallium is separated from small amounts
of aluminum and traces of other elements by electro-
deposition.
A process for extracting and purifying the gallium
contained in an industrial solution of sodium aluminate by
fixing the gallium on a stationary phase constituted by
porous home-made complexing ion-exchanger adsorbent
resin is in operation at bench-scale. After elution of the
gallium, the resultant gallium salt solution is purified and
concentrated so as to be reduced directly to the state of
high purity metallic gallium by electrolysis. Subjecting the
concentrated and purified gallium solution to electrolysis
led to metallic gallium.
Before the electrolysis, organic impurities, especially
humic and fulvic acids, are removed from the alkali gallate
solution by acid precipitation and refined by means of a
special cross-linked absorber.
The determination of trace impurities in gallium samples
have been made by ICP-MS, GDMS (glow discharge mass
spectrography) and INAA (instrumental neutron activation
analysis). This last procedure operating at the IPEN
Radiochemistry Division allowed the determination of
several elements, including four rare earths: lanthanum,
cerium, neodymium and samarium.
Determination of trace impurities in some representative elemental
gallium samples (errors associated with the results are one standard
deviation considering counting statistics)
2
1
Element
Concentration (mg g
Batch [25
)
Batch [26
Batch [27
La
Ce
Nd
Sm
Cr
,0.05
,0.07
,0.2
,0.01
11.860.3
100610
0.8160.03
17.760.7
,0.07
11.460.8
,0.07
5.360.5
,0.01
,0.05
,0.07
2.460.2
,0.01
1.360.1
,10
,0.01
7.260.4
,0.07
2.960.1
2763
Fe
Co
Zn
Se
0.1260.01
18.560.5
0.1560.04
the metallic electrodes suffered some electrocorrosion.
Especially iron and chromium were codeposited with
gallium and contaminated the metal.
Table 6 shows the results of the analyses of some recent
representative elemental gallium samples obtained after the
exchange of the electrodes. In Table 7 are shown the
results obtained for gallium sample [28, which was
further cleaned with an acid treatment. This procedure is
beneficial and contributed to partial or total decontamina-
tion of the impurities analyzed.
4
. Conclusions
Gallium is produced by electro-deposition from an
alkaline solution. The electrolysis is conducted in the
presence of a small amount of aluminum as the main
impurity and minor amounts of other elements such as
iron, molybdenum, chromium, zinc, cobalt, and rare earth
elements. The concentration of sodium hydroxide was as
high as 4 M.
The analytical results for some samples of gallium
which has been obtained by electrolysis from sodium
hydroxide medium show that the metal is highly pure. The
decontamination of the impurities from metallic gallium is
also enhanced by stripping with a dilute mineral acid.
A highly efficient process for producing metallic gallium
References
Table 7
Determination of trace impurities in a gallium sample submitted to acid
treatment (errors associated with the results are one standard deviation
considering counting statistics)
[
1] A.P. Chaves, W. Avristcher, H.O. Krentz, A. Abrao, Aproveitamento
˜
de g a´ lio da lix ´ı via do processo Bayer por troca io
ˆ
nica, in: Anais do
2
1
XVI Encontro Nacional de Tratamento de Min e´ rios e Hidrometalur-
gia, Rio de Janeiro, Metalurgia Extrativa,Vol. II, 1995, pp. 167–176,
Element
Concentration (mg g
Batch [ 28
)
Batch [28
after acid scrubbing
3
-6 Set.
[
[
[
2] A. Carvalho, B. Boulang e´ , A.J. Melfi, Y. Lucas, Brazilian Bauxites,
USP/FAPESP, S a˜ o Paulo, 1997, ORSTOM, Paris.
3] P.A. Riveros, Recovery of gallium from Bayer liquors with an
amidoxime resin, Hydrometallurgy 25 (1990) 1–18.
4] F. Vernon, Chelating ion-exchangers: the synthesis and uses of
poly(hydroxamic acid) resins, Pure Appl. Chem. 54 (11) (1982)
La
Ce
Nd
Sm
Cr
16.160.9
15.561.0
11.861.1
3.660.3
49.460.8
26567
1.1960.02
,1
8.560.2
10.260.8
,0.07
,0.2
,0.01
,0.15
0.5560.23
,0.01
51.160.7
2.260.9
2
151–2158.
Fe
[
5] A.P. Chaves, A. Abr a˜ o, W. Avritscher, Gallium recovery as a
by-product of bauxites, in: R.D. Peterson (Ed.), Light Metals 2000,
Minerals, Metals & Materials Society, 2000, pp. 891–896.
Co
Zn
Sb