Reduction of indium(III) oxide to indium through mechanochemical route

Article abstract of DOI:10.1246/cl.2008.204

A nonthermal reduction of indium(III) oxide (In₂O₃) to metallic indium (In) was achieved through mechanochemical route in this work. A mixture of In₂O₃ and lithium nitride (Li₃N) under ammonia (NH₃) and/or nitrogen (N₂) gas environments was milled in a planetary ball mill with uni-size ZrO₂ balls to induce mechanochemical reaction between the starting materials. Metallic indium was obtained after milling for 120 min, and the results are confirmed by X-ray diffraction (XRD) analysis. Washing of the milled product with water to remove by-products using the planetary ball mill for a further 10 min resulted in formation of pellets which were analyzed by EPMA, results clearly show that high purity indium metal was obtained. Copyright

Full text of DOI:10.1246/cl.2008.204

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204
Chemistry Letters Vol.37, No.2 (2008)
Reduction of Indium(III) Oxide to Indium through Mechanochemical Route
Junya Kano,ꢀ Eiko Kobayashi, William Tongamp, and Fumio Saito
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577
(Received November 13, 2007; CL-071259; E-mail: kano@tagen.tohoku.ac.jp)
A nonthermal reduction of indium(III) oxide (In2O3) to
metallic indium (In) was achieved through mechanochemical
route in this work. A mixture of In2O3 and lithium nitride (Li3N)
under ammonia (NH3) and/or nitrogen (N2) gas environments
was milled in a planetary ball mill with uni-size ZrO2 balls to in-
duce mechanochemical reaction between the starting materials.
Metallic indium was obtained after milling for 120 min, and
the results are confirmed by X-ray diffraction (XRD) analysis.
Washing of the milled product with water to remove by-products
using the planetary ball mill for a further 10 min resulted in for-
mation of pellets which were analyzed by EPMA, results clearly
show that high purity indium metal was obtained.
moved for characterization, and the milled product was further
washed in the same mill with water for 10 min to remove the
by-product. The milled samples were characterized by X-ray
powder diffraction (XRD) analysis using Rigaku, RINT-2200/
˚
PC system with a Cu Kꢀ irradiation source (ꢁ ¼ 1:5405 A) at
40 kV and 20 mA in a continuous scan mode between 5 and
60ꢂ in 2ꢂ. The solid pellets obtained after washing was analyzed
by an Electro-Probe Micro-Analyzer (EPMA).
X-ray diffraction patterns of In2O3 milled with Li3N under
NH3 and N2 gas environments are shown in Figure 1; (a) In2O3
before milling, (b) and (c) patterns of powder fractions obtained
after milling of the starting materials. It could be seen from the
X-ray diffraction patterns that peaks of In2O3 have been com-
pletely reduced within 120 min of milling at 300 rpm, and that
peaks of In metal appear dominant in the product. Unreacted
fractions of the starting materials are reduced to amorphous
phase and may be below detection limit, and lithium compounds
after reaction remain in amorphous phase owing to the milling
effect. Intensity of the patterns obtained with N2 as gas environ-
ment was slightly lower than that obtained with NH3 gas; how-
ever, in both experimental systems In2O3 was successfully re-
duced to indium metal.
Indium (In) is a rare element principally obtained as a by-
product of the electrolytic refining of zinc. It has many important
applications; mainly as thin films of indium–tin oxide (ITO) for
liquid-crystal displays. It also finds application as constituent of
fusible alloys with precious and base metals to lower their melt-
ing points and as electrical components and semiconductors in
the form of indium phosphide (InP).1–3 Demand for indium in
Japan reached 335 t in 2000, of which about half of the material
was recovered from scrap: a large amount could be recovered
from weld metal alloys, scraped ITO, and indium phosphide in
LCDs.1 Recovery of indium by dissolving in chloride media
and subsequent extraction and separation is reported by other
researchers.4,5 A reductive decomposition of In2O3 to metallic
indium by cathodic reduction is also reported in the literature.6
Mechanochemical route to material synthesis could be ap-
plied, and recently, mechanochemical reaction between Ga2O3
and Li3N to prepare GaN has been applied.7
Washing the powder products obtained after milling for
120 min at 300 rpm and a further 10 min with water to remove
the by-products resulted in formation of larger pellets of size
around 10 mm. EPMA patterns of the pellet obtained is shown
In2O3
In
In this work, we performed a nonthermal reductive decom-
position of In2O3 to In metal by milling to effect mechanochemi-
cally induced solid-state reactions with Li3N as a reactant under
NH3 and/or N2 gas environments.
(a) In2O3
Starting materials, indium oxide (In2O3) and lithium
nitride (Li3N), were supplied by Wako pure chemical industries,
Ltd., Japan. A planetary ball mill (P-7, Fritcsh, Germany),
having a pair of ZrO2 mill pots, charged with 24 ꢁ 10 mm
diameter ZrO2 balls each was used for the milling of In2O3
and Li3N, and the milling was conducted under NH3 and/or
N2 gas environments to induce mechanochemical reaction
between the starting materials. The diameter and length of the
two mill pots are 40 mm, and inner pot vol is 45 cm3. In2O3
(2.0 g) and Li3N (0.76 g) (1:3 (mol/mol) ratio) were carefully
mixed inside a glove box under argon gas environment and
charged into the mill pot, and the pot was set in a container made
of stainless steel (overpot). The inner air in the mill pot was
degassed with a vacuum pump, and both NH3 and N2 gases
were charged at 0.8 MPa. The charged mill pots were set on mill
device and rotated at 300 rpm for 120 min. After the milling
operation, a portion of the fine powder in the product was re-
(b) In2O3 + Li3N + NH3
(c) In2O3 + Li3N + N2
10
20
30
40
50
60
2θ (degree, CuKα)
Figure 1. X-ray diffraction patterns of; (a) pure In2O3 before
milling, (b) In2O3/Li3N mixture milled under NH3 gas environ-
ment; (c) In2O3/Li3N mixture milled under N2 gas environment.
All samples were milled for 120 min at 300 rpm.
Copyright Ó 2008 The Chemical Society of Japan

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Chemistry Letters Vol.37, No.2 (2008)
205
1000
500
In2O3
In
In
In
(a)
0
1000
(b)
(c)
500
In
In
0
In
In
8000
In
In
In
In
4000
0
3
4
5
6
7
Wavelength / Å (10-10 m)
Figure 2. EPMA pattern of In-metal pellet obtained after
milling In2O3 and Li3N mixture (molar ratio 1:3) for 120 min
under NH3 gas environment.
10
20
30
40
50
60
2θ (degree, CuKα)
Figure 4. X-ray diffraction patterns of sample mixtures milled
for 120 min at 300 rpm; (a) In2O3 under NH3 gas; (b) In2O3/
Li3N mixture without NH3/N2 gases; (c) In2O3/Li3N mixture
under NH3 gas environment.
metal appeared when In2O3 was milled with Li3N without NH3
gas (Figure 4b); however, peaks of In2O3 also remain after
120 min of milling time. Milling of In2O3 with Li3N in the pres-
ence of NH3 gas is shown in Figure 4c. It shows only dominant
peaks of indium metal.
Characterization of both powder products obtained after
milling and indium pellets obtained after washing of the milled
powder products shows that In2O3 could be reduced by mecha-
nochemical reaction between In2O3 and Li3N. The rate of reac-
tion is significantly increased when the milling operation is con-
ducted under NH3 or N2 gas. High purity In metal can be pre-
pared within 120 min of milling and at a moderate milling speed
of 300 rpm. Based on this finding, we propose that a mechano-
chemical route to recovery of In metal by milling in either
NH3 or N2 gas environments of In2O3 and Li3N could be devel-
oped to treat scrap containing indium such as ITO wastes.
Figure 3. Photograph of In-metal pellet obtained after milling
In2O3 and Li3N mixture (1:3 = In2O3:Li3N molar ratio) for
120 min under NH3 gas environment.
in Figure 2, indicating dominant peaks of In metal, and a photo-
graph of In pellet obtained from milling operation is shown in
Figure 3.
From the results obtained, the mechanochemically induced
solid-state reaction between In2O3 and Li3N under NH3 and
N2 gases can be represented by the following reaction mecha-
nisms (1) and (2), respectively;
References
1
J. D. Jorgenson, M. W. George, U.S. Geological Survey,
Open-File Report 2004-1300 2005, http://pubs.usgs.gov/of/
2004/1300/index.html.
2
3
A. M. Alfantazi, R. R. Moskalyk, Miner. Eng. 2003, 16, 687.
RUTLEY’S Elements of Mineralogy, 27th Edition, Revised
by C. D. Gribble, 1988.
In2O3 þ Li3N þ NH3 ! 2In þ 3LiOH þ N2
In2O3 þ 2Li3N þ N2 ! 2In þ 3Li2O þ 2N2
ð1Þ
ð2Þ
4
5
6
X. Zhang, G. Yin, Z. Hu, Talanta 2003, 59, 905.
S. V. Vartak, V. M. Shinde, Talanta 1998, 45, 925.
Figure 4 shows In2O3 milled under different conditions for
120 min; (a) under NH3 gas but without Li3N, (b) with Li3N
but without NH3 gas, and (c) with Li3N in NH3 gas. Milling
of In2O3 in NH3 gas but without Li3N could not lead to forma-
tion of indium metal as indicated by Figure 4a. Peaks of indium
´
S. Omanovic, M. Metikos-Hukovic, Thin Solid Films 1995,
ˇ
´
266, 31.
J. Kano, L. Jenfeng, I. Kang, W. Tongamp, E. Kobayashi,
F. Saito, Chem. Lett. 2007, 36, 900.
7
Published on the web (Advance View) February 5, 2008; doi:10.1246/cl.2008.204