5th UT2 Graduate Student Workshop (University of Tokyo – University of Toronto), 2006
Production of Titanium Powder Directly from Titanium Ore
by Preform Reduction Process (PRP)
Haiyan Zheng 1 and Toru H. Okabe 2
1
Ph.D. Candidate, Department of Materials Engineering, Graduate School of Engineering, University of Tokyo
2
Associate Professor, Institute of Industrial Science, University of Tokyo
Subject Categories: Preform reduction process (PRP), Calciothermic reduction, Titanium powder, Selective chlorination
With this background, numerous researches on processes
such as the FFC process [2], OS process [3], EMR process
[4], PRP [5], and so on, have been carried out globally for
determining a new process for producing high quality
titanium with low cost. The first three abovementioned
processes are based on the direct reduction of titanium ore by
an electrochemical method in a molten salt. Although it is
anticipated that the electrochemical method has the potential
to replace the Kroll process, it is difficult to control the
oxygen level in the obtained titanium, and several technical
problems need to be resolved before a large-scale
commercial process can be established.
Abstract
To develop a new process for producing metallic titanium
powder directly from titanium ore, the preform reduction
process (PRP) based on the calciothermic reduction of
titanium ore was investigated. A new method for removing
iron from the ore by selective chlorination was developed,
and the de-ironized feed was reduced by the PRP to
metallic titanium. In a fundamental experiment, titanium
feed preform was fabricated at room temperature by a
casting slurry, which is a mixture of titanium ore (rutile
(94.6%): TiO2 with impurities, e.g., iron), flux (CaCl2),
carbon powder, and a binder. The fabricated preform was
calcined at elevated temperatures, and iron was removed by
selective chlorination. The obtained preform was then
reduced using metallic Ca vapor as the reductant, and the
reduced preform was subject to leaching to remove the
CaO, Ca, and other impurities. When the de-ironized rutile
ore mixed with the CaCl2 flux was reduced, metallic
titanium powder with the purity exceeding 98% was
obtained. This study demonstrated that the PRP is feasible
to produce titanium powder directly from titanium ore. This
process has the potential to enable the development of a
new environmentally sound high speed low cost process for
producing titanium powder.
In the present study, the preform reduction process (PRP)
based on the calciothermic reduction of titanium ore was
investigated [5]. The overall reduction process is listed as
the following reaction [6]:
TiO2(s) + 2Ca(g) = Ti(s) + 2CaO(s) G = −288 kJ at 1300 K
The PRP involves four major steps: (1) preform fabrication
by a mixture of natural rutile ore, calcium chloride (CaCl2)
as the flux, and collodion as the binder at room
temperature; (2) calcination/iron removal of the preform at
an elevated temperature; (3) reduction by Ca vapor at an
elevated temperature; and (4) leaching at room temperature.
In this study, carbon powder was introduced into the feed
preform; this is a new method to achieve iron removal with
a high efficiency.
Introduction
Titanium (Ti) is used in various fields because of its
excellent physical and chemical properties. Furthermore, it
is the ninth most abundant element in the earth’s crust, and
its mineral resource is abundant. Therefore, it possesses the
potential to become a common and prosperous material in
the future. However, the production volume of metallic
titanium is significantly lower than that of common metals
such as iron and aluminum due to the high cost and low
productivity of the current titanium production process—
the Kroll process [1]. Although the Kroll process can
produce high quality titanium, it is a slow batch-type
process and is capital and labor intensive.
Experimental
The feed preform was fabricated from a slurry, which was
made by mixing approximately 6.26 g of natural rutile ore,
1.74 g of CaCl2 as the flux, 0.20 g of carbon powder, and
collodion as the binder. The fabricated preform was then
heated at 1273 K for 1 h for removing the iron in the
titanium ore by a selective chlorination method. In this
calcination/iron removal process, the binder and water in
the preform were also removed. A schematic illustration of
the experimental apparatus for the reduction is shown in
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Figure 1. In this reduction step, two to ten pieces of
sintered preform and calcium shots were set in a stainless
steel reaction vessel. The reaction vessel was then heated at
1273 K for 9 h for the reduction of the titanium ore by Ca
vapor. After the reduction, the reaction vessel was removed
from the furnace and quenched in water. The preform in the
reaction vessel was mechanically recovered at room
temperature and subjected to the following leaching
process. In the leaching step, the obtained sample from the
reduction process was reacted with a 50% acetic acid
solution (CH3COOH) for 8.7 h and hydrochloric acid (HCl)
for 1 h to remove by-product (CaO) and the excess
reductant (Ca) in the sample; this was followed by rinsing
three times with distilled water, two times with
isopropanol, and one time with acetone at room
temperature. Finally, the obtained powder was dried in a
vacuum dryer.
sintered mixture of natural rutile ore and CaCl2 flux, with
Ca vapor.
In the future, the mass balance and detailed mechanism of
the reactions will be investigated. Moreover, a more
effective method for removing iron from titanium ore by the
selective chlorination method will be investigated for
developing an innovative process for producing high purity
titanium powder with low cost.
(a)
: Ti JCPDS # 44-1294
20
TIG welding
40
60
80
100
(b)
Stainless steel
reaction vessel
Stainless steel cover
Feed preform
after Fe removal
Stainless steel net
Stainless steel holder
5μｍ
Reductant (Ca shots)
Ti sponge getter
Figure 2. X-ray diffraction (XRD) pattern (a) and scanning
electron microscopic (SEM) image (b) of titanium powder
obtained by preform reduction process (PRP).
Figure 1. Schematic illustration of the experimental
apparatus for reduction.
Table I. Analytical results of obtained titanium powder by
preform reduction process using natural rutile ore.a
Concentration of element i,
Ci (mass%)b
Exp. step
Al
Cl
Ca
Ti
Fe
Results and discussion
Figure 2 (a) shows the XRD pattern of the obtained sample
after leaching. Only the -Ti phase was detected in the
sample. Figure 2 (b) shows the SEM image of the obtained
sample after leaching. Titanium powder in the form of
sponge with a primary particle size of 2–3 m was obtained
successfully.
After fabrication
0.50
20.29
10.20
67.64
1.36
After calcination
0.08
22.15
11.65
65.99
0.13
n.d.
13.09
67.98
18.79
0.10
0.56
c
0.98
98.23
0.23
After reduction
After leaching
Table I shows the results of the obtained samples analyzed
by XRF. As shown in this table, titanium powder with
98.23% purity was obtained. This also indicates that the
concentration of iron after calcination decreased from
1.36% to 0.13%, demonstrating that iron can be
successfully removed in the calcination step.
c
n.d.
a
: Natural rutile ore produced in South Africa (TiO2: 94.58%, Fe2O3:
3.69%, V2O5: 1.73% ).
b
: Determined by X-ray fluorescence (XRF) analysis.
c
: Not detected, which is below detection limit of XRF (<0.01%).
References
[1] W. Kroll, “The Production of Ductile Titanium,” Tr. Electrochem. Soc.,
78 (1940), 35–47.
[2] G.Z. Chen, D.J. Fray, and T.W. Farthing, “Direct Electrochemical
Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride,”
Nature, 407 (2000), 361–364.
[3] R.O. Suzuki, K. Teranuma, and K. Ono, “Calciothermic Reduction of
Titanium Oxide and in-situ Electrolysis in Molten CaCl2,” Metallurgical
and Materials Transactions B, 34B (2003), 287–295.
[4] T.H. Okabe and T. Uda, “Reduction Process of Titanium Oxide Using
Molten Salt,” Titan, 50 (2002), 325–330.
Conclusions
It is demonstrated that iron was successfully removed by
selective chlorination in the calcination step, and high
purity (above 98%) metallic titanium powder can be
successfully obtained by reacting the preform, which is a
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[5] T.H. Okabe, T. Oda, and Y. Mitsuda, “Titanium Powder Production by
Preform Reduction Process (PRP),” Journal of Alloys and Compounds,
364 (2004), 156–163.
[6] I. Barin, Thermochemical Data of Pure Substances, 3rd ed. (Weinheim,
Federal Republic of Germany, VCH Verlagsgesellschaft mbH, 1997).
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