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 Tokyo2 Associate Professor, Institute of Industrial Science, University of Tokyo

Subject Categories: Preform reduction process (PRP), Calciothermic reduction, Titanium powder, Selective chlorination

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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.

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.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.

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.

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 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.

Stainless steel net

Reductant (Ca shots)

Stainless steel reaction vessel

Ti sponge getter

Feed preformafter Fe removal

TIG welding

Stainless steel cover

Stainless steel holder

Stainless steel net

Reductant (Ca shots)

Stainless steel reaction vessel

Ti sponge getter

Feed preformafter Fe removal

TIG welding

Stainless steel cover

Stainless steel holder

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Figure 1. Schematic illustration of the experimental apparatus for reduction.

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.

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.

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 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.

Figure 2. X-ray diffraction (XRD) pattern (a) and scanning electron microscopic (SEM) image (b) of titanium powder obtained by preform reduction process (PRP).

Table I. Analytical results of obtained titanium powder by preform reduction process using natural rutile ore.a

Exp. stepConcentration of element i,

Ci (mass%)b

Al Cl Ca Ti FeAfter fabrication 0.50 20.29 10.20 67.64 1.36After calcination 0.08 22.15 11.65 65.99 0.13After reduction n.d.c 13.09 67.98 18.79 0.10

After leaching 0.56 n.d.c 0.98 98.23 0.23

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. [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).

(a)

5μ ｍ

(b)

20 40 60 80 100

JCPDS # 44-1294: Ti(a)

5μ ｍ5μ ｍ

(b)

20 40 60 80 100

JCPDS # 44-1294: Ti

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