Thermodynamic Consideration of the Removal of Iron from Titanium Ore by Selective Chlorination
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INTRODUCTION
IN recent years, interest in a method that allows inexpensive low-grade titanium ore to be used in the titanium (Ti) smelting industry has increased along with the price of Ti ore.[1–3] Currently, low-grade Ti ore is upgraded to a high-grade titanium dioxide (TiO2) feed by an upgrading process for removing impurities (mainly iron) prior to use as a feedstock in Ti smelting. This is because low-grade Ti ore is an unsuitable feed to the chlorinator for the current Kroll process, because it makes the chlorinator hard to operate owing to problems such as clogging of pipes by condensed chlorides (e.g., FeClx) due to the production of large amount of chloride waste. In addition, the chlorine loss in Ti smelting also increases because of the chloride waste produced. For these reasons, interest in a method for the removal of iron to produce a high-grade TiO2 feed from Ti ore has risen. A variety of research on upgrading Ti ore has been conducted in the past, and several processes are already used in industry. However, the slag process utilizing high-temperature reactions above 1923 K to 1973 K (1650 C to 1700 C) for directly separating iron from Ti ore is the only process that has been developed using pyrometallurgical method for industrial application.[4–6]
JUNGSHIN KANG, Graduate Student, is with the Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. TORU H. OKABE, Professor, is with the Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan. Contact e-mail: [email protected] Manuscript submitted October 4, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
Figure 1 shows an outline of the materials flow for the current process for the production of titania pigment and Ti metal.[4,6–8,42–45] As shown in Figure 1, the sulfate process,[4,7] the slag process,[9,10] the UGS process,[9,10] the Becher process,[11,12] the Benilite process,[13–15] and the chloride process[4,7,16,17] for upgrading Ti ore have been implemented for practical use, and TiO2 that meets the quality requirements is produced by combining these processes. Many processes for upgrading Ti ore are hydrometallurgical processes that use acidic solutions for dissolving and leaching iron in the ore. However, the slag process and the chloride process are pyrometallurgical processes conducted at high temperatures. Hydrometallurgical processes such as the sulfate process or the Benilite process have the advantage of upgrading Ti ore at a relatively low energy cost. However, the disadvantages of these processes are the treatment of the precipitate and the cost of the treatment of the large amount of waste aqueous solution produced, which contains heavy metals because of the use of a large amount of acid.[9,13] The treatment of waste solutions containing heavy metals such as iron and manganese is a problem in some countries that have strict environmental regulations.[18] The slag process and the chloride proc
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