The Effects of Thermal Pretreatment on Leaching of Yunnan Ilmenite with Hydrochloric Acid
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ILMENITE accounts for 90 pct of the world demand for titanium minerals, mainly for the production of titanium dioxide pigment. Titanium dioxide pigment is produced industrially by the sulfate and chloride processes. The chloride process generally enjoys more favorable economics and generates less waste. However, the chloride process needs natural rutile, synthetic rutile, or high-grade titanium slag as raw materials. The shortage of natural rutile has encouraged research efforts to convert ilmenite into synthetic rutile to meet the raw material requirements of the chloride pigment manufactures.[1–3] Hydrochloric acid leaching of ilmenite is used in the so-called Benilite process to manufacture synthetic rutile. It is also used in the Austpac process, which is still at the pilot stage.[4] Many leaching studies of ilmenite by hydrochloric acid were performed in order to obtain optimum conditions for upgrading the ilmenite into synthetic rutile. The leaching rate of iron and the recovery of titanium are affected by the acid concentration, temperature, acid to ilmenite mole ratio, particle size, and additives.[2,5–7] Furthermore, the reactivity toward hydrochloric acid also depends on the nature of the mineral, whether it has been altered or not.[2] In order to enhance the leaching rate of iron, a reduction is necessary to convert the ferric into ferrous which is more soluble in hydrochloric acid.[8] It has also been found that oxidation prior to reduction of ilmenite
SONG-LI LIU, Associate Professor, is with the Resources and Environmental Engineering College of Panzhihua University, Panzhihua 617000, Sichuan, China, and also with the Kunming Metallurgy Research Institute, Kunming 650031, Yunnan, China. JUN-YI XIANG, Ph.D. Candidate, is with the Materials Science and Engineering College of Xihua University, Chengdu 610039, Sichuan, China. Contact e-mail: [email protected] Manuscript submitted April 27, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
can enhance the rate of reduction and leaching.[9] The high-temperature oxidation process can remove the organic components, which limit the leaching rate. Furthermore, the heating process can produce cracks permitting faster penetration of acid solution into the ore grain. The oxidation treatment also converts the titanium in ilmenite to rutile, which is less soluble in hydrochloric acid, and a high recovery of titanium is obtained.[10,11] However, some investigators observed that oxidation before leaching has no advantages in the manufacture of synthetic rutile.[12] It is possible that the nature of the mineral was different in that study. The quality of synthetic rutile is mainly influenced by two factors. Namely, the percentage of titanium content and the particle size of the material. Generally speaking, the higher content of titanium and the less impurities, the better synthetic rutile is as raw material for the chloride process. In order to meet the chlorination fluid bed requirements, the particle size of synthetic rutile must be in the range of 10 and +200
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