Study On Electric Titanium Slag Removing Impurities By Activated Roasting-acid Leaching

Ilmenite resources are extremely rich in Pan-xi zone, which accout for 90.54% of total ilmenite reserves in China, but the titanium slag produced by ilmenite concentrate electric smelting has a high content of Ca and Mg, so this kind of titanium slag is not suitable as a raw material for chloride process and titanium sponge production. Therefore, removing impurities from electric furnace titanium slag to prepare raw material suitable for chloride process and titanium sponge production has important theoretical and practical significance for the development of China's titanium industry.In this paper, investigations has been conducted on titanium slag from Panzhihua Iron and Steel Co. by applying thermodynamic principles and various modern micro-test methods such as X-ray diffraction, optical microscope, scanning electron microscopy, etc. Based on the physicochemical properties and acid dissolution behavior of titanium slag, the technique and mechanism of removing impurities by activated roasting—acid leaching was systematically investigated, and a method which can effectively remove Ca, Mg and other major impurities in titanium slag was developed. The conclusions were obtained as following:(1) Physicochemical properties and process mineralogy of titanium slag showed that the main impurities in titanium slag were Ca, Mg, Al, Si, and Fe. The main mineral in the titanium slag was anosovite. The main silicate minerals included olivine, enstatite and siliceous vitreous. The major impurities Mg, Al, Fe were mainly occured in anosovite. Ca and Si were mainly occured in silicate minerals.(2) Acid dissolution behavior of titanium slag showed that TiO2 grade after acid leaching cannot be substantially increased, which was mainly due to poor acid-solubility of the impurities in anosovite solid solution.(3) The research of activated roasting—acid leaching showed that impurities such as Ca and Mg in titanium slag can be effectively removed by phosphoric acid activated roasting—acid leaching and TiO2 grade of the product was favorablely improved. Consequently, high-quality synthetic rutile containing 88.54% TiO2,0.42%(CaO+MgO) was obtained under the conditions that the dosage of H3PO4 7.5%, roasting temperature 1000℃, roasting time 2h, liquid-solid ratio 10:1, stirring speed 500rpm, boiling leaching 2h, sulfuric acid concentration 15% in the first leaching process, sulfuric acid concentration 40% in the second leaching process.(4) Mechanism of phosphoric acid activated roasting of titanium slag showed that phosphoric acid can react with anosovite solid solution and silicate minerals, as a result, titanium components in titanium slag turned into rutile TiO2, impurities turned into acid-soluble phosphate and quartz. Activated roasting destroyed the structures of anosovite solid solution and silicate minerals. Therefore, Ca, Mg and other impurities in titanium slag can be effectively removed, and TiO2 grade of products significantly improved.This study examined the essential mechanism on why TiO2 cannot substantially be enriched by acid leaching, and developed a new technology for preparation of high quality synthetic rutile. Titanium slag activated roasting—acid leaching has presented a new way for preparing high-quality raw materials for chloride process and titanium sponge production.