Study On The Preparation Of Ilmenite By Electrolytic Reduction Of Ilmenite With CaCl 2 - -NaCl And CaCl 2

The application of ferrotitanium (FeTi) in iron and steel industry, new energy materials and magnetic materials has broad application prospects and high economic value. However, at present, the industrial production of ferrotitanium has the disadvantages of complicated process, high equipment requirement and strict raw material requirement, which lead to the high cost. FFC method is a new electrochemical reduction technique for the preparation of ferrotitanium, which has advantages of the electro-reduction process compared with other extractive metallurgical processes are fewer processing steps, low labor requirements, the ability to directly reduce a combination of different metal oxides to form alloys, and environmental friendliness. In this paper, an equal-molar CaCl2-NaCl mixed molten salt is used as electrolyte to prepare ferrotitanium from ilmenite by FFC process with synthesized ilmenite as the raw material. The effects of sintering temperature, electrolysis time, cell voltage, electrolytic temperature and CaO addition on the electrolytic process and the product are studied. The major research results are drawn as follows:Ferrotitanium alloy is prepared successfully from synthesized ilmenite through FFC method in equal-molar CaCl2-NaCl molten salt. In the sintering temperature range of 400～1100℃, the porosity of the ferrotitanium decreases with the increase of sintering temperature. Through the comparison of the electrolytic products that come from ilmenite sintered at different temperatures, it is found that when sintering temperature is too low, the prepared pellet would break into pieces and powders after immersion in molten salts. This can be ascribled to the low strength of the ilmenite cathode. The ilmenite is accumulated on the bottom of the reactor so that the ilmenite cannot be reduced. However, when the sintering temperature is too high, the poor contaction between electrode and molten salt inhibits the migration of ions due to the low porosity of cathode, resulting in the reduction with low efficient. Compared to the experimental results, the best sintering temperature is 800～900℃.Electrolysis time is an important influence factor for the molten salt electrolysis. After electrolysis of 1h at 800℃ for 3.2V, there are CaTiCl2 and metallic Fe generated while parts of FeTiCl2 still remain. With the extension of electrolytic time to 4h, CaTiO3 became the main phase as well as FeTiCl2 phase disappeared. And there are Fe2Ti and Fe-Ti-O formed but the target product FeTi has not been detected. As the electrolysis progresses, the reduction of CaTiO3 and further deoxidation of Fe-Ti-O are the main reactions in the subsequent electrolysis process. In the whole electrolysis process, the current is increased rapidly at first and and then gradually tends to be stable. It is observed that the particles of ferrotitanium has a uniform size in the intial period of time. Along with the electrolysis time extension, however, the particles connect with each other to form the strips which can be ascribed to honeycomb structure.With the increase of the voltage from 2.7-3.2V, the current is considerably increased. The relatively high voltage is benefical to improve the reduction speed of ilmenite and obtain more pure products in shorter time. The morphology of the product is changed by the larger, irregular particles into regular small particles. The larger of the electrolytic voltage, the smaller the particle size.With the increase of the temperature from 600～1000℃, the current is increased at 3.2V. When the reaction temperature is 1000℃, the main product is FeTi after 8h. However, the ilmenite can not be reduced to FeTi until the reaction time is 18h at 800～900℃. With the increase of electrolytic temperature, the particle size of products is increased gradually.The addion of CaO into NaCl-CaCl2 molten salt plays an important role in the electrochemical deoxidaion process for the preparation of ferrotitanium from ilmenite. The optimized CaO addition amount is 1mol% and this suitable content of CaO in the molten salt can significantly improve the reduction rate of ilmenite. On the contrary, adding too much CaO will impede the reduction of intermediate CaTiO3. Besides, the micromorphology of the ferrotitanium product is porous with addition of 1mol% CaO. As the extension of electrolysis time, the particles can be connected with each other to form strips.With Qinzhou Guangxi titanium concentrate as raw material, the cathode with different shapes including flake, pellet and powders are reduced by electrolysis with serveal kinds of self-designed electrolytic devices. The major research results are drawn as follows:With Qinzhou Guangxi titanium concentrate as raw material, the reduction rate of ilmenite in CaCl2 molten salt is faster than that in CaCl2-NaCl molten salt. The ilmenite pellet can be reduced to form pure FeTi for 20h in CaCl2 molten salt, when the volume of the pellet is too large, the inner part of the flake can not be deoxygenated leading to the impure of products. When pellet titanium concentrate is used as cathode, the diameter of the pellet has significant effect on the electrolysis process. When the titanium concentrate powders are used as cathode, the poor contaction between these powders and current collector brings about low current efficiency.