Synthesis of titanium tetrachloride through arbothermal reduction and chlorination of ilmenite oncentrate

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Date
2018-08-01
Authors
Eltefat Ahmadi
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The synthesis of titanium oxycarbonitride (TiOxCyNz) from ilmenite and its chlorination at low temperatures for production of titanium tetrachloride (TiCl4) was investigated in this research. The effects of reduction/nitridation temperature, time, atmosphere and addition of waste polyethylene terephthalate (PET) plastic into coal on the formation of TiOxCyNz and iron (Fe) from ilmenite were investigated in carbothermal reduction and nitridation (CTRN) process at 1100-1250 °C for 60-180 minutes with four different PET-to-coal ratios (C/Ored) ranging from 25 to 100 wt%. Field-emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectrometer (EDX) analyses showed that the product synthesized by 75 wt% PET had a unique microstructure in which spherical Fe particles were distinctly separated from TiO0.02C0.13N0.85 phase. The highest extents of reduction and nitridation of the sample synthesized by 75 wt% PET were 99.15% and 85.47%, respectively. Iron was also removed by an aeration leaching process at 70 °C in the presence of ammonium chloride (NH4Cl) and 0.1 wt% AQ-2 (Anthraquinone-2- sulfonic acid sodium salt monohydrate) as the effective catalysts. The efficiency of Fe removal was 98.5%, and final TiO0.02C0.13N0.85 contained 0.48 wt% Fe as determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis. The chlorination mechanism of titanium nitride (TiN) and TiOxCyNz were extensively investigated at 250 °C - 400 °C. The extent of chlorination moderately increased with increasing the temperature and decreasing particle size of TiN at constant flow rate of N2-Cl2 gas mixture. The highest extents of chlorination of TiN at 250 °C and 400 °C were about 85.6% and 97.7% in 60 minutes, respectively. The results also indicated that a shrinking core model with mixed-control mechanism governed the chlorination rate. The surface chemical reaction of chlorine gas on the surface of TiN particles was rate controlling in the initial stage and, during later stage, internal (pore) diffusion through the intermediate product layer was rate controlling step. The apparent activation energy (Ea) of about 10.97 kJ/mole was obtained for the chlorination of TiN. The extent of chlorination of TiO0.02C0.13N0.85 was 93.5% at 400 °C in 60 minutes. The TiCl4 with the purity of about 99% was eventually produced from ilmenite and the residue of the chlorination contained high amounts of rear earth elements (REEs) as well as refractory metals. This research demonstrated that a three-step process could be a feasible and sustainable method for production of relatively pure TiCl4 from ilmenite.
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