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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Abstract
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.