| Titanium is one of the most important metals in the 21st century and is widely used in aviation,marine,military and life science fields because of its strong corrosion resistance,high specific strength and excellent biocompatibility.China’s titanium resources reserves rank first in the world,with 99%exists in the form of ilmenite.This kind of ore will be sent to the blast furnace for smelting,and nearly half of the titanium resources will be brought to the titanium-bearing blast furnace slag.However,it is difficult to directly use the slag because of the complex state of titanium and hence it is disposed of.This results in a large amount of titanium resources waste and environmental pressure.Molten oxide electrolysis,a method using metal oxides as the electrolyte for direct electrolysis,however,will have silica preferentially reduced when using titanium-bearing blast furnace slag as a raw material.In addition,the structure of the slag and state of titanium in molten slag is not clear.If titanium or titanium alloy can be obtained by direct electrolysis of molten titanium-bearing blast furnace slag,it will have guiding significance for the extraction of titanium metal and comprehensive utilization of titanium-bearing compounds,and provide a novel idea for the efficient utilization of titanium-bearing blast furnace slag in Panxi region.This paper measured the physical properties such as melting temperature and electrical conductivity of molten titanium-bearing blast furnace slag,obtained the liquid cathodes by means of theoretical calculations and experiments,developed a novel molten oxide electrolysis-vacuum distillation process for titanium-bearing blast furnace slag by optimizing electrolysis parameters and vacuum distillation.The specific results of this paper are as follows:(1)The structure and activity of each substance in the melt of titanium-bearing slag under various conditions were calculated using ion-molecule coexistence theory,and the structure and state of titanium in molten titanium-bearing blast furnace slag and titanium-bearing slag with CaF2 were investigated.The results showed that titanium exists mainly as TiO2 and CaTiO3 within the molten titaniumbearing slag,and titanium exists in TiO44-and other structures with 5coordination and 6-coordination structures.Compared with molten titaniumbearing blast furnace slag,molten titanium-bearing slag with CaF2 had better fluidity and conductivity by measuring of physical properties of titanium-bearing slag.Molecular dynamics simulations showed that the diffusion rate of titanium in the melt was faster with the addition of CaF2,and the coordination number of titanium-oxygen decreased from 4.83 to 4.05.The calculation results of ionmolecule coexistence theory showed that the alkalinity has a greater influence on the activity of SiO2 in titanium-bearing slag,the activity of SiO2 decreased more significantly than that of TiO2 in titanium-containing slag with increasing alkalinity,indicating that titanium-bearing slag with higher alkalinity was more favorable for titanium deposition.(2)The strong binding ability of liquid tin,bismuth,antimony and copper to titanium was confirmed by evaluating the basic physical properties of common lowmelting metals and calculation of the binding energy of Ti4+and Si4+with liquid tin,lead,bismuth,antimony and copper at 1400℃,respectively.After that,it was proved that liquid tin,bismuth,antimony and copper cothodes can realize depolarization deposition of titanium,but bismuth also caused silicon deposition,so tin,antimony and copper were selected as liquid cathodes for electrolysis of molten titanium-bearing blast furnace slag.Meanwhile,the activities of titanium,silicon and calcium in tin-titanium,antimony-titanium,tin-silicon and antimonycalcium alloys were measured by the EMF method,and the results showed that the activity of titanium in tin-titanium alloy(lwt%titanium)at 1500 ℃(8.00 × 10-6)was much smaller than that of silicon in tin-silicon alloy(0.5wt%silicon)(9.64 ×10-4),while the activity of calcium at 1400℃ in antimony-calcium(lwt%calcium)is extremely low(2.00 ×10-9),much smaller than the activity of titanium in antimony-titanium(0.5wt%titanium)(6.50 × 10-6)at 1400℃.(3)The deposition potentials of Ti4+and Si4+in liquid tin cathode at 1500℃versus Ti4+ and Ca2+in liquid antimony cathode at 1400℃ were calculated using the Nernst equation,and it was found that a larger positive potential shift of Ti4+could be achieved by using these two liquid cathodes,which led to the depolarization deposition of titanium.The effect of electrolysis parameters on titanium deposition was investigated through the experimental study of electrolysis of molten titanium-bearing slag by tin,antimony and copper cathodes,and liquid antimony and tin cothodes had better depolarization deposition ability of titanium,and the antimony cathode also achieved depolarization deposition of calcium,and when the TiO2 content in the electrolyte was around 11 wt%and the electrolysis current density was less than 0.1 A cm-2,～10%and～64%of the cathodic current efficiency was achieved for liquid tin and antimony cothodes,respectively.(4)The anodic behavior of iridium anode in the electrolysis of molten titanium-bearing blast furnace slag and titanium-bearing slag with CaF2 was investigated.The study showed that,stable IrO2 was generated at the iridium anode interface to prevent further corrosion,but IrO2 easily reacted with CaO to form CaIrO3,Ca2IrO4 and Ca4IrO6 to corrode the anode,and thus iridium had better effect in slag with less alkalinity.The chemical corrosion rates of iridium in the two molten slags were calculated at about 0.07 mm h-1(0.11 g h-1)and 0.14 mm h-1(0.22 g h-1),respectively,and the electrochemical corrosion rates(anodic current density of 1.5 A cm-2)in these two molten slags were about 0.13 mm h-1(0.20 g h1)and 0.17 mm h-1(0.26 g h-1),respectively.Simultaneously,vacuum refining studies were conducted on the cathodes after electrolysis,and suitable distillation parameters were determined.A novel molten oxide electrolysis-vacuum distillation process was developed by regulating the electrolysis parameters of titanium-bearing blast furnace slag with iridium anode and liquid antimony cathode,and titanium,by-products oxygen and calcium can be obtained by treating titanium-bearing blast furnace slag with this process. |
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