The Electrochemical Extraction Of Titanium By Casting Anode Via USTB Process

The molten salt electrolysis method is considered to be the most promising titanium extraction technology to replace the Kroll process.In recent years,investigation for the extraction of metallic titanium by molten salt electrolysis has been mainly focused on the anode electrolysis of consumable titanium compounds(such as USTB,MER,etc.)and the cathode of the electrolytic reduction deoxidation of titanium oxide(such as FFC,OS,etc.).Taking the USTB process as a representative,the TiC-TiO-TiN solid solution anodes are used for consumable anodes to electrolytic extraction of titanium.However,the traditional preparation methods of soluble anodes are generally prepared via vacuum sintering or spark plasma sintering,etc.,which have problems such as low dissolution rate,low density,and the anode loss during the electrolysis process.On the other hand,the soluble anode electrolysis process firstly needs to use Ti to reduce TiCl4 to prepare a low-valent titanium electrolyte(NaCl-KCl-TiCln),which still has disadvantages such as high cost,long time,and TiCl4 pollution.In view of this,in this dissertation,a soluble titanium-containing solid solution anode with a dense structure is prepared by the melting and casting method,and the titanium is directly and continuously electrolytically prepared in an electrolyte without low-valent titanium ions.The electrochemical reduction behaviors and in-suit alloying of titanium ions based on active liquid Zn metal cathode are proposed.The migration behavior of Al2O3 impurities in the electrolysis process of titanium carbon oxygen anode is systematically studied.The research work in this dissertation will provide a theoretical basis for improving the clean and efficient electrolytic extraction of titanium by the USTB process.(1)A casting TiC0.5O0.5 solid solution was prepared by smelting TiC and TiO using an arc melting furnace.And the industrial CT analysis shows that the porosity of the cast TiC0.5O0.5 solid solution is about 2.5%.Electrochemical analysis shows that compared with traditional sintered soluble electrodes,the casting anode has a faster dissolution rate and a relatively negative polarization potential.In the NaCl-KCl electrolyte without low-valent titanium ions at 1023 K,the reduction potential of the titanium ions dissolved in the casting TiC0.5O0.5 solid solution is about-0.56 V vs.Ag/AgCl.The square wave voltammetry test shows that the titanium ions have the number of transferred electrons is 2.Which is electrochemically dissolved in the form of Ti2+into the NaCl-KCl electrolyte,and further migrates to the surface of the solid cathode,where it is electrochemically reduced to metallic titanium in one step(Ti2+ +2e-→Ti).During the electrolysis process,the anode non-metallic elements are discharged in the form of CO gas,and no anode slime is generated.The metal was successfully prepared on the solid electrode after 12 h constant electrolysis at a current density of 0.4 A cm-2,indicating that in the NaCl-KCl electrolyte without low-valent titanium ions,continuous electrolysis of molten salt can produce titanium.(2)The TiCxOyNz powder were prepared by carbothermic reduction of TiO2 in a nitrogen atmosphere,using a suspension melting furnace for casting.The lattice spacing of the casting TiOxOyNz anode is about 0.4318 nm,and the synchrotron radiation fine structure analysis shows that the TiCxOyNz solid solution anode has a face-centered cubic crystal structure,and the bond lengths of the Ti-N,Ti-C and Ti-O bonds are 2.39 A,1.89 A and 1.39 A,respectively.It is confirmed that N2 participates in the reaction process of carbothermic reduction of TiO2.Cyclic voltammetry and square wave voltammetry tests show that titanium is electrochemically dissolved in the form of ions during the anodic dissolution of TiCxOyNz solid solution,and a one-step with two electron transfer reduction process is realized.The entire electrochemical reduction process shows a quasi-reversible diffusion process,and the non-metallic elements on the anode surface are formed of CO and N2,no anode slime is formed,which is a green electrochemistry metallurgical process.(3)A method for depolarization and in-situ alloying on a liquid Zn metal cathode based on the casting TiC0.5O0.5 anode is proposed.The study found that compared with solid cathode,the Ti2+dissolved from the casting TiC0.5O0.5 anode has a more positive reduction potential on the liquid Zn cathode,and the reduction potential is approximately at-0.5 V vs.Ag/AgCl.The dissolved Ti2+ is via a one-step two-electron reduction process on the surface of liquid zinc cathode,and the reduction process is a quasi-reversible diffusion process,in which the diffusion coefficient of Ti2+ to the surface of liquid zinc cathode is 4.35 × 10-5 cm+2 s-1.Using constant current electrolysis at a current density of 0.3 A cm-2 for 3 h to quickly obtain stabilized Ti-Zn alloy at the cathode.This research expands the application range of the USTB process,and titanium can be quickly deposited in the liquid cathode to prepare titanium alloys or titanium products.(4)The migration behavior of typical impurity Al2O3 in the process of·TiC0.5O0.5 anode electrolytic titanium extraction was proved.Al2O3 is a typical impurity component for preparing titanium oxycarbide solid solution by carbothermic reduction of titanium ore.Using TiO2,Al2O3 and C as raw materials,TiC0.5O0.5@Al2O3 solid solution was prepared by selective reduction.The conductivity of the sample obtained after sintering under 10 MPa at 1700℃ for 4 hours is decreased from 275.8 S cm-1 at room temperature to 143.1 S cm-1 at 900 K,showing a conductivity phenomenon of like-metal properties.With the increase of Al2O3 content,the electrical conductivity of TiC0.5O0.5@Al2O3 solid solution at room temperature decreased from 275.8 S cm-1 to 255.1 S cm-1.The XPS and XRD analysis of the components in the cathode product and molten salt after electrolysis with different anode current densities show that:the anode slime was formed by the Al2O3 in the NaCl-KCl melts and it will not discharge at the cathode to affect the deposition of titanium during the electrolysis process.