US20240240344A1

US20240240344A1 - Method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide

Info

Publication number: US20240240344A1
Application number: US18/289,835
Authority: US
Inventors: Zhongwei ZHAO
Original assignee: Zhengzhou University
Current assignee: Zhengzhou University
Priority date: 2021-05-08
Filing date: 2022-04-21
Publication date: 2024-07-18
Also published as: WO2022237489A1; CN115305516A

Abstract

The present application relates to a method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide, the method includes: constructing an electrochemical system, including an anode chamber filled with an anodic molten salt electrolyte and inserted with an anode, and a cathode chamber filled with a cathodic molten salt electrolyte and inserted with a cathode, where the anodic molten salt electrolyte and the cathodic molten salt electrolyte are connected through a liquid alloy accommodated at an inner bottom of the electrolytic cell without contacting with each other; and adding titanium dioxide to the anode chamber, and energizing for electrolysis to obtain metallic titanium at the cathode. The method of the present application has advantages such as low requirements for the titanium dioxide raw material, simple process flow, low energy consumption, environmental friendliness, and direct acquisition of high-purity metallic titanium.

Description

TECHNICAL FIELD

The present application belongs to the field of titanium metallurgy, and specifically relates to a method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide.

BACKGROUND

Metallic titanium has a high specific strength and corrosion resistance, and is widely used in fields such as aerospace, chemicals, energy, and medical care.
Minerals containing titanium mainly include rutile (TiO₂) and ilmenite (FeTiO₃). Due to a strong affinity of titanium with oxygen, carbon, and other elements, it is very difficult to extract titanium. Ilmenite needs to be treated first to obtain a high-titanium slag (a main component of the slag is titanium dioxide TiO₂). Titanium in rutile or high-titanium slag is then converted into titanium tetrachloride TiCl₄through carbochlorination, then impurities are removed through rectification to obtain pure TiCl₄, and the pure TiCl₄is then thermally reduced by a metal to obtain titanium sponge. Currently, there are mainly two thermal reduction methods: Kroll method (magnesium reduction) and Hunter method (sodium reduction), where the Kroll method is the mainstream industrially.
The Kroll method involves a long process flow, a large number of procedures, discontinuous production, and a long cycle, which makes a cost remain high. Therefore, the inventor Kroll himself believed that the magnesium thermal reduction method would soon be replaced by electrolysis.
In fact, researchers have been putting a lot of effort into investigation of electrolysis. However, the electrolysis of any of TiO₂, K₂TiF₄, and TiCl₄encounters insurmountable problems. Due to a factor such as high impurity content in a product, low current efficiency, heavy corrosion, complicated device structure, deposition of titanium dendrites and difficult separation of titanium dendrites from a molten salt, or high environmental cost, the electrolysis has so far not been industrially used.
In 2000, the University of Cambridge introduced the Fray-Farthing-Chen (FFC) method. Unlike the idea of the traditional electrolysis method, a medium used in the FFC method is a calcium chloride molten salt, rather than a fluoride molten salt; and thus the FFC method is more eco-friendly than the traditional electrolysis method. The FFC method does not pursue the dissolution of a titanium compound in the molten salt, but adopts a titanium dioxide pellet as a cathode. The FFC method also has a different working principle from the traditional electrolysis method. In the FFC method, titanium is not precipitated from the molten salt, but based on the characteristics of valve metal oxides (unilateral conductivity: these valve metal oxides cannot conduct electricity as an anode, but can conduct electricity as a cathode) and the cathodic polarization, titanium ions in the cathode are reduced into metallic titanium in situ. In the FFC method, during reduction, oxygen anions leave the cathode and enter a melt, migrate to the anode under an action of a Coulomb force, and are oxidized into oxygen (when a carbon anode is used, oxygen further reacts with carbon to produce CO and CO₂). However, the titanium dioxide pellet cathode is gradually reduced from outside to inside, and during this process, the diffusion of oxygen ions are increasingly difficult, resulting in small cathode current density and high overvoltage. The preparation of titanium with a low oxygen content requires severe overelectrolysis, resulting in low current efficiency. Moreover, impurities such as iron and carbon can easily enter a product.
The OS method of the Kyoto University in Japan also adopts a calcium chloride electrolyte. In the OS method, calcium ions are reduced into calcium on a cathode titanium mesh; and titanium dioxide is no longer pressed or sintered, but is continuously added in molten salt as the form of powder, which is reduced into a titanium powder by calcium near the cathode. Compared with the FFC method, the dispersed granular cathode titanium dioxide is more conducive to the diffusion and migration of oxygen ions than the solid titanium dioxide pellet. However, metallic calcium dissolved in CaCl₂increases the electronic conductivity of the molten salt and causes the reduction of current efficiency. Moreover, a produced metal is mixed with a molten salt and can hardly be separated; a large amount of the molten salt is required; and impurities such as iron and carbon can also easily enter the product.
In the EMR/MSE method proposed by Japan, the reduction of TiO₂is conducted in stages. In the EMR/MSE method, a Ca—Ni alloy is first prepared through molten salt electrolysis, and then the Ca—Ni alloy is used as a reducing agent to reduce TiO₂into metallic titanium. Given that titanium is easily contaminated due to alloying with nickel, TiO₂is immersed in a molten salt in a hanging basket to avoid direct contact with the Ca—Ni alloy. The EMR/MSE method can operate semi-continuously, but the metallic titanium, the Ca—Ni alloy, and the molten salt coexist, resulting in difficult product separation and complicated equipment and process.
A liquid metal such as bismuth and zinc is also used as a cathode for molten salt electrolysis of titanium dioxide, where a Bi—Ti or Zn—Ti alloy is first produced. However, it is reported that the obtained bismuth alloy includes only 0.6 at % to 2.2 at % of titanium, but includes 17.9 at % to 34.9 at % of calcium. When liquid zinc is used, it is reported that the titanium content at the cathode can reach about 20%. However, the obtained alloys also need to be treated by electrolysis or distillation to obtain metallic titanium.
Therefore, it can be seen that the existing processes for electrolysis of titanium dioxide to produce titanium have various problems to be overcome, and thus the Kroll method is still the main method industrially. In order to obtain qualified metallic titanium, the above methods have very strict purity requirements for a titanium dioxide raw material used.

SUMMARY

An objective of the present application is to provide a method for preparing metallic titanium by molten salt electrolysis with titanium dioxide as a raw material. The method has advantages such as low requirements for the titanium dioxide raw material, simple process flow, low energy consumption, environmental friendliness, and direct acquisition of high-purity metallic titanium.
To achieve the above objective, the present application adopts the following technical solutions:

- A method for preparing metallic titanium through molten salt electrolysis reduction of titanium dioxide is provided. The method is implemented with an electrolytic cell; the electrolytic cell includes an anode chamber and a cathode chamber; the anode chamber is filled with an anodic molten salt electrolyte and inserted with an anode, the cathode chamber is filled with a cathodic molten salt electrolyte and inserted with a cathode, and a liquid alloy is accommodated at the inner bottom of the electrolytic cell; the anodic molten salt electrolyte and the cathodic molten salt electrolyte are connected through the liquid alloy without contacting with each other; and
- the method includes: adding titanium dioxide to the anode chamber, and powering on the electrolytic cell, the titanium dioxide in the anode chamber is reduced into titanium atoms at an interface between the anodic molten salt electrolyte and the liquid alloy and dissolved in the liquid alloy, the titanium atoms in the liquid alloy are oxidized into titanium ions at an interface between the liquid alloy and the cathodic molten salt electrolyte and enter the cathodic molten salt electrolyte, and the titanium ions to be reduced into titanium atoms on the surface of the cathode, thereby forming the metallic titanium.

With respect to the method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide according to the specific implementation of the present application, the anodic molten salt electrolyte and the cathodic molten salt electrolyte both are a halide molten salt. Preferably, the anodic molten salt electrolyte includes one or more selected from the group consisting of CaCl₂, BaCl₂, LiCl, NaCl, KCl, CsCl, LiF, NaF, and KF. The cathodic molten salt electrolyte includes one or more selected from the group consisting of LiCl, NaCl, KCl, CaCl₂, and MgCl₂, and TiCl₂and/or TiCl₃. Electrolytes in the cathode chamber and the anode chamber of the present application both are halides, or common halide, which have specified solubility for low-valent titanium. Given an effect on the precipitation of titanium impurities at the cathode, only chlorides are selected as an electrolyte in the cathode chamber.
With respect to the method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide according to the specific implementation of the present application, the anode is graphite, and the cathode is a stainless steel, tungsten, or molybdenum cathode. Graphite as anode can react with oxygen ions in the anodic molten salt electrolyte to produce CO or CO₂; and the cathode is a high-temperature-resistant conductor.
With respect to the method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide according to the specific implementation of the present application, the liquid alloy is an alloy produced from a solute metal Ti and a matrix metal. The matrix metal has a lower metal activity than the titanium, and is mixed with the titanium to produce an alloy with a low melting point of lower than 1,000° C.; and specifically, the matrix metal can be one or more selected from the group consisting of Cu, Sn, Sb, Zn, Pb, Bi, and Ni.
At work, solid titanium dioxide is added to the anode chamber; an area of the cathode is 1 to 20 times of an area of the anode; and under continuous operating conditions, electrolysis is conducted at an anode current density of 0.05 A/cm²to 2.0 A/cm²and a temperature of 400° C. to 1,000° C. CO and CO₂gases are precipitated evolve at the anode, and the metallic titanium product is precipitated at the cathode. Further, in order to improve a flatness of titanium precipitated at the cathode, a reverse current accounting for 1% to 5% of a total electrolysis time is increased during the electrolysis to homogenize dense titanium precipitated at the cathode.
During the electrolysis, the titanium dioxide in the anode chamber is reduced into titanium atoms at an interface between the anodic molten salt electrolyte and the liquid alloy, and dissolved in the liquid alloy by contacting the liquid alloy. Oxygen ions originally binding to titanium move to the anode under driving by an electric field, then lose electrons and are oxidized into zero-valent oxygen, and react with the anode to produce CO and CO₂, which escape. Moreover, titanium atoms in the liquid alloy at a side of the cathode chamber are oxidized into titanium ions at the interface between the liquid alloy and the cathodic molten salt electrolyte and enter the cathodic molten salt electrolyte, then move to the cathode under driving of an electric field, and acquire electrons and are reduced into titanium atoms to produce the metallic titanium product. During a titanium reduction process in the anode chamber, metals more active than metallic titanium are difficult to enter the liquid alloy; and during a titanium oxidation process in the cathode chamber, metals more inert than metallic titanium are difficult to enter the cathodic molten salt electrolyte, such that a high-purity metallic titanium product is finally obtained at the cathode.
The present application has the following beneficial effects:

- (1) Strong operability. Titanium dioxide is added to the anode chamber, and during electrolysis, a current density is controlled and titanium in the liquid alloy is replenished in real time to obtain titanium precipitated at the cathode. The whole process is simple and easy to implement, has high electrolysis efficiency, is eco-friendly, does not have high requirements for devices, and allows industrial applications.
- (2) Lowered requirements for a quality of a raw material. A titanium dioxide raw material with a specified impurity content can be used for electrolysis to produce metallic titanium, which avoids the raw material procurement and production costs caused by the need for a high-purity titanium dioxide raw material required in the traditional electrolysis method.
- (3) Guaranteed purity of a product. Impurity ions with different electrochemical behaviors can be effectively controlled in the anodic molten salt electrolyte or the liquid alloy, and thus the prepared metallic titanium has a high purity.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of a cross section of the electrolytic cell in the embodiment of the present application,

- where 1—anode; 2—anodic molten salt electrolyte; 3—liquid alloy; 4—titanium dioxide inlet; 5—cathode; and 6—cathodic molten salt electrolyte.

DETAILED DESCRIPTION OF THE EMBODIMENTS

To make the objectives, technical solutions, and advantages of the present application clearly, the technical solutions of the present application will be described in detail below. Apparently, the described examples are some rather than all of the examples of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the examples of the present application without creative efforts should fall within the protection scope of the present application.
The method for preparing metallic titanium through molten salt electrolysis reduction of titanium dioxide in the following examples of the present application is implemented with an electrolytic cell shown in FIG. 1 , where a liquid alloy 3 is accommodated at the inner bottom of the electrolytic cell, and a zone above the liquid alloy 3 inside the electrolytic cell is divided by a partition into an anode chamber and a cathode chamber; the anode chamber is filled with an anodic molten salt electrolyte 2 and inserted with an anode 1, and the cathode chamber is filled with a cathodic molten salt electrolyte 6 and inserted with a cathode 5; and the anodic molten salt electrolyte 2 and the cathodic molten salt electrolyte 6 are connected through the liquid alloy 3 without contacting with each other.

EXAMPLE 1

Anodic molten salt electrolyte: 200 g of CaCl₂was weighed. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 7.8 wt % low-valent titanium chloride (TiCl₂: TiCl₃: 4:1) was added. 400 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 73:16:11.
The metal alloy was placed in the electrolytic cell and heated to 950° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm²(an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h;

- 27 g of metallic titanium was replenished to the liquid metal, the original current density was remained, titanium dioxide was added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h;
- 27 g of metallic titanium was further replenished to the liquid metal, a current density of 50 mA/cm²was further remained, titanium dioxide was further added at a uniform rate, and electrolysis was conducted for 24 h; and
- the cathode was taken out, and a mass of the cathode was measured to obtain 138.3 g of metallic titanium.

EXAMPLE 2

Anodic molten salt electrolyte: CaCl₂and NaCl were mixed according to a mass ratio of 54:46 to obtain 2 kg of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 2 kg of a mixture, and then 8.7 wt % low-valent titanium chloride (TiCl₂: TiCl₃: 5:1) was added. 4 kg of a metal alloy was prepared from Sn and Ti according to a mass ratio of 90:10.
The metal alloy was placed in the electrolytic cell and heated to 900° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While industrial titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 100 mA/cm²(an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 12 h;

- 270 g of metallic titanium was replenished to the liquid metal, the original current density was remained, industrial titanium dioxide was added at a uniform rate to the anode chamber, and electrolysis was conducted for 12 h;
- 270 g of metallic titanium was further replenished to the liquid metal, a current density of 100 mA/cm²was further remained, industrial titanium dioxide was further added at a uniform rate to the anode chamber, and electrolysis was conducted for 12 h; and
- the cathode was taken out, and a mass of the cathode was measured to obtain 1276.5 g of metallic titanium.

EXAMPLE 3

Anodic molten salt electrolyte: CaCl₂and KCl were mixed according to a mass ratio of 54:46 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 11.3 wt % low-valent titanium chloride (TiCl₂) was added. 4,000 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 23:74.5:2.5.
The metal alloy was placed in the electrolytic cell and heated to 700° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While industrial titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm²(an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h;

- 27 g of metallic titanium was replenished to the liquid metal, the original current density was remained, industrial titanium dioxide was added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h;
- 27 g of metallic titanium was further replenished to the liquid metal, a current density of 50 mA/cm²was further remained, industrial titanium dioxide was further added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h; and
- the cathode was taken out, and a mass of the cathode was measured to obtain 145.39 g of metallic titanium.

EXAMPLE 4

Anodic molten salt electrolyte: 200 g of CaCl₂was weighed. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 10.6 wt % low-valent titanium chloride (TiCl₃) was added. 400 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 73:16:11.
The metal alloy was placed in the electrolytic cell and heated to 950° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm²(an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h and then stopped.
The stainless steel cathode was taken out. A corundum tube wrapped with a metal W rod was connected to the liquid metal; tungsten at a top of the corundum tube was allowed to be in contact with the liquid metal, and tungsten at a bottom of the corundum tube was connected to a power supply; the electrode of the anode chamber was connected to an anode of the power supply, and the W rod was connected to a cathode of the power supply; and a current density was controlled at 50 mA/cm², titanium dioxide was added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h and then stopped.
With a graphite electrode as an anode and a stainless steel plate as a cathode, while titanium dioxide was added at a uniform rate to the anode chamber, an electric field was applied, a current density was controlled at 50 mA/cm², and electrolysis was conducted for 24 h and then stopped.
The cathode electrode was taken out and weighed to obtain 84.4 g of metallic titanium.

EXAMPLE 5

Anodic molten salt electrolyte: CaCl₂and BaCl₂were mixed according to a mass ratio of 35:65 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: 200 g of NaCl was weighed, and then 9.3 wt % low-valent titanium chloride (TiCl₂: TiCl₃: 1:1) was added. 400 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 73:16:11.
The metal alloy was placed in the electrolytic cell and heated to 1000° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 2,000 mA/cm²(an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 1 h and then stopped.
The stainless steel cathode was taken out. A corundum tube wrapped with a metal W rod was connected to the liquid metal; tungsten at a top of the corundum tube was allowed to be in contact with the liquid metal, and tungsten at a bottom of the corundum tube was connected to a power supply; the electrode of the anode chamber was connected to an anode of the power supply, and the W rod was connected to a cathode of the power supply; and a current density was controlled at 2,000 mA/cm², titanium dioxide was added at a uniform rate to the anode chamber, and electrolysis was conducted for 1 h and then stopped.
With a graphite electrode as an anode and a stainless steel plate as a cathode, while titanium dioxide was added slowly to the anode chamber, an electric field was applied, a current density was controlled at 2,000 mA/cm², and electrolysis was conducted for 1 h and then stopped.
The cathode electrode was taken out and weighed to obtain 60.3 g of metallic titanium.

EXAMPLE 6

Anodic molten salt electrolyte: CaCl₂, LiCl, and NaCl were mixed according to a mass ratio of 8:1:1 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 8.5 wt % low-valent titanium chloride (TiCl₂: TiCl₃: 3:1) was added. 400 g of a metal alloy was prepared from Cu and Ti according to a mass ratio of 3:1.
The metal alloy was placed in the electrolytic cell and heated to 950° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 1,000 mA/cm²(an area of the cathode was 10 times an area of the anode), and electrolysis was conducted for 2 h;

- 22 g of metallic titanium was replenished to the liquid metal, the original current density was remained, titanium dioxide was added at a uniform rate to the anode chamber, and electrolysis was conducted for 2 h;
- 22 g of metallic titanium was further replenished to the liquid metal, a current density of 1,000 mA/cm²was further remained, titanium dioxide was further added at a uniform rate to the anode chamber, and electrolysis was conducted for 2 h; and
- the cathode was taken out, and a mass of the cathode was measured to obtain 133.4 g of metallic titanium.

EXAMPLE 7

Anodic molten salt electrolyte: CaCl₂, LiCl, and NaCl were mixed according to a mass ratio of 8:1:1 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 8 wt % low-valent titanium chloride (TiCl₂) was added. 1,000 g of a metal alloy was prepared from Sb and Ti according to a mass ratio of 96:4.
The metal alloy was placed in the electrolytic cell and heated to 900° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While a high-titanium slag powder (TiO₂>94%) was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm²(an area of the cathode was 20 times an area of the anode), and electrolysis was conducted for 24 h, where during the electrolysis, a reverse current of 1 min was increased every 29 min;

- 27 g of metallic titanium was replenished to the liquid metal, the original current density was remained, the high-titanium slag powder was added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h;
- 27 g of metallic titanium was further replenished to the liquid metal, a current density of 50 mA/cm²was further remained, the high-titanium slag powder was further added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h; and
- the cathode was taken out, and a mass of the cathode was measured to obtain 142.9 g of metallic titanium.

EXAMPLE 8

Anodic molten salt electrolyte: CaCl₂and LiCl were mixed according to a mass ratio of 54:46 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: NaCl and KCl were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 11.3 wt % low-valent titanium chloride (TiCl₂) was added. 4,000 g of a metal alloy was prepared from Cu, Sn, and Ti according to a mass ratio of 23:74.5:2.5.
The metal alloy was placed in the electrolytic cell and heated to 700° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While industrial titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 50 mA/cm²(an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h;

- a circuit was disconnected; a corundum rod wrapped with a metal wire was inserted into the liquid alloy, with a metal end in contact with the liquid alloy; with the graphite electrode of the anode chamber as an anode and the metal wire connected to the cathode, energization was conducted for 24 h to make a metallic titanium content in the liquid alloy reach an initial content; then the cathode of the corundum rod (internal metal wire) was taken out, and the stainless steel of the cathode chamber was allowed to serve as a cathode; the original current density was remained, industrial titanium dioxide was further added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h;
- 27 g of metallic titanium was further replenished to the liquid metal, a current density of 50 mA/cm²was further remained, industrial titanium dioxide was further added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h; and
- the cathode was taken out, and a mass of the cathode was measured to obtain 145.39 g of metallic titanium.

EXAMPLE 9

Anodic molten salt electrolyte: LiCl and KCl were mixed according to a mass ratio of 45:55 to obtain 200 g of a mixture. Cathodic molten salt electrolyte: LiCl and KCl were mixed according to a mass ratio of 45:55 to obtain 200 g of a mixture, and then 2.3 wt % low-valent titanium chloride (TiCl₂) was added. 4,000 g of a metal alloy was prepared from Sn and Ti according to a mass ratio of 99.7:0.3.
The metal alloy was placed in the electrolytic cell and heated to 400° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and tungsten was adopted as a cathode. While industrial titanium dioxide was added at a uniform rate to the anode chamber, an anode current density was controlled at 0.05 A/cm²(an area of the cathode was 20 times an area of the anode), and electrolysis was conducted for 24 h;

- a circuit was disconnected; a corundum rod wrapped with a metal wire was inserted into the liquid alloy, with a metal end in contact with the liquid alloy; with the graphite electrode of the anode chamber as an anode and the metal wire connected to the cathode, energization was conducted for 24 h to make a metallic titanium content in the liquid alloy reach an initial content; then the cathode of the corundum rod (internal metal wire) was taken out, and the stainless steel of the cathode chamber was allowed to serve as a cathode; the original current density was remained, industrial titanium dioxide was further added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h;
- 27 g of metallic titanium was further replenished to the liquid metal, a current density of 50 mA/cm²was further remained, industrial titanium dioxide was further added at a uniform rate to the anode chamber, and electrolysis was conducted for 24 h; and
- the cathode was taken out, and a mass of the cathode was measured, obtain metallic titanium.

COMPARATIVE EXAMPLE

Anodic molten salt electrolyte: 200 g of CaCl₂was weighed. Cathodic molten salt electrolyte: NaCl, KCl, TiCl₂, and TiCl₃were mixed according to a mass ratio of 1:1 to obtain 200 g of a mixture, and then 7.8 wt % low-valent titanium chloride (TiCl₂: TiCl₃: 4:1) was added. 400 g of a metal alloy was prepared from Cu and Sn according to a mass ratio of 3:1.
The metal alloy was placed in the electrolytic cell and heated to 950° C. for melting; and the anodic molten salt electrolyte and the cathodic molten salt electrolyte were separately added to a crucible and melted. A graphite electrode was adopted as an anode, and stainless steel was adopted as a cathode. While titanium dioxide was added at a uniform rate to the anode chamber, the same current density as in the examples was controlled (an area of the cathode was 1 time an area of the anode), and electrolysis was conducted for 24 h.
A metallic titanium with high tin contents was produced at the cathode.
The above are merely specific implementations of the present application, but are not intended to limit the protection scope of the present application. Any variation or replacement readily conceived by a person skilled in the art within the technical scope disclosed in the present application shall fall within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

What is claimed is:

1. A method for preparing metallic titanium by molten salt electrolysis reduction of titanium dioxide, wherein

the method is implemented with an electrolytic cell; the electrolytic cell comprises an anode chamber and a cathode chamber, the anode chamber is filled with an anodic molten salt electrolyte and inserted with an anode, the cathode chamber is filled with a cathodic molten salt electrolyte and inserted with a cathode, and a liquid alloy is accommodated at an inner bottom of the electrolytic cell; the anodic molten salt electrolyte and the cathodic molten salt electrolyte are connected through the liquid alloy without contacting with each other; and

the method comprises: adding titanium dioxide to the anode chamber and powering on the electrolytic cell, the titanium dioxide in the anode chamber is reduced into titanium atoms at an interface between the anodic molten salt electrolyte and the liquid alloy and dissolved in the liquid alloy, the titanium atoms in the liquid alloy are oxidized into titanium ions at an interface between the liquid alloy and the cathodic molten salt electrolyte and enter the cathodic molten salt electrolyte, and the titanium ions to be reduced into titanium atoms on a surface of the cathode, thereby forming the metallic titanium.

2. The method for preparing metallic titanium through molten salt electrolysis reduction of titanium dioxide according to claim 1, wherein the anodic molten salt electrolyte and the cathodic molten salt electrolyte both are halide molten salts.

3. The method for preparing metallic titanium through molten salt electrolysis reduction of titanium dioxide according to claim 2, wherein the anodic molten salt electrolyte comprises one or more selected from the group consisting of CaCl₂, BaCl₂, LiCl, NaCl, KCl, CsCl, LiF, NaF, and KF.

4. The method for preparing metallic titanium through molten salt electrolysis reduction of titanium dioxide according to claim 2, wherein the cathodic molten salt electrolyte comprises TiCl₂and/or TiCl₃, and one or more selected from the group consisting of LiCl, NaCl, KCl, CaCl₂, and MgCl₂.

5. The method for preparing metallic titanium through molten salt electrolysis reduction of titanium dioxide according to claim 1, wherein the anode is graphite, and the cathode is a stainless steel, tungsten, or molybdenum cathode.

6. The method for preparing metallic titanium through molten salt electrolysis reduction of titanium dioxide according to claim 1, wherein the liquid alloy is formed from a solute metal Ti and a matrix metal; the matrix metal has a lower metal activity than the titanium, and is mixed with the titanium to produce an alloy with a low melting point of lower than 1,000° C.; and preferably, the matrix metal is one or more selected from the group consisting of Cu, Sn, Sb, Zn, Pb, Bi, and Ni.

7. The method for preparing metallic titanium through molten salt electrolysis reduction of titanium dioxide according to claim 1, wherein an area of the cathode is 1 to 20 times an area of the anode; and when the electrolytic cell operates normally, an anode current density is 0.05 A/cm²to 2.0 A/cm²and a temperature is 400° C. to 1,000° C.