Patent Application
20240200218
The present disclosure belongs to the field of titanium metallurgy, and particularly relates to a method for preparing titanium metal by molten salt electrolysis.
Titanium, as a typical rare metal, is known as the “21st century metal” after iron and aluminum due to its advantages of low density, high strength and corrosion resistance. The natural resource reserves of titanium are relatively rich and more than 60 times greater than copper reserves, ranking tenth in the earth crust in content. However, the energy consumption and device cost in the titanium preparation process are relatively high, resulting in a high price of titanium. Therefore, titanium cannot be comprehensively popularized like iron and aluminum.
The titanium resource is characterized by multi-metal symbiosis. Most titanium exists in a form of ilmenite, which is usually used an iron-making raw material and titanium is discarded as slag, such as vanadium titano-magnetite. Ilmenite is a usable titanium-containing mineral, which is usually reduced by an electric furnace to obtain titanium-rich slag first (more than 80% of TiO2, and containing a small amount of impurities such as Fe and Si); then the titanium-rich slag is subjected to high-temperature carbon reduction-chlorination process to obtain crude titanium tetrachloride; the crude titanium tetrachloride is further purified to obtain refined titanium tetrachloride; and then the refined titanium tetrachloride is used for preparing titanium metal.
At present, the relatively mature process for preparing titanium metal is a Kroll process that is proposed in 1940. Its basic process is as follows: the above refined titanium tetrachloride is used as a raw material, and is subjected to metal thermal reduction process to react with magnesium metal at a high temperature; Porous sponge titanium is obtained after separation of MgCl2 and Mg; and then the porous sponge titanium is crushed and smelted again to obtain a compact titanium material. Another Hunter process for preparing titanium is similar to this process, but the difference is that sodium metal is used as the metal reductant instead of magnesium metal.
Because of the discontinuous operation, long process flow and production cycle of the metal thermal reduction method, researchers and scholars have been proposing new smelting processes for 80 years, among which electrolysis is the most promising direction to replace metal thermal reduction method to prepare titanium. For example, scientists in the Soviet Union and the United States have proposed the method for preparing TiCl4 by KCl—LiCl—NaCl electrolysis to obtain titanium metal, but impurity content in metal is relatively high TiO2 particles are directly electrolyzed in molten chloride (65-80% of CaCl2), 10-25% of BaCl2 and 10-25% of NaCl) and titanium metal is directly deposited on a cathode, but the obtained titanium contains 4-6% of impurities (mainly Fe and Si).
Around 2000, the FFC process of molten salt electrolysis was proposed in the University of Cambridge, which can directly prepare titanium metal from titanium oxides. According to this method, titanium dioxide is used as the cathode after being pressed into blocks, CaCl2) is used as electrolytic molten salt and graphite is used as the anode. During electrolysis, titanium dioxide is reduced to titanium metal, and oxygen ions enter the CaCl2) molten salt and migrate to the anode to react with the graphite electrode. After electrolysis, porous titanium is crushed to obtain titanium metal powder. During electrolysis, oxygen ions on the surfaces of the titanium dioxide pellets are easily separated in the early stage. As electrolysis progresses, it becomes increasingly difficult for oxygen ions inside the pellets to diffuse outwards through solid phase, which makes it difficult to expand production. Moreover, pure titanium dioxide is required as a raw material to prevent impurities in the original titanium dioxide pellets from being left in the product titanium. Therefore, FFC process still cannot be industrialized after nearly 20 years of research.
As for the Japanese OS process, CaCl2) is also used as the molten salt for electrolysis to prepare titanium metal. But the electrolytic voltage of OS process is higher than that of FFC process. Ca2+ in the molten salt is reduced to metal Ca to further reduce granular TiO2. This method avoids the problem of difficult diffusion of ions in a large solid sample, and titanium dioxide can be continuously added to obtain titanium metal powder. However, the electronic conductivity of the melt is high because of dissolution of calcium metal, resulting in a low current efficiency. In addition, as with the FFC process, this process also has the problem of high impurity content in the product. In view of the problem that titanium-containing mineral and iron coexist, and titanium is produced as the slag in the iron making process, Chinese patent CN109055994A provides a method for preparing titanium metal by “continuous electrolysis” using titanium-containing slag as the raw material. The first step is to reduce titanium and make titanium enter molten metal using carbon as the anode and molten metal as the cathode. When the content of titanium in the slag is reduced to a relatively low level, the first step is stopped and the second step is carried out. In the second step, the liquid metal is converted into an anode to carry out electrolysis in another chamber. Titanium is deposited on the cathode until the content of titanium in the molten metal is decreased to a relatively low level. The “continuous electrolysis” method essentially involves two sets of electrolysis devices working alternatively, and the content of titanium in the slag and molten metal needs to be controlled and monitored to avoid over-electrolysis. Once the over-electrolysis occurs, iron in the molten metal will be dissolved and deposited on cathode, resulting in low quality titanium.
In conclusion, the current mainstream titanium preparation process has not fundamentally changed for 80 years. Moreover, the requirement for purity of titanium-containing compounds in various processes is very high, and it is difficult for new titanium smelting methods to achieve continuous operation. Therefore, complex titanium-containing materials cannot be directly treated.
An objective of the present disclosure is to provide a method for directly preparing pure titanium metal from complex titanium-containing raw materials by molten salt electrolysis. The method has the advantages of low requirement for titanium raw materials, continuous operation and high electrolysis efficiency. Moreover, titanium metal with relatively high quality can be directly obtained.
To achieve the above objective, the present disclosure adopts the following technical solutions:
A method for preparing titanium metal by molten salt electrolysis includes: the method is implemented using an electrolytic cell, the electrolytic cell includes an anode chamber and a cathode chamber, the anode chamber is filled with an anode molten salt electrolyte that contains titanium-containing raw material and inserted with an anode, the cathode chamber is filled with a cathode molten salt electrolyte and inserted with a cathode, the bottom of the electrolytic cell is filled with a liquid alloy, the anode molten salt electrolyte and the cathode molten salt electrolyte are connected by the liquid alloy and not in contact with each other;
According to the method for preparing titanium metal by molten salt electrolysis in a specific embodiment of the present disclosure, the titanium-containing raw material is titanium-containing slag or titanium-rich slag (more than 80% TiO2, and containing a small amount of impurities such as Fe and Si).
According to the method for preparing titanium metal by molten salt electrolysis in a specific embodiment of the present disclosure, the anode molten salt electrolyte further includes one or more of Al2O3, CaO, Na2O, CaF2, SiO2, FeO and MgO, and the mass fraction of TiO2 in the anode molten salt electrolyte is not greater than 40%. According to the present disclosure, the anode molten salt electrolyte is a titanium-containing oxide melt whose component is the combination of common oxides; and the component is adjusted to obtain a proper melting point (avoiding overhigh melting point) and have certain solubility on titanium dioxide (an overhigh mass fraction of the titanium dioxide leads to an overhigh melting point).
According to the method for preparing titanium metal by molten salt electrolysis in a specific embodiment of the present disclosure, the anode is made of a carbon material, preferably graphite or modified graphite, or is an inert anode; and the cathode is made of any one of stainless steel, tungsten and molybdenum materials, preferably stainless steel. The carbon anode is a consumable anode, which consumes oxygen in the anode melt to generate CO or CO2; the inert anode is a non-consumable anode, which consumes oxygen in the anode melt to generate O2; and the cathode electrode is non-consumable and is a common high-temperature-resistant conductor.
According to the method for preparing titanium metal by molten salt electrolysis in a specific embodiment of the present disclosure, the cathode molten salt electrolyte is halide molten salt, and the halide molten salt is formed by one or more of NaCl, KCl, CaCl2), MgCl2, NaF, KF, CaF2 and MgCl2, which contains different proportions TiCl2 and TiCl3. According to the present disclosure, the cathode molten salt is characterized as a halide molten salt with a certain amount of dissolved titanium ions, which is composed of common fluorides and chlorides.
According to the method for preparing titanium metal by molten salt electrolysis in a specific embodiment of the present disclosure, the liquid alloy is formed from the solute metal Ti and the solvent metal. The metal activity of the solvent metal is lower than that of titanium, and the solvent metal and titanium can form the low-melting-point alloy having a melting point lower than 1,000° C. The liquid alloy is preferably formed by Ti and one or more of Cu, Sn, Sb, Zn, Pb, Bi, Ni and Co.
According to the method for preparing titanium metal by molten salt electrolysis in a specific embodiment of the present disclosure, because of the melting point difference and the volatility difference caused by different molten salt components, when the electrolytic cell works normally, the temperature of the anode molten salt electrolyte is controlled between 700° C. and 1,400° C., the temperature of the cathode molten salt electrolyte is controlled between 400° C. and 1,100° C., and the anode current density ranges from 0.01 A/cm2 to 2 A/cm2.
During the electrolysis process, TiO2 in the anode chamber is reduced, titanium ions obtain electrons to form titanium atoms, the titanium atoms are dissolved in the liquid alloy, and oxygen ions lose electrons to generate CO/CO2/O2 on the surface of the anode. In the cathode chamber, the titanium atoms in the liquid alloy are oxidized to titanium ions, and the titanium ions enter the cathode molten salt electrolyte (halide molten salt) and are reduced to titanium atoms on the cathode to form the titanium metal product. The total reaction process is continuously carried out, the titanium ions in the anode molten salt electrolyte are sequentially subjected to reduction, oxidization and reduction to form the titanium metal product attached to the cathode. During the titanium reduction process in the anode chamber, it is difficult for the metals that are more active than titanium to enter the liquid alloy. During the titanium oxidation process in the cathode chamber, it is difficult for the metals that are more inert than the titanium metal to enter the cathode molten salt electrolyte. Finally, the titanium metal product with relatively high purity is obtained on the cathode.
The present disclosure has the following beneficial effects:
(1) The electrolytic production process is continuous. In principle, only TiO2 is consumed in the electrolysis process, so continuous production can be achieved in a manner that the titanium-containing raw material is supplemented into the anode chamber timely, and titanium metal products are taken out of the cathode chamber timely, and the production efficiency is high.
(2) The requirement for the quality of the raw materials is lowered. Pure titanium metal is directly obtained from the complex titanium-containing raw materials by electrolysis, and the raw material purchasing and production cost caused by the use of high-purity titanium-containing raw material in traditional electrolysis methods is reduced.
(3) The product purity is guaranteed. Impurity ions with different electrochemical behaviors can be effectively controlled in the anode molten salt electrolyte or the liquid alloy, and therefore the purity of the prepared titanium metal is high.
The FIGURE is a schematic diagram of a section of the electrolytic cell according to an embodiment of the present disclosure.
In the FIGURE: 1—anode; 2—anode molten salt electrolyte; 3—liquid alloy; 4—inlet of titanium-containing raw material; 5—cathode; and 6—cathode molten salt electrolyte.
In order to make the objective, technical solutions and advantages of the present disclosure more clear, the technical solutions of the present disclosure will be described in detail below. Obviously, the described examples are only part of the examples of the present disclosure, not the whole examples. Based on the examples in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present disclosure.
According to the following examples of the present disclosure, methods for preparing titanium metal by molten salt electrolysis are implemented using a U-shaped electrolytic cell shown in the FIGURE. The bottom of the electrolytic cell is filled with a liquid alloy 3. A portion of the electrolytic cell above the liquid alloy 3 is divided into an anode chamber and a cathode chamber. The anode chamber is filled with an anode molten salt electrolyte 2 and has an anode 1. The cathode chamber is filled with a cathode molten salt electrolyte 6 and has a cathode 5. The anode molten salt electrolyte 2 and the cathode molten salt electrolyte 6 are connected by the liquid alloy 3 and not in contact with each other.
This example provides a method for preparing titanium metal by molten salt electrolysis. The method included: 400 g of Cu—Sn—Ti alloy (Cu:Sn:Ti=73:16:11) was added to the bottom of the electrolytic cell, the alloy was heated to form liquid and completely separate the anode chamber from the cathode chamber; 400 g of anode molten salt electrolyte (anode molten salt consisted of Al2O3, SiO2, CaO and TiO2 in a mass ratio of 14:57:18:11) was added to the anode chamber, and 400 g of cathode molten salt electrolyte (prepared from NaCl and KCl according to a mass ratio of 1:1, and 7.8 wt % of low-valence titanium chloride consisting of TiCl2 and TiCl2 was added, the mass ratio of TiCl2 to TiCl3 is 4:1) was added to the cathode chamber; and a graphite anode and a stainless steel cathode were inserted into the anode molten salt electrolyte and cathode molten salt electrolyte, respectively.
Titanium-containing slag was added to the anode molten salt electrolyte, the temperature of anode molten salt electrolyte was controlled to be 1,400° C., the temperature of cathode molten salt electrolyte was controlled to be 1,000° ° C., and the cathode chamber was protected by argon atmosphere. During this electrolysis process, the current density was controlled to be 0.05 A/cm2, and the electrolysis was carried out for 24 h. After the cathode was taken out, 14.8 g of titanium metal was obtained, and the electrolysis could be continuously carried out by adding the titanium-containing slag to the anode chamber.
This example provides a method for preparing titanium metal by molten salt electrolysis. The method included: 4 kg of Cu—Sn—Ti alloy (Cu:Sn:Ti=73:16:11) was added to the bottom of the electrolytic cell, the alloy was heated to form liquid and completely separate the anode chamber from the cathode chamber; 4 kg of anode molten salt electrolyte (anode molten salt consisted of Al2O3, SiO2, CaO and TiO2 in a mass ratio of 14:57:18:11) was added to the anode chamber, and 4 kg of cathode molten salt electrolyte (prepared from NaCl, and 7.8 wt % of low-valence titanium chloride consisting of TiCl2 and TiCl3 was added, the mass ratio of TiCl2 to TiCl3 is 4:1) was added to the cathode chamber; and a graphite anode and a stainless steel cathode were inserted into the anode molten salt electrolyte and cathode molten salt electrolyte, respectively.
Titanium-containing slag was added to the anode molten salt electrolyte, the electrolytic cell is powered on and running, the temperature of anode molten salt electrolyte was controlled to be 1,400° C., the temperature of cathode molten salt electrolyte was controlled to be 1,000° C., and the cathode chamber was protected by argon atmosphere. During this electrolysis process, the current density was controlled to be 0.05 A/cm2, and the electrolysis was carried out for 24 h. After the cathode was taken out, 149 g of titanium metal was obtained, and the electrolysis could be continuously carried out by adding the titanium-containing slag to the anode chamber.
This example provides a method for preparing titanium metal by molten salt electrolysis. The method included: 400 g of Cu—Sn—Ti alloy (Cu:Sn:Ti=73:16:11) was added to the bottom of the electrolytic cell, the alloy was heated to form liquid and completely separate the anode chamber from the cathode chamber; 400 g of anode molten salt electrolyte (anode molten salt consisted of Al2O3, SiO2, CaO and TiO2 in a mass ratio of 9:37:44:10) was added to the anode chamber, and 400 g of cathode molten salt electrolyte (prepared from NaCl and KCl according to a mass ratio of 1:1, and 7.8 wt % of low-valence titanium chloride consisting of TiCl2 and TiCl3 was added, the mass ratio of TiCl2 to TiCl3 is 4:1) was added to the cathode chamber; and a graphite anode and a stainless steel cathode were inserted into the anode molten salt electrolyte and cathode molten salt electrolyte, respectively.
Titanium-containing slag was added to the anode molten salt electrolyte, the electrolytic cell is powered on and running, the temperature of anode molten salt electrolyte was controlled to be 1,400° C., the temperature of cathode molten salt electrolyte was controlled to be 1,100° C., and the cathode chamber was protected by argon atmosphere. During this electrolysis process, the current density was controlled to be 0.05 A/cm2, and the electrolysis was carried out for 24 h. After the cathode was taken out, 15.2 g of titanium metal was obtained, and the electrolysis could be continuously carried out by adding the titanium-containing slag to the anode chamber.
This example provides a method for preparing titanium metal by molten salt electrolysis. The method included: 400 g of Cu—Sn—Ti alloy (Cu:Sn:Ti=73:16:11) was added to the bottom of the electrolytic cell, the alloy was heated to form liquid and completely separate the anode chamber from the cathode chamber; 400 g of anode molten salt electrolyte (anode molten salt consisted of Al2O3, SiO2, CaO and TiO2 in a mass ratio of 14:57:18:11) was added to the anode chamber, and 400 g of cathode molten salt electrolyte (prepared from NaCl and KCl according to a mass ratio of 1:1, and 5.2 wt % of low-valence titanium chloride consisting of TiCl2 and TiCl3 was added, the mass ratio of TiCl2 to TiCl3 is 2:1) was added to the cathode chamber; and a graphite anode and a stainless steel cathode were inserted into the anode molten salt electrolyte and cathode molten salt electrolyte, respectively.
Titanium-containing slag was added to the anode molten salt electrolyte, the electrolytic cell is powered on and running, the temperature of anode molten salt electrolyte was controlled to be 1,400° C., the temperature of cathode molten salt electrolyte was controlled to be 900° C., and the cathode chamber was protected by argon atmosphere. During this electrolysis process, the current density was controlled to be 0.05 A/cm2, and the electrolysis was carried out for 24 h. After the cathode was taken out, 15.3 g of titanium metal was obtained, and the electrolysis could be continuously carried out by adding the titanium-containing slag to the anode chamber.
This example provides a method for preparing titanium metal by molten salt electrolysis. The method included: 400 g of Cu—Ti alloy (Cu:Ti=80:20) was added to the bottom of the electrolytic cell, the alloy was heated to form liquid and completely separate the anode chamber from the cathode chamber; 400 g of anode molten salt electrolyte (anode molten salt consisted of Al2O3, SiO2, CaO, MgO and TiO2 in a mass ratio of 16:24:28:10:22) was added to the anode chamber, and 400 g cathode molten salt electrolyte (prepared from NaCl, KCl and CaF2 according to a mass ratio of 9:9:2, and 7.8 wt % of low-valence titanium chloride consisting of TiCl2 and TiCl3 was added, the mass ratio of TiCl2 to TiCl3 is 4:1) was added to the cathode chamber; and a graphite anode and a tungsten cathode were inserted into the anode molten salt electrolyte and cathode molten salt electrolyte, respectively.
Titanium-containing slag was added to the anode molten salt electrolyte, the electrolytic cell is powered on and running, the temperature of anode molten salt electrolyte was controlled to be 1,400° C., the temperature of cathode molten salt electrolyte was controlled to be 1,000° C., and the cathode chamber was protected by argon atmosphere. During this electrolysis process, the current density was controlled to be 2 A/cm2, and the electrolysis was carried out for 24 h. After the cathode was taken out, 14.2 g of titanium metal was obtained, and the electrolysis could be continuously carried out by adding the titanium-containing slag to the anode chamber.
This example provides a method for preparing titanium metal by molten salt electrolysis. The method included: 400 g of Cu—Sn—Ti alloy (Cu:Sn:Ti=73:16:11) was added to the bottom of the electrolytic cell, the alloy was heated to form liquid and completely separate the anode chamber from the cathode chamber; 400 g of anode molten salt electrolyte (anode molten salt consisted of Al2O3, SiO2, CaO and TiO2 in a mass ratio of 9:37:44:10) was added to the anode chamber, and 400 g of cathode molten salt electrolyte (prepared from NaCl and KCl according to a mass ratio of 1:1 and 7.8 wt % of low-valence titanium chloride consisting of TiCl2 and TiCl3 was added, the mass ratio of TiCl2 to TiCl3 is 4:1) was added to the cathode chamber; and a Cr—Fe alloy inert anode and a stainless steel cathode were inserted into the anode molten salt electrolyte and cathode molten salt electrolyte, respectively.
Titanium-containing slag was added to the anode molten salt electrolyte, the electrolytic cell is powered on and running, the temperature of anode molten salt electrolyte was controlled to be 1,400° C., the temperature of cathode molten salt electrolyte was controlled to be 1,000° C., and the cathode chamber was protected by argon atmosphere. During this electrolysis process, a current density was controlled to be 50 mA/cm2, and the electrolysis was carried out for 24 h. After the cathode was taken out, 15.2 g of titanium metal was obtained, and the electrolysis could be continuously carried out by adding the titanium-containing slag to the anode chamber.
This example provides a method for preparing titanium metal by molten salt electrolysis. The method included: 400 g of Cu—Sn alloy (Cu:Sn=3:1) was added to the bottom of the electrolytic cell, the alloy was heated to form liquid and completely separate the anode chamber from the cathode chamber; 400 g of anode molten salt electrolyte (anode molten salt consisted of Al2O3, SiO2, CaO and TiO2 in a mass ratio of 14:57:18:11) was added to the anode chamber, and 400 g of cathode molten salt electrolyte (prepared from NaCl and KCl according to a mass ratio of 1:1 and 7.8 wt % of low-valence titanium chloride consisting of TiCl2 and TiCl3 was added, the mass ratio of TiCl2 to TiCl3 is 4:1) was added to the cathode chamber; and a graphite anode and a stainless steel cathode were inserted into the anode molten salt electrolyte and cathode molten salt electrolyte, respectively.
Titanium-containing slag was added to the anode molten salt electrolyte, the temperature of anode molten salt electrolyte was controlled to be 1,400° C., the temperature of cathode molten salt electrolyte was controlled to be 1,000° ° C., and the cathode chamber was protected by argon atmosphere. Electrolysis was controlled to be carried out under a same cell voltage condition as Example 1, and no titanium metal was obtained on the cathode.
The above is only the specific embodiments of the present disclosure, but the scope of protection of the present disclosure is not limited to this. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present disclosure, which will be included in the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure is to be based on the scope of protection of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110499892.4 | May 2021 | CN | national |
This application is the national phase entry of International Application No. PCT/CN2022/088930, filed on Apr. 25, 2022, which is based upon and claims priority to Chinese Patent Application No. 202110499892.4, filed on May 8, 2021, the entire contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2022/088930 | 4/25/2022 | WO |
