Metallurgical Knowledge Titanium Metallurgy 1

6. The production of titanium-rich materials, whether it is the production of titanium sponge or titanium dioxide, must involve the preparation of titanium-rich materials. The so-called preparation of titanium-rich materials refers to the processing of ilmenite concentrate to obtain higher-grade titanium materials. Generally speaking, its TiO2 mass fraction should be greater than 85%. 6.1 The purpose of producing titanium-rich materials is (1) to reduce the consumption of other raw materials and production costs (2) to reduce the burden of subsequent separation, purification and treatment of by-products, and to simplify the process (3)_Increase the production capacity per unit volume of equipment 6.2 According to the classification of the final product, the production method of titanium-rich materials can be divided into reduction smelting method to produce titanium slag, and selective chlorination method, reduction rust method, acid leaching method and reduction magnetic separation method to produce artificial rutile. 6.2.1 Reduction smelting method of ilmenite. Iron in various ilmenite concentrates mainly exists in the form of FeO and Fe2O3. Since titanium and iron have different affinities for oxygen, the ease of their reduction is also different. Generally speaking, iron oxides are relatively easy to be reduced to obtain pig iron, while titanium oxides are relatively stable and enriched in the residue. The specific process is to use anthracite or petroleum coke as a catalyst in a submerged arc furnace at a high temperature of 1600 to 1800°C to reduce iron oxides to pig iron. The titanium oxides are not reduced but remain in the residue. The pig iron has a high density and a low melting point, so it is layered with titanium slag. The slag phase floats on top and the molten iron is below, so that titanium is enriched in the slag. We call this titanium-rich material titanium slag. Reduction smelting includes: 1. Solid-state reduction process 2, and melting and slagging process. (1) Solid-state reduction process: The main reactions that occur are: Fe2O3+C(CO)=2FeO+CO(CO2). FeTiO2+TiO2+C(CO)=2FeTiO3+CO(CO2). FeTiO3+C(CO)=Fe+TiO2+CO(CO2). CO2+C=2CO (2) Melting and slagging process: When the temperature reaches the melting temperature of metallic Fe, the pig iron begins to melt and the slag stratifies. The components in the slag are mainly unreacted ilmenite, titanium oxides and other impurity oxides. Reduction smelting equipment Most reduction smelting equipment now uses closed electric furnaces, which have the advantages of reducing heat loss, increasing titanium recovery rate, reducing dust and improving working conditions. Production of titanium slag Most of the production of titanium slag adopts periodic operation methods. The normal operating procedures are: Ramming → Adding material → Put down the electrode → Send power for melting → Put slag (kneading, pellet making) → In the next operation cycle, the molten iron and titanium slag flow out from the same tap hole and enter the fixed mold. The molten iron and titanium slag can be separated naturally after solidification in layers in the fixed mold. The low-priced titanium oxide contained in the slag can be oxidized into high-priced titanium oxide by the oxygen in the air. After the slag is crushed and magnetically separated to separate the mechanically mixed metallic iron and unreduced ilmenite, a titanium-rich material that meets the requirements - titanium slag is obtained. 7. Production of titanium tetrachloride (TiCl4) 7.1 Production of crude TiCl4 7.2 Refining of crude Ticl4 7.1 Production of crude TiCl4 7.1.1 The physical and chemical basis of chlorination reaction The reaction formula of titanium dioxide and chlorine can be expressed as: TiO2(s)+2Cl2(g)=TiCl4(g)+O2(g) The standard free enthalpy change of this reaction is 199024-51.88T (J). It can be seen that at 900°C, its △G = 115KJ. Therefore, under standard conditions and without a reducing agent, TiO2 and Cl2 cannot spontaneously form TiCl4. However, in the presence of reducing agent carbon, the chlorination reaction of titanium dioxide (TiO2) can proceed smoothly at a lower temperature (700~900°C). The total reaction formula can be expressed as: TiO2(s)+2Cl2(g)+C(s)=TiCl4(g)+CO2 =-194815-53.30T

7.1.2 Chlorination process There are three chlorination processes in production, namely: 1. Fixed bed chlorination, 2. Boiling chlorination 3. Molten salt chlorination. Among them, fixed bed chlorination is basically no longer used. 7.1.2.1 In boiling chlorination industrial production, the chlorination of titanium slag is generally carried out at 800 to 1000°C. At such a high temperature, the chlorination process is diffusion controlled. Therefore, strengthening material exchange and heat exchange is a key measure to strengthen the chlorination process. The characteristic of the boiling layer is that certain particles of solid fuel are absorbed by gases with a certain flow rate (the chlorination process is It is held up by Cl2) and rolls violently in the reaction zone, just like liquid boiling, so the gas and solid matter are fully contacted, and the mass transfer and heat transfer effects are very good. Boiling chlorination accelerates the reaction speed, the production process is strengthened, the process is easy to continue, and the equipment production capacity and labor productivity are improved. The structure of the boiling roasting furnace is as shown in the figure. Chlorine gas enters the gas chamber from the bottom of the furnace, and passes through the sieve plate so that the air flow can evenly distribute the entire cross-section of the reaction section, blowing up the internal furnace materials into a suspended state. The sieve plate is composed of graphite, with an opening rate of 0.8 to 1.0%. Titanium-rich slag with a certain particle size and ratio is mixed with petroleum coke and added to the furnace after being air-selected. The chlorination temperature is controlled at 800-1000°C. The titanium-rich slag is The thermal effect is relatively large when the low-valent oxides of medium titanium are chlorinated. Therefore, for boiling roasting, generally speaking, the chlorination process of titanium slag can be carried out by self-heating. However, if there is too much titanium in the form of TiO2 in titanium-rich slag, the thermal effect of chlorination of TiO2 is small, that is, there is little heat release, and the chlorination reaction will be difficult to maintain self-heating. The chlorination reaction is carried out in the reaction section. There are two types of reaction sections: cylindrical and expanded. The expanded reaction section can slow down the speed of the air flow at the outlet, thereby reducing the amount of smoke and dust, reducing the burden on the dust collection system, and improving the working environment. The TiCl4, CO, CO2, Cl2, impurity chloride and other gases generated by the reaction are discharged to the dust collection and condensation system through the furnace top outlet. The slag is discharged from the slag discharge port, and the slag discharge speed is usually controlled at about 7% of the feeding speed. 7.1.2.2 In addition to the TiCl4 vapor generated by the reaction, the gas discharged from the furnace gas of the dust collection condensation system also contains some fine particles of solid materials and other gas products such as FeCl3, MnCl2, MgCl2, SiCl4, AlCl3, VoCl3, CO, CO2 and unreacted Cl2. Various gas products can be divided into three categories according to their boiling points: Category 1: The boiling point of chlorides is lower than 150°C and is liquid at room temperature such as TiCl4, VoCl3, SiCl4, CCl4, etc. Category 2: The boiling point of chlorides is between 150 and 350°C, which is characterized by directly changing from gaseous state to solid substances, such as AlCl3, FeCl3, etc. Category 3: Chlorides with high boiling points, such as MgCl2, CaCl2, FeCl2, MnCl2, etc. Connection diagram of chlorination roasting equipment and its condensation process. Dust collection and condensation process. The following dust collection and condensation process is usually used in industry. After the furnace gas escapes from the top of the chlorination furnace, it first enters the partition dust collector to separate and remove the entrained solid particles as much as possible. Each dust collector is controlled so that the temperature is 400~300℃, 20 0～150℃, 150～130℃. In this way, the high boiling point chlorides MgCl2, CaCl2, FeCl2, MnCl2, FeCl3 and part of AlCl3 are condensed into solids and collected in the dust collector. TiCl4, SiCl4, VoCl3 and other low boiling point gases Entering the elution tower, liquid TiCl4 at room temperature or treated with frozen brine is sprayed in the elution tower to make the TiCl4 in the gas phase become liquid as much as possible. Since TiCl4 has a large vapor pressure at room temperature, in order to maximize the collection of TiCl4, a coil condenser or cold trap is usually installed, and the cooling medium The substance is generally frozen brine. After such treatment, TiCl4 and a small amount of SiCl4, VoCl3, CCl4 and other low-boiling point gases are condensed into liquids and remain in the elution tower and condenser. Other gaseous substances such as CO, CO2, Cl2, O2, N2, HCl, etc. enter the tail gas treatment system. The liquid crude TiCl4 obtained by leaching and condensation enters the Dole concentration machine to settle and separate the mechanically mixed solid suspension. The settled mud is evaporated and recovered by the evaporator, and the residue is returned to the chlorination furnace for re-chlorination. Exhaust gas treatment methods There are three methods for exhaust gas treatment, mainly to treat the Cl2 contained in the exhaust gas. 1. Water absorption method 2. FeCl2 aqueous solution absorption method 3. Alkali neutralization method 1. Water absorption method is the most economical method, and the reaction is: Cl2+H2O=HCl+HClO. After multi-stage elution, HCl in the tail gas can also be dissolved in the wash water. 2. FeCl2 aqueous solution blowing method, the reaction is: 2FeCl2+Cl2=2FeCl3. Cl2 in the tail gas can react with FeCl2 according to the above formula, and the generated FeCl3 reacts with the scrap iron chips immersed in the solution to regenerate FeCl2 for recycling. The reaction is 2FeCl3+Fe=3FeCl2. 3. The alkali neutralization method uses lime milk alkali solution to rinse the chlorination furnace tail gas, and the following reaction occurs: 2Ca(OH)2+2Cl2=Ca(ClO)2+CaCl2+H2O Through this process, we can obtain crude TiCl4, whose purity can reach 97.8%. The main impurity components include FeCl3, MnCl2, MgCl2, SiCl2, etc. 7.1.2.3 Molten salt chlorination Molten salt chlorination refers to a method in which mixed salts of a certain composition and properties are put into a molten salt chlorination furnace to melt, titanium-rich slag and carbonaceous reducing agents are added, and chlorine gas is passed through for chlorination. In the molten salt chlorination process, a screw feeder is used to feed the mixture of titanium-rich slag and petroleum coke to the surface of the melt. Chlorine gas is introduced from the bottom, and the melt is stirred vigorously to make it contact with the material, resulting in good heat transfer and mass transfer conditions. The titanium in the titanium-rich material and the chlorination products of some low-boiling point substances are discharged from the furnace outlet. High-boiling chlorides such as MgCl2, CaCl2, etc. remain in the melt. In the body. The specific process is that titanium-rich slag and carbon solid particles suspended in the molten salt interact with the blown chlorine bubbles. The generated TiCl4 and other low-boiling point gas substances enter the bubbles, are taken out of the melt by the bubbles, and enter the dust collection, leaching, and condensation systems to obtain crude TiCl4. Refractory substances such as MgCl2, CaCl2, etc. are dissolved into the molten salt. A suitable molten salt medium is the key to ensuring the physical and chemical properties of molten salt. The waste electrolyte of magnesium metal is usually produced by electrolyzing carnallite. Characteristics of molten salt chlorination Compared with boiling chlorination, molten salt chlorination has the following characteristics: First, the raw materials have strong adaptability. It is suitable for the chlorination of high-titanium slags containing high calcium and magnesium and high-titanium materials such as rutile. Secondly, the partial pressure of TiCl4 in the gas phase product is high. The volume fraction of CO2 in the tail gas is much higher than CO, which saves the reducing agent and is conducive to the condensation of TiCl4. Thirdly, the impurity content in crude TiCl4 is less. NaCl and KCl in the molten salt can form chlorochromium salts (such as K3AlCl6, Na3AlCl6, KFeCl6, etc.) with chlorides such as AlCl3 and FeCl3, so the molten salt itself has an impurity removal effect, and the resulting crude TiCl4 The impurity content in the medium is low. Fourthly, molten salt chlorination requires molten salt and produces waste salt, which increases the burden of "three wastes" treatment.

8 Refining of crude TiCl4 8.1 Necessity The Mg thermal reduction method is used. For every ton of titanium sponge produced, about 4 tons of TiCl4 are needed, and the impurities brought into the reduction system are almost all enriched in the product sponge titanium. Therefore, the impurity content in the sponge titanium will be 4 times higher than the impurity content in the raw material TiCl4. Therefore, in order to produce abundant titanium sponge, it is necessary to first prepare refined TiCl4 with higher purity. 8.2 Classification of impurities in crude TiCl4 8.2.1 Impurity composition: (1) Gas impurities: O2, N2, CO2, Cl2, COCl2, COS, HCl, etc.; (2) Liquid impurities: SiCl4, VOCl3, CCl4,...; (3) Solid impurities: Some substances that are solid at normal temperature and pressure. Such as FeCl3, AlCl3, TiO2... 8.2.2 Impurities: According to the difference between the boiling point and TiCl4, impurities can be divided into high boiling point impurities, low boiling point impurities and impurities with similar boiling points. High boiling point impurities: FeCl3, AlCl3, TiOCl2; Low boiling point impurities: SiCl4, CCl4, etc.; Similar boiling point impurities: VOCl3. 8.3 Separation method (1) Gas impurities: They can be volatilized and removed from TiCl4 by heating; (2) Solid suspended solids: remain in the evaporator during the distillation process; (3) High-boiling impurities: control the outlet temperature of the evaporator to be lower than the boiling point or sublimation point of the high-boiling impurities so that they remain in the kettle; (4) Low-boiling impurities: volatilize from the top of the distillation tower using the distillation method; (5)_Impurities with similar boiling points: VOCl3 (126.8℃), TiCl4 (136℃) are removed by chemical or organic treatment methods. 8.4 Principle of purification of crude TiCl4 1._ Distillation method to remove high boiling point impurities 2._ Refining method to remove low-boiling point impurities 3. Use chemical or organic methods to remove impurities VOCl3 with similar boiling points Refining method Using refining method to separate miscible components must meet the following conditions: 1. The two components must have different volatilities, or the relative volatility deviates far from 1 2. During the operation, the characteristics of the rectification method must be refluxed. There must be multiple trays in the rectification tower. On each tray, the solution is partially vaporized and partially condensed to approximately reach equilibrium. During the rectification process, part of the condensate must be refluxed. Introduction to the distillation process: The steam from the bottom of the kettle enters the distillation tower and rises, and meets the reflux from the top of the tower. Since the temperature in the tower gradually decreases along the direction of the top of the tower, heat and mass transfer occur when the rising steam meets the descending liquid flow. The less volatile TiCl4 will gradually be enriched in the liquid phase. On the contrary, the more volatile SiCl4 will gradually become concentrated in the rising gas phase. As long as the number of tray stages is sufficient, the purpose of phase separation of TiCl4 and low boiling point impurities can be achieved. 3. Use chemical or organic methods to remove impurities VOCl3 with similar boiling points. Industrially, there are three methods to remove vanadium, namely: copper or aluminum method to remove vanadium, hydrogen sulfide method or hydrocarbon method. All these methods are nothing more than using the property of tetravalent vanadium compound (VOCl2) to be insoluble in TiCl4 to reduce pentavalent vanadium compound (VOCl3) to tetravalent VOCl2. (1) Removal of vanadium by copper or aluminum method: Use copper powder, copper wire, copper scraps or copper-based alloys to cause the following reduction reaction of VOCl3 in TiCl4: VOCl3+Cu= VOCl2+CuCl. When using copper powder to remove vanadium, when the mass fraction of AlCl3 in TiCl4 is greater than 0.1%, AlCl3 will passivate the copper, so use humidified charcoal or table salt to remove AlCl3 first. AlCl3+H2O=AlOCl↓+2HCl The mass fraction of the copper-vanadium compound obtained by using copper as the reducing agent is roughly: Cu: 20.2~26.2%, TiO2: 10~12%, Cl2: 45%, and the rest is aluminum, iron, etc. It can be sent to recover copper and vanadium. Vanadium removal by aluminum method: When aluminum is used as the reducing agent, the following reaction occurs: 3TiCl4+Al=3TiCl3+AlCl3 TiCl3+VOCl3=TiCl4+VOCl2 The above reaction must involve the participation of catalytic AlCl3, so that the reaction between aluminum and TiCl4 can proceed effectively. Therefore, after adding aluminum powder, chlorine gas is added. When the reaction proceeds, the chlorine gas is turned off. The obtained precipitates of VOCl2, TiCl3 and AlCl3 are sent to extract vanadium. (2) Vanadium removal by hydrogen sulfide. This method slowly introduces H2S gas into TiCl4 at 90 degrees. The reaction is as follows: 2VOCl3+H2S=2VOCl2+2HCl+S. The reducing agent used in this method is relatively cheap and has good vanadium removal effect. The precipitate contains a high vanadium content, but the H2S gas is highly toxic, so be careful when operating. (3) Hydrocarbons: This method is to add a small amount of hydrocarbons to TiCl4, heat it to about 130 degrees and stir to carbonize the hydrocarbons. The newly carbonized fine particles have great potential to remove vanadium using the copper or aluminum method. It should be set up after removing low-boiling point impurities and high-boiling point impurities to reduce copper consumption. For vanadium removal using H2S gas or hydrocarbons, vanadium is often removed first, and then low-boiling point impurities and high-boiling point impurities are removed. 8.5 Distillation process The distillation and purification of TiCl4 is carried out in a stainless steel distillation tower. There are two stages of distillation: the first stage is to keep the temperature at the top of the tower at 57~70 degrees, the temperature at the bottom of the tower at 139~141 degrees, and control the still at 142~146 degrees. The pressure is 14.66~18.66Kpa to distill away low-boiling impurities such as SiCl4. The second stage is to distill out TiCl4 to separate it from high-boiling impurities, so the temperature at the top of the tower is controlled at 136 degrees. The distilled TiCl4 vapor is condensed to obtain a colorless, transparent or slightly yellow TiCl4 liquid with very little impurity content. The recovery rate of TiCl4 in the refining process is 96%._ The product TiCl4 during the distillation process 2) Low-boiling point distillate: The low-boiling point distillate is mainly SiCl4, and there is also some TiCl4. After purification, SiCl4 can be used as a raw material for producing single crystal silicon and quartz. 3) High-boiling point impurities: Return to the chlorination process to recover the valuable component titanium. 8.6 Magnesothermal production of titanium sponge 8.6.1 The selection of reducing agent is based on the relationship between the standard free energy of formation of metal chlorides and temperature. We know that under standard conditions, Li, K, Na, Mg, Ba, Mn, Al and other metals can be used as reducing agents to produce titanium metal from TiCl4. However, considering all aspects, the most suitable reducing agents are only magnesium and sodium. 8.6.2 The basic principle of the reduction process is to use the magnesium reduction method to produce titanium metal in a closed steel reactor. Place the metal magnesium in the reactor and fill it with inert gas. Heat it to melt the magnesium (melting point 650 degrees). At 800-900 degrees, TiCl4 is put in at a certain flow rate to react with the molten metal magnesium. It can be expressed by the following formula: TiCl4+2Mg=2MgCl2+Ti. The equilibrium constant of this reaction is KP=7.051014, so from a thermodynamic point of view, the reaction proceeds very thoroughly. At the reaction temperature, the generated MgCl2 (melting point 714 degrees) is in a liquid state and can be discharged in time. At 900-1000 degrees, MgCl2 and excess Mg have a high vapor pressure, and the residual MgCl2 and Mg can be distilled away under a certain degree of vacuum to obtain sponge-like metallic titanium. Magnesium reduces TiCl4. In fact, the reaction of magnesium reducing TiCl4 to obtain metallic titanium is completed one after another through the reaction process of generating low-priced chlorides. There are the following series of reactions: 2TiCl4+Mg=2TiCl3+MgCl2 2TiCl3+Mg=2TiCl2+ MgCl2 TiCl4+Mg=TiCl2+ MgCl2 TiCl2+Mg=Ti+ MgCl2 2TiCl3+Mg=2Ti+ During the reaction process of MgCl2, sometimes when the reducing agent is insufficient, the following reduction reaction may occur: 3TiCl4+Ti=4TiCl3 TiCl4+Ti=2TiCl2 TiCl3+Ti=3TiCl2 The standard free energy of formation of these reactions is also very negative. Therefore, it may occur automatically under standard conditions. These reactions are not what we want to happen. It can be seen that the reduction of TiCl4 by magnesium is a quite complex multi-phase chemical reaction. The magnesia thermal reduction reaction is an exothermic reaction with a very large thermal effect. In order to maintain the normal reaction temperature, heat dissipation must be carried out. The heat dissipation process directly affects the speed of the reaction and limits the enlargement of the equipment. _ At high temperatures, titanium is easily contaminated by N2, O2, and water vapor in the atmosphere. Therefore, in order to obtain high-quality titanium sponge, it must be carried out in isolation from the air. 8.6.2 Reduction operation: After the reaction tank is inspected to be well sealed, it is hoisted into the furnace by a crane and filled with argon. After it is heated to 700-750 degrees, liquid magnesium is put into the tank through a magnesium tube and TiCl4 is introduced. At this time, the heating furnace should be closed and the flow rate of TiCl4 should be adjusted to keep the temperature of the reaction tank between 850-900 degrees. In order to improve production efficiency, air is passed into the annular gap between the outer wall of the tank and the furnace to dissipate the waste heat. During the reduction process, the wall temperature of the reaction tank needs to be adjusted and controlled. The flow rate of TiCl4 is best to ensure that the reaction process can proceed at the maximum speed at the reaction temperature. During the reduction process, if the reaction releases too much heat, the heater in the reaction section furnace can automatically Close to prevent overheating. At the end of the reaction, in order to maintain the temperature in the tank and better allow MgCl2 to settle, after stopping heating (after the utilization rate of magnesium reaches 60-65%), the reaction tank needs to be kept at 900 degrees for 1 hour, and then the MgC should be drained as much as possible After l2, turn off the electric furnace. During the entire reaction process, the pressure in the tank should always be kept slightly higher than atmospheric pressure to prevent air infiltration. When the reaction tank cools to 800 degrees in the furnace, lift it out of the furnace and place it in a cooling tank. Use cold water or blast to remove the reaction tank. The tank should be cooled to 40-25 degrees. The mass fractions of Ti, Mg, and MgCl2 in the reduction product are 55-65%, 25-35%, and 9-12% respectively. It is then subjected to vacuum distillation to separate and remove magnesium and magnesium chloride in the titanium sponge. 8.6.2 Vacuum distillation of reduction products and treatment of titanium sponge. Vacuum distillation is based on the fact that at a temperature of 800-1000 degrees, magnesium and MgCl2 have a large vapor pressure, allowing them to evaporate under vacuum and condense on the condenser. The vapor pressure of titanium is very small, leaving In the original reduction tank, titanium is separated from other components. In a distillation tank with a vacuum degree higher than 1.3 Pa, the reduction product is heated at 900-950 degrees for a long time. Magnesium and magnesium chloride can be volatilized and removed, and condensed on the condenser.

Thermodynamics and kinetic thermodynamics of vacuum distillation: 1) Mg volatilizes first, then MgCl2, and the condensation order is reversed. 2) The influence of distillation temperature: increasing the temperature is beneficial to the volatilization of magnesium and MgCl2, but it will cause the iron in the distillation tank wall to migrate into the sponge titanium. At 1085 degrees, a titanium-iron eutectic can be generated, so it is generally believed that the distillation temperature should not be higher than 1020 degrees. 3) Heating rate: Distillation needs to absorb the latent heat of phase change, but the heating rate should not be too fast. Kinetics: The distillation process is divided into two stages. The first stage: There is a constant speed stage in the early stage of distillation. During this period, the volatilization of MgCl2 mainly occurs on the outer surface of the sponge titanium lump. The magnesium and MgCl2 at the bottom of the early distillation tank and inside the sponge titanium diffuse to the outer surface along the capillary pores of the sponge titanium to maintain its constant rate of volatilization. Second stage: As the distillation process proceeds, the free MgCl2 content in the sponge titanium lump gradually decreases, and its volatilization rate gradually slows down. In the first stage, the distillation rate is almost independent of the structure of the sponge titanium lump. In the second stage, the distillation rate depends largely on the structure of the sponge titanium lump. Factors affecting vacuum distillation: 1) Distillation temperature 2) Condensation speed: releases latent heat of phase change 3) Influence of vacuum degree: High vacuum degree is conducive to the volatilization of distilled substances, and the faster the distillation rate. However, vacuum degree can only change the distillation cycle, not the Cl- content in the product. 4) Distillation time: When the MgCl2 content drops to a certain level, extending the distillation time will not further reduce the MgCl2 content. 5) The impact of the sea surface titanium structure on the distillation process: the denser the structure of sponge titanium, the higher the closed porosity rate, and the more difficult vacuum distillation is. The closed capillary pores of sponge titanium are mainly due to two aspects. One is improper control of the feeding speed during the reduction process, resulting in a high closed porosity rate; the other is that the temperature rise rate is too fast during the distillation process, causing the sea surface titanium to sinter and increase the closed porosity rate. There are two methods of vacuum distillation. One is to directly carry out vacuum distillation without taking out the reduction product from the reduction tank. For example, an empty reduction tank is buckled together as a condenser. After distillation, the reduction tank condensed with magnesium and MgCl2 is returned for reduction. This method can greatly reduce the time the reduction product is exposed to the air and the working hours. The other method is to take the reduction product out of the reduction tank and put it into a special vacuum distillation equipment for distillation. This method can improve the productivity of the distillation equipment and shorten the distillation time. There are two types of distillation equipment structures, namely the upper-cooling type and the bottom-cooling type. Although the difference is only the reversal of the mutual positions of the distillation kettle and the condenser, the bottom-cooling type can make the molten MgCl2 flow down instead of relying on evaporation alone, so it can shorten the distillation cycle and save energy, but the heating furnace must be at the top. The vacuum distillation operation uses the above equipment to produce 2 tons of titanium sponge as an example. The temperature is maintained at 400 degrees for 4-6 hours to remove the adsorbed gas and crystal water in the product; the temperature is gradually raised to 800 degrees and kept for 3-5 hours to remove magnesium and most of MgCl2. This The degree of vacuum should not be too high during a period of time, so as not to cause part of the magnesium and MgCl2 to be pumped into the vacuum system due to too late cooling; then gradually increase the temperature to 930-960 degrees and maintain it for 40-60 hours to remove the residual MgCl which only accounts for 1-2% of the total amount. 2. In the later stage of distillation, it must be stable for a period of time at a high vacuum of 6.6710-4-1.3310-5. After closing the vacuum valve twice, reduce the high vacuum to 2.67Pa, and then cool down for 2-3 hours. Then fill with argon gas for cooling After cooling, move the distillation tank to a water-cooling tank for cooling, and use water to cool it to room temperature. Then open the distillation tank. Use a pneumatic pick or ejector machine to take out the titanium sponge lumps. After crushing, sorting, sampling analysis, grading, and batching into packaging aluminum barrels, they can be shipped from the factory after being sealed, evacuated, and filled with argon. The main technical and economic indicators of the magnesium reduction method 1) The metal recovery rate is 95-98% from TiCl4 and less than 80% from high titanium slag. 2) The product qualification rate is 92-96% 3) The direct utilization rate of magnesium metal is 60-70% 8.7 Production of titanium metal by sodium reduction method 8.7.1 Basic Principle The sodium reduction method of TiCl4 to produce titanium metal is based on the following chemical reaction: TiCl4(g)+Na(l)=Ti(s)+4NaCl(l) At 1200K, the thermal effect of this reaction is -755KJ, which is larger than the thermal effect of magnesium thermal reduction reaction. The sodium reduction reaction is carried out in stages: TiCl4(g)+ Na(l)=TiCl3(l)+NaCl(l) TiCl3(l)+ Na(l)=TiCl2(l)+NaCl(l) 1/2TiCl2(l)+Na(l)=1/2Ti(s)+NaCl(l) The generated TiCl3 and TiCl2 can be dissolved in the NaCl melt to form a eutectic, and metallic sodium can be dissolved in the NaCl melt. Therefore, the sodium reduction reaction of low-valent titanium chloride is carried out in the NaCl melt. At the reduction temperature of 900-920 degrees, the reaction proceeds very thoroughly. Like the magnesia thermal reduction method, the sodium reduction method is also protected by inert gas. It is carried out in a closed container. Although titanium powder can be obtained at a significant reduction reaction speed when the melting point of metallic sodium is above 98 degrees, the temperature of industrial production generally needs to be above the melting point of sodium chloride (800 degrees). The molten reaction product is allowed to penetrate through the sponge titanium layer into the bottom of the reaction tank, and the surface of the reactant titanium is continuously exposed to obtain metallic titanium with a sponge titanium structure. In industrial practice, there are one-stage method and two-stage method for sodium reduction of TiCl4. The one-stage method is carried out in a stainless steel reaction tank. The tank is filled with argon and heated to 650-700 degrees. During the reduction process, TiCl4 and molten sodium are successively put into the tank in strict accordance with n(TiCl4):n(Na)=1:4. At the end of the reduction reaction, when the sodium addition is completed, slowly add TiCl4 to Until the utilization rate of sodium reaches 100%. After the reaction starts, external heating is stopped and the temperature inside the tank is controlled at 850-880 degrees. To prevent a large amount of heat from being released during the reaction, cold air can be used to blow the outer wall of the reaction tank or use other methods to export the waste heat. At the end of the reduction process, increase the temperature to 950-970 degrees and keep it for a period of time. The reaction product contains w (Ti) = about 17%, w (NaCl) = about 83%, as well as trace amounts of sodium and low-priced titanium chloride impurities. The reaction product is finely crushed and slowly placed in an acid-resistant tank with a stirring tank, and leached with an HCl solution containing about 1%. After filtering, wash with water until neutral. Spin dry on a centrifuge, and dry the resulting nickel powder in a vacuum drying oven, which is the finished titanium._ Two-stage reduction method The two-stage reduction method is to reduce to TiCl2 in the first stage to obtain the TiCl2-NaCl eutectic molten salt; in the second stage, it is reduced from the molten salt to metallic titanium. In the first stage of reduction, press n(TiCl4):n(N a)=1:2 Add materials and start reduction at 700-750 degrees. When the melt accumulates to a certain amount in the reaction tank, it is sent to the second reaction tank under argon pressure. The second stage reaction is carried out at 650-900 degrees. At this time, slowly add the same amount of sodium for supplementary reduction. When the reduction is completed, keep it at 950 degrees for a period of time, and then perform cooling, crushing, water immersion, etc. The operations are the same as the one-stage reduction method. The two-stage reduction releases 70% of the heat generated by the total reaction in the first stage, and the remaining 30% is released in the second stage, so that the reaction heat can be exported in two times. Moreover, the second stage reduction process is concentrated in molten salt, which is conducive to the generation of large particles of titanium powder. Therefore, its purity is very high. In terms of production, it takes 2.05 metal sodium to produce one ton of titanium sponge._2.2 tons, concentrated hydrochloric acid 1.4 tons, argon 25M3.

8.8 Refining of titanium 8.8.1 Electrolytic refining Electrolytic refining is to press the crude titanium containing impurities into a rod-shaped anode or place it in an anode basket. Alkali metal chloride is used as the electrolyte, and low-valent titanium chloride (TiCl2, TiCl3) is dissolved in it. A steel cathode is used. The anode dissolves during electrolysis, and the titanium is transferred into the molten salt in the state of Ti2+, Ti3+, etc., and the low-valent titanium ions are reduced to metallic titanium on the cathode. Electrolysis is performed at 80 It is carried out at 0-850 degrees. Electrolytic refining is based on the different precipitation potentials of impurities and titanium. Titanium and other more electronegative elements are preferentially dissolved from the anode and enter the molten salt in an ionic state; while impurity elements that are more electronegative than titanium remain in the anode mud. Iron, nickel, and oxygen (TiO2) remain in the anode mud. Electrolytic refining is powerless for impurities such as Cr, Mn, Al, and V whose precipitation potential is lower than titanium. 8.8.2 Iodide refining The iodide refining process of titanium can be expressed as: _ Ti(s)+2I2(g)100~200 degrees TiI(g) 1300~1500 degrees Ti(s) 2I2(g) Titanium can react with iodine at a lower temperature to generate titanium iodide vapor, which then decomposes on the high-temperature metal wire. The released iodine reacts with the crude titanium again in the lower temperature zone. In this cycle, pure titanium is transported to the metal wire by iodine. The iodination method can remove oxygen, nitrogen and other impurities. Because titanium oxides and nitrides cannot interact with iodine at this time. The speed of titanium deposition mainly depends on the diffusion speed of titanium iodide to the surface of the metal wire. temperature and the speed of diffusion of iodine vapor to the surface of the metal wire. Generally, the temperature is controlled at 1300-1400 degrees, and the deposition speed is fast enough. The metal wire is made of titanium wire, and the temperature of the metal wire is controlled by adjusting the current and voltage. The impurities of iron, nitrogen, oxygen, manganese, magnesium, etc. contained in titanium refined by the iodide method are one order of magnitude lower than those of magnesium-reduced titanium. Therefore, titanium refined by the iodide method has good plasticity and lower hardness._ 9. Production of titanium dioxide 9.1 Sulfuric acid method 9.2 Chlorination method 9.1 If titanium slag is used in the sulfuric acid method, due to the relatively high grade of titanium, the consumption of concentrated sulfuric acid is relatively small. Correspondingly, the by-product FeSO4.7H2O and dilute sulfuric acid are also relatively small. However, whether ilmenite is used as raw material or titanium slag is used as raw material, the basic principle of producing titanium dioxide by sulfuric acid method is the same, and the production process is also similar. 9.1.2 Production principle and main technical indicators 1. Acid decomposition and leaching (1) The main reaction is that the iron in ilmenite is converted into FeSO4 and Fe2(SO4)3, and titanium is converted into TiOSO4 and Ti(SO4)2. FeTiO3+2H2SO4= TiOSO4+ FeSO4+2H2O FeTiO3+3H2SO4= Ti(SO4)2+ FeSO4+3H2O (2) Process conditions After ilmenite or titanium slag is ground, it reacts with concentrated sulfuric acid at a temperature of 180 to 200 degrees. The main reaction lasts for 5 to 10 minutes and the product solidifies. In order to complete the reaction, it usually needs to be matured for 1 to 2 hours after solidification. (3) The solid product decomposed by the leaching acid is leached with water, and TiOSO4, FeSO4, and Fe2(SO4)3 enter the liquid phase. 1,_ In order to make iron crystallize and precipitate as much as possible in the form of FeSO4.7H2O, the Fe3+ in the leach solution should first be converted into Fe2+. During production, iron filings are used to reduce the Fe3+ in the solution to Fe2+. In order to reduce the iron ions to divalent as much as possible and prevent Fe2+ from being re-oxidized to Fe3+ by oxygen in the air, a small amount of titanium ions are often reduced. 2,_ reduction _ _In order to make iron crystallize and precipitate in the form of FeSO4.7H2O as much as possible, the Fe3+ in the leach solution should first be converted into Fe2+. During production, iron filings are used to reduce the Fe3+ in the solution to Fe2+. In order to reduce the iron ions to divalent as much as possible and prevent Fe2+ from being re-oxidized to Fe3+ by oxygen in the air, a small amount of titanium ions are often reduced to 3,_ Separation: Freeze the solution to -3~5 degrees, so that Fe2+ crystallizes out in the form of FeSO4.7H2O, while titanium remains in the solution, thereby achieving the purpose of separating iron and titanium from each other. 4,_ Hydrolysis: Concentrate the solution containing titanium ions after removing iron to 200~400g/l, and heat the solution to hydrolyze the titanium ions. TiOSO4+nH2O=Ti.(n-1)H2O↓+H2SO4 In order to accelerate the hydrolysis reaction and make the product particle size uniform and have a specific crystal structure, seed crystals need to be added to the system during hydrolysis. The amount of seed crystals is controlled at 0.2~0.5% to produce R-TiO2 Add orthotitanic acid seed crystals; add metatitanic acid seed crystals to produce A-TiO2. The hydrolyzate is washed and bleached to reduce the iron mass fraction to below 4 10-5, and then undergoes salt treatment to facilitate metatitanic acid to generate a specific crystal form during calcination. When producing anatase titanium dioxide, compounds containing Zn, Sb and other compounds need to be added to the system. 5,_ Calcined at 850-950 degrees, the salt-treated hydrolyzate is calcined in a rotary kiln to dehydrate the hydrated TiO2 and obtain a specific crystal form of TiO2. Since the hydrolyzate is generally represented by TiO2.xSO3.yH2O. TiO2.xSO3.yH2O=TiO2+xSO3↑+yH2O↑ 6,_ Surface treatment: After pulverizing the calcined product TiO2, particles with a particle size of 0.2~0.5um are generated, which are then coated with water glass, sodium metaaluminate, etc. to form a layer of SiO2, Al2O3, etc. films on the surface of the TiO2 particles to enhance the dispersion and acid resistance of the titanium dioxide product. 7,_ The disadvantages of the sulfuric acid method are the large consumption of sulfuric acid and the production of dilute acid. For every ton of TiO2 produced, 3~4 tons of FeSO4.7H2O are produced. 9.2 Chlorination method The chlorination method uses TiCl4 as raw material to produce pigment titanium dioxide. It reacts with O2 at 1000~2000 degrees to generate TiO2 and release Cl2. The generated Cl2 can be reused to prepare TiCl4. The reaction is: TiCl4+ O2= TiO2+2 In order to increase the chlorination reaction speed in Cl2 production, AlCl3 accounting for 1~2% of the amount of TiCl4 is usually added. Since AlCl3 is easier to oxidize than TiCl4, Al2O3 is preferentially generated as the core of the TiCl4 oxidation reaction. In addition, when AlCl3 is present, it helps the product TiO2 transform from anatase type to rutile type. During the production process, TiCl4 and O2 are first preheated respectively. Since TiCl4 is more corrosive at higher temperatures, it is limited by the material of the preheating device. Generally, only TiCl4 is preheated to 450~650 degrees, and O2 is preheated to 1600~2000 degrees. Although the oxidation reaction of TiCl4 is an exothermic reaction, it is not enough to maintain self-heating, and heat energy still needs to be added to the system. According to the heating method Depending on the formula, this method can be divided into internal heating method and external heating method. The post-processing of titanium dioxide products produced by chlorination method is the same as that of sulfuric acid method. Although titanium dioxide produced by chlorination method has relatively light environmental pollution, it has the following shortcomings: technical difficulty, and the oxidation furnace is prone to scarring._