WO2009139666A1 - Method and device for producing chemically active metals by rod electrical resistance - Google Patents

Abstract

The invention relates to the production of chemically active metals. The aim of the invention is to reduce electric power consumption and to increase the productivity. The inventive method involves loading a reaction burden, which consists of a metal oxide to be reduced and a reducing metal, into a reaction area, heating the burden so as to produce a metal and a slag and separating said metal and slag. The reduction and separation processes are carried out by means of contacts in the form of a cathode and anode. Heat is produced by the eclectic resistance in the burden when electric current pases therethrough and when a voltage is supplied to the contacts during the movement of the thus formed reduced metal to the cathode and the slag to the anode. Heat energy for separating the metal and slag is generated by permanently pressing the contacts against the burden with a specified force and by transmitting high- and low-frequency vibration via said contacts. The device comprises a vertical body with an insulating layer for accommodating the reaction burden and the contacts which are used as an anode and cathode for generating the burden eclectic resistance when a voltage is supplied to the contacts. The cathode is disposed in the lower part of the body and is also used as a bottom plate. Each contact is provided with a pressing punch and is coolable.

Description

 CHEMICAL METHOD AND DEVICE OF PRODUCTION

ACTIVE METALS BY THE ROD METHOD

ELECTRICAL RESISTANCE

Technical field

The present invention relates to the production of chemically active metals and can be used to produce titanium, zirconium, vanadium, tungsten, niobium, etc. metals.

State of the art

The method of metallothermal reduction of metals due to the initial heating of the reaction mixture to a certain temperature was selected as an analogue (Yu.L. Pliner, S.I.Suchilnikov, E.A. Rubinshtein - Aluminothermic production of ferroalloys and alloys, - Moscow: State Scientific and Technical -in literature on ferrous and nonferrous metallurgy), 1963, p. 28-29).

The minimum temperature required to start a spontaneous metallothermic reaction should exceed the melting point of the reduced oxides by 1.5-2 times.

The need to exceed the temperature of the after-furnace process over the melting temperature of the oxide part of the charge was first expressed by V.A. Bogolyubov. This dependence, apparently, is primarily due to the fact that obtaining high reaction rates necessary for the spontaneous occurrence of an out-of-furnace process at temperatures lower than the melting point of the reduced oxide is difficult due to the low diffusion rates in solids.

Another factor determining the temperature of the metallothermic process is the temperature of slag crystallization. If the process temperature is lower than the melting temperature of the slag, the separation of metal and slag formed as a result of reduction reactions, it turns out ι SUBSTITUTE SHEET (RULE 26) impossible. The process temperature should be chosen so that the temperature of the melt at the end of the precipitation period of the droplets of the reduced metal, continuing during the industrial smelting, is higher than the crystallization temperature of the slag, since the slag must have sufficient fluid mobility throughout the formation of the metal ingot.

In the case of smelting ligatures having high melting points (alloys with niobium, tungsten, molybdenum, metal chromium, etc.), a necessary condition for successful industrial smelting is the excess of the process temperature over the melting point of the alloy. At a process temperature close to the melting point of the metal, the ingot contains many slag inclusions and gas bubbles and is poorly separated from the slag. To eliminate this defect, significant overheating of the liquid metal is necessary.

Based on the above factors, the process temperature should be as low as possible, since an increase in the temperature of the after-furnace process is associated with additional costs and can lead to a decrease in the reducibility of the reaction mixture and increased evaporation of elements during melting.

The closest technical solution selected as a prototype is a method for the recovery of titanium and zirconium with calcium. (A.N. Zelikman - Metallurgy of refractory rare metals, - Moscow: Izd-vo "Metallurgy", 1986, pp. 414-419).

This method is carried out in sealed apparatus, where the briquetted mixture is loaded. The apparatus is filled with argon, heated to a temperature of 1000-1100 ⁰ C, maintained at this temperature for one hour. The reduction product is crushed, treated with a large volume of water, then diluted with hydrochloric acid, washed with water and dried in vacuum. The reduction of titanium and zirconia with calcium is used to obtain fine-grained powders of titanium and zirconium, which can be used to obtain products by powder metallurgy, as well as in the form of powders (mainly zirconium) in pyrotechnics and as getters in electronic devices.

The reduction of TiO ₂ and ZrO ₂ with calcium proceeds according to the reaction:

MeO ₂ + 2Ca = Me + 2CaO; (1) where Me is Ti or Zr.

The reduction of TiO ₂ and ZrO ₂ by reaction (1) is accompanied by a significant heat release (ΔH ° i ₃ oОк ⁼ -392 kJ for TiO ₂ and -240 kJ for ZrO ₂ ), but it is not enough for the spontaneous course of the process. It is necessary to constantly heat the reactor at 950-1100 ⁰ C. Even with an excess of calcium in the mixture of 50-100% and carrying out the process in an airtight apparatus filled with pure argon, it is fundamentally impossible to obtain titanium and zirconium powders with an oxygen content below 0.1%. This is because, at an oxygen content of 0.005-0.07%, the affinity of calcium for oxygen at 1000-1100 ⁰ C is equal to the affinity of zirconium and titanium for the oxygen dissolved in them. The actual oxygen content in the powders is 0.2-0.3%, since part of the oxygen is in them in the form of oxide films formed when the powders are washed from calcium.

In accordance with thermodynamic calculations for HOO ⁰ C, in the case of magnetothermal reduction of titanium oxides, the Gibbs energy of the redox process assumes a zero value when the oxygen content in titanium is 0.42% (by mass). In practical conditions, due to kinetic difficulties due to the low speed of diffusion processes in solids, an equilibrium state is not achieved. Therefore, the residual oxygen content is higher: during magnetothermic reduction up to 2.5%.

Calcium reduction is carried out in sealed apparatus made of heat-resistant steel, where a briquetted mixture of TiO ₂ or ZrO ₂ with s calcium (in the form of chips). Distilled calcium must be used. The apparatus is pumped out, filled with argon, heated to 1000–1100 ^° C and maintained at this temperature for about 1 hour. The reduction product is crushed, treated with a large volume of water [to remove part of CaO in the form of Ca (OH) ₂ ], then diluted with HCl, washed with water and dried in vacuum at 40-50 ⁰ C.

As a result of the recovery, finely dispersed powders of titanium and zirconium (2-3 microns in size) are obtained, since interlayers of refractory calcium oxide interfere with their growth. Particle enlargement is facilitated by the addition of calcium chloride (CaCl ₂ ), which forms the liquid phase. The mechanism of action of calcium chloride is that the resulting calcium oxide is dissolved in molten CaCl ₂ . At 1000 ⁰ C, the solubility of CaO is ~ 25%. Even if the amount of CaCl ₂ added to the charge is not enough for CaO to completely dissolve in it, the remaining undissolved CaO particles recrystallize through the melt, acquiring some mobility, which allows titanium crystals to coalesce into larger particles. By adding various amounts of CaCl ₂ to the initial charge (TiO ₂ + Ca + CaCl ₂ ), it is possible to control the particle size of the resulting titanium powder. If calcium chloride is introduced in an amount sufficient to dissolve all the CaO formed (approximately in molar ratios CaO: CaCl ₂ = 2: 1), metal particles of up to 10 μm are obtained. The disadvantage of this technical solution is:

- significant energy costs;

- the duration of the process;

- insufficient yield.

The closest analogue to the claimed device is a device for producing titanium (A.N. Zelikman - Metallurgy of refractory rare metals, - Moscow: Izd. "Metallurgy", 1986, p. 423), containing a casing with refractory lining, placed in it anodes, cathode basket with cathode rods, terminals for connecting current. On top of the cell is closed by a lid with a pipe for supplying raw materials.

The disadvantage of this device is the insignificant yield due to the low speed of the process, because the electrolyte cannot be heated to high temperatures, the high cost of assembly, high energy costs.

In order to solve the problem of obtaining a chemically active metal from its compounds cheaper and faster than during electrolysis and more qualitatively and purely on inclusions than with metallothermy, this method was proposed.

Disclosure of invention

The technical task of the proposed invention is to develop a method and device for its implementation, which allows to reduce energy costs, increase productivity, yield by increasing the speed of the process, the uniformity of heating.

The specified technical result is achieved by the fact that the method for the production of reactive metals by the method of rod electrical resistance involves heating the reaction mixture by providing electrical resistance, in the presence of a reducing agent, with reduction at the metal cathode and oxygen anode, at V this charge is not formed into an electrode, but preliminarily laid in the reaction zone, holding the inner cavity of a special insulated body, and the metal recovery process is carried out according to the following chain: power heating of the recoverable charge inside the case due to the creation of electrical resistance when voltage is applied to the contacts, metallothermal reduction of the metal inside the case, separation of the reaction charge into metal. In this case, the metal under the action of force gravity moves to the cathode, due to electrolysis, being cleaned of non-metallic inclusions, and slag is forced out to the anode, on which oxidizing agents are released. The necessary thermal energy for the separation of metal and slag comes from electrical resistance, after the start of the reaction, with constant compression of the contacts to the reaction mixture with a certain force. The process of heating the charge begins when it reaches its optimal resistance under the influence of compression pressure, and during melting a strictly defined amount of heat is supplied from the outside, which contributes to the maximum recovery of the recovered metal.

The specified technical result is achieved by the fact that in the device for the production of chemically active metals by the method of rod electrical resistance, containing a vertically arranged housing with an insulating layer, an anode and a cathode, according to the invention, the function of the anode and cathode is performed by the contacts, the latter being located at the bottom of the housing and is simultaneously a pallet Moreover, each contact is equipped with a compression punch and is cooled.

Besides:

- through the contacts on the reaction mixture serves high-frequency or low-frequency vibration, providing maximum extraction of the recovered metal; the optimal charge resistance is selected due to the specific packing of the charge components inside the container, while the metal reducing agents can be used in the form of a rod, spiral, mesh, etc.

Brief Description of the Drawings

Figure l shows a device that implements the proposed method for the production of chemically active metals by the method of rod electrical resistance. The best embodiment of the invention

The proposed method implements using the device shown in Fig.l, which shows a vertical section.

The device comprises a tubular body 1 with an insulating layer 2, where the reaction mixture is placed. Above and below are placed copper cooled contacts 3, which are connected to opposite poles, the top to the positive, and the bottom to the negative pole. The contacts are pressed by two punches 4 to the reaction mixture, which during the reaction is divided into slag 5 and metal being reduced 6. The reaction mixture is closed in the insulating layer 2 and held by the tubular body 1. The reaction mixture is heated by creating electrical resistance, which is widely used in industry for heating metal lengthy workpieces.

The electrical contact heating method is based on the ability to connect a heated body to an electrical circuit. At the same time, heat is released in it according to the Joule-Lenz law:

Q = 0.24 1 ² Rt, (2) where: I - current strength; R is the resistance of the conductor; t is the current passage time.

In case of electric contact heating (ESC), the reaction mixture seems to be included in the secondary circuit of the transformer, while a large current flows through it, and since the heat generated in accordance with formula (2) is proportional to the square of the current, it quickly heats up.

The advantages of this method are as follows:

1) high efficiency (up to 93%) and reduction of energy consumption by 1.5 ÷ 2 times compared with heating in resistance furnaces;

2) high speed and uniformity of heating;

3) improvement of sanitary and hygienic working conditions. Fast and uniform heating of the reaction mixture, preventing oxidation and significant heat loss, makes this method the most rational in the production of metals from their oxides and other compounds.

An important condition for rational heating of the reaction mixture is the ability to accurately and quickly measure the temperature and reliably regulate it. With contact heating, various temperature control methods can be applied. Since the amount of heat generated is proportional to the duration of heating in accordance with formula (2), the temperature can be adjusted by turning off the current in time.

Currently, contact installations are widely used for heating various metals, for heating long products from titanium alloys. So, for example, the Brown-Bover company produces up to 12 sizes of such plants. The diameters of the heated workpieces range from 90 to 130 mm, while their length is 1500-8000 mm. All operations (feed, clamp, heat on, temperature control and shutdown) are mechanized. Temperature control is carried out by the amount of energy supplied.

The work of the proposed method and device can be disclosed by the example of reduction of iron and titanium from ilmenite. According to studies, the electrical conductivity of ilmenite concentrate is approximately 2.0 ... 2.5 Ohm ^ -cm ^"1 , that is, the impurities present in it increase the resistance. Moreover, ilmenite has such conductivity even in the solid state at a temperature of about 1000 ⁰ C, which practically does not change during the transition from a solid to a liquid state. The ilmenite melt is characterized by a weak temperature dependence of electrical conductivity. Moreover, unlike other melts, the electrical conductivity of ilmenite decreases. This indicates that titanium-containing slags differ not in ionic but in electronic conductivity. in them, TiO ₂ , the melt resistance decreases sharply and high-titanium slag in electrical conductivity approaches metals. The melting temperature (1320 ... 1350 ⁰ C) and the viscosity of the initial ilmenite are also close to those of some slags used in electroslag technologies. The experiments carried out in an electroslag furnace with a capacity of 260 kV-A showed that with correctly selected electrical parameters, melting of ilmenite in the resistance mode does not cause any difficulties. Ilmenite concentrate is the main raw material for producing ferrotitanium. Due to the proposed method, it is possible to produce from ilmenite 25 ... 35% of ferrotitanium in an aluminothermic method. In this case, the initial energy necessary for slag formation and achievement of the required temperature, when the reduction of titanium oxides actively begins to take place, is released due to the heat of reactions of the interaction of aluminum with oxidizing agents introduced into the charge.

To reduce the melting point of the resulting slag, fluxing components are also introduced into the charge. This contributes, in addition to necessary for the reduction of titanium and iron oxides, the additional use of aluminum.

The process is enhanced by the occurrence of electrolytic reactions.

Using the proposed method, it is possible to smelting ferrotitanium containing 65 ÷ 75% titanium. It is known that in order to obtain metallic titanium from pure titanium dioxide by the out-of-furnace aluminothermic method, in order to increase the specific heat of the process, airborne salt and calcium peroxide are set in the mine. In this case, there is no need to use thermal additives, since the specific heat of the process increases due to electrical resistance, with the passage of current through the reaction mixture.

The principal features of the method are that the required amount of heat at different stages of the metallothermal reactions can be precisely controlled based on the Joule-Lenz formula (2). Unlike conventional resistance heating lengthy metal billets, the process of metallothermal reduction of metals is complicated by the fact that due to the flow of chemical, electrolytic, etc. processes, the resistance of the reaction mixture will change all the time.

In this regard, in accordance with Ohm's law:

R = U / J (3), if you simultaneously measure the voltage at the cooled terminals and the current flowing through the reaction mixture, then you can find the resistance at each moment of the reaction time. At the same time, at any time, the amount of heat supplied from the outside to the reaction mixture can be determined, and therefore, if the temperature mode of melting in time is calculated for a given volume of the reaction mixture, it can be adjusted based on the readings of devices, voltmeter, and ammeter.

When 70% of ferrotitanium is smelted, the missing heat, which is required for the reduction of titanium from oxides, will come from the outside in the amount required by the process. In this way, it is possible to recover titanium from its dioxide without adding any thermite mixtures, which in this case will be iron oxide, during the reaction of which an excess of heat occurs with aluminum.

When additional heat is introduced into the reaction mixture through cooled copper contacts 3, which are constantly pressed against the reaction mixture as the reaction proceeds, it is possible to recover from oxides of metals such as titanium, niobium, zirconium, molybdenum, chromium, nickel, etc. In this case, magnesium, aluminum, calcium, sodium, carbon, etc. can serve as metal reducing agents.

The reduction of the metal is enhanced by the electrolytic reaction, since the lower contact 3, where the reduced metal 6 is collected, serves as the cathode, and non-metallic reaction products are oxidized on the anode 3. Yu In contrast to the heating of metal lengthy workpieces, heating the reaction mixture can be, on the other hand, easier, since the reaction mixture can have a resistance much greater than that of metal, therefore, the tubular body 1 can have a shorter length but a larger diameter, which allows produce a correspondingly greater volume of recoverable metal.

It should also be borne in mind that the reaction mixture can change its resistance at the stage of its preparation, before the reaction. That is, at a certain pressure by the punches 4, through the cooled contacts 3, when the charge particles are compressed, its electrical resistance will change. Therefore, the technology of the metallothermal process takes into account these features. That is, the operator, when compressing the reaction mixture, passes a current and voltage of a certain magnitude through it in order to determine the changing resistance, while the magnitude of the current and voltage are selected so as not to cause sufficient heating of the mixture and spontaneous recovery reaction. Upon reaching the calculated resistance due to the external compression pressure, the operator passes such a current and voltage through the reaction charge that triggers a spontaneous metal reduction reaction. As the reaction proceeds, as mentioned above, the operator, according to a given program, introduces from the outside exactly as much energy as to recover as much metal as possible. At the beginning of the reaction, the voltage inside the reaction mixture is set so that due to the flow of electrolytic processes, as much as possible to restore the metal.

It should be noted that the resistance of the reaction mixture will depend on the amount of fluxing additives in this mixture, which can serve as CaF ₂ , CaO, Al ₂ O ₃ , etc. Therefore, it is possible to regulate it by selecting the amount and type of fluxing additives. In addition, the total resistance of the reaction mixture can be selected by the arrangement of its components inside the container. So, for example, if the overall resistance of the mixture is too high, if it is uniformly mixed, it will be impossible to supply a sufficiently large current and voltage to it for initial heating. In this case, to reduce the resistance of the charge should be specialized laying of its components. That is, metal reducing agents having low resistance can be stacked inside the container in the form of separate rods, spirals, etc., connecting the upper and lower contacts with each other, thereby passing current through them these places will heat up the entire volume of the reaction mixture, by itself, giving an impetus to the development of a spontaneous reaction. Reducing metals can also be used in the form of a rod, wire, pipe, wire mesh, etc., laid inside the container, around which the remaining reaction mixture is poured.

As you know, the smaller the heat loss in the reaction mixture, the higher the pressure due to the gases released during the reaction, the greater the yield of metal.

The lower cooled copper contact 3 in this device serves as a simultaneously cooled tray on which the reduced metal crystallizes, thereby mixing the reaction to the right and increasing the yield of metal.

In connection with the foregoing, we can conclude that the proposed method and device for the production of metals from various compounds is promising for production, since this process is economical, efficient and controllable, and the device is quite simple and reliable both in manufacture and in operation. Therefore, this invention may be useful for widespread implementation in production. The advantages of this method are as follows: 1) high efficiency (up to 93%) and reduction of energy consumption by 1.5 ÷ 2 times compared with heating in resistance furnaces;

2) high speed and uniformity of heating;

3) improvement of sanitary and hygienic working conditions.

To achieve these results, the following conditions must be observed:

1) the cross section of the heated billet should be constant;

2) the diameter of the workpiece due to the increase in heating time should not be more than 150 mm or it is necessary to use installations of excessively high power;

3) the ratio of the length of the workpiece to the diameter should be at least 30: 1;

4) insufficiently high resistance of the contacts supplying electricity to the heated product.

LITERATURE

[one]. Yu.L. Pliner, S.I. Suchilnikov, E.A. Rubinshtein.

Aluminothermic production of ferroalloys and alloys - Moscow:

State scientific and technical literature on the literature on the black and color metallurgy ”, 1963, pp. 28-29.

[2]. A.N. Zelikman. Metallurgy of Refractory Rare Metals - Moscow: Izd. "Metallurgy", 1986, pp. 414-419.

[3]. V.K.Alexandrov, N.F. Anoshkin et al. Semi-finished products from titanium alloys - Moscow: ONTI VILS, 1996, pp. 118-119.

[four]. Magazine N2l - Modern Electrometallurgy (EMS). Section “Electroslag technology)), M.L. Zhadkevich, F.K.Biktagirov and others, article“ Application of electroslag smelting for the production of ferroalloys from mineral raw materials)), 2005.

Claims

CLAIM 1. A method for the production of chemically active metals by the method of rod electrical resistance, including heating the reaction mixture in the presence of a reducing agent, reduction at the metal cathode and at the oxygen anode, characterized in that the mixture is laid in the reaction zone, holding the internal cavity of a special insulated housing, and the metal recovery process is carried out along the following chain: gradual heating of the recoverable charge inside the housing due to electrical resistance, metallothermal reduction of meta inside the casing, separation of the reaction mixture into metal and slag, while the metal under the influence of gravity moves to the cathode due to electrolysis, being cleaned of non-metallic inclusions, the slag is displaced to the anode, on which oxidizing agents are released, and the thermal energy necessary to separate the metal and the slag created by the electrical resistance comes after the start of the reaction with constant contact pressing to the reaction mixture with a certain force. 2. The method according to p. 1, characterized in that the process of heating the charge begins when it reaches its optimal resistance under the influence of compression pressure, and during melting a strictly defined amount of heat is supplied from outside, which contributes to the maximum recovery of the metal being recovered. 3. A device for the production of chemically active metals by the method of rod electrical resistance, containing a vertically placed housing with an insulating layer, an anode and a cathode, characterized in that the function of the anode and cathode is performed by the contacts, the latter being located at the bottom of the housing and is simultaneously a pallet, with each contact equipped with a punch and is cooled. 4. The device according to p. 3, characterized in that through the contacts to the reaction mixture serves high-frequency or low-frequency vibration, ensuring maximum recovery of the recoverable metal. 5. The device according to p. 3, characterized in that the optimal resistance of the mixture is selected due to the specific packing of the components of the mixture inside the container, while the metal reducing agents can be used in the form of a rod, spiral, mesh, etc.