RU2634820C2 - Method for preparing metal neodymium from its oxide - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves mixing neodymium oxide with graphite powder followed by pressing the produced mixture into briquettes and heating the produced briquettes in vacuum or vacuum-hydrogen furnace for reduction of oxide. The reduction is carried out in four stages: the first stage briquettes are heated in vacuum of 1-10 Pa to a temperature of 1000°C. At the second stage heating is performed under argon atmosphere to temperature 1750-1900°C with holding at this temperature for 120-180 min; at the third stage heating is performed at 500…600°C for 120…420 min in hydrogen containing atmosphere. At the fourth stage heating is carried out in vacuum of 1-10 Pa to temperature from 900-1000°C with holding at this temperature for 60-180 min followed by cooling to room temperature. Each subsequent stage is carried out immediately after completion of the previous stage with appropriate heating or cooling.

EFFECT: preparation of neodymium from oxide without contamination with oxygen and carbon.

1 tbl, 2 ex

Description

The invention relates to metallurgy, in particular to the production of metallic neodymium from its oxide

Known carbothermal method for producing rare earth metals (REM), in particular, neodymium (Mikhaylichenko AM, Mikhlin EB, Patrikeev Yu.B. Rare earth metals. M: Metallurgy, 1987. - 232 S., p. 189), including following technological operations:

- at the first stage, a reaction proceeds between the rare-earth oxide (R) oxide and graphite:

- at the second stage, the obtained carbide is dissociated with the evaporation of rare-earth metals:

The disadvantage of this method is that the dissociation of neodymium carbide occurs extremely slowly. The reference book (Thermodynamics of carbides and nitrides. Reference publication / I.S. Kulikov. - Chelyabinsk: Metallurgy, Chelyabinsk Branch, 1988. - 320 p., P. 67, formula (5.105)) formulas are given for calculating the pressure of neodymium vapor during dissociation neodymium carbide and neodymium evaporation. This allows us to calculate the amount of neodymium that evaporates after dissociation of neodymium carbide and precipitates on a water-cooled condenser, depending on temperature (the atomic mass unit is assumed to be 1.661 * 10 ^-24 g, 1 atmosphere is taken to be equal to 750 mm Hg). The calculation data are summarized in a table.

Thus, even when heated to a temperature of 2227 ° C (2500 K) from a crucible with a diameter of 500 mm, for example, when holding for 3 hours, the amount of neodymium that can be deposited on the condenser does not exceed 16.1 g.

Closest to the claimed method is a plasma-carbon method for producing rare earth metals and a device for its implementation, described in RF patent No. 2499848, IPC C22B 59/00, C22B 5/10, patent publication date November 27, 2013. This method includes mixing powdered rare-earth metal oxides with a carbon-containing component, heating the mixture without air to a temperature of more than 2000 ° C with evacuation of carbon oxides released during reduction and obtaining pure carbides powders. Chilled neodymium carbide is removed from the vacuum thermal installation, mixed with powders of pure refractory metals, for example tungsten, heated in vacuum to a temperature of at least 1800 ° C and, during the course of the exchange reaction with the formation of carbides of refractory metals and metallic rare-earth metals, REM is evaporated with its deposition on a cooled condenser.

This method has the following disadvantages. Firstly, in accordance with the data on the state diagrams of neodymium with refractory metals: Nd - W, Nd - Mo and Nd - Ta (State diagrams of binary metal systems: Handbook in 3 volumes: T.3, Book 1 / Subtotal Edited by N.P. Lyakishev. - M .: Mashinostroenie, 2001. - 872 pp .; p. 612, 417, 600 respectively) there is mutual solubility (albeit limited) between the refractory metal and neodymium. Therefore, there is a risk of contamination of carbide of a refractory metal, which the authors of the method under consideration intend to use in a hard alloy, neodymium, and also neodymium, in a refractory metal.

Secondly, the recovered neodymium carbide with stirring according to the considered method can interact with water vapor in the air, as a result of such a chemical reaction, neodymium hydroxide is formed:

Thirdly, when airborne rare-earth carbides are mixed with refractory metal powders, there is a possibility of the formation of oxycarbides (Mikhaylichenko A.I., Mikhlin E.B., Patrikeev Yu.B. Rare-earth metals. M: Metallurgy, 1987. - 232 p. , p. 190).

The objective of the present invention is to develop a method for producing metallic neodymium from its oxide.

The problem is solved in that to implement the claimed technical solution, neodymium oxide powder is mixed with graphite powder, the resulting mixture is pressed into briquettes and the resulting briquettes are heated in a vacuum or vacuum-hydrogen furnace; recovery is carried out in four stages. On the first - briquettes are heated in a vacuum; on the second - in an inert gas atmosphere; in the third, in an atmosphere containing hydrogen; in the fourth, in vacuum, followed by cooling in the same medium. At the first stage of reduction, which is carried out by heating to a temperature of 900 ... 1000 ° С with holding at this temperature for 30 ... 60 minutes, the destruction of Nd (OH) ₃ present in neodymium oxide occurs with the formation of Nd ₂ О ₃ and vapors water that is pumped out by a vacuum pump. At the second stage, heating to a temperature of 1700 ... 1900 ° C and holding at this temperature for 120 ... 360 minutes is carried out in an atmosphere of inert gas (for example, argon) with a pressure of 30 ... 70 kPa. This allows you to reduce the loss of Nd ₂ About ₃ associated with the sublimation of this oxide, in comparison with heating carried out in vacuum. The third stage includes heating at a temperature of 500 ... 600 ° C, followed by exposure to a medium containing hydrogen. At this stage, the reaction of interaction of neodymium carbide with hydrogen proceeds with the formation of neodymium hydrides and hydrocarbons. The fourth stage is heating in a vacuum of 1 ... 10 Pa to a temperature of 900 ... 1000 ° C. At this temperature, dehydrogenation of neodymium hydrides occurs with the evacuation of hydrogen and the formation of metallic neodymium. After completion of dehydrogenation, cooling to room temperature is carried out in a vacuum of 1 ... 10 Pa.

The selected ranges of the parameters of the present invention are due to the following considerations.

The interaction of neodymium oxide with graphite powder is a solid-phase reaction, for the course of which it is necessary to ensure a sufficient interface area. A force of 20 ... 25 MPa allows you to get a briquette that retains a given shape, and also provides the possibility of a reaction:

Briquettes are loaded into a graphite crucible. From briquettes in the crucible, the furnace loading is formed.

At stage 1, heating in vacuum to a temperature of 900 ... 1000 ° C leads to decomposition of the hydroxide in neodymium oxide (taking into account the low thermal conductivity of the load, the process is carried out until the residual pressure decreases to a constant value). Lowering the temperature unnecessarily increases the time of isothermal exposure. An increase in temperature leads to an intensification of the interaction of graphite with water vapor and the removal of carbon in the form of gaseous oxides from the reaction zone.

Carrying out the heating in the second stage to carry out reaction (2) is carried out in an inert gas atmosphere (for example, argon) to reduce (or eliminate) losses of neodymium oxide caused by its sublimation. A sufficient value of the residual pressure are values of 30 ... 70 kPa. The presence of compressed briquettes (rather than a mixture of powders) allows to reduce the temperature of the reaction (2) to 1700 ... 1900 ° C (according to the prototype - RF patent No. 2499848, IPC С22В 59/00, С22В 5/10, the temperature of this reaction is not less than 2000 ° C.) Depending on the mass of the load and its location in the graphite crucible, the reaction time is 180 ... 360 minutes.

In the course of reaction (2), neodymium carbide reacts with hydrogen (hydrogen into the duct or with a single inlet into the furnace) at the third stage, and converts to neodymium hydrides with the formation of hydrocarbons. For example, when methane is formed, the reactions are as follows:

Reactions (3) - (6) are exothermic. Since hydrocarbons at a temperature of 700 ... 800 ° С, as follows from thermodynamic calculations, decompose with the formation of carbon and hydrogen, then at stage 3 the temperature should be 500 ... 600 ° С.

After completion of the formation of neodymium hydrides, in the fourth stage, a dehydrogenation operation is carried out with evacuation of the generated hydrogen. Taking into account the melting temperature of neodymium, which is approximately equal to 1020 ° C, depending on the ability of the regulator to supply power to the furnace and its design features, the dehydrogenation temperature will be 900 ... 1000 ° C.

Example 1

After vacuum cleaning, graphite powder (20.435 g) and neodymium oxide powder (90.950 g) of the composition (mass fraction,%): Nd-77%, Pr-0.2%, Ba-0.1%, Cd-0, 1%, Сl - 0.1% was mixed in a turbulent С 2.0 mixer with a rotation speed of 40 rpm. within 60 minutes The resulting mixture was pressed on a 400 kN laboratory hydraulic press; pressing pressure of 20 MPa. The resulting briquettes were placed in a graphite crucible previously annealed in vacuum. The crucible, crucible with briquettes and crucible with briquettes placed in a specialized container were weighed on an AJH-620 CE laboratory electronic balance.

After weighing, the crucible was installed in the working space of a vacuum electric furnace; pumped out until a residual pressure of 1 ... 10 Pa was reached and heating was turned on to a temperature of 1000 ° C. Exposure was carried out at this temperature for 30 minutes. Turned off the heat. After cooling to room temperature, argon was introduced into the furnace, the crucible was loaded into a specialized container, and the container with the crucible was weighed, inside which briquettes were placed. The mass loss of briquettes amounted to 7.3%.

Re-loaded the same briquettes in a vacuum oven. We pumped it to a pressure of 1 ... 10 Pa, filled argon to a pressure of 30 kPa, turned on the heating. The temperature was brought up to 1750 ° C; the exposure at this temperature was 120 minutes. The heating was turned off, the furnace was cooled to room temperature, the argon was blown into the working volume of the furnace to atmospheric pressure, briquettes were removed, one of which was placed in a specialized container (argon in the container).

Using an X-ray diffractometer (hereinafter, X-ray studies were carried out on a DRON-4 diffractometer in Co _Kα radiation), the phase composition (powder method) was determined. The NdC ₂ phase has been identified.

The remaining briquettes were loaded into a vacuum furnace, pumped out to a residual pressure of 1 ... 10 Pa, hydrogen was inlet and heated to a temperature of 550 ° C. Exposure was carried out at this temperature for 120 minutes (the exposure time is determined, in particular, by the consumption of hydrogen). The heating was turned off, the hydrogen atmosphere in the furnace was replaced with an argon atmosphere with a pressure of 101 kPa, after the furnace was cooled to room temperature, the briquettes were removed by placing one of them in a specialized container (argon in the container).

An X-ray diffractometer determined the phase composition (powder method). The phases NdH ₂ and NdH _{3 were} identified.

The remaining briquettes were loaded into a vacuum oven, pumped out to a residual pressure of 1 ... 10 Pa, heating was turned on to a temperature of 900 ° C, holding at this temperature was 90 minutes.

The heating was turned off, the furnace was cooled to room temperature, the argon was blown into the working volume of the furnace to atmospheric pressure, and the briquettes were removed. One of the briquettes was placed in a specialized container (in the container is an argon atmosphere).

An X-ray diffractometer determined the phase composition (powder method). The Nd phase has been identified.

Example 2

After vacuum cleaning, graphite powder (159.393 g) and neodymium oxide powder (709.511 g) of the same composition as in Example 1 were mixed in a turbulent C 2.0 mixer with a rotation speed of 40 rpm for 60 min.

The resulting powder mixture was pressed into briquettes on a 400 kN laboratory hydraulic press; pressing pressure 25 MPa.

Briquettes were loaded into graphite crucibles, previously annealed at a temperature of 1900 ° C in a vacuum of 1 ... 10 Pa for 60 minutes, and placed in a vacuum oven. After pumping the furnace to a pressure of 1 ... 10 Pa, heating was turned on to a temperature of 1000 ° C. Exposure was carried out at this temperature for 60 minutes. The pumping was stopped and argon was introduced into the furnace to a pressure of 70 kPa. The temperature was raised to 1850 ° C, and exposure was carried out at this temperature for 180 minutes. The furnace was cooled to a temperature of 600 ° C; the atmosphere in the furnace working space was replaced from an argon atmosphere to a hydrogen atmosphere (hydrogen pressure 101 kPa). Exposure was carried out under these conditions for 300 minutes. After completion of exposure, hydrogen was evacuated and the furnace was evacuated to a pressure of 1 ... 10 Pa with a simultaneous increase in temperature to 1000 ° C. Upon reaching this temperature, holding was carried out for 180 minutes. The furnace was cooled to room temperature without interrupting pumping. The pumping was turned off, argon was introduced into the furnace to atmospheric pressure, and crucibles with briquettes were removed.

The contents of one of the crucibles (one briquette) were placed in a specialized container with argon. An X-ray diffractometer determined the phase composition. The Nd phase has been identified.

Claims (1)

A method of producing metal neodymium from its oxide, comprising mixing neodymium oxide with graphite powder, pressing the resulting mixture into briquettes and heating the resulting briquettes, characterized in that the production of neodymium is carried out in a vacuum or vacuum-hydrogen furnace in four stages, the first of which the briquettes are heated in a vacuum, in the second in an inert gas atmosphere, in the third in an atmosphere containing hydrogen, and in the fourth in a vacuum, while the first stage is heated in a vacuum of 1-10 Pa to a temperature of 1000 ° C, the second stage is heated APEs are conducted in an argon atmosphere to a temperature of 1750-1900 ° С with holding at this temperature for 120-180 minutes, at the third stage, heating is carried out at a temperature of 500-600 ° С for 120-420 minutes in an atmosphere containing hydrogen, and the fourth stage, heating is carried out in a vacuum of 1-10 Pa to a temperature of 900-1000 ° C with holding at this temperature for 60-180 minutes, followed by cooling to room temperature, and each subsequent stage is carried out immediately after completion of the previous one with appropriate heating or cooling .