JPH1171694A - Reduction of metallic oxide, and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the post-treatment of waste gas generated in the electrolysis of a molten salt to simplify the reducing process, and to reduce the quantity of or to dispense with a reducing gas to be fed from the outside in the pre- treatment reducing process of the molten salt electrolysis. SOLUTION: In the reducing method of a metallic oxide an which excessive oxygen in the metallic oxide is partly reduced by a reducing gas and removed, and the reduced metallic oxide is further reduced through the electrolysis of the molten salt to collect the metal at a cathode, carbon monoxide gas generated through the electrolysis of the molten salt is used as a part of or whole of the reducing gas. A reducing device is provided with a rotary kiln to reduce the metallic oxide by the reducing gas, a molten salt electrolytic bath which is connected to an outlet of the rotary kiln and reduces the reduced metallic oxide through the electrolysis of the molten salt, a waste gas pipe one end of which is connected to the electrolytic bath and the other end of which is connected to a reducing gas inlet of the rotary kiln, and a solid/gas separation filter interposed in the waste gas pipe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal oxide reduction method and apparatus for reducing a metal oxide to recover a metal.

[0002]

2. Description of the Related Art Conventionally, it has been known that after roasting and reducing a metal oxide, the roasted and reduced metal oxide is further subjected to molten salt electrolytic reduction to recover the metal. For example, as shown in FIG. 4, in the case of producing metal uranium by refining yellow cake as a raw material, the yellow cake is dissolved in nitric acid, which is purified by a solvent extraction method, denitrated and converted to uranium trioxide. After that, uranium was roasted in a nitrogen atmosphere to triuranium octoxide, and further reduced to uranium dioxide in a hydrogen atmosphere was used as a raw material for molten salt electrolysis to convert uranium to a cathode by a molten salt electrolysis method using a graphite consumable anode. It is being studied to precipitate them. In the molten salt electrolysis using such a graphite consumable anode, a gas based on oxide ions is generated from the anode during the molten salt electrolysis. This gas is composed of carbon monoxide gas and carbon dioxide gas because graphite is used for the anode. Since the carbon monoxide gas in the waste gas is harmful, it is usually subjected to post-treatment of the waste gas such as burning by a burner or the like, and is released to the atmosphere as harmless carbon dioxide gas.

[0003]

However, in the above-mentioned method in which the roasted and reduced material is electrolyzed by molten graphite using a graphite consumable anode as a raw material for molten salt electrolysis, the reducing gas used in the reduction step is Hydrogen gas is required, and furthermore, in molten salt electrolysis, treatment of waste gas, carbon monoxide gas, is required, and there is a problem that a process of producing a metal from a metal oxide is complicated. Further, since carbon monoxide gas generated by molten salt electrolysis is harmful, it is necessary to take safety management in the reduction step of metal oxide. An object of the present invention is to provide a method and an apparatus for reducing a metal oxide which can facilitate post-treatment of waste gas generated in molten salt electrolysis and simplify the step of reducing the metal oxide. Another object of the present invention is to provide a method and an apparatus for reducing a metal oxide which can reduce or eliminate the amount of a reducing gas supplied from the outside in a reduction step which is a pretreatment of molten salt electrolysis. .

[0004]

According to a first aspect of the present invention, there is provided a method for reducing a metal oxide, as shown in FIG. Another object of the present invention is to improve a method of reducing a metal oxide in which the metal oxide is further reduced by molten salt electrolysis to recover the metal to a cathode. The characteristic configuration is that carbon monoxide gas generated by molten salt electrolysis is used as part or all of the reducing gas. The amount of hydrogen gas used as a reducing agent is reduced by using carbon monoxide gas generated by molten salt electrolytic reduction as a part of the reducing gas in the reduction step, and is used as all of the reducing gas in the reduction step. This eliminates the need for hydrogen gas as a reducing agent. Also, by using the carbon monoxide gas generated by the molten salt electrolytic reduction as a part or all of the reducing gas in the reduction step, the carbon monoxide gas is oxidized and converted into harmless carbon dioxide, and the molten salt electrolysis is performed. Eliminates the need for an independent treatment step for carbon monoxide gas generated by reduction.

[0005] According to a second aspect of the present invention, there is provided an apparatus for reducing a metal oxide.
As shown in FIG. 2, a rotary kiln 20 for reducing a metal oxide by a reducing gas, and a molten salt connected to an outlet 24a of the rotary kiln 20 for further performing molten salt electrolysis on the reduced metal oxide and reducing the molten metal An electrolytic cell 30 having one end connected to the molten salt electrolytic cell 30 and the other end
A waste gas pipe 34 connected to the reducing gas inlet 27 of
This is a metal oxide reduction device including a solid-gas separation filter 36 interposed in a waste gas pipe 34. Rotary kiln 20
And the molten salt electrolyzer 30. The molten salt electrolyzer 30 and the rotary kiln 20 are connected by a waste gas pipe 34, and the gas generated in the molten salt electrolyzer 30 is used as a reducing gas to reduce the rotary kiln 20. By providing the gas supply means 41 for guiding to the gas inlet 27, the oxide from which excess oxygen in the metal oxide has been removed is supplied to the molten salt electrolysis tank 30,
A molten salt electrolysis system capable of releasing the gas generated in the electrolytic cell 30 without treatment is constructed, and the reliability of the system is improved by interposing a solid-gas separation filter 36 in the waste gas pipe 34.

[0006]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 shows an apparatus for reducing a metal oxide according to the present invention. The apparatus includes a rotary kiln 20 for roasting and reducing metal oxides with a reducing gas, and a molten salt electrolysis tank 30 connected to the rotary kiln 20 for further electrolyzing and reducing the roasted and reduced metal oxides. Prepare. The metal oxide reduced by this reduction device is uranium trioxide obtained by purifying and denitrating a yellow cake dissolved in nitric acid by a solvent extraction method. A hopper 10 containing uranium trioxide as a raw material is connected to a rotary kiln 20 via a supply pipe 11 and a feeder 23. A supply valve 13 is provided in the middle of the supply pipe 11 so that the supply amount of the raw material supplied from the hopper 10 to the rotary kiln 20 can be adjusted.

The rotary kiln 20 includes a core tube 21, a driving device 22, a discharge unit 24, a heater 26, and a reducing gas inlet 2.
7 and a waste gas discharge unit 28. The core tube 21 is arranged with a slight inclination, and a spiral guide blade 21a is fixed to the inner surface of the core tube from one end to the other end. The furnace tube 21 is rotated by a driving device 22 near both ends thereof. The driving device 22 includes a pair of driving rollers 22a on which the core tube 21 is placed and in which the outer periphery of the core tube 21 is in contact. The rotating shaft is driven by a motor (not shown). The feeder 23 has one end connected to the lower end of the supply pipe 11 and the other end inserted into one end of the core tube 21. The discharge unit 24 is provided at the other end of the furnace tube 21, and is configured to be able to discharge the metal oxide roasted and reduced in the furnace tube 21 from a discharge port 24 a formed at a lower portion.

The heater 26 is provided around the furnace tube 21 and is not in contact with the furnace tube 21. The heater 26 is controlled by a controller (not shown) so that the inside of the furnace tube 21 has a temperature distribution suitable for roasting and reducing raw materials. Heat to The reducing gas inlet 27 is formed at the upper part of the discharge part 24, and the waste gas discharge part 28 is provided at one end of the furnace tube 21. The reducing gas supplied from the reducing gas inlet 27 passes through the furnace tube 21 to reduce the raw material, and the reduced gas is discharged from the waste gas discharge unit 28. A discharge pipe 29 is connected to the upper end of the waste gas discharge section 28, and the discharge pipe 29
Is provided with a valve 29a in the middle.

The discharge port 24a of the discharge section 24 has a nozzle tube 2
The upper end of 4b is connected, and the lower end of the nozzle tube 24b is connected to the molten salt electrolytic cell 30. The molten salt electrolyzer 30 is housed in an electric furnace 31 for heating the electrolyzer. The molten salt 30 a is stored in the electrolytic cell 11. The electric furnace 31 is closed by a lid 32, and a nozzle tube 24 b is provided at a substantially central portion of the lid 32 so as to penetrate therethrough. In addition, an introduction pipe 33 for introducing an inert gas into the electric furnace 31 as necessary in order to effectively release gas generated by electrolysis from the inside of the electric furnace 31.
And one end of the waste gas pipe 34 is provided to penetrate. A solid-gas separation filter 36 is interposed in the waste gas pipe 34, and the gas generated by the electrolysis is guided to the solid-gas separation filter 36 through the waste gas pipe 34 so that the salt vapor and the gas are separated. It is composed of A backwash pipe 36a for blowing backwashing inert gas is connected to the upper end of the solid-gas separation filter 36.

In the molten salt 30a of the electrolytic cell 30, a consumable anode 37 and a cathode 38 made of graphite are provided. A DC voltage is applied to the anode 37 and the cathode 38 from a DC power supply (not shown). A control output of a controller (not shown) is connected to a heater 31a of the electric furnace 31, and the controller is configured to control the temperature of the electrolytic cell 30 via the heater 31a according to a temperature condition for electrolytic reduction. In FIG. 2, the anode and the cathode are shown in a vertical type, but the cathode is arranged horizontally in the electrolytic cell and connected to the liquid reducing metal as long as the reducing metal is handled as a liquid. May be a so-called horizontal type in which is used as a cathode. If the apparatus is large, so-called internal heating may be used in which a heater is provided directly in the electrolytic cell and the temperature of the molten salt is controlled by a DC power supply.

The other end of the waste gas pipe 34 is connected to the rotary kiln 20.
Is connected to the reducing gas inlet 27. The other end of the connection pipe 41 having one end connected to the gas tank 42 is connected to the discharge part 24 near the reducing gas inlet 27. This connection pipe 4
1 is provided with a valve 41a, and is configured to open the valve 41a to introduce the gas stored in the gas tank 42 into the core tube 21 through the connection tube 41.

Next, a method for reducing a metal oxide using uranium trioxide as a raw material by using the above-configured apparatus will be described with reference to FIGS. <Roasting Reduction Step> First, the driving device 22 rotates the furnace tube 21 at a speed according to the processing capacity, and at the same time, the temperature in the furnace tube 21 is reduced by the heater 26 from the feeder 23 to the discharge unit 24.
Is set so as to have a temperature distribution of about 300 ° C. to about 800 ° C. In this state, the supply valve 13 is opened to supply a predetermined amount of uranium trioxide obtained by purifying and denitrating the yellow cake from the hopper 10 to the feeder 23, and the valve 41a provided in the connection pipe 41 is opened. .
By opening this valve 41a, a mixed gas of N ₂ -H ₂ is introduced into the furnace tube 21 through the connection tube 41, and the waste gas pipe 34 is a waste gas generated from the molten salt electrolysis tank 30 described later. Carbon monoxide gas is introduced into the furnace tube 21.

A reducing gas composed of a mixed gas of N ₂ -H ₂ and a carbon monoxide gas passes through the inside of the furnace tube 21 from a reducing gas inlet 27 and is discharged by a guide blade 21 a to an outlet 24.
Is reduced in the furnace tube 21. The reducing gas obtained by reducing uranium trioxide in the furnace tube 21 is discharged from a waste gas discharge unit 29. Uranium trioxide reduced in the furnace tube 21 is converted to uranium dioxide and reaches the discharge unit 24. The uranium dioxide reaching the discharge section 24 is injected into the molten salt electrolytic tank 30 from the discharge port 24a through the nozzle tube 24b.

<Molten Salt Electrolysis Step> The molten salt 30 a heated by the heater 31 a is stored in the electrolytic bath 30, and an inert gas such as argon gas is introduced from the introduction pipe 33.
A DC voltage is applied between both electrodes of the graphite consumption anode 37 and the cathode 38 from a DC power supply (not shown), and the uranium dioxide dropped into the molten salt 30a is electrolytically reduced inside the electrolytic bath 30 by the molten salt and the cathode 38 Will be collected.

Along with the electrolysis of uranium dioxide, a waste gas containing carbon monoxide gas is generated from the anode 37. This waste gas is discharged from the inside of the electric furnace 31 through the waste gas pipe 34 by the inert gas introduced from the introduction pipe 33.
The waste gas is passed through a waste gas pipe 34 to the solid-gas separation filter 3.
6 to separate the salt vapor from the gas. The waste gas that has passed through the solid-gas separation filter 36 is further discharged to a waste gas pipe 34.
Through the reducing gas inlet 27 of the rotary kiln 20
And passes through the inside of the furnace tube 21 as a reducing gas together with the N ₂ -H ₂ mixed gas as described above. That is, carbon monoxide gas in the waste gas as it passes through the interior of the core tube 21 from the reducing gas inlet 27 together with a mixed gas of N ₂ -H _2, moving towards the discharge portion 24 by the guide vanes 21a The uranium trioxide is roasted and reduced in the furnace tube 21. The carbon monoxide gas itself obtained by roasting and reducing uranium trioxide is converted into harmless carbon dioxide gas and discharged from the waste gas discharge unit 28 through the discharge pipe 29.

The electrolytic cell 30 in the above-described embodiment has a cylindrical graphite consumable anode 37 and an electrolytic cell 3 respectively.
Although a cathode 38 was installed at the bottom of the crucible, the electrolytic cell was not shown in the figure, but a non-conductive cylindrical graphite crucible with a bottom, a rod-shaped graphite cathode inserted and fixed in the crucible, and this cathode It may be constituted by a cylindrical graphite anode provided so as to surround it. In the above-described embodiment, N ₂ −
The carbon monoxide gas generated by the molten salt electrolytic reduction was passed through the inside of the furnace tube 21 together with the mixed gas of H ₂ , and the carbon monoxide gas was used as a part of the reducing gas for the roasting reduction. After the carbon monoxide gas is generated by the electrolysis, the waste gas generated by the electrolysis may be used as all of the reducing gas for the roasting reduction by closing the valve 41a. Furthermore, in the above-described embodiment, the introduction pipe 33
The inert gas was introduced into the electric furnace 31 from the furnace, but as long as the waste gas generated by the molten salt electrolytic reduction passed through the furnace tube 21 through the waste gas tube 34, the inert gas was It does not have to be introduced into the furnace 31.

[0017]

EXAMPLES In order to confirm the effectiveness of the present invention, analysis of gas components generated by molten salt electrolysis, a reduction test of uranium oxide based on the gas components, and a solid-gas separation device for separating gas components from salt vapor were conducted. The separability was confirmed. <Analysis of Gas Components> LiF (11% by weight) -BaF ₂ was placed in an electrolytic cell provided with an anode and a cathode made of a graphite rod.
A mixed salt of (74 wt%)-UF ₄ (15 wt%) was stored, and uranium dioxide was electrolyzed at 1200 ° C. and 200 A.
The change with time of the composition of the waste gas generated by the electrolysis obtained at that time was analyzed by a mass spectrometer. The result is shown in FIG.
Shown in <Reduction test of uranium oxide> Using a small electric furnace, 5 g of uranium oxide (U ₃ O ₈ or UO ₃ ) was weighed into a boat-like container, and a reducing gas composed of 5% CO or 3% H ₂ was measured. Depending on the type, the reduction reaction was performed under the temperature conditions and times shown in Table 1. The reduction rate reduced to uranium dioxide by this reduction reaction was measured by a gravimetric method. Table 1 shows the results.

[0018]

[Table 1]

<Confirmation of Separability of Solid-Gas Separation Apparatus> A sintered filter was installed in the waste gas line of the electrolytic cell in the investigation of gas components, and the state of migration of the salt components after the filter was measured inside the piping after the filter. The presence or absence of salt attachment was visually inspected.
As a result, no salt was found to adhere to the inside of the pipe after the filter. It should be noted that salt adhesion was observed on the sintered filter, but it was confirmed that the salt adhesion could be easily recovered by air washing simulating blowback. <Evaluation> From the results shown in FIG. 3, it was confirmed that most of the waste gas generated during the electrolytic reduction was carbon monoxide gas having a reducing property. Also, the generation rate of carbon monoxide gas shows stable generation with the electrolysis time, and it can be seen that the gas can be used effectively as a reducing gas source. Further, as is clear from Table 1, it can be seen that uranium oxide can be sufficiently reduced even with carbon monoxide gas generated during electrolytic reduction. Furthermore, it can be seen that if a solid-gas separation filter is installed in the waste gas line of the electrolytic cell, the salt components will not migrate into the piping after the filter. From these results, it can be seen that the present invention is sufficiently established.

[0020]

As described above, according to the present invention, carbon monoxide gas generated by molten salt electrolytic reduction is used as a part or all of the reducing gas for roasting reduction, thereby reducing hydrogen as a reducing agent. Gas usage can be reduced or eliminated. In addition, by using the carbon monoxide gas generated by the molten salt electrolytic reduction as part or all of the reducing gas for roasting reduction, the carbon monoxide gas is oxidized and converted into harmless carbon dioxide. As a result, the post-treatment of the waste gas generated in the molten salt electrolysis becomes easy, and the reduction step of the metal oxide can be simplified. In addition, a rotary kiln and a molten salt electrolyzer are provided, and the molten salt electrolyzer and the rotary kiln are connected by a waste gas pipe, and the reducing gas of the rotary kiln is introduced by using generated gas inside the molten salt electrolyzer as a reducing gas. By providing gas supply means for guiding to the mouth, an oxide from which excess oxygen in the metal oxide has been removed is supplied to the molten salt electrolytic cell, and a molten salt electrolytic system capable of releasing the gas generated in the electrolytic cell without treatment is provided. Can be built.
By interposing a solid-gas separation filter in the waste gas pipe in this electrolysis system, the reliability of the system can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a UO ₃ reduction process according to the method of the present invention.

FIG. 2 is a configuration diagram of a reduction device of the present invention.

FIG. 3 is a diagram showing the composition of waste gas generated by electrolysis.

FIG. 4 is a process diagram corresponding to FIG. 1 showing a conventional reduction process.

[Explanation of symbols]

 Reference Signs List 20 rotary kiln 24a outlet 27 reducing gas inlet 30 molten salt electrolyzer 34 waste gas pipe 36 solid-gas separation filter 37 graphite exhaust anode

Claims (2)

[Claims] 1. A method of reducing the amount of excess oxygen in a metal oxide by a reducing gas and then reducing the reduced metal oxide by molten salt electrolysis to recover the metal to a cathode. In the reduction method, a carbon monoxide gas generated by the molten salt electrolysis is used as a part or all of the reducing gas. 2. A rotary kiln (20) for reducing a metal oxide by a reducing gas, and a molten salt electrolysis of the reduced metal oxide connected to an outlet (24a) of the rotary kiln (20). A molten salt electrolyzer (30) for reducing and reducing, and a waste gas pipe having one end connected to the molten salt electrolyzer (30) and the other end connected to a reducing gas inlet (27) of the rotary kiln (20) (34) A metal oxide reduction device comprising: a waste gas pipe (34); and a solid-gas separation filter (36) interposed in the waste gas pipe (34).