JPS5944377B2 - Zirconium reduction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing zirconium with a reducible metal such as aluminum, which is more economical than the prior art.

The normally naturally occurring mineral for obtaining zirconium is zircon, i.e. ZrO2,5in2 (usually about 2% by weight H
fO2・S t 02).

The usual way to obtain zirconium in metallic form is to first chlorinate zirconium ore to obtain ZrCl4.

For example, by the following reaction. The zirconium tetrachloride is then reduced with a reducing metal, usually magnesium.

A typical reduction reaction is as follows.

This reduction reaction is typically carried out in a Kroll furnace where about 80% or more excess magnesium is required to complete the reduction and the reaction products (zirconium, magnesium, chloride and excess magnesium) are must be mixed after the reaction and then separated.

This is clearly an expensive method for reducing zirconium from ore, so a practical and less expensive alternative method has often been sought.

For example, since magnesilla is a relatively expensive metal,
The use of other less expensive reducing metals has been proposed.

One inexpensive reducing metal that has been considered is aluminum.

However, when used in the Kroll method described above, the following reaction occurs.

Here, ZrA11x is a series of intermetallic compounds ranging from ZrAl3 to Zr3Al, all of which have strong intermetallic bonds.

Therefore, due to high aluminum contamination, reducing metals cannot be used in cladding fuel rods during nuclear reactions, one of the main uses for zirconium.

In this special specification of zirconium, 75p, p
, m or more aluminum.

Another metal reduction method that uses aluminum as the reducing metal to reduce oxides is the thermite method.

For example, such a method is used to reduce niobium by the following reaction.

The thermite process is attractive for many applications because once the reaction begins, it generates enough heat to be self-sustaining.

However, if the thermite process is used for zirconium, the following reaction occurs.

The reason why this method cannot be used for zirconium is due to the zirconium-aluminum intermetallic reaction product.

It was widely known that aluminum cannot be used as a reducing metal to recover zirconium because of the known reactions described in equations (3) and (5) above.

See, for example, Warren B. Blumenthal's "Chemical Behavior of Zirconium," which is the leading comprehensive text on zirconium and its properties.

It is therefore an object of the present invention to provide an improved process for reducing Zirco,-Rum.

Another object of the present invention is to provide an improved method for reducing zirconium that allows the use of reducible metals such as aluminum.

Still another object of the present invention is to provide an improved process for reducing zirconium using aluminum as the reducing metal and in which the resulting zirconium is not contaminated by aluminum.

Briefly stated, the present invention provides a method for reducing zirconium in which a reducible metal, preferably aluminum, is dissolved in a solvent metal, preferably zinc, in the molten state.

This molten metal phase is contacted with a molten salt phase containing as one of its components the zirconium salt to be reduced.

The desired reduction takes place by reciprocal transfer.

That is, aluminum is transferred from the molten metal phase to the molten salt phase to replace zirconium in the salt, while zirconium is transferred from the molten salt phase to the molten metal phase.

Next, the molten salt phase and the molten metal phase are separated, and the solvent metal and zirconium are separated by distillation or the like.

BRIEF DESCRIPTION OF THE DRAWINGS In order to fully understand the invention and to make other objects and advantages of the invention clear, a detailed description of the invention will now be described with reference to the drawings.

The present invention eliminates the above-mentioned problems by first dissolving the reducible metal in a suitable metal solvent before contacting the molten salt containing zirconium to be reduced, and by intertransferring the reducible metal such as aluminum. Achieve reduction of zirconium by metal.

The molten metal phase is then vigorously agitated with the molten salt phase to incorporate the molten salt phase into the molten metal phase.

It has been found that with sufficient agitation, the mixture reaches equilibrium within 5 minutes, sometimes within 1 minute.

When the mixture is then allowed to stand, the molten salt phase floats to the top of the mixture while the molten metal phase sinks below the molten salt phase.

The molten salt phase can then be separated off or removed via a suitable plug at the bottom of the reactor.

If desired, the molten metal phase can be again subjected to the same process twice to remove most of the reducible metal from the molten metal phase.

The entire process can then be repeated as many times as necessary until the desired purity of zirconium is obtained.

The solvent metal is then separated from the zirconium by a suitable method such as distillation or sublimation.

Solvent metals are metals that have the following properties:

First of all, of course, neither zirconium nor reducing metals
It must be a metal that can melt at least to a significant extent.

The boiling point of the solvent metal must be such that both the solvent metal and the molten salt phase are in liquid phase within the operating temperature range of the reaction.

The solvent metal should be a metal that separates relatively easily from the zirconium once the reaction is complete.

In order not to displace zirconium and hafnium in the salt phase, the solvent metal must be less electropositive than zirconium and hafnium.

Finally, it is desirable that the metal has more similarity to zirconium than to aluminum so that the aluminum atoms of the metal phase can more easily undergo intertransference reactions with the zirconium ions of the salt phase.

In fact, it is known that the best metal as a solvent metal is zinc, although cadmium, lead, bismuth, copper and tin can also be used as solvent metals.

The main characteristic of reducible metals is that they are more electropositive than zirconium, thus displacing zirconium in the salt and reducing it to the metal.

Another characteristic of the reducible metal is that it has less similarity than zirconium to the solvent metal, preferably zinc, so that the reducible metal and zirconium do not form an alloy, but instead the zinc alloys with zirconium. is formed and rejects reducing metals.

Also, of course, it is important that the reducing metal and salt formed after the reduction reaction are liquid at the temperature at which the reaction occurs.

As shown in the equation below, in the method of the present invention, the above-mentioned disadvantageous aluminum-zirconium reaction does not occur, and therefore, it is possible to realize the economy of using aluminum as the reducing metal. It is aluminum.

However, it is readily understood that other reducing metals such as magnesium, sodium and calcium can also be used in a similar manner.

The characteristics of salt are as follows.

First of all, the cations of salts other than zirconium salts are more electropositive than zirconium and are not reduced by the reducing agent of the metal phase.

Preferred cations are alkali elements, preferably sodium and potassium, alkaline earth metals, rare earth elements and aluminum.

The anion in the salt is preferably a halide or a complex of the halide and the above-mentioned cation, so the salt is a halide salt.

As explained in more detail below, the preferred halides are chlorides and fluorides, which have the following advantages in turn.

As mentioned below, the zirconium salt of this method is usually Z
If it is rC114 or ZrF4 and is assumed to be a chloride salt or a fluoride salt, it forms ZrC1x or ZrFx whose charge is a function of X.

The anion formed is usually ZrF... ZrC1j6
...or ZrF6...

These complex anions reduce the vapor pressure of the zirconium salt to an appropriate level at the temperature at which the separation is carried out.

In order for both the salt and the metal to be present in liquid phase at the same time, the melting point of the salt must be lower than the boiling point of the metal used as a solvent for the zirconium.

As is well known, the melting point of a salt, as well as the viscosity of the salt, can be changed by mixing different salts.

Therefore, it is often advantageous to add a salt such as sodium chloride to the salt phase to lower the melting point of the salt and reduce its viscosity.

As mentioned above, it is known that the best salts for use are all chloride salt systems, mixed chloride-fluoride salt systems, or all fluoride bases.

Systems that are all chloride salts have the advantage of being easy to mix.

As is well known, the presence of fluoride in the molten salt phase is difficult to suppress because the molten fluoride tends to undergo many undesirable reactions with the container materials and other substances present in the system.

The disadvantage of all chloride base yarns is that they form low-charge chlorides such as ZrC112 and convert from salts to Z r Cl!
In addition, the zinc metal tends to react with the zirconium and hafnium salts and mix into the salt phase.

In contrast, chloride-fluoride base threads have lower vapor pressures, much less reaction between the salt phase and zinc, and much less tendency to form low-charge zirconium compounds in the salt phase.

An all fluoride salt system has the advantage of a chloride-fluoride base thread and can be used when zirconium fluoride salts are formed from ore.

However, in systems where all fluoride salts are present, care must be taken in selecting the concentration of salts.

Aluminum-fluoride compounds are present as reaction products after reduction reactions, and these compounds tend to be very volatile or otherwise insoluble at reaction temperatures unless the salt system is carefully selected. It is in.

The reaction vessel must be chosen carefully so that it contains the reactants at the temperature at which the reaction occurs, but does not itself participate in the reaction.

Although a variety of materials have been readily tried, preferred containers are known to be made of graphite or carbon.

Having described the general conditions of the present invention, an example will now be described in which the present method was used to reduce zirconium.

FIG. 1 shows a block diagram illustrating a method for reducing zirconium in accordance with the present invention.

In FIG. 1, a reduced metal inlet 10, a salt inlet 12, and a solvent metal population 14 are placed in a suitable vessel in which the desired reaction will take place.

Of course, the reducing metal to be added is preferably aluminum.

This metal is fed to the reduction step 16 along with a salt component which is a mixture of zirconium tetrachloride (which is the zirconium compound to be reduced) and potassium chloride.

For every 3 moles of zirconium tetrachloride, approximately 10 moles of potassium chloride are used.

Zirconium tetrachloride and 7 parts of potassium chloride are melted and the following reaction takes place.

(6) ZrC74+2KCl→ to 2ZrC1° Typically, a sufficient amount of solvent metal, preferably zinc, is present in reduction step 1.
6, yielding approximately 12% by weight of zirconium at the end of the operation.

As shown below, this addition of zinc is necessary only at the beginning; in the next step, zinc is recovered and reduced in step 16.
Re-inject into.

A typical example of the input of reduction 16 is as follows.

Table 1 Input ingredients Weight ZrCl 445.4 kg (100 lbs) KCl
44 ky (96 lb) A16.31 kg (
The 152 kg (334 lb) Zn mixture is then heated to about 900°C and stirred vigorously to incorporate the molten metal phase into the molten salt phase.

At this time, according to the present invention, aluminum in the metal phase reduces zirconium in the salt phase by the following reaction.

As stated above in describing the desirable characteristics of salt,
Excess KCJ' reduces the vapor pressure of ZrC114 at the temperature at which the reaction occurs.

After continuing this vigorous stirring for 5 to 30 minutes, the mixture is allowed to stand and the molten salt phase containing the aluminum salt is placed on top.
A molten metal phase containing zirconium metal is allowed to separate to the bottom.

After separation by a suitable method, the salt phase is introduced into step 18 in order to recover the salt for further use, if necessary.

The metal phase component is input into a distillation step 20.

Here, zinc metal is distilled from zirconium and reinjected into the reduction step 16 for the next reduction reaction, as described above.

Before the distillation, the metal phase contains the following components:

Table 2 Ingredients Weight Zn 152 kg (334 lb) Zr
16.0 kg (35,2 lb)1
? 0.016 kg (0,035 lb)
Zirconium metal is obtained in the zirconium production step η, which again consists of sponge metal.

FIG. 2 shows a block diagram of a second embodiment of the invention.

The process illustrated in FIG. 2 is essentially the same as that illustrated in FIG. 1 with the following exceptions.

That is, the initial heating and mixing are completed as described above,
After the salt phase is removed from the vessel in which the reduction step 16 was carried out, a metal phase remains in the reduction step 16, weighing approximately 7.3 kg (16 kg).
Potassium chloride (bond) is added to the container.

The salt-metal mixture is then heated again to about 900°C and
．． 9 kg (2 lbs) of oxidizing gas2 such as C7172
4 is passed through the metal and reacts with the zirconium and aluminum in the metal phase to form zirconium and aluminum chlorides, which are absorbed into the salt phase.

The two phases are then mixed well again and the process is completed in the manner described above.

This two-step process can produce zirconium metal with an aluminum content of less than 40 pm.

In the embodiment of FIG. 2, rather than using chlorine gas as the oxidizing gas, the appropriate material is directly injected into the mixture to form the zirconium salt and fed into the second stage of the desired rearrangement reaction; The aluminum can be separated from the metal phase into the salt phase.

For example, zinc chloride is suitable, and in some cases it is desirable to inject a zirconium salt, such as zirconium tetrachloride, directly into the mixture into the second stage of separation.

The foregoing description of the conditions of the invention and the description of FIGS. 1 and 2 illustrate the principles on which the invention is based.

The actually preferred embodiment of the invention is a somewhat more complex process than the relatively simple process of Figures 1 and 2, in which the input material is zirconium ore and the final product is a It consists of a complete process that yields zirconium.

FIG. 3 is a block diagram of the entire process, illustrating the actually preferred embodiment of the invention.

In Figure 3, the input raw materials are relatively low levels of HfO2・SiO□ and sodium fluorosilicide (Na
It is a zirconium ore that is ZrO2/SiO2 containing 2SiFc, ).

These input ports are indicated at 30 and 32, respectively, in FIG.

These raw materials are supplied to the ore crushing step 34, where the following reactions are performed.

Typically, ore crushing step 34 is conducted in an indirectly heated furnace at about 700° C. for about 1 hour.

The product was removed from the furnace and replaced with Na2ZrF6 and Na
2 Hf Fa is filtered from S t 02 and crystallized from the filtrate.

This is a good purification method for zirconium and removes it from most of the other impurities present in the ore other than hafnium.

Na2ZrF6 and Na2HfFa are then fed to a reductive separation step 36.

Here, they are dissolved in a solvent metal, such as zinc, as described above in connection with FIGS. 1 and 2.

Aluminum reducible metal 38 is also provided to a reductive separation step 36.

In the reduction separation step 36, zinc, aluminum and N
a 2 Z r F a and Na2HfF6 are approximately 9
The entire mixture is heated to a temperature of 00° C. and melted, and the melt is stirred vigorously as in FIGS. 1 and 2.

At this time, the following reaction occurs. In a preferred embodiment of the invention, approximately 85% to 95% of the aluminum required to complete the above reaction is fed to the reductive separation step 36 so that virtually all of the aluminum present is salted. phase and a small amount of Na2ZrF6 remains in the mixture.

No. 6 of the above-mentioned application, filed on October 17, 1975.
As detailed and claimed in No. 23325, the hafnium metal formed according to the formula αυ above is replaced with zirconium in the salt by the following reaction.

After vigorous stirring, the mixture is allowed to stand and the salt phase is removed from the metal phase in the manner described above.

The separated metal phase is again subjected to a distillation step 40, where zinc is distilled from zirconium.

The zinc is then recycled for reuse in a reductive separation step 36.

Pure zirconium is obtained at the zirconium production port 42.

Table 3 below shows the input materials and products (zirconium sponge) obtained in five tests conducted according to the method just described.
shows.

Table 3 Input raw materials Produced zirconium Na2ZrF6 39 kg (
85 lbs) No.HfF. -〇.3kg (0.
7po71) 1□,.

幀. 4.2 tons? 71') Zn -104kg
(230 lbs) All -4,4 to 9 (9,6 lbs) Na2ZrF6 -39
kg (85 lb) Na 2 Hf Fa
O, 3 kg (0,7 po” 11.0 kg (
24,3P7),)Zn-104kg(
231 lbs) Al -4,4kg
(9,6 lbs) Na2ZrF6 39 kg
(85 lbs.) Na,, HfF, -o°
3kg (o°7po” 11.3kg (24,9ho7)
1') Zn -107 kg (236 lb)
Al-4,4 kg (9,8 lb) Na2ZrF6 -39 kg (85 lb) N"・HfF, -0・3 kg (o・7fy
lS) 1□, 2kg (24,7 bore, ・) Zn
-107 kg (235 lb) A#
Input 4.4 kg (9.8 lb)
Raw material Produced zirconium N
a ZrP -39kg (85 lbs.) 6 N...HfF. -〇.37 (o.7 pod) 1□, 2kg (24, 7 pod.) Zn
-107 kg (235 lb) kl
- 4.4 kg (9.8 lb) According to another feature of the invention, after the above-mentioned reaction is completed, the reductive separation step 3
Once the salt phase is removed from 6, it is fed into a salt treatment step 44.

At this time, the salt phase is again (Nap)1.5.hu3. N
a2ZrF6 and N a 2 Hf F a , but is much richer in hafnium than the input salt of the reductive separation step 36.

In the salt treatment step 44, these salts are remelted and mixed with the molten zinc bath, again supplying the bath with a reducing metal such as aluminum.

However, compared to the reductive separation step 36 described above, a sufficient amount of aluminum is provided to the entire salt phase to complete the reactions of equation (10) and 200 above.

After the end of this reaction, pure molten (NaF)t,5.
AlF3 is removed from the molten metal phase and these materials are
The water is supplied from two outlet ports 46 and 48, respectively.

Salt called pseudo cryolite (NaF), , , A7
F3 is itself a preferred product and is also available commercially to the aluminum industry.

Therefore, the only salt by-product of the third step is itself useful and not waste.

Similarly, metal production port 48 re-distills the zinc and reuses it in the process and removes hafnium, zirconium and a small amount of aluminum as product metals of the process.

If necessary, these metals can be returned to the reductive separation step 36 to further extract zirconium therein.

Regardless, with this method, the amount of product metal remaining at outlet 48 is only about 5% of the metal that was in the zirconium ore at input 38.

If a higher separation factor of zirconium from aluminum and hafnium is required in the embodiment of FIG.
In the method described in FIG. 2 above, the reductive separation step 36 can also be carried out in the molten state.

If this is necessary, the actually preferred method of doing this is to inject a large amount of ZnF2 into the zinc-zirconium molten metal after the salt phase has been removed from the metal phase.

At this time, the following reaction occurs. (13) 2ZnF2+
Zr-+ZrF4+22n The zirconium tetrafluoride thus formed is then reacted with the remaining aluminum and hafnium in the metal phase according to the following formula:

If this second stage separation is required, it is a practical preferred method to provide sufficient zirconium fluoride to oxidize about 2% of the zirconium in the metal phase.

Therefore, among the quantities given in the example of Table 3 above,
Approximately 0.5 kg (1,1 lb) of Z for the melt operation
Preference is given to using nF2.

If excess ZnF2 is supplied, aluminum and hafnium can be sufficiently removed, but a large amount of zirconium is lost, which is uneconomical.

Similarly, when less ZnF2 is used, less hafnium is removed, but a large amount of zirconium remains in the metal phase.

In contrast to the processes described in FIGS. 1 and 2 above, the actually preferred embodiment described in FIG. 3 does not feed excess salts, such as potassium chloride or sodium fluoride, to the reductive separation step. It should be noted that

As stated above, the embodiment of FIG. 3 forms pseudo cryolite salt (NaF)1.5.AlF3.

If an excess of sodium fluoride is fed to this phase of the reaction, the salt formed will be normal cryolite, i.e.
NaF)341F3, which does not melt up to a temperature of 1000 DEG C., which is higher than the boiling point of the zinc-zirconium metal mixture.

It will be appreciated that the embodiment of Figure 3 reduces hafnium metal from the hafnium compound in the same way that zirconium is reduced.

Therefore, this method can also be used to reduce hafnium and is a superior reduction method to previous hafnium reduction methods.

FIG. 4 is a block diagram of a modified version of the method of FIG. 3, showing a two-stage countercurrent reduction step to further reduce aluminum and hafnium in zirconium to lower levels.

In the fourth stage, the reduction separation step 36 is divided into two stages, 36a and 36b.

In the first step, first stage 36a is initially charged with Na2ZrF6, which also contains Na2HfF6, aluminum and zinc.

Once the reaction is complete, the resulting salt is introduced into the salt treatment step 44 as described above, and the metal phase is introduced into the second stage 36b of the reductive separation step.

The metallic phase at this point typically has about 1000 to 1
500 p, p, m aluminum and 500 p, p-m
of hafnium (both of which express only the relationship with zirconium).

This level is too high for zirconium for nuclear use.

In the second stage 36b, the metal phase is mixed with the input salt from the ore crushing step 34, and the mixture is again heated to about 900° C. and vigorously stirred.

At this time, the following reaction occurs again.

At this time, in this reaction, both hafnium and aluminum in the metal phase are reduced to less than 100% relative to zirconium.

The mixture is separated and separated as previously described.

The metal phase is introduced into the black part process 40, where the zinc is recycled to the first stage 36a of the reductive separation process, and new high purity zirconium is introduced into the zirconium production process 42.

salt phase (a small amount of hafnium and aluminum
(almost unchanged in the second stage 36b) is fed into the first stage 36a of the reductive separation process, where fresh aluminum and zinc from the Kurobe process are again supplied.

Thus, this variant, termed the two-stage countercurrent reductive separation method,
High purity zirconium can be obtained without using the melting process shown in FIG. 2 above.

The present invention has been disclosed above, and several embodiments have been described in detail.
The present invention is not limited to these examples.

Many modifications are possible within the spirit and scope of the invention.

Accordingly, the invention is limited only by the scope of the claims.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the invention, illustrating the principles of the invention. FIG. 2 is a block diagram of a second embodiment of the invention. FIG. 3 is a block diagram of a third, actually preferred embodiment. FIG. 4 is a block diagram of a method that is a partial modification of the embodiment of FIG.

Claims (1)

[Scope of Claims] 1 A molten salt phase containing a zirconium compound to be reduced is produced, a molten metal phase comprising a reducing metal more electropositive than zirconium and a solvent metal less electropositive than zirconium, and the molten salt phase. the zirconium compound is reduced by the reducing metal, and the zirconium is transferred from the molten salt phase to the molten metal phase, while the reducing metal is transferred from the molten metal phase to the molten salt phase. A method for reducing zirconium from zirconium compounds. 2. A method according to claim 1, characterized by the steps of separating the molten metal phase from the molten salt phase and then separating the solvent metal from the zirconium. 3 The solvent metal is zinc, cadmium, lead, bismuth,
3. A method as claimed in claim 1 or 2, characterized in that the metal is selected from the group consisting of copper and tin. 4. The method according to claim 1 or 2, wherein the solvent metal is zinc. 5. A method according to any one of claims 1 to 4, characterized in that the reducing metal is selected from the group consisting of aluminum, magnesium, sodium, sodium and calcium. 6. The method according to any one of claims 1 to 4, wherein the reducing metal is aluminum. 7 Zirconium compound is N a 2 Z r Fe
The method according to any one of claims 1 to 4, characterized in that: 8 The reducing metal is aluminum and Na2ZrF6
8. A process according to claim 1, characterized in that aluminum is used in an amount to reduce 85% to 95% of the zirconium present in the zirconium. 9 After separating the molten salt phase from the molten metal phase, all the zirconium consisting of aluminum and solvent metal and in Na2ZrF6 is reduced to form pure (NaF)1. , into a second molten metal phase containing sufficient aluminum to obtain Al1F3, and then (N
aF)1. , A#F3 from the second molten metal phase. 10. A method according to any one of claims 1 to 9, characterized in that the molten salt phase contains a salt other than a zirconium compound in which the 10 cations are more electropositive than zirconium. 11. Process according to claim 10, characterized in that at least some of the cations in the molten salt phase are selected from the group consisting of alkali elements, alkaline earth elements, rare earth elements and aluminum. 12. The method according to claim 10, wherein at least some of the cations in the molten salt phase are alkali elements. 13. The method according to claim 12, wherein at least some of the cations in the molten salt phase are sodium. 114 Claim 1, characterized in that at least a portion of the cations in the molten salt phase are potassium.
The method described in Section 2. 15. The method according to any one of claims 1 to 14, characterized in that the molten salt phase contains a salt other than a zirconium compound that is a 15 halide salt. 16. The method of claim 15, wherein at least a portion of the 16 valide salt is a fluoride salt. 17. The method according to claim 15, wherein at least a portion of the halide salt is a chloride salt. 18 separating the molten metal phase from the molten salt phase; contacting the molten metal phase with a second molten salt phase containing the zirconium compound to be reduced; separating the molten metal phase from the second molten salt phase; A method according to claim 1, characterized in that it comprises the step of separating solvent metals from. 19 After separating the second molten salt phase and the molten metal phase, contacting the second molten salt phase with a second molten metal phase consisting of a reducing metal that is more electropositive than zirconium and a solvent metal that is less electropositive than zirconium. 19. The method according to claim 18, characterized in that: