JP2003313694A - Method for separating hafnium from zirconium by anodic electrolysis - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method for separating hafnium from zirconium. <P>SOLUTION: In the method for separating hafnium from zirconium, this method is characterized by anodically electrolyzing metals containing both components in an organic electrolytic solution, thereby anodically dissolving hafnium into the electrolytic solution, collecting hafnium from the electrolytic solution, and collecting enriched zirconium from the electrolysis residue. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating zirconium from hafnium. The present invention relates to a method for separating zirconium and hafnium by anodic dissolution utilizing the difference in corrosion resistance against electrolytic corrosion.

[0002]

2. Description of the Related Art Zirconium and hafnium are listed as one of the most difficult to separate because their chemical properties are very similar. In the periodic table, there is a series of lanthanoids in front of hafnium. Hafnium has its 4f electron shell clogged with electrons, and the interaction between the nucleus and the electron works strongly. So-called lanthanoid contraction causes hafnium to have an ionic radius of 5th. Very similar to zirconium belonging to the cycle. Therefore, the separation of the two is said to be the most difficult of all the elements. It is said that naturally occurring minerals and ores containing zirconium are usually accompanied with 1 to 5% of hafnium. Therefore, in the process of chemically treating ore with zirconium and separating and recovering these components, hafnium, which has a similar chemical property, is also deposited and separated together.

At present, a so-called solvent extraction method is known and practiced as a method for separating the two. However, this solvent extraction method has many problems in terms of separation efficiency and the discharge of a considerable amount of waste liquid containing harmful organic solvents, and an alternative separation method is required. Therefore, in recent years, regarding the method of separating zirconium and hafnium,
Several separation methods have been proposed. JP-A-5-33
No. 072 and Japanese Patent Publication No. 2001-507323 disclose hexane or methyl isobutyl ketone (MIB
The separation method by the solvent extraction method using an organic solvent such as K) is used as a precondition technology in the past, and in this precondition technology, a treatment liquid containing harmful organic substances, which is a problem in terms of environmental measures, is discharged from the treatment process. Since there is a problem in that point, it is described that an attempt is made to propose a separation method which does not have such a problem, that is, an alternative to the solvent extraction method in which harmful waste liquid such as an organic solvent does not occur as much as possible.

The outline of the measures taken for that purpose is to provide a former method for purifying zirconium and hafnium by chromatographic separation in a single operation step without producing liquid waste. Yes, a crude zirconium-hafnium hydrolyzate feedstock was prepared from zircon sand and introduced into the resin medium at the first position of a rotating continuous annular chromatograph, and HCl was placed at a second position at an angle deviated from the first position, H ₂ SO ₄ , HN
An aqueous acid eluent such as O ₃ , H ₃ PO ₄ and HClO ₄ is supplied to elute the supplied aqueous solution. The zirconium fraction and hafnium fraction are collected at the bottom of the chromatograph,
By rotating the chromatograph, various waste fractions and impurities are separated, and these are collected and discarded. The acid eluent is refluxed and reused. The zirconium fraction and hafnium fraction are individually evaporated and concentrated, roasted to the corresponding oxide, chlorinated and reduced to give pure metal zirconium and metal hafnium, while the evaporator and This is due to the above steps of concentrating and refluxing the eluent from the overhead stream of the roasting machine.

And the latter (Special table 2001-507323)
(Japanese Unexamined Patent Publication) describes a separation method by chromatography using an anion exchange resin, which roughly comprises the following processes. (I) Zircon sand containing zirconium and hafnium is chlorinated in the presence of carbon at high temperature to produce zirconium tetrachloride and hafnium tetrachloride fractions, and (ii) zirconium tetrachloride and hafnium tetrachloride fractions are diluted with dilute sulfuric acid. Dissolving in a solution to produce an aqueous zirconium oxychloride and hafnium oxychloride solution, (iii) precipitating the zirconium oxychloride and hafnium oxychloride solution in concentrated sulfuric acid solution to produce zirconium sulfate and hafnium sulfate fractions, (Iv) The zirconium sulfate and hafnium sulfate fractions are dissolved in a dilute sulfuric acid solution to obtain an aqueous sulfate raw material solution, and (v) the aqueous sulfate raw material solution is applied to a continuously operating ion exchange chromatography column containing an anion exchange resin. Inject (vi) the aqueous sulfate eluent into the column to Eluted from-exchange resin, (vi
i) A method for separating zirconium from hafnium, which comprises the steps of separately collecting a substantially pure zirconium fraction, a substantially pure hafnium fraction and at least one waste fraction from a column.

However, the conventional separation methods, including the separation method proposed by the above prior art, are extremely complicated in their processes, and thus are difficult to carry out because their process control is extremely troublesome. , Still had problems. Further, the apparatus for carrying out the process is also composed of a series of processing apparatuses, and is not a single apparatus at all, and it is costly in plant design. Therefore, as a method for separating zirconium and hafnium, it has been required to develop a simpler separating method and means.

[0007]

SUMMARY OF THE INVENTION The present invention is to provide a novel means for separating hafnium and zirconium and to meet the above demand. Therefore, the inventors of the present invention have conducted extensive studies, and as a result, have found that zirconium and hafnium in the organic electrolyte have completely different corrosion resistances. It is known that titanium, zirconium, and hafnium which are Group 4 elements are metals having excellent corrosion resistance. Since the corrosion resistance of these metals is due to the oxide film on the surface, the corrosion resistance in the organic electrolytic solution containing no oxygen supply source does not always match the generally known corrosion resistance. The present inventors
It was found that among the group elements, titanium and zirconium exhibit corrosion resistance even when subjected to anodic electrolysis in an organic electrolytic solution, whereas hafnium loses corrosion resistance when subjected to anodic electrolysis in an organic electrolytic solution. The present invention has been made based on this finding. That is, it was conceived to solve the above problems by positively utilizing the difference in corrosion resistance between the two when the anode electrolysis was performed.

That is, the inventors of the present invention have made earnest studies, and as a result, have solved and achieved the above-mentioned problems by taking the technical constitutions described below. (1) In the method for separating zirconium and hafnium,
A method for separating zirconium and hafnium, which comprises subjecting a metal containing both components to anodic electrolysis in an organic electrolytic solution, and thereby hafnium is anodicly dissolved in the electrolytic solution. (2) The method for separating zirconium and hafnium according to the item (1), wherein the organic electrolytic solution is a non-aqueous organic electrolytic solution containing a lithium salt as an electrolyte. (3) LiClO ₄ , LiBF ₄ , LiPF _{4 as} the lithium salt
₆ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , Li
(CF ₃ SO ₃ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ S
1 selected from the group consisting of O ₃ ) ₃ C and LiBPh _4.
The method for separating zirconium and hafnium according to the item (2), which is a lithium salt of one kind or two or more kinds. (4) The non-aqueous organic electrolytic solution is ethylene carbonate (E
C: Ethylenecarbonate), Propylene carbonate (PC: polypropylenecarbo)
nate), butylene carbonate (BC; butyl)
ene carbonate), γ-butyl lactone (GML; γ-butyrolactone), 1,2
-Dimethoxyethane (DME; 1,2-dimetho
xyethane), tetrahydrofuran (THF; t
Etrahydrofuran), 2-methyltetrahydrofuran (2MeTHF; 2-metyltetra)
hydrofuran), dioxolane (DOL; 1,
3-dioxolane), methyl formate (MF;
methyl formate), methyl acetate (MA; methyl acetate), methyl propionate (MP)
e), dimethyl carbonate (DMC; dimethy)
l carbonate), ethyl methyl carbonate (EMC; ethyl methyl carbona)
te), diethyl carbonate (DEC; diety)
The method for separating zirconium and hafnium according to any one of (1) to (3) above, which contains one or more organic solvents selected from the group consisting of . (5) After completion of the electrolysis operation, the electrolytic residue and the organic electrolytic solution are subjected to solid-liquid separation, hafnium is recovered from the organic electrolytic solution, and zirconium is recovered from the electrolytic residue. The method for separating zirconium and hafnium according to any one of 1. (6) The means for recovering hafnium from the organic electrolytic solution includes a step of concentrating the electrolytic solution, a step of oxidizing and roasting the concentrated solution, a step of chlorinating after oxidizing and roasting, and reducing hafnium chloride obtained by chlorination to hafnium. The method for separating zirconium and hafnium according to the item (5), which includes a step of obtaining a metal. Here, the reason why the organic electrolytic solution is used in separating both metals is that only hafnium is selectively dissolved by anodic electrolysis in the organic electrolytic solution as compared with the case of using a water-soluble electrolytic solution ( This is because zirconium remains unchanged as a solid phase without any change, and hafnium on the one hand dissolves in the liquid phase, and the two are naturally separated. Is.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings.
The principle will be explained. However, this is merely an aspect disclosed for facilitating the understanding of the present invention and is not intended to limit the present invention. That is, the present invention is to provide a method for separating zirconium from hafnium, and as long as this object is achieved, the embodiment of the present invention has no particular reason to limit this. That is, as long as the object of the present invention and the technical idea based on this object, it is possible to appropriately change, the present invention is limited by this, is not hindered, the embodiment of the present invention It is included.

A description will be given below. FIG. 1 is a schematic view of a separation apparatus used for carrying out an anode dissolution operation of zirconium and hafnium according to the present invention, in which a non-aqueous organic electrolysis in which an electrolyte composed of a halogen lithium salt is dissolved in an anode electrode and a cathode electrode. It is immersed in the liquid and attached. That is, it is no different from the usual electrolysis device itself. The present invention basically uses a normal electrolysis device as a separation device. For the anode electrode, use a material obtained by processing a raw material metal containing a metal to be separated as an electrode, or attach the raw material metal through an anode electrode made of a corrosion-resistant metal, and then separate these metals to be separated by anodic polarization. To do. On the other hand, as a counter electrode, an electrode made of platinum is set as a cathode electrode. Apply an applied voltage of appropriate potential between both electrodes,
When the anode is polarized, only hafnium is eluted from the source metal into the electrolytic solution.

It should be noted that FIG. 1 itself is a schematic view of an apparatus for explaining in principle the means for separating zirconium and hafnium, which is the object of the present invention. It is obvious to those skilled in the art that this device is nothing but an ordinary electrolytic cell itself, as is clear from this figure, and as is clear from the above description. There is no difference from normal operation. That is, regarding the design of the device and the like, it is not the gist of the invention to disclose the details thereof, and therefore all of them are left to the prior art and omitted here. That is, the purpose of the present invention is to provide a separating means for zirconium and hafnium, that is, a unique aim to provide an effective separating means for the most difficult to separate elements.
It will be apparent from the examples to be described later that what is disclosed below is an effort to disclose the essential requirements therefor. That is, the peculiar solution means for achieving the peculiar aim shown in the above is sufficiently disclosed by the basic matters and the principle explanations described in the following examples, and the plausibility is established. It is what

The separation method according to the present invention is fundamentally different in principle from the conventional solvent extraction methods or the separation methods shown in the above-mentioned prior art.
It is a new separation method, and it can be said to be an extremely effective and promising technology. Moreover, the apparatus itself to carry out was never said to be difficult to obtain or required complicated process control. It is sufficient to use an ordinary electrolytic cell, and in addition to being easily available, its dissolution and separation operation is required. Also, it can be said that the separation method and the separation device are excellent in operability because it is sufficient to energize between both electrodes. There is no need for a series of complicated operations as in the above-mentioned prior art and prior art.

The electrolyte used here is a non-aqueous electrolyte, that is, an organic electrolyte. The reason why the aqueous electrolytic solution is not used is that when water is contained, both zirconium and hafnium do not elute or dissolve even when subjected to anodic polarization. On the other hand, when an organic electrolytic solution is used, zirconium does not change so much, whereas hafnium has elution and dissolution phenomena, and a remarkable difference is observed between the two. That is, the present invention has been made on the basis of the discovery of a significant difference based on the difference in corrosion resistance between the both of them against the electrolytic solution.

The cause of the difference in the elution and dissolution phenomena of both metals with respect to the electrolytic solution used is not always clear at present, but this can be explained as follows. That is, in the electrolytic solution containing water,
Water itself acts as an oxygen supply source and acts on zirconium metal and hafnium metal, both of which form a corrosion-resistant passivation film on the surface, and as a result, exist stably even in corrosive organic electrolytes. However, without being corroded, it shows resistance to anodic dissolution, elution,
It is considered that dissolution does not occur. On the other hand, when the organic electrolytic solution is used, the situation is different and there is no oxygen supply source such as water, and it is considered that the difference between the two metals with respect to the organic electrolytic solution appears. That is, zirconium metal continues to exhibit its chemically stable corrosion resistance, which is the basic property of organic zirconium oxide, while hafnium metal differs from zirconium metal in this respect. , It is considered that the corrosion resistance cannot be sustained in this system.

As the electrolyte of the organic electrolytic solution used in the separation operation of the present invention, a lithium salt that dissociates in an organic solvent is used. Examples of such lithium salt include Li
ClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiS
bF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₃ ) ₂ N, Li
_{C 4 F 9 SO 3, Li} (CF 3 SO 3) 3 C, LiBPh 4 , and the like.

The organic solvent used in the electrolyte shown above is ethylene carbonate (EC).
carbon dioxide), propylene carbonate (P
C: propyrene carbonate), butylene carbonate (BC: butyrene carbon)
onate), γ-butyl lactone (GML; γ-bu
1,2-dimethoxyethane (DME; 1,2-dimethyloxyethane)
e), tetrahydrofuran (THF; tetrahydr)
rofuran), 2-methyltetrahydrofuran (2
MeTHF; 2-metyltetrahydrofu
ran), dioxolane (DOL; 1,3-dioxo)
lane), methyl formate (MF; methyl)
format), methyl acetate (MA; meth)
yl acetate), methyl propionate (M
P; methyl propionate), dimethyl carbonate (DMC; dimethyl carbon)
ate), ethyl methyl carbonate (EMC; eth)
yl methyl carbonate), diethyl carbonate (DEC; diethyl carbon)
ate) and the like.

The organic electrolytic solution of the present invention is appropriately selected and prepared from the electrolyte described above and an organic solvent. The concentration of the electrolyte can be used in an appropriate range and is not particularly limited as long as the object of the present invention can be achieved, but when the concentration is high, the viscosity of the electrolytic solution is increased, the electrolytic solution is handled, and the solid-liquid contact property is improved. Should be restricted where appropriate as it will worsen. The 1 molar concentration disclosed in Examples described later can be referred to as a preferable concentration. Using this as a guide, the optimum range for hafnium elution may be determined.

Example 1 Using Hafnium Metal LiClO ₄ was used as an electrolyte, and this was prepared using polypropylene carbonate (PC) and 1,2-dimethoxyethane (D).
ME) was mixed and dissolved in a 1: 1 mixed solution (Vol ratio) to a molar concentration of 1 to prepare an organic electrolytic solution. An electrolytic cell was filled with this electrolytic solution, and an anode electrode and a cathode electrode were set. A hafnium metal plate was used as the anode electrode, and this was used as the anode electrode. A platinum electrode was attached to one of the electrodes, and this was used as a cathode electrode. To investigate the reaction of the hafnium metal anode, a current-potential (i-E) curve was determined and the results were plotted in FIG. That is, as a result of measuring the electrode potential and the current flowing between the electrodes by changing the potential of hafnium metal as an anode electrode, the obtained current-potential voltammogram is as shown in FIG. According to the voltammogram shown in FIG. 2, when hafnium metal is anodic polarized,
The current began to flow from around 1.9 VvsAg, and the current tended to increase even after potential inversion. (Dotted line is 2
The cycle cycle is shown. ) Regarding this, the cause was examined and it was found that (00
It is presumed that this is because the initial oxide film on the hafnium metal surface is dissolved as described in 19) and the electrode area is increased accordingly.

FIG. 3 is a diagram (micrograph) comparing hafnium metal before and after anodic polarization treatment. A clear difference was observed between before and after treatment. That is, according to this photograph, hafnium is corroded by the anode polarization treatment and is eluted and transferred to the electrolytic solution. The evidence of this elution transition is observed from the photograph showing the numerous holes formed. This is shown in the previous (0018)
In addition to the theory of increasing the electrode area given as the reason for the increase in current after potential reversal described in (4). That is, FIG. 3 (photograph)
It can be said that this is proof of this.

In addition to the observation record by the micrograph, the remaining solid component is recovered after the completion of the anode polarization operation to show that the hafnium is eluted, and the solid component is sufficiently dissolved in a solvent containing no electrolytic solution. It was washed, dried, and the recovered weight was determined. It was found that the weight was reduced compared to the weight of the electrode before treatment. That is, it was confirmed that the amount of hafnium was eluted and separated by the anodic treatment. Furthermore, it was confirmed that hafnium was contained in the recovered electrolytic solution. The electrolyte was recovered, concentrated, roasted and then chlorinated in the presence of carbon. When this was further reduced, hafnium metal was obtained. It was verified and confirmed by these items that hafnium metal was anodic polarized, and thereby hafnium was eluted and dissolved in the electrolytic solution.

The above shows the case where the hafnium metal is directly used for the anode electrolysis. Next, the same experiment was conducted with the zirconium metal. The results are shown in FIGS. 4 and 5. (Example 2 using zirconium metal) That is, FIG.
Is a voltammogram of zirconium metal in a 1 molar concentration of LiClO ₄ / PC + DME (1: 1 mixed solution of polypropylene carbonate and 1,2-dimethoxyethane) organic electrolyte. When anodic polarized, 2.
0 V vs. A current started to flow from around Ag, the current increased linearly with respect to the voltage, and after the potential reversal, the current decreased along the same locus. This is because the zirconium metal does not dissolve and anodic oxidation decomposition of the electrolytic solution occurs.
FIG. 5 is a diagram (photograph) showing zirconium metal after anodic decomposition in a 1 molar concentration of LiClO ₄ / PC + DME organic electrolytic solution. No trace, sign, or change indicating the elution of was found.

(Example 3 of Zirconium Metal and Example 4 of Titanium Metal) Experiments were carried out on zirconium under the same conditions as in the above-mentioned Examples except that the electrolyte used was changed. That is, LiPF ₆ , LiBF ₄
For each electrolyte, use PC + DME for each electrolyte.
(1: 1 mixed solution) was mixed and prepared to have a molar concentration of 1 to prepare respective electrolytic solutions, and zirconium metal was subjected to anodic polarization in both organic electrolytic solutions. As a result, zirconium exhibited corrosion resistance and did not dissolve in any of the electrolytic solutions as in Example 2. In addition, this experiment was also performed on titanium, which is the same Group 4 element and has corrosion resistance. As a result, titanium, like zirconium, exhibited corrosion resistance and did not dissolve.

In each of the above examples, each pure metal is used as a sample, and anodic polarization is performed by this. The reason for using these metals is that each metal reacts with anodic polarization. That there is a difference between hafnium and the other Group 4 elements based on whether or not they are dissolved in the anode, and that it is effective as a separation method by showing this difference. The pure metal is used as a sample for the purpose of showing. A crude zirconium metal containing hafnium was subjected to anodic polarization treatment under the same conditions as in the above-mentioned examples. Hafnium was eluted in the electrolytic solution, and enriched zirconium metal was recovered from the electrolytic residue. I was able to. That is, it was confirmed to be effective as a separating means.

From the examples shown above, only hafnium was the only element of the Group 4 elements that was dissolved in the organic electrolyte by anodic dissolution. It was possible to separate zirconium and hafnium by utilizing the difference in chemical property for anodic polarization using this organic electrolyte. That is,
It has succeeded in providing a completely new method for separating zirconium and hafnium, which are said to be the most difficult to separate due to their very similar chemical properties.
Moreover, this separation method, as is clear from the above description, has a very simple separation process and an apparatus for carrying out this process, which is remarkable as compared with the conventional means, and its significance is extremely significant. It is considered remarkable.

[0025]

INDUSTRIAL APPLICABILITY According to the present invention, zirconium and hafnium, which are difficult to separate, are subjected to anodic polarization under an organic electrolytic solution to dissolve and dissolve only hafnium in the electrolytic solution and fix zirconium metal other than hafnium as it is. It succeeded in separating both metals. Until now, it has been extremely significant to provide a novel separation method for zirconium and hafnium, which have been difficult to separate because of their very similar chemical properties. That is, until now, extremely complicated operation and management were required, and the conventional technique by the solvent extraction method, which was carried out based on a separation plant consisting of a series of multiple separation devices, or ion exchange resins, etc. Compared to the prior art based on column separation technology, it is extremely easy to operate and manage.
That is, the fact that it has become possible to separate by anodic polarization treatment is, of course, needless to say,
It's a striking and big harvest. And it is considered that it is obvious to those skilled in the art that it has novelty and inventive step.

[0026]

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an electrolytic cell used as a means for separating zirconium and hafnium according to the present invention.

FIG. 2 is a voltammogram of hafnium metal subjected to anodic polarization in 1M LiClO ₄ / PC + DME.

FIG. 3 Photomicrographs of hafnium metal before and after anodic polarization of hafnium metal in 1M LiClO ₄ / PC + DME.

FIG. 4 is a voltammogram of anodic polarized zirconium metal in 1M LiClO ₄ / PC + DME.

FIG. 5 Photomicrographs of hafnium metal before and after anodic polarization of zirconium metal in 1M LiClO ₄ / PC + DME.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Endo             1-155 Tateyama, Yonezawa City, Yamagata Prefecture (72) Inventor Yusuke Sakamoto             3-1-17 Honmachi Heights, Yonezawa City, Yamagata Prefecture Honmachi Heights             110 F term (reference) 4K058 AA21 BA09 BB01 BB03 CA05                       CA14 EA02 EB02 EB13 ED04                       FA05 FA22 FC03 FC21

Claims (6)

[Claims] 1. A method for separating zirconium and hafnium, which comprises subjecting a metal containing both components to anodic electrolysis in an organic electrolytic solution, and thereby hafnium is anodicly dissolved in the electrolytic solution. 2. The method for separating zirconium and hafnium according to claim 1, wherein the organic electrolytic solution is a non-aqueous organic electrolytic solution containing a lithium salt as an electrolyte. 3. The lithium salt is LiClO ₄ , LiBF ₄ , L
_{iPF 6, LiAsF 6, LiSbF 6} , LiCF 3 S
O ₃ , Li (CF ₃ SO ₃ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li
_{4. The} method for separating zirconium from hafnium according to claim 3, wherein the lithium salt is one or more lithium salts selected from the group consisting of (CF ₃ SO ₃ ) ₃ C and LiBPh ₄ . 4. The non-aqueous organic electrolytic solution is ethylene carbonate (EC),
Propylene carbonate (PC)
carbon dioxide), butylene carbonate (BC;
butylene carbonate, γ-butyrolactone (GML; γ-butyrolacton)
e), 1,2-dimethoxyethane (DME; 1,2-d
imethoxyethane), tetrahydrofuran (THF; tetrahydrofuran), 2-methyltetrahydrofuran (2MeTHF; 2-mety)
ltetrahydrofuran), dioxolane (DOL; 1,3-dioxolane), methyl formate (MF; methyl acetate), methyl acetate (MA).
e), methyl propionate (MP; methyl pr)
opionate), dimethyl carbonate (DMC;
dimethyl carbonate), ethyl methyl carbonate (EMC; ethyl methyl carbonate)
carbonate), diethyl carbonate (DE
The method for separating zirconium and hafnium according to any one of claims 1 to 3, further comprising one or more kinds of organic solvents selected from the group consisting of C (diethyl carbonate). 5. The electrolytic residue and the organic electrolytic solution are solid-liquid separated after completion of the electrolysis operation, hafnium is recovered from the organic electrolytic solution, and zirconium is recovered from the electrolytic residue. The method for separating zirconium and hafnium according to any one of claims 1. 6. A means for recovering hafnium from an organic electrolytic solution includes a step of concentrating the electrolytic solution, a step of oxidizing and roasting the concentrated solution, a step of chlorinating after oxidizing and roasting, and reducing hafnium chloride obtained by chlorination. 6. The method for separating zirconium and hafnium according to claim 5, further comprising the step of obtaining hafnium metal by means of the method.