JPH0440435B2 - - Google Patents

Abstract

1. A process for the preparation of a rare earth metal or an alloy of rare earth metal with at least one metal selected from the group consisting of rare earths and transition metals by electrolysis in a bath of molten salts, characterised by effecting on solid electrodes the electrolysis of at least one chloride of a rare earth in a bath of salts essentially comprising lithium chloride and lithium fluoride ; the cathode being a cathode of tungsten or formed by at least one rare earth metal when preparing a rare earth metal or an alloy of rare earth metals, the cathode being formed by a transition metal or an alloy of a rare earth metal and a transition metal when preparing an alloy of at least one rare earth metal and at least one transition metal.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for electrolytically producing rare earths or their alloys in a molten salt bath. In the following description, the term rare earth (RE) is used to denote any element belonging to the group consisting of yttrium and the lanthanides, excluding samarium, europium, ytterbium and thulium. [Prior Art] Currently, the electrolysis of rare earth chlorides, especially neodymium, in molten media is problematic because the yields obtained are very low. This is due to the high level of metal solubility in the presence of chloride. A method of this kind is described in an article by T. Kurita [Electrochemistry (1967), Vol. 35(7), pp. 496-501]. This article describes pure neodymium yields of less than 20% for molten baths formed with neodymium chloride and potassium chloride. [Object of the Invention] Therefore, the object of the present invention is to produce rare earths or alloys thereof by electrolytic method under conditions such that the process can be carried out on an industrial scale. [Means for Solving the Problems] In order to achieve the above object, the present invention uses a rare earth metal or an alloy of a rare earth metal and at least one metal selected from the group consisting of rare earth metals and transition metals. , provides a method for producing by electrolysis of molten salt. That is, the present invention provides a method for producing a metal or alloy by electrolyzing a bath of a molten salt consisting essentially of at least one rare earth chloride and at least one of lithium chloride and lithium fluoride using solid electrolysis. This is the manufacturing method. The process of the invention allows metals of good purity levels or alloys containing high proportions of rare earths to be produced with high metal yields that can exceed 80% under conditions suitable for use on an industrial scale. do. Other features and advantages of the invention will become readily apparent from the following description and examples, which also refer to the accompanying drawings, which illustrate an apparatus for carrying out the method. As mentioned above, the present invention relates to the production of rare earths and their alloys, and in particular to the production of neodymium metal from neodymium chloride, which in fact provides particularly significant yield improvements in the case of neodymium. The invention further relates to the manufacture of alloys, in particular of neodymium. Alloys that can be produced using this method include, for example, Nd-
Alloys between rare earths such as La, Nd-Ce or Nd-Pr, or alloys between one or more rare earths and a metal selected from the group consisting of transition metals. Transition metals that can be used include all metals that have a melting point higher than the temperature of the molten salt at the time of electrolysis, said temperature being for example between 650 and 1100°C.
can vary within the range of Examples of such metals include iron, cobalt, nickel and chromium. According to the invention, therefore, in particular the following alloys can be produced:
Nd-Fe, La-Fe, Nd-La-Fe and Pr-Fe. According to the invention, the starting point of the process is the rare earth chloride to be produced as a metal. To produce alloys of several rare earths, the starting point employed is a bath containing a mixture of the respective chlorides of these rare earths. Chlorides of this type preferably have a water content of less than 6% by weight. It has proven advantageous for the baths used in the electrolytic operation to contain, in addition to rare earth chlorides, at least one of lithium chloride and lithium fluoride.
The presence of these lithium halides in the bath has the effect of significantly increasing the yield. The proportion of rare earth chlorides in the bath can vary in the range from 10 to 70% by weight, especially in the range from 15 to 45%. Furthermore, the weight ratio between lithium chloride on the one hand and lithium fluoride on the other preferably varies from 1.5:1 to 3:1. Finally, it is advantageous to use baths with a content of one or more lithium fluorides of at least 15%. The bath temperature during the electrolytic operation is set to be higher than the melting temperature of the electrolytic bath. Generally, this temperature is between 650° and 1100°C, especially between 700° and
It is 900℃. Conditions particularly relevant to the electrolytic operation will be explained below. As an electrode, the device generally uses a graphite anode. The type of cathode can vary depending on the type of material being manufactured. When producing pure rare earths, tungsten cathodes are advantageously used. Furthermore, it is also possible to use cathodes made of the same rare earths as the type to be manufactured. To produce mutual rare earth alloys, the same type of cathode is used. When producing alloys of rare earths and transition metals, the cathode is a consumable cathode made of the transition metal or of the same rare earth-transition metal alloy being produced. The voltage at the terminals of the electrodes is generally 4 to 10 volts. Cathode current density (ccd) is 70A・dm ^-2 ~700A・
It can be varied in the range of dm ^-2 , especially in the range of 100 to 250 A.dm ^-2 . The anode current density (acd) generally ranges from 50 to 250 A·dm ⁻² . Furthermore, the partial pressure of chlorine in the gas phase is at least
It has been found advantageous to carry out the electrolytic operation under conditions such that the pressure is 1.01×10 ⁴ Pa (0.1 atm). In this case, the conversion of the oxychloride present in the bath takes place according to the reaction equation TROCl+Cl ₂ →TRCl ₃ +1/2O ₂ . In fact, oxychlorides are introduced as impurities together with rare earth chlorides. In this case, the starting materials used can be rare earth chlorides with an oxychloride content of up to 25% by weight. [Example] Examples are shown below, and the described experiment was performed using a diameter of 10~
It was carried out in an alumina crucible with a 25 mm graphite anode. The spacing between the poles was 65 mm in Examples 1-4.
For each electrolysis operation, the metal produced was collected after cooling in the crucible. The composition of the baths is given as % by weight. The metal yields indicated refer to the ratio of the rare earth metal obtained to the metal corresponding to the introduced rare earth chloride (TRCl ₃ ). Example 1 Production of neodymium metal The following composition: NdCl ₃ : 13.3%; LiCl: 62.0%:
LiF: 24.7%, electrolysis of 800g of molten mixture of 850
The experiments were carried out with a tungsten cathode (φ=4 mm) at a temperature of .degree. The electrolytic operation was carried out at a current intensity of 8.5 A, corresponding to a cathodic current density (ccd) of 690 A·dm ^-2 and an anodic current density (acd) of 60 A·dm ^-2 . The voltage at the terminals of the electrodes ranged from 4.6 to 5.0 volts. A 4 hour electrolysis with a metal yield of 40% gave 24.1 g of metal with neodymium, lithium and tungsten contents of 98%, 0.07% and <1%, respectively. Example 2 Production of a neodymium-iron alloy with low iron content A composition very similar to that corresponding to the electrolyzed mixture in Example 1, NdCl ₃ : 13%; LiCl:
800 g of a bath of 62%; LiF: 25% was used. The electrolytic operation was carried out at 730° C. with a cathode made of 65 g of Nd/Fe alloy containing 20% iron (this alloy was previously prepared by Calciothermy). Electrical contacts were made by steel rods. The intensity of the electrolytic current was high, i.e. 25A, but the low ccd
(110A・dm ^-2 ), ACD is 250A・dm ^-2
And so. After 1 hour and 20 minutes of electrolysis, 48 g of metal was recovered (metal yield 80.4%), which is at least 89%
of Nd, 8.7% iron and 0.1% lithium. Example 3 Manufacture of neodymium-iron alloy The material, composition and temperature of the electrolytic bath used were:
Same as used in Example 2 (neodymium chloride contained 7.5% oxychloride and 2.7% water). The intensity of the electrolysis current was low (13.5A). (Consumption) CCD was set to 100A・dm ^-2 with a cathode formed by iron grid and steel contact. The value of acd is
It was set to 135A・dm ^-2 . After 2 hours and 30 minutes of electrolysis,
50 g of metal was obtained (metal yield 84%), containing at least 85% Nd, 12% iron and 0.7% lithium. In the following examples (Examples 4-8), the time of the electrolytic operation is "to" the time theoretically required to reduce all of the _TRCl3 if the metal yield is 100%.
It was shown as Example 4 Production of pure lanthanum The starting point used was a bath with the following composition: :
_LaCl3 : 13%; LiCl: 62%; LiF: 25%. The process uses a cathode made from a tungsten rod,
CCD is 690A・dm ^-2 and ACD is 60A・dm ^-2
And so. The distance between the electrodes was 65 mm, and the temperature was 800°C. After t=to, metal with a random content of at least 95% was produced, and the metal yield was 33%. Example 5 Preparation of a lanthanum-iron alloy The composition of the bath is as follows: _LaCl3 : 25%; LiCl: 53%; LiF: 22%. The cathode used was made with an iron rod, and the CCD was 165A・dm ^-2
and the ACD is 215A・dm ^-2 and the distance between the poles is
It was set to 60mm. The temperature was 840°C. After t=1.5to, an alloy consisting of 92% La and 7% iron was produced. The metal yield was 34%. Example 6 Manufacture of neodymium-lanthanum alloy The starting point was a bath with the composition: _NdCl3 : 26%; _LaCl3 : 9%; LiCl: 46%;
LiF: 19%. The cathode is a tungsten rod, and the CCD
26A・dm ^-2 , ACD was 235A・dm ^-2 , and the distance between poles was 63mm. The temperature is 860℃. After an electrolysis time of t=0.7to, an alloy having the following composition was obtained with a metal yield of 57%. :Nd:81%;
La: 18%; lithium content 0.1%. Example 7 Manufacture of neodymium-lanthanum-iron alloy The composition of the bath is as follows: _NdCl3 : 15%; _LaCl3 : 10%; LiCl: 53%:
LiF: 22%. The cathode is an iron rod, and the CCD is 100A/dm.
^-2 , ACD was set to 142A・dm ^-2 , and the spacing between the cathodes was set to 40mm. The temperature is 750℃. After setting t=1.5to, an alloy having the following composition was obtained with a metal yield of 74%. Nd: 55%; La: 37%; Fe: 9.2%,
and Li: 0.5%. Example 8 Preparation of praseodymium-iron alloy A bath with the following composition was used: _PrCl3 : 25%; LiCl: 53%; LiF: 22%. The cathode was the same type as used in Example 7, and the CCD was
The ACD was set to 100A·dm ^-2 , the ACD was set to 140A·dm ^-2 , and the distance between poles was set to 45mm. The temperature of the bath is 750°C. After setting t=1.5to, an alloy having the following composition was obtained. :Pr:86%;Fe:12%;Li:0.5
%. The metal yield was 60%. Example 9 Preparation of pure lanthanum A bath with the following composition was used: LaCl ₃ : 30%; KCl: 38.6%; LiCl: 31.4%. The anode was graphite and the cathode was a lanthanum with steel contacts. CCD is 55A・dm ^-2 , and ACD is
130A・dm ^-2 and the distance between poles is 40mm. The temperature of the bath is 690°C. After 3 hours and 31 minutes,
67 g of metal was obtained, giving a metal yield of 56%. Example 10 This example concerns the production of neodymium-iron alloys. The composition of the bath was varied. In all cases, the anode was graphite and the cathode was an iron bar. The results are shown in the table below. In the table, T indicates the temperature of the bath (° C.), t indicates the time of the electrolytic operation regarding the above to, Di indicates the distance between the electrodes (mm), and R indicates the metal yield described above.

【table】

TABLE From the table it can be seen that high yields are obtained when using a molten salt bath containing at least one of lithium chloride and lithium fluoride. On the other hand, it can be seen that the yield is low in baths that do not contain lithium chloride or lithium fluoride (bath compositions 6th and 7th in the table). Example 11 This example concerns the production of gadolinium-iron alloys. A bath with the following composition was used: _GdCl3 : 26%; LiCl: 52.3%; LiF: 21.7%. The anode is made of graphite and the cathode is made of iron, and the temperature of the bath is
The temperature is 940℃, the ACD is 89A・dm ^-2 , and the CCD is
250A・dm ^-2 and the distance between poles was 46mm.
After setting t=0.94to, an alloy with the following composition was obtained: Gd: 86%; Fe: 14%. Metal yield is 42%
It was hot. A device for carrying out this method will be described below. The electrolytic cell was designed so that the produced metal or alloy could be injected or withdrawn from the bottom. Therefore, a withdrawal area or drainage area is provided in the lower part, in which the products formed are collected by settling, and this drainage area is shaped so that the metal or alloy can be easily extracted, or is provided with drainage means. Ta. 1 and 2 show an electrolytic cell 1 formed by a generally cylindrical tank 2 in its upper part and a conduit 3 in its lower part forming a drainage area. The conduit 3 has an inner cross-section smaller than the cross-section of the vessel 2, preferably extends in alignment perpendicularly to the vessel 2, and advantageously has a cylindrical cross-section. conduit 3
preferably opens in the center of the bottom 4 of the tank 2. To facilitate the injection of substances, tank 2 contains e.g.
Bottom part 4 slightly inclined downward at an angle of about 10°
can be provided. Tank 2 is of electric radiation, contact or induction heating type;
Alternatively, an external heating means of gas or fuel oil combustion type is provided. Figures 1 and 2 show two specific embodiments of drainage areas. Referring to FIG. 1, the drainage area or conduit 3 is
It is formed by two separate bands: a connecting band 5, a central band 6 and an outer band 7. central band 6
is separated from the other two zones by valves 8 and 9, which form the total opening and are under remote control. The zone 6 thus formed forms a settling space. Zones 5 and 6 are each provided with heating means, for example of the electrical heating type. Regarding dimensions, the diameter and height of the zone 6 depends on the frequency of drainage. Generally, the height of zone 6 may be 2.5 to 6 times the height of zone 5. The drainage zone 3 shown in FIG.
1 and an outer band 12. The outer band 12 itself is divided into two parts: a part 13 adjacent to the band 11 and an outer part 14 . These two parts are substantially distinguished from each other by being provided with independent heating means. Zone 11 is also provided with heating means. For sections 13 and 14 electrical heating means operated by contact or by radiation are preferably used, for section 14 if necessary heating means operated by induction and also for zone 11 for example by means of fuel oil or gas. Preferably, highly flexible heating means of the combustor type are used. The dimensions of the conduit 3 in this example also depend on the frequency of draining the electrolytic cell. Preferably, the dimensions of the connecting zone 10 and the outer zone 12 are the same and have a ratio of about 2 to 4 to the diameter of the central zone 11. Regarding the height, the connection band 10 and the central band 11 and the part 1
3 can be given a fairly approximate height, the height of part 3 being 3-5 times more. The entire electrolytic cell is made of materials that can withstand the temperature of the bath and the corrosion caused by the different substances involved. Suitable materials that may be mentioned are cast iron, especially gray cast iron with foliated or nodular graphite. moreover,
It is also possible to use cast iron alloyed with chromium or nickel or preferably with molybdenum-silicon. Different electrode shapes and arrangements can be used in the electrolyte layer according to the invention. Generally, graphite anodes are used. As for the cathode, its properties depend on the type of material produced, as described above. Tungsten is used for pure rare earths, or a transition metal or rare earth-transition metal alloy consumable cathode is used to process alloys. Generally, electrolytic cells use a cylindrical cathode placed vertically within the cell, preferably in the center. Especially when the waste liquid area of the electrolytic layer is formed by a cylindrical conduit,
Advantageously, the cathode is aligned perpendicularly to the conduit. Preferably the cathode is hollow and cylindrical. Furthermore, rare earth chlorides can also be supplied to the electrolytic cell via the hollow central part of the cathode. Furthermore, it is also possible to use horizontal cathodes. Various different forms of anodes can be used. As can be seen from FIG. 1, the anode 15 is the cathode 16
can be formed by one or more vertical cylinders disposed around the periphery of the cylinder. for example,
Six cylinders can be used. In the embodiment of FIG. 2, the anode 17 is the cathode 16.
It can also be formed by a cylindrical ring centered at . Instead of rings it is also possible to use partial rings. Furthermore, it should be noted that the electrodes are advantageously arranged in the electrolytic cell in such a way that the lower end of the cathode is closer to the bottom of the cell than the lower end of the anode. The operating method of the above device will be explained below. Rare earth chloride is continuously supplied to the electrolytic cell via a hopper. In the case of hollow cathodes of the above type, the chloride is introduced into the central part of the electrode. The metals or alloys produced during the electrolytic operation fall to the bottom of the vessel and are periodically recovered through the drainage area, conduit 3. When using the apparatus of FIG. 1, valve 8 is opened and valve 9 is closed to completely fill zone 6 with metal or alloy. After this filling operation is completed, valve 8 is closed and valve 9 is opened to allow the product to flow into external zone 7. When using the arrangement shown in FIG. 2, the portion 14 of the outer zone 12 is kept cool, i.e. below the melting temperature of the bath, and the metal or alloy is allowed to settle in the portion 13 and the connecting zone 10,
Central zone 11 and section 13 are heated. Then,
Zone 11 is cooled very rapidly and a metal or alloy plug is formed therein. The outer portion 14 of the outer zone 12 is then rapidly heated to pour out the product collected in the portion 13. Part 13 and outer part 14 are then cooled to form a new plug of metal or alloy in zone 12, and zone 11 is heated in turn. The above arrangement can be applied to any type of electrolysis in a bath of molten salts in which the final product is collected by settling. Therefore, its use is not specifically limited to the baths described in the present invention. The invention is not limited to the above specific examples, which are described only as examples. [Effects of the Invention] The method of the present invention produces alloys containing a high proportion of rare earth metals with good purity levels and high metal yields exceeding 80% under conditions that can be used on an industrial scale. make it possible.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an electrolytic cell used in the present invention. Second
The figure is a schematic cross-sectional view of a second example of an electrolytic cell used in the present invention. 1: Electrolytic cell, 2: Tank top, 3: Conduit, 4: Tank bottom, 15: Cylindrical anode, 16: Cathode, 17:
Ring-shaped anode.

Claims (1)

[Scope of Claims] 1. A method for producing, by electrolysis, a rare earth metal or an alloy of a rare earth metal and at least one metal selected from the group consisting of rare earth metals and transition metals, comprising: 1. A method for producing a metal or alloy, comprising electrolyzing a bath of a molten salt consisting of a rare earth chloride and at least one of lithium chloride and lithium fluoride using a solid electrode. 2. The method according to claim 1, wherein a graphite anode is used as the anode. 3. To produce pure rare earth metals or alloys of rare earth metals as cathodes, use cathodes made of tungsten or rare earth metals; to produce alloys of rare earth metals and transition metals, 3. The method according to claim 1 or 2, which uses a transition metal or an alloy of a rare earth metal and a transition metal. 4. The method according to any one of claims 1 to 3, wherein the rare earth chloride is neodymium chloride. 5 Claims 1 to 3 in which the rare earth chloride is neodymium chloride and the transition metal is iron
The method described in any one of paragraphs. 6. The method according to claim 1, in which the electrolysis is carried out using neodymium chloride as a rare earth chloride, in a bath containing lithium chloride and lithium fluoride, and using a graphite anode and a tungsten or neodymium cathode as a solid electrode. . 7 Electrolysis with neodymium chloride as rare earth chloride,
2. The process as claimed in claim 1, which is carried out in a bath containing lithium chloride and lithium fluoride, with a graphite anode and a consumable iron cathode as solid electrodes. 8 The weight ratio of lithium chloride to lithium fluoride is
2. A method as claimed in claim 1, characterized in that a bath is used in which the ratio of chloride of at least one rare earth element ranges from 1.5:1 to 3:1 and the proportion of chloride of at least one rare earth element ranges from 10 to 70% by weight. 9. Process according to claim 1, characterized in that a bath is used in which the proportion of lithium fluoride is at least 5% by weight. 10. The method according to claim 1, wherein the electrolysis is carried out at a temperature of 650 to 1100°C. 11 The partial pressure of chlorine is at least 0.01×10 ⁴ Pa (0.1
2. The method according to claim 1, wherein the electrolysis is carried out under conditions such that the atmospheric pressure is maintained.