FR2555611A1 - Process for the preparation of alloys of aluminium and of rare earths - Google Patents

Abstract

Process for the preparation of alloys of aluminium and of rare earths with a low rare-earth content. The said process consists in reducing at least one oxide of a rare-earth metal with aluminium at a temperature above 700 DEG C. An alternative form of the invention also consists in recovering the rare-earth metals present in the mixed oxide powder obtained at the same time as the alloy. The alloys obtained according to the invention have many applications especially in the nuclear, aeronautical and metallurgical industries.

Description

PROCESS FOR THE PREPARATION OF ALLOY ALLOYS
AND RARE EARTHS
The present invention relates to a process for the preparation of aluminum alloys and rare earths. More specifically, it relates to the production of aluminum alloys containing a low content of rare earths.

 It is known from FR-A 2 202 950 to prepare aluminum or magnesium and rare earth alloys according to a process which is based on the simultaneous electrolytic reduction of a magnesium or aluminum oxide and an oxide. of rare earth dissolved in a bath of molten electrolyte salts containing the fluorides of a corresponding rare earth and lithium.

This process makes it possible to obtain alloys rich in rare earths containing 30 to 90% rare earths.

 The applicant was looking for a process for obtaining aluminum alloys and rare earths by a technique not involving electrolysis as in the prior art.

 It has now been found a process for preparing an aluminum alloy containing a low rare earth content, characterized in that it consists in reducing at least one metal oxide of a rare earth with aluminum to a temperature above 7000C.

 In the following description of the invention, the term rare earth content, an alloy containing less than 35% by weight of one or more rare earth metals.

 The rare earth metal oxide is selected from the group consisting of yttrium and lanthanides. There may be mentioned yttrium or lanthanide oxides such as lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium or a mixture of these oxides. It may be particularly advantageous to use mixtures of these oxides, for example, the mixed oxides of light rare earth metals from natural monazite or bastnäsite, thus making it possible to obtain mischmetal-aluminum alloys.

 The metal TR is generally used in the form of its oxide, the most common. These oxides are most often in the form of sesquioxide TR203 except for cerium, praseodymium and terbium which are in peroxide form CeO2, Pur6011, Tb407.

 Preferably, gadolinium, neodymium or yttrium sesquioxide is employed.

 It is desirable that the oxide used is of high purity so that it does not contain impurities that can be found in the final alloy. It may be advantageous to use one or more oxides having a degree of purity of at least 99%.

 The particle size of rare earth metal oxides is related to their purity. In the process of the invention, it is not critical.

 With regard to the reducing metal, it is preferable that the aluminum also has a purity of at least 99%.

 Aluminum is used in its commercial form, that is to say in the form of a powder.

 As regards the proportion of the rare earth metal oxide and aluminum, it is found that it conditions both the kinetics of the reaction and the composition of the alloy obtained.

a Au203 + 2a TR (I)
La réaction (I) n'est pas thermodynamiquement possible.If one considers, more closely, the process of the invention, the aluminum reduction of moles of Tu30, leads to the formation of 2 moles of rare earth metal according to the equation a TR203 + 2a Al

to Au203 + 2a TR (I)
The reaction (I) is not thermodynamically possible.

a Au203 + {TR2a ' b} (Il)
On a trouvé que l'on obtient un tel alliage selon cette réaction (II) que si le rapport entre le nombre de moles d'aluminium et le nombre de moles de métal TR c'est-à-dire 2a + b est supérieur 2a ou égal à 40. On the other hand, an excess of aluminum is formed, a liquid alloy at the temperature of the reaction which gives, after cooling, a compound defined according to reaction (II) a-TR 2 O 3 + (2 a + b) Al

to Au203 + {TR2a 'b} (Il)
It has been found that one obtains such an alloy according to this reaction (II) that if the ratio between the number of moles of aluminum and the number of moles of metal TR that is 2a + b is greater than 2a or equal to 40.

 In other words, by choosing said ratio greater than or equal to 40, an alloy containing less than 15% by weight of rare earth metal is prepared according to the process of the invention. The rare earth weight yield in the alloy expressed relative to the rare earths contained in the starting oxides is good since it varies from 80 to 95%.

(a - c) Al203, c TR2 3 + (TR2(a - c) s AC + 2c3 (III)
Lorsque le rapport 2a + b est supérieur ou égal à 10 et
2a inférieur à 40, on obtient un alliage plus riche en terres rares et l'oxyde mixte prépondérant est TR203, A1203. We introduce a number of moles of Al in excess (b), 73 times greater than that of Tu203
It has also been found that for a ratio of the number of moles Al to the number of moles TR less than 40, mixed oxides are formed according to the reaction a TR203 ± (2a + b) Al

(a - c) Al 2 O 3, c TR 2 3 + (TR 2 (a - c) s AC + 2c 3 (III)
When the ratio 2a + b is greater than or equal to 10 and
2a less than 40, a richer rare earth alloy is obtained and the predominant mixed oxide is TR203, Al 2 O 3.

 The alloy obtained contains from 9 to 30% by weight of rare earth metal but the yield decreases in the direction of the ratio and is between 15 and 80 Z.

 In a practical way, when the ratio is equal to 10, a number of moles of Al in excess 18 times greater than that of TR203 is introduced. The amounts of reactants to be introduced are easily calculated in the same manner when said ratio varies within the aforementioned range.

When we choose a ratio 2a + b less than 10, we
2a collects an alloy even richer in rare earths and a mixed oxide richer in rare earths 2 TR203, Al203. It is advantageous to choose a lower limit of the ratio equal to 3.

By choosing said ratio greater than or equal to 3 and less than 10, it is possible to obtain alloys containing at most 35% rare earth metal but the yield decreases to reach values as low as 10%.
The rare earth oxide (s) and aluminum constitute a "filler" having the desired weight composition. The constituents of this feed are first mixed until
a homogeneous mixture. We can perform this operation either
manually, using any suitable mechanical stirrer.

The reaction is carried out at a temperature greater than
700 ° C. Preferably, a temperature is chosen
between 9000C and 1100C.

The reaction is carried out under atmospheric pressure but
in an inert gas atmosphere. For this purpose, air is excluded by
lowering the pressure to a non-critical value, by
example between 1 and 200 mm of mercury then one assures a
inert gas sweep: rare gases, especially argon. It is
desirable to subject the rare gas to dehydration treatment
and deoxygenation carried out according to the usual techniques
for example by passing through a molecular sieve.

We maintain the inert atmosphere all during the
reduction.

The duration of the reaction depends on the ability to
appáreillage and its ability to rise quickly in tempera
ture. Generally, once the desired temperature is reached,
maintains it for a variable duration of approximately 1 hour to 24
hours.

During heating, a metallic phase is formed
formed by the alloy aluminum - rare earth metal on which
supersedes a powder consisting of an oxide of aluminum or oxides
mixtures whose composition depends on the molar ratio between alumina
nium and the rare earth metal.

At the end of the aforementioned heating time, the
heating.

We can immediately separate the liquid alloy from the
oxide powder (s) by making a skimming of the latter and then
pour it hot in a mold. We can also leave the mass
reaction to cool under an inert gas atmosphere
ambient temperature (15 to 25 ° C) so that the alloy solidifies and
can be easily separated from the oxide powder (s). I1 are then
unmolded.

 The method of the invention as described, can be implemented in a conventional type of apparatus used in metallurgy.

 The reduction is conducted in a crucible placed in a reactor resistant to the high temperature conditions of the reaction.

It may be chosen from refractory steel, for example steel containing 25% of chromium and 20% of nickel but preferably of inconel which is an alloy containing nickel, chromium (20%), iron (5%), molybdenum (8-10%).

Said reactor is equipped with a temperature control device (for example thermocouple), an inlet and an outlet of inert gases. It is provided in its upper part with a double envelope in which circulates a coolant.

 This reactor is placed in a furnace heated by electric resistances.

A crucible in which the temperature control device plunges is placed at the bottom of the reactor. It must be made of a material that supports high temperatures and does not contaminate the resulting alloy: it may be alumina or silicon carbide.

 Once the reaction is carried out, the molten alloy can be cast in molds, for example cast iron.

 It is found that the yield of rare earth metals expressed relative to the rare earth metals contained in the oxides involved varies from 10 to 95%.

 As mentioned earlier, the lower the content of rare earth metals in the alloy, the lower the yield.

 In the case where the yield is considered insufficient, for example, when it becomes less than 80%, another object of the invention is to provide a method for recovering the rare earth metals in the mixed oxides obtained.

 One variant of the invention therefore consists in dissolving the mixture of aluminum oxides and rare earth metals, in acidic medium, to selectively precipitate rare earth oxalates by adding an oxalate of alkali metal or alkaline earth or ammonium, and then subject the precipitate obtained to a calcination to recover the rare earth metals in the form of their oxides.

 The mixture of mixed oxides is dissolved by etching in an acidic medium. This acidic medium consists of pure or dilute acids, alone or as a mixture. At least one of the following acids is used: hydrochloric acid, nitric acid and perchloric acid. Preferably, hydrochloric acid is used alone or as a mixture with nitric acid.

 The attack conditions vary according to the nature of the acid, its concentration and the reaction temperature.

 The attack is carried out under good conditions by putting the oxide powder in suspension in water and then adding pure acid and concentrated.

 The dry matter content of the aqueous starting slurry is not critical but is preferably between 25 and 70 g / l.

 The amount of added acid is such that a residual acidity of greater than 6N is obtained.

 The etching reaction may be carried out in a temperature range from room temperature (15 ° C to 250 ° C) up to the reflux temperature of the reaction medium.

 It is preferable to dissolve the said oxides in two stages: the first being carried out cold at room temperature because the attack reaction is quite violent.

The undissolved oxides are separated by filtration, and on the one hand a precipitate and a filtrate A containing the ions A1 and TR3 + are collected.

 The duration of this cold attack can vary between 4 and 5 hours.

 The precipitate obtained is subjected to a second attack, which is then carried out under heat at the reflux temperature of the reaction mixture.

 This operation can last between 4 and 72 hours.

 At the end of the attack, a very small amount of solid residue is collected which is then removed by filtration. We thus obtain a second filtrate B.

 The filtrate A and the filtrate B or the filtrates A and B which can be combined are brought to a pH of between 1 and 2 by addition of a basic agent, especially ammonia.

 The solution is boiled and then added with an alkali metal, alkaline earth metal or ammonium oxalate to precipitate the rare earth metals as their oxalate. Preferably, ammonium oxalate is used.

 The amount of oxalate added is at least equal to the stoichiometric amount but it is desirable to carry out an excess. This quantity (expressed by weight) is in general 15 to 20 times that of the initial oxide powder.

 The reaction medium is preferably maintained at its boiling point for 5 minutes while stirring well.

 The precipitate is then allowed to decant and its decantation can be accelerated by cooling with any suitable means.

 Filtration of the rare earth oxalate precipitate which is washed several times with a solution of oxalic acid (for example 30 g / l) acidified with nitric acid (40 cm3 per liter).

 Finally, the rare earth oxalates are calcined by heating in air at a temperature ranging between 8000 ° C. and 1000 ° C., preferably 90 ° C.

 Duration of calcination is not critical.

 Generally, 1 to 2 hours are enough.

 The rare earth metals are recovered in the form of their oxides, they are directly recyclable to be reduced by aluminum.

 According to this variant of the process of the invention, the rare earth metals contained in the mixed oxides are recovered with a very good yield since it is possible to obtain total yields of rare earth metals oscillating between 80% and 100%. .

The alloys obtained according to the present invention have the following weight composition
- from 65 to 99 Z of aluminum
- from 1 to 35 Z of rare earth metal
The preferred compositions of the alloys obtained are as follows:
- from 85 to 92 Z of aluminum
- from 8 to 15 Z of rare earth metal
The alloys obtained according to the process of the invention can be used in many fields.

For example, there may be mentioned nuclear applications where the aluminum-rare earth alloy used in reactor screens contains about 0.1% rare earth metal.

In the aerospace industry, alloys containing 1 to 10% rare earth metal are employed as refractory alloys.

Finally, we can note the influence of additions of rare earths (lanthanum, cerium, neodymium, mischmetal at a rate of 0.5 to 1%) on the machinability and the mechanical properties of aluminum or alloys based on 'aluminum.

 If the alloys of the invention do not have the desired composition for the intended application, they can serve as alloys and be diluted by aluminum introduced into powder or in the form of ingots in the molten alloy, generally between 6600C and 700 "C thereby obtaining the desired aluminum-rare earth alloy.

Before detailing the examples embodying the practical implementation of the invention, the methods for determining the various constituents of the alloy will be briefly described by the following techniques:
the rare earth metals are determined according to a method
chemical that consists
dissolving the alloy sample in an acidic medium,
to bring to the boil the resulting solution, and to add
ammonium oxalate in order to obtain oxalate from
rare earth,
. to calcine the oxalate of rare earth at 9O00C during
1 hour to turn it into oxide,
. to weigh the quantity of oxide obtained thus making it possible to
calculate the amount of rare earth contained in
alloy
the aluminum is titrated by atomic absorption.

 In the following description of the invention, an example is given (Example 1) of preparation of aluminum-rare earth alloy with a good primary yield (95%), and four examples (Examples 2 to 5) of preparation of alloys with low primary yields (less than 60%) and which required the implementation of the variant of the invention to recover the rare earth metals in the mixed oxides obtained.

 The following examples 3 illustrate the invention without limiting its scope. The percentages mentioned in the examples are expressed by weight. It will be noted that the "input-output" material balances generally indicate a metal loss TR of between 0.6 and 3.6.

EXAMPLE 1
Preparation of an aluminum-gadolinium alloy containing 12.1%
gadolinium
A mixture of 130 g of gadolinium oxide with 99% purity and 868 g of aluminum powder of the same purity is carried out, the quantities engaged are such that the ratio 2a + b previously defined is equal to 45. 2a
The aluminothermic reduction reaction of the gadolinium oxide is carried out in a 1 liter alumina crucible placed at the bottom of an inconel reactor which is equipped with an inlet and an outlet of argon and an thermocouple introduced into a thermowell that is immersed in the reaction medium contained in the crucible: the upper part of the reactor is provided with a jacket in which circulates cold water (about 10 C).

 The mixture obtained is introduced into the bottom of the crucible, which is then returned to the reactor which is closed, the pressure is lowered to around 20 mm of mercury in order to expel the air and then a dry argon sweep is made which will be maintained throughout the reaction.

 At the same time, a rise in temperature is carried out until the temperature set at 1050 ° C. is reached, this temperature being held constant for about 10 hours.

 After slug cooling of the reactor, an ingot having a mass of 887 g and 101 g of an oxide powder consisting essentially of alumina is collected, as shown by X-ray analysis (Debye and Scherrer method in transmission). .

 An aluminum-gadolinium alloy having a mean gadolinium content of 12.1% is obtained.

 The primary gadolinium yield expressed relative to the gadolinium contained in the gadolinium oxide is 95% (Table I).

TABLE I

<tb><SEP> load <SEP> initial <SEP> products <SEP> obtained
<tb> mass <SEP> of <SEP> Gd2O3 <SEP>: <SEP> 130 <SEP> g <SEP> alloy <SEP>:
<tb> 23 <SEP>
<tb><SEP> - <SEP><SEP> nug of <SEP> ingot <SEP>: <SEP> 887 <SEP> g
<tb><SEP> - <SEP> content <SEP> in <SEP> Gd <SEP>: <SEP> 12.1 <SEP>% <SEP>
<tb> mass <SEP> of <SEP> Al <SEP>: <SEP> 868 <SEP> g
<tb> (2a <SEP> + <SEP> b) <SEP> / <SEP> 2 <SEP> a <SEP>: <SEP> 45 <SEP> mass <SEP> of <SEP> the <SEP> powder <SEP>: <SEP> 101 <SEP> g
<tb>. <SEP> Yield <SEP> in <SEP> Gd <SEP>: <SEP> (1) <SEP> without <SEP> recovery <SEP>: <SEP> 95.0 <SEP>%
<Tb>
EXAMPLE 2
The procedure used is similar to that described in Example 1 but the temperature was maintained at 10000C for 5 hours. As regards the initial charge introduced into an alumina crucible, it has been sought to obtain a value of the ratio 2a + b close to 30; the weight of gadolinium oxide is 5.9 g
2a and that of aluminum of 26.5 g.

 After reaction, a 24.1 g ingot grading 12.1% gadolinium (Table II) is obtained.

 Since the primary yield is only 57%, the gadolinium contained in the 8.1 g of mixed oxide powder obtained is recovered.

 An operating procedure specifying this recovery treatment is given below.

 The etching of 6.9 g of oxides powder at room temperature (230 ° C.) is carried out using 300 cm 3 of 6N hydrochloric acid. The duration of this cold attack, with stirring, lasts 4 hours.

 The undissolved oxides are separated, ie 2.2 g by Buchner filtration.

 A filtrate is collected which is brought to pH = 2 by adding ammonia and then boiling.

 30 g of ammonium oxalate are then added and the boiling is continued for 5 minutes.

 The decantation of the gadolinium oxalate precipitate obtained by cooling in ice is accelerated, generally for at least 4 hours.

 The precipitate obtained is filtered and washed several times with a solution containing 30 g / l of oxalic acid and 40 cm3 / 1 of nitric acid.

 The 2.2 g of undissolved oxides recovered after the first attack is subjected to a second attack carried out by the addition of 300 cm 3 of 6N hydrochloric acid at the reflux temperature of the reaction mixture. The heating is maintained for 4 hours.

 A solid residue is filtered off in a very small amount.

 On the filtrate obtained, the precipitation of gadolinium oxalate, which is filtered on Büchcer and also washed identically, is carried out in a manner similar to that described above.

 The two gadolinium oxalate precipitates obtained are combined and calcined in a muffle furnace at 1000 ° C. for 1 hour.

 Thus, after carrying out the treatment described above on the 8.1 g of oxide powder, 1.86 g of gadolinium was thus recovered, which corresponds to an overall yield of 93.4%.

TABLE II

<tb><SEP> recovered
<tb><SEP> load <SEP> initial <SEP> products <SEP> of <SEP> Gd <SEP> powder
<tb><SEP> in <SEP> the <SEP> powder
<tb> mass <SEP> of <SEP> Gd203 <SEP>: <SEP> 5.9 <SEP> g <SEP> alloy <SEP>: <SEP> lere <SEP> attack <SEP>: <SEP> 1 , 14 <SEP> g
<tb><SEP> - <SEP> - <SEP> mass <SEP> of the <SEP> ingot <SEP>: <SEP> 24.1 <SEP> g
<tb><SEP> - <SEP> content <SEP> in <SEP> Gd <SEP>: <SEP> 12.1 <SEP>% <SEP>
<tb> mass <SEP> of <SEP> Al <SEP>: 26.5 <SEP> g <SEP> 2nd <SEP> attack <SEP>: <SEP> 0.72 <SEP> g
<tb><SEP> (residue <SEP>: <SEP> 1.18 <SEP> g)
<tb> (2a <SEP> + <SEP> b) <SEP> / <SEP> 2 <SEP> a <SEP>: 30.1 <SEP> mass <SEP> of <SEP> the <SEP> powder <SEP>:<SEP> 8.1 <SEP> g
<tb> Yields <SEP> in <SEP> Gd <SEP>: <SEP> (1) <SEP> without <SEP> Recovery <SEP>: <SEP> 57.0 <SEP>%
<tb><SEP> (2) <SEP> with <SEP> recovery <SEP>: <SEP> 93,4 <SEP>%
<Tb>
EXAMPLES 3, 4, 5
Preparation of rare-earth aluminum-rare earth alloys
strong in rare earth
The experiments corresponding to these last three examples are relative to different rare earths (neodymium for example 3, gadolinium for example 4 and yttrium for example 5) but were all carried out with values of ratio 2a + b (less than or equal to 15) according to a
2a procedure identical to that of example 2.

 The primary yields obtained (Tables III, IV and P) are all less than or equal to 30%.

 The rare earths contained in the mixed oxide powders were thus recovered according to the variant of the invention, which made it possible to reach overall yields of between 84 and 97%.

TABLE III

<tb>: <SEP> Mass <SEP> of <SEP> Nd <SEP> retrieved
<tb><SEP> load <SEP> initial <SEP> products <SEP> obtained <SEP> in <SEP> the <SEP> powder <SEP> I
<tb><SEP> mass <SEP> of <SEP> Nd2O3 <SEP>: <SEP> 38.0 <SEP> g <SEP> alloy <SEP>: <SEP> 1st <SEP> attack <SEP>: <SEP> 19.03 <SEP> g <SEP>
<tb><SEP> 23 <SEP>
<tb><SEP> - <SEP> mass <SEP> of the <SEP> ingot <SEP>: <SEP> 53.0 <SEP> g
<tb><SEP> - <SEP> content <SEP> in <SEP> Nd <SEP>: <SEP> 17,1 <SEP>%
<tb><SEP> mass <SEP> of <SEP> A1 <SEP>: <SEP> 92.0 <SEP> g <SEP> 2nd <SEP> attack <SEP>: <SEQ> 3.43 <SEP> g
<tb><SEP> (residue <SEP>: <SEP> 0.45 <SEP> g)
<tb><SEP> (2a <SEP> + <SEP> b) / - 2 <SEP> a <SEP> = <SEP> 15.0 <SEP> mass <SEP> of <SEP> the <SEP> powder <SEP>: <SEP> 73.1 <SEP> g
<tb><SEP> Yields <SEP> in <SEP> Nd <SEP>: <SEP> (1) <SEP> without <SEP> Recovery <SEP>: <SEP> 27.9 <SEP>%
<tb> (2) <SEP> with <SEP> recovery <SEP>: <SEP> 96.9 <SEP>%
<Tb>
TABLE IV

<tb><SEP> Hasse <SEP> of <SEP> Gd <SEP> Recovered
<tb><SEP> load <SEP> initial <SEP> products <SEP> obtained <SEP> Nasse <SEP> from <SEP> G '! <SEP> recovered <SEP>
<tb><SEP> in <SEP> the <SEP> powder
<tb><SEP> p <SEP> load <SEP> initial <SEP> products <SEP> obtained <SEP> in <SEP> the <SEP> powder
<tb> mass <SEP> of <SEP> Gd2O3 <SEP>: <SEP> 25.0 <SEP> g <SEP> alloy <SEP>: <SEP> 1st <SEP> attack <SEP>: <SEP> 4 , 80 <SEP> g
<tb><SEP> - <SEP> mass <SEP> of the <SEP> ingot <SEP>: <SEP> 28.3 <SEP> g
<tb><SEP> - <SEP> content <SEP> in <SEP> Gd <SEP>: <SEP> 23 <SEP>%
<tb> net <SEP> of <SEP> Al <SEP>: <SEP> 36.7 <SEP> g <SEP>: <SEP> 2nd <SEP> attack <SEP>: <SEP> 8.00 <SEP > g
<tb><SEP> (residue <SEP>: <SEP> 0.66 <SEP> 0.66 <SEP> g)
<tb> (2a <SEP> + <SEP> b) <SEP> / <SEP> 2 <SEP> a <SEP> = <SEP> 9.8 <SEP> mass <SEP> of <SEP> the <SEP > powder <SEP>: <SEP> 31.2 <SEP> g
<tb> Yields <SEP> in <SEP> Gd <SEP>: <SEP> (1) <SEP> without <SEP> Recovery <SEP>: <SEP> 30.0 <SEP>%
<tb><SEP> (2) <SEP> with <SEP> recovery <SEP>: <SEP> 88.9 <SEP>%
<Tb>
TABLE V

<tb><SEP> load <SEP> initial <SEP> obtained <SEP> products <SEP> sse <SEP><SEP> of <SEP> Y <SEP><SEP> recovered <SEP>
<tb><SEP> in <SEP> initial <SEP> products <SEP> obtained <SEP> in <SEP><SEP> powder <SEP> J
<tb> J
<tb><SEP> mass <SEP> of <SEP> Y203 <SEP>: <SEP> 20.0 <SEP> g <SEP> alloy <SEP>: <SEP> lere <SEP> attack <SEP>: <SEP> 6.4 <SEP> g
<tb><SEP> - <SEP> mass <SEP> of the <SEP> ingot <SEP>: <SEP> 15.7 <SEP> g
<tb><SEP> - <SEP> content <SEP> in <SEP> Y <SEP>: <SEP> 15.3 <SEP>% <SEP>
<tb><SEP> mass <SEP> of <SEP> Al <SEP>: <SEP> 43.0 <SEP> g <SEP> 2nd <SEP> attack <SEP>: <SEP> 4.5 <SEP> g
<tb><SEP> (residue <SEP>: <SEP> 0.10 <SEP> g)
<tb><SEP> (2a <SEP> + <SEP> b) <SEP> / <SEP> 2 <SEP> a <SEP> = <SEP> 9.0 <SEP> mass <SEP> of <SEP> the <SEP> powder <SEP>: <SEP> 45.3 <SEP> g
<tb><SEP> Yields <SEP> in <SEP> Y <SEP>: <SEP> (1) <SEP> without <SEP> Recovery <SEP>: <SEP> 15.3 <SEP>% <SEP>
<tb><SEP> (2) <SEP> with <SEP> recovery <SEP>: <SEP> 84.7 <SEP>% <SEP>
<Tb>

Claims (26)

1 - A process for preparing an aluminum alloy containing a low content of rare earths, characterized in that it consists in reducing at least one metal oxide of a rare earth with aluminum, at a higher temperature at 700 ° C. 2 - Process according to claim 1 characterized in that the rare earth metal oxide is yttrium oxide or lanthanide such as lanthanum, cerium, praseodymium, neodymium, samarium, europium , gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium or a mixture of these oxides or mixed oxides of light rare earth metals from monazite or from the bastnàsite. 3 - Process according to one of claims l and 2 characterized in that the rare earth oxide and aluminum have a purity of at least 99 Z. 4 - Process according to one of claims 1 to 3 characterized in that the ratio between the number of moles of aluminum and the number of moles of rare earth metal 2a + b is greater than or equal to 40. 2a 5 - Method according to one of claims 1 to 3 characterized in that the ratio between the number of moles of aluminum and the number of moles of rare earth metal 2a + b is greater than or equal to 10 and less than 40. 2a 6 - Process according to one of Claims 1 to 3, characterized in that the ratio between the number of moles of aluminum and the number of moles of rare earth metal 2a + b is greater than or equal to 3 and less than 10. 2a 7 - Method according to one of claims 1 to 6 characterized in that one carries out a homogeneous mixture of the rare earth oxide with aluminum. 8 - Process according to one of claims 1 to 7 characterized in that the reaction is carried out under atmospheric pressure, but in an inert gas atmosphere. 9 - Process according to one of claims 1 to 8 characterized in that the reaction is carried out at a temperature between 900 ° C and 1100 C. 10 - Process according to claim 8 characterized in that one carries out an inert gas atmosphere by exclusion of air, ~ then by scanning dry argon. 11 - Process according to one of claims 1 to 10 characterized in that one maintains the selected temperature for a period ranging from 1 hour to 24 hours. 12 - Process according to one of claims 1 to 11 characterized in that one separates the liquid alloy of the oxide powder (s) by performing a skimming of the latter and that one collects the alloy either by hot casting in a mold or after cooling under an inert gas atmosphere. 13 - Process for recovering the rare earth metals contained in the mixed oxide powder obtained according to claim 12 characterized in that it consists in operating the dissolution of the mixture of aluminum oxides and earth metals rare, in an acidic medium, to selectively precipitate rare earth oxalates by adding an alkali metal or alkaline earth oxalate or ammonium, and then to subject the precipitate obtained to a calcination to recover the rare earth metals under the shape of their oxides. 14 - Process according to claim 13 characterized in that the dissolution is carried out using hydrochloric acid alone or in mixture with nitric acid. 15 - Process according to one of claims 13 and 14 characterized in that one carries out a first acid attack cold mixed oxides at room temperature. 16 - Process according to claim 15 characterized in that the duration of the cold attack varies from 4 to 5 hours. 17 - Process according to one of claims 15 and 16 characterized in that the undissolved oxides are separated by filtration and that a filtrate A is collected. 18 - Process according to one of claims 15 to 17 characterized in that it carries out a second acid attack of undissolved oxides at the reflux temperature of the reaction mixture. 19 - Process according to claim 18 characterized in that the duration of the attack varies between 4 and 72 hours. 20 - Method according to one of claims 18 and 19 characterized in that the solid residue is separated by filtration and that a filtrate is collected B 21 - Method according to one of claims 17 and 20 characterized by the The filtrate A and the filtrate B or the combined filtrates A and B are brought to a pH of between 1 and 2. 22 - Process according to claim 21 characterized in that one adds the oxalate of alkali metal or alkaline earth or ammonium. 23 - Process according to claim 22 characterized in that the amount of oxalate is at least equal to the stoichiometric amount or in excess representing 15 to 20 times the weight of the initial oxide powder. 24 - Method according to one of claims 22 and 23 characterized in that the stirring medium is maintained at its boiling point for 5 minutes. 25 - Method according to one of claims 22 to 24 characterized in that is filtered after decantation, the rare earth oxalate precipitate. 26 - Process according to claim 25, characterized in that one or more washing of the precipitate is carried out with a solution of oxalic acid acidified with nitric acid. 27 - Process according to one of claims 21 to 26 characterized in that one carries out the calcination of rare earth oxalate at a temperature ranging between 8O00C and 1000 "C. 28 - Process according to claim 27 characterized in that the calcination time is 1 to 2 hours. 29 - Aluminum alloy obtained according to claim 4 containing less than 15% by weight of rare earth metal. Aluminum alloy obtained according to claim 5 containing from 9 to 30% by weight of rare earth metal. 31 - Aluminum alloy obtained according to claim 6 containing up to 35% by weight of rare earth metal.