Recovery of gallium/rare earth values from oxide mixtures thereof
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 670,061, filed Nov. 9, 1984, now abandoned, which is a continuation-in-part of Ser. No. 360,559, filed Mar. 22, 1982, now abandoned, which in turn is a continuation of Ser. No. 162,492, filed June 24, 1980, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for the treatment of particulate admixtures of rare earth oxides and gallium oxides, and, more especially, relates to the recovery of gallium and rare earth values from mixed oxides thereof, e.g., from the waste fines which result upon production of garnets, by acidulation/dissolution of such admixtures, followed by liquid/liquid extraction, phase separation and ultimate recovery. 
     2. Description of the Prior Art 
     It is currently virtually impossible to produce gallium/rare earth garnets in yields in excess of 40%. This is due to the large number of off-standard garnets, namely, crucible residues, cutting residues and polishing residues, i.e., waste fines. The recovery of the raw starting materials originating from these various sources constitutes a most significant problem in view of the cost of the gallium oxides and the rare earth oxides. 
     SUMMARY OF THE INVENTION 
     Accordingly, a major object of the present invention is the provision of an improved process for the treatment of mixtures of rare earth oxides and gallium oxides, enabling, on the one hand, the recovery of gallium, and on the other hand the recovery of the rare earths, in very high yields and, in certain cases, very high in purity. 
     Briefly, the present invention features a process for the treatment of particulate admixtures of rare earth oxides and gallium oxides, characterized in that such mixture is dissolved in acid, the gallium and the rare earths are separated into two solutions and the gallium and the rare earths are then recovered therefrom. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE of Drawing is a diagrammatic illustration of a liquid/liquid extraction unit suitable for carrying out the process according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     More particularly according to the present invention, the expression &#34;mixtures of rare earth oxides and gallium oxides&#34;, or like terminology, is to be understood as meaning either mixtures of simple gallium oxides and simple rare earth oxides, or mixed oxides containing at least some gallium and at least one rare earth. The term rare earth is to be understood as meaning at least one element taken from the group comprising the lanthanides (the elements having an atomic number ranging from 57 to 71 inclusive) and yttrium (the element having an atomic number of 39). 
     More precisely, the mixtures of rare earth oxides and gallium oxides which can be treated in accordance with the process of the present invention contain at least a mixture of Ga 2  O 3  and RE 2  O 3  (RE representing an element selected from among the group comprising the rare earths) and/or one mixed oxide of the formula (RE) x  (Ga) y  O z , in which x, y and z are any numbers (RE representing at least one element taken from the group comprising the rare earths), it being understood that this mixed oxide can contain elements other than Ga and RE by way of substitution and/or inclusion in the structure of the mixed oxide. 
     A preferred emobdiment of the process according to the invention involves the treatment of mixed oxides containing at least some gallium and at least one rare earth and/or waste and/or residues from the production of the said mixed oxides. 
     Purely by way of illustration, the mixed oxides which can be treated in accordance with the process of the invention are, in particular: 
     (1) Mixed oxides having a structure of the garnet type. 
     Among such mixed oxides, exemplary are those having the formula: ##STR1## in which RE is at least one element selected from the group comprising gadolinium, yttrium, samarium and neodymium, A is selected from the group comprising aluminium and scandium, α=±0.20, and 0&lt;x&lt;1. 
     Also exemplary of the class are the mixed oxides of the formula: 
     
         (RE.sub.1).sub.3-x-y (RE.sub.2).sub.x M.sub.x Fe.sub.5-z Ga.sub.z Ge.sub.y O.sub.12 
    
     in which O&lt;x&lt;0.5, y≧O, O&lt;z≦1.5, RE 1  is selected from the group comprising yttrium and lutetium, RE 2  is selected from the group comprising samarium and europium in the trivalent state, and M is calcium. 
     Also exemplary of this class are the mixed oxides of the formula: 
     
         RE.sub.3-x M.sub.x Ga.sub.5-x A.sub.x O.sub.12 
    
     in which O≦x&lt;1, RE is at least one element selected from the group comprising gadolinium, samarium and neodymium, M is selected from the group comprising calcium, strontium and magnesium, and A is selected from the group comprising tin and zirconium. 
     Also exemplary are the mixed oxides of the formula: 
     
         (RE).sub.3-x Bi.sub.x Fe.sub.5-y A.sub.y O.sub.12 
    
     in which 0.2&lt;x&lt;2, O&lt;y&lt;1.5, RE is at least one element selected from the group comprising yttrium, neodymium, samarium and gadolinium, A=Ga 1- α M.sub.α with O≦α&lt;1, and M is selected from the group comprising aluminum, indium and scandium. 
     Also exemplary are the mixed oxides of the formula: 
     
         Y.sub.3 Al.sub.5-x Ga.sub.x O.sub.12 :Ce.sup.3+ 
    
     in which O&lt;x≦5. 
     (2) Mixed oxides having a structure of orthogallate type. 
     In this class, exemplary are the mixed oxides of the formula: 
     
         (RE)MO.sub.3 :Nd.sup.3+ 
    
     in which RE is at least one element selected from the group comprising yttrium, gadolinium, lutetium and lanthanum, and M=Al 1-x  Ga x  with O&lt;x≦1. 
     (3) Mixed oxides having a structure of spinel type. 
     In this class, exemplary are, the mixed oxides of the formula: 
     
         MA.sub.2 O.sub.4 :Eu.sup.2+ 
    
     in which M is an element selected from the group comprising magnesium, calcium, barium and strontium, and A=Ga x  Al 1-x  with 0&lt;x≦1. 
     (4) Mixed oxides having a structure of the magnetoplombite type. 
     In this class, exemplary are the mixed oxides of the formulae: ##STR2## in which M is an element selected from the group comprising magnesium, calcium, strontium and barium, RE is at least one element selected from the group comprising cerium in the trivalent state and gadolinium, and A=Al 1-x  Ga x  with 0&lt;x≦1. 
     More particularly, it is envisaged to treat gadolinium/gallium garnets and/or waste and/or residues from the production of the said garnets. These garnets correspond to the formula Gd 3  Ga 5  O 12 . 
     The production residues, or waste fines, treated in accordance with the process of the present invention can originate, in particular, from the crucible residues formed during the production of mixtures of rare earth oxides and gallium oxides and/or from cutting residues and/or from polishing residues of the said mixtures. 
     The production waste treated in accordance with the process of the present invention generally consists of mixed oxides, the composition and/or structure of which deviate from the standards defined for these products. 
     In certain cases and, in particular, when treating cutting or polishing residues, it can be advantageous to remove the organic materials present in these residues by means of processes which are well known to those skilled in the art, such as treatment on active charcoal or on adsorbent polymers or treatment by extraction into an organic phase which is noncomplexing with respect to the gallium and the rare earths. 
     One of the advantages of the process according to the present invention is that it enables treatment of all such waste and/or these residues regardless of their origin. 
     The subject mixture is dissolved by means of attack by an acid medium. This acid medium consists of pure or dilute acids, by themselves or in a mixture. It is preferred to use at least one acid selected from the group comprising hydrochloric acid, nitric acid, sulfuric acid, perchloric acid and phosphoric acid. The nature of the acid is preferably selected in accordance with the subsequent separation step; hydrochloric acid or nitric acid is advantageously used. 
     The conditions of attack, or acidulation/dissolution, vary according to the acids used; the speed of attack depends, in particular, on the nature of the acid, its concentration and the temperature. Good conditions are generally achieved when the attack is carried out with concentrated pure acids under boil. 
     According to the process of the invention, it is advantageous to effectuate a certain residual acidity of the medium after attack has taken place; for this purpose, attack can be carried out under reflux, using an excess of acid, relative to stoichiometry. The production of a residual acidity of more than 2N is especially advantageous. 
     The size of the particles attacked is not a critical factor according to the process of the invention; however, if fairly rapid attack is desired, it is advantageous to use particles having a fairly fine size, and preferably particles having a diameter of less than about 400 microns; more particularly, the process is quite easy to carry out if particles having a diameter of between about 50 and 200 microns are used. 
     The concentration of dissolved oxides in the solutions obtained is adjusted, in a manner known to those skilled in the art, by the conditions under which attack is carried out. For the purpose of the subsequent separation step, it can be advantageous to obtain the highest possible concentrations and preferably concentrations of more than 100 g/liter. In the particular case where attack is carried out in a hydrochloric acid or nitric acid medium, concentrations of about 400 g/liter of dissolved oxide can be achieved, and these are especially favorable for the separation. 
     The step involving separation of the gallium and the rare earths into two solutions is carried out by means of liquid/liquid extration, the aqueous solution resulting from attack being brought into contact with an organic phase containing at least one-water-insoluble extraction agent, optionally dissolved in a diluent. 
     The extraction agent used in accordance with the process of the invention is selected from the class of the anionic extraction agents, the class of the solvating extraction agents or the class of the cationic extraction agents. 
     The anionic extraction agents used are, in particular, long-chain organic compounds containing primary, secondary or tertiary amine groups, or quaternary ammonium, sulfonium or phosphonium salts. 
     Preferably, the hydrocarbon chains of these compounds generally have between about 5 and 30 carbon atoms. 
     Examples of such extractants are: 
     The products marketed under the trademark Primene JM and consisting of primary amines of the formula: ##STR3## in which R is a hydrocarbon radical having from 18 to 24 carbon atoms; 
     The products marketed under the trademark Amberlite LA-1 and consisting of secondary amines of the formula: ##STR4## in which the hydrocarbon radicals R 1 , R 2  and R 3  are such that the sum of the carbon atoms therein is between 12 and 14; 
     The products marketed under the trademarks Alamine 336 and Adogen 364 and consisting of tertiary amines of the formula R 3  N, in which the hydrocarbon radical R has from 8 to 10 carbon atoms; 
     The products marketed under the trademarks Adogen 464 and Aliquat 336 and consisting of quaternary ammonium salts of the formula: ##STR5## in which the hydrocarbon radical R has from 8 to 10 carbon atoms and X represents an anion, preferably chloride, nitrate or sulfate; and 
     The sulfonium salts of the general formula: ##STR6## in which the hydrocarbon radical R has from 10 to 18 carbon atoms and X represents an anion, preferably chloride or nitrate. 
     The amines and the quaternary ammonium salts described in U.S. Pat. Nos. 3,294,494 2,877,250 too are exemplary. 
     Depending upon the nature of the anion present in the aqueous attacking solution, either the gallium or the rare earths are preferentially extracted into the organic phase by the anionic extraction agent. Thus, in a chloride medium, the gallium is preferentially extracted, whereas, in a nitrate or sulfate medium, it is the rare earths which are preferentially extracted into the organic phase. 
     Furthermore, in a chloride medium, all of the aforesaid anionic agents can be used. In a nitrate medium, the tertiary amines or the quaternary ammonium salts are preferably used, and, in a sulfate medium, the primary amines are preferably used. 
     In order to favor or aid the extraction, it can be advantageous, in a chloride medium, to add hydrochloric acid to the aqueous phase. It is necessary for the molar concentration of acid in the aqueous phase to be at least equal to the molar concentration of the gallium. 
     Depending upon the nature of the anion present in the aqueous phase, it can also be advantageous to add, to the latter, non-extractable neutral salts, namely, respectively, chlorides, nitrates or sulfates of alkali metals, alkaline earth metals or aluminum. 
     The solvating extraction agents used are, in particular, esters, ethers, sulfoxides, ketones and alcohols, neutral organophosphorus compounds and trialkylamine oxides. 
     Solvating extraction agents which are exemplary are: 
     The esters of the general formula: ##STR7## in which R 1  and R 2  are aromatic and/or aliphatic hydrocarbon radicals preferably having at least 4 carbon atoms, for example, ethyl acetate and butyl acetate; 
     The ethers of the general formula R 1  --O--R 2 , in which R 1  and R 2  are aromatic and/or aliphatic hydrocarbon radicals preferably having at least 4 carbon atoms, for example, diethyl ether and isopropyl and di-n-butyl ethers; 
     The sulfoxides of the general formula: ##STR8## in which R 1  and R 2  are aromatic and/or aliphatic hydrocarbon radicals preferably having at least 4 carbon atoms, for example di-n-pentylsulfoxide, di-n-octylsulfoxide and diphenylsulfoxide; 
     The ketones of the general formula: ##STR9## in which R 1  and R 2  are aromatic and/or aliphatic hydrocarbon radicals preferably having at least 4 carbon atoms, for example, diisopropyl ketone, methyl isobutyl ketone and mesityl oxide; 
     The alcohols of the general formula ROH, in which R is an aliphatic and/or cycloaliphatic hydrocarbon radical preferably having at least 4 carbon atoms, for example cyclohexanol, n-hexan-1-ol, 2-ethylhexanol, n-heptanol and n-octanol; 
     The neutral organophosphorus compounds of the general formulae: ##STR10## in which R 1 , R 2  and R 3  represent aromatic and/or aliphatic hydrocarbon radicals preferably having at least 4 carbon atoms, for example, the stearyl and cetyl esters of phosphoric acid, tributyl phosphate, dibutyl butylphosphonate, 2-ethylhexyl bis-(2-ethylhexyl) phosphonate, butyl bis-(chloromethyl) phosphonate and tri-n-octylphosphine oxide. Among such compounds, it is preferred to use tributyl phosphate; and 
     The trialkylamine oxides of the general formula R 3  N═O, in which R is an aliphatic hydrocarbon radical preferably having at least 4 carbon atoms, for example, trioctylamine oxide. 
     Depending upon the nature of the anion present in the aqueous attacking solution, either the gallium or the rare earths are preferentially extracted into the organic phase by the solvating extraction agent. Thus, in a chloride medium, the gallium is preferentially extracted, whereas, in a nitrate medium, it is the rare earths which are preferentially extracted into the organic phase. 
     Furthermore, in a chloride medium, any solvating agent can be used. In a nitrate medium, the organophosphorus derivatives and the sulfoxides are preferably used. 
     When the solvating extraction agents are used in a chloride medium, it is advisable for the molar concentration of acid in the aqueous phase to be at least equal to the molar concentration of the gallium in the aqueous attacking solution; for this purpose, it can also be advantageous to add hydrochloric acid to the attacking solution in order to carry out the separation of the gallium solution and the rare earth solution under good conditions. 
     In order to favor extraction, it can be advantageous to add, to the aqueous phase, non-extractable neutral salts such as, for example, the chlorides or nitrates of alkali metals, alkaline earth metals or aluminum. 
     The cationic extraction agents used are, in particular, organophosphorus acids, aliphatic or aromatic acids, halogen-containing aliphatic, aromatic or cycloaliphatic acids, naphthenic acids, heavy acid fractions, sulfonic acids, &#34;Versatic&#34; acids and β-diketones. 
     Cationic extraction agents which are exemplary include: 
     The organophosphorus acids of the general formulae: ##STR11## in which R 1  and R 2  represent aliphatic or aromatic hydrocarbon radicals which are such that the total number of carbon atoms in these groups is equal to at least 10. Bis-(2-ethylhexyl)phosphoric acid and bis-(2-ethylhexyl)-phosphonic acid are preferably used; 
     Aliphatic acids in which the hydrocarbon radicals have from 3 to 20 carbon atoms, in particular butanoic, valeric, octoic, caproic, caprylic, capric, pelargonic and lauric acids; 
     Halogen-containing aliphatic, aromatic or cycloaliphatic acids, such as, for example, alpha-bromolauric acid; 
     The naphthenic acids having the general formula: ##STR12## in which n is &gt;1; 
     Heavy acid fractions containing, in particular, mixtures of C 5  -C 6 , C 7  -C 9 , C 9  -C 11 , C 10  -C 16 , C 10  -C 13  and C 12  -C 16  acids; 
     Sulfonic acids, such as di-nonylnaphthalene-sulfonic acid; 
     The &#34;Versatic&#34; acids (registered trademark of the Societe Shell Chemicals) having the general formula: ##STR13## in which R 1  and R 2  are substituted or unsubstituted hydrocarbon radicals, in particular &#34;Versatic 911&#34; acid (registered trademark of Shell Chemicals) which is a mixture of saturated tertiary monocarboxylic acids in which R 1  and R 2  are hydrocarbon radicals in which the sum of the carbon atoms in the two radicals is equal to 6, 7 or 8, and which is manufactured by the oxo synthesis from C 9  -C 11  olefins; &#34;Versatic 15/19&#34; acid (registered trademark of Shell Chemicals) in which R 1  is a hexyl radical and R 2  is an octyl radical; and &#34;Versatic 10&#34; acid (registered trademark of Shell Chemicals) which is derived by the Shell process for the carboxylation of C 9  olefins and in which R 1  and R 2  are hydrocarbon radicals in which the sum of the carbon atoms in the two radicals is equal to 7; and 
     β-Diketones, such as acetylacetone. 
     Since the selectivities observed when using cationic extraction agents are generally lower than in the case of anionic and solvating agents, it may be preferred, according to the invention, to use these latter two classes of extraction agents in order to achieve efficient separations under the most advantageous economic conditions. 
     The proportion of extraction agent in the organic phase is not critical and can vary over wide limits. However, it is generally advantageous if the proportion is as high as possible. Thus, in the case of anionic and cationic extraction agents, a proportion of between 10 and 40% by volume, relative to the organic phase, leads to advantageous hydrodynamic conditions of separation. In the case of solvating extraction agents, some of them (the least viscous) can be used pure, i.e., undiluted, and this is extremely advantageous because it affords very large extraction capacities. 
     The diluents used in accordance with the process of the invention are those diluents which are normally used for liquid/liquid extraction. They can be used either by themselves or in a mixture. The diluents which are exemplary include aliphatic compounds, such as, for example, heptane, dodecane, hexane and petroleum cuts of the kerosene type, aromatic compounds, such as, for example, benzene, toluene, ethylbenzene, xylene and cuts of the Solvesso type (registered trademark of the Societe Exxon), and finally halogen derivatives of these compounds, such as, for example, chloroform and carbon tetrachloride. 
     As is well known in the field of liquid/liquid extraction, the organic phase can also contain modifiers. Exemplary modifiers include substances with an alcohol group, in particular heavy alcohols in which the number of carbon atoms is between 6 and 15, such as n-decanol and isodecanol, and heavy phenols, such as nonylphenol. 
     The step involving separation of the gallium and the rare earths into two solutions leads to the production of an aqueous solution which contains the element or elements which have not been extracted from the attacking solution, and of an organic solution which contains the element or elements which have been extracted. As hereinabove described, either the gallium or the rare earths are extracted into the organic solution, depending upon the nature of the anion present in the attacking solution. 
     The step involving recovery, in aqueous solution, of the gallium or the rare earths which have been extracted into the organic solution is carried out: 
     In the case where anionic or solvating agents have been used for the separation, by bringing this organic solution into contact with water or a weakly acid aqueous solution in which the concentration of H +   ions is preferably less than or equal to 0.1N, the extracted element or elements transferring from the organic phase into the aqueous phase; or 
     In the case where a cationic agent has been used for the separation, by bringing this organic solution into contact with an aqueous solution of a strong acid. The strong acid used can be identical to or different from that used for attack, the extracted element or elements transferring from the organic phase into the acid aqueous solution. The concentration of acid used is adjusted according to the nature of the extraction agent and to the desired concentration of the element recovered in the aqueous phase. 
     Starting from the neutral or aqueous acid solutions obtained in this way, the gallium and the rare earths can be recovered after an optional complementary purification by the usual methods. 
     As is well known, this complementary purification can in particular consist, in the case of the rare earth or rare earths, of the precipitation of the hydroxides, oxalates or carbonates and, in the case of the gallium, of the precipitation of gallium trioxide or of electrolysis in order to obtain gallium metal. 
     Furthermore, the process of the present invention makes it possible, in certain cases, to obtain a gallium solution, the purity of which is such that it can be used to prepare a gallium oxide of sufficient purity for direct reuse in the manufacture of the mixed oxides. 
     The separation and recovery steps can be carried out in the conventional devices employed for liquid/liquid extraction processes. Such devices generally comprise several stages of mixer-settler systems, or of packed and/or stirred columns, which are arranged for carrying out the operations of extraction, selective washing and recovery of the extracted elements in aqueous phase. 
     In order to further illustrate the present invention and the advantages thereof, the following specific examples are given, it being understood that same are intended only as illustrative and in nowise limitative. 
     EXAMPLE 1 
     The following example illustrates the acid attack, or acidulation/dissolution, of residues or waste fines emanating from the production of gallium/gadolinium garnets, Gd 3  Ga 5  O 12  corresponding to the composition of gallium and gadolinium, expressed as oxides, of 54% by weight of Gd 2  O 3  and 46% by weight of Ga 2  O 3 . 
     These residues were ground in order to obtain a powder having a mean particle diameter of about 200 microns (90% of the particles having a diameter of between 100 and 300 microns). 
     One gram of powder was contacted, at a boil and under reflux, with 25 ml of acid of various concentrations, for y hours, under stirring. The Table below summarizes the results obtained regarding the percentage by weight of garnet solubilized and the residual acidity of the resulting solution A, B, C, D, E, F, G or H. 
     
                                           TABLE I                                 
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                          %                                               
             Concentration                                                
                     Time of                                              
                          Solubilized                                     
                                Residual                                  
             in %    attack y                                             
                          (greater                                        
                                acidity                                   
Solution                                                                  
     Acid    by weight                                                    
                     in hours                                             
                          than) (normality)                               
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A    HNO.sub.3   64  6    &gt;99   13                                        
B    HCl         36  3    &gt;99   11                                        
C    HNO.sub.3 /HCl                                                       
             HCl 24       &gt;99                                             
     mixture HNO.sub.3                                                    
                 21  5    &gt;99   11.7                                      
D    H.sub.3 PO.sub.4                                                     
                 85  3    &gt;99   14                                        
E    H.sub.2 SO.sub.4                                                     
                 95  4    &gt;99   17                                        
F    HCl/H.sub.2 SO.sub.4                                                 
             HCl 18  3    &gt;99   14                                        
     mixture H.sub.2 SO.sub.4                                             
                 47.5                                                     
G    HNO.sub.3 /H.sub.2 SO.sub.4                                          
             H.sub.2 SO.sub.4                                             
                 47.5                                                     
                     3    &gt;99   15                                        
     mixture HNO.sub.3                                                    
                 32                                                       
H    H.sub.3 PO.sub.4 /H.sub.2 SO.sub.4                                   
             H.sub.3 PO.sub.4                                             
                 42.5                                                     
                     4    &gt;99   15.5                                      
     mixture H.sub.2 SO.sub.4                                             
                 47.5                                                     
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     EXAMPLE 2 
     330 grams of a powder as obtained in accordance with Example 1 were contacted, under reflux, with 1 liter of boiling 10N nitric acid for 20 hours; the efficiency of attack was greater than 99% and the residual acidity was 2N. 
     The resulting solution contained gallium and gadolinium in the following concentrations: 
     Ga 2  O 3  : 150 g/liter, which corresponds to Ga: 112 g/liter. 
     Gd 2  O 3  : 176 g/liter, which corresponds to Gd: 153 g/liter. 
     The separation and the recovery of the gallium and the gadolinium from this solution were carried out in a multistage liquid/liquid extractor, with the organic and aqueous phases circulating in countercurrent. This extraction device is represented diagrammatically in the Figure of Drawing. It comprised an extraction section E, composed of seven (7) stages, a selective washing section L, composed of six (6) stages, and a regeneration section R, composed of four (4) stages. The organic phase containing the extraction agent was circulated successively through the sections E, L and R at a flow rate V. The feed solution (flow rate v A ) resulting from the acidulation/dissolution was injected into the extraction zone. The 4M ammonium nitrate solution (flow rate v L ) which performed the selective washing was introduced into the section L. The aqueous solution containing the purified gallium was recovered at the outlet of the extraction zone (flow rate v A  +v L ). A weakly acid aqueous solution, namely, 0.1N HNO 3 , was introduced into the section R (flow rate v R ). This aqueous phase was recovered at the outlet of the section R. It then contained the purified gadolinium. 
     The Table below summarizes, with reference to the Figure of Drawing, the flow rates employed and the results obtained in the case of: 
     (1) the use of an anionic extraction agent, namely, Aliquat 336 (in nitrate form) diluted to 0.5 mol/liter in Solvesso 150; and 
     (2) the use of a solvating extraction agent, namely, tributyl phosphate (TBP) diluted to 50% strength by volume in kerosene. 
     
                                           TABLE II                                
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              RESULTS                                                     
FLOW RATES    Solution of  Solution of                                    
V      V.sub.A                                                            
         V.sub.L                                                          
            V.sub.R                                                       
              purified gallium                                            
                           purified gadonlinium                           
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Aliquat                                                                   
    5.85                                                                  
       1 0.18                                                             
            1 Flow rate v.sub.A + v.sub.L = 1.18                          
                           Flow rate v.sub.R = 1                          
              Ga.sub.2 O.sub.3 : 127 g/liter                              
                           Gd.sub.2 O.sub.3 : 176 g/liter                 
              Gd.sub.2 O.sub.3 &lt; 1 mg/liter                               
                           Ga.sub.2 O.sub.3 &lt; 1 mg/liter                  
              Ga: 94.4 g/liter                                            
                           Gd: 153 g/liter                                
TBP 2.86                                                                  
       1 0.14                                                             
            1.3                                                           
              Flow rate = 1.14                                            
                           Flow rate = 1.3                                
              Ga.sub.2 O.sub.3 : 131.6 g/liter                            
                           Gd.sub.2 O.sub.3 : 134.6 g/liter               
              Gd.sub.2 O.sub.3 &lt; 1 mg/liter                               
                           Ga.sub.2 O.sub.3 &lt; 1 mg/liter                  
              Ga: 97.8 g/liter                                            
                           Gd: 116.6 g/liter                              
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     It has been determined that the process according to the invention enables obtainment of purified solutions containing less than 10 ppm of each element Ga or Gd in the other element. 
     EXAMPLE 3 
     330 g of a powder as obtained in accordance with Example 1 were contacted, under reflux, with 1 liter of boiling 10N hydrochloric acid for 4 hours. The degree of attack was greater than 99%. 
     The resulting solution had the following composition: 
     Ga 2  O 3  : 150 g/liter, which corresponds to Ga: 112 g/liter 
     Gd 2  O 3  : 176 g/liter, which corresponds to Gd: 153 g/liter. 
     The separation and the recovery of the gallium and the gadolinium from this solution were carried out in the same multi-stage extractor as that described in Example 2. 
     The 0.1N hydrochloric acid solution (flow rate v L ) which performed the selective washing was introduced into the section L. The aqueous solution containing the purified gadolinium was recovered at the outlet of the extraction section (flow rate v A  +v L ). A weakly acid aqueous solution, namely, 0.1N HCl, was introduced into the section R (flow rate v R ). This aqueous phase was recovered at the outlet of the section R. It then contained the purified gallium. 
     The Table below summarizes, with reference to the Figure of Drawing, the flow rates employed and the results obtained in the case of: 
     (1) the use of an anionic extraction agent, namely, Aliquat 336 (in chloride form) diluted to 0.5 mol/liter in Solvesso 150; and 
     (2) the use of a solvating extraction agent, namely tributyl phosphate (TBP) diluted to 50% strength by volume in kerosene. 
     
                                           TABLE III                               
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              RESULTS                                                     
FLOW RATES    Solution of                                                 
                         Solution of                                      
V     V.sub.A                                                             
        V.sub.L                                                           
           V.sub.R                                                        
              purified gallium                                            
                         purified gadolinium                              
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Aliquat                                                                   
    5 1 0.25                                                              
           10 Flow rate v.sub.R = 10                                      
                         Flow rate v.sub.A + v.sub.L = 1.25               
              Ga.sub.2 O.sub.3 : 15 g/liter                               
                         Gd.sub.2 O.sub.3 : 140.8 g/liter                 
              Gd.sub.2 O.sub.3 : &lt; 1 mg/liter                             
                         Ga.sub.2 O.sub.3 &lt; 1 mg/liter                    
              Ga: 11.2 g/liter                                            
                         Gd: 122.4 g/liter                                
TBP 2.2                                                                   
      1 0.1                                                               
           2.2                                                            
              Flow rate = 2.2                                             
                         Flow rate = 1.1                                  
              Ga.sub.2 O.sub.3 : 68.2 g/liter                             
                         Gd.sub.2 O.sub.3 : 160 g/liter                   
              Gd.sub.2 O.sub.3 &lt; 1 mg/liter                               
                         Ga.sub.2 O.sub.3 &lt; 1 mg/liter                    
              Ga: 50.9 g/liter                                            
                         Gd: 139 g/liter                                  
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     As in the preceding example, the process according to the invention enables obtainment of purified solutions in only two steps (attack and separation by liquid/liquid extraction), under very advantageous economic conditions. It was noted that the gallium was present in the gadolinium in an amount of less than 10 ppm; in the case of the gadolinium present in the gallium, the purity indicated was at the analytical limits of the method of determination employed; although the solutions of purified gallium obtained are concentrated, less than 10 ppm of gadolinium in the gallium were in fact analyzed. 
     EXAMPLE 4 
     This example illustrates the treatment of residues of the manufacture of various crystals used in the electronics field (magnetic bubbles, semiconductors, laser crystals). 
     The residues were ground in a manner to obtain a powder the average particle diameter of which was approximately 200 microns. 
     300 g of the powder was placed in contact at boiling and with reflux with 1 liter of hydrochloric or nitric acid of different concentrations for y hours under agitation. The table below compiles the results obtained with respect to the % by wieght of solubilized crystals and the residual activity of the solution (Table IV). 
     
                                           TABLE IV                                
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           Solu-                                                          
              Normal Con-                                                 
                     Treatment                                            
                           % Solu-                                        
                                Residual                                  
                                     [Ga]                                 
                                         [Tr]                             
Compounds                                                                 
       Acid                                                               
           tion                                                           
              centration                                                  
                     Time, H                                              
                           bility                                         
                                Acidity                                   
                                     g/l g/l                              
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Y.sub.3 Ga.sub.5 O.sub.12                                                 
       HCl A  10 N   14    99   2.2 N                                     
                                     129 100                              
       HNO.sub.3                                                          
           B  10 N   15    99   2.2 N                                     
                                     129 100                              
Sm.sub.3 Ga.sub.5 O.sub.12                                                
       HCl C  10 N   14    99   2.2 N                                     
                                     105 150                              
       HNO.sub.3                                                          
           D  10 N   15    99   2.1 N                                     
                                     105 150                              
Gd.sub.2 CaGa.sub.5 O.sub.12                                              
       HCl E  10 N   4     99   2.2 N                                     
                                     118.5                                
                                         102                              
       HNO.sub.3                                                          
           F  10 N   12    99   2.2 N                                     
                                     118.5                                
                                         102                              
Y.sub.3 Al.sub.3 Ga.sub.2 O.sub.12                                        
       HCl G  10 N   4     99   2.2 N                                     
                                     60  100                              
       HNO.sub.3                                                          
           H  10 N   20    99   2.1 N                                     
                                     60  100                              
LaGaO.sub.3                                                               
       HCl I  10 N   4     99   2.2 N                                     
                                     81  162                              
(dope Nd3+)                                                               
       HNO.sub.3                                                          
           J  10 N   12    99   2.2 N                                     
                                     81  162                              
Y.sub.2 GaFe.sub.5 O.sub.12                                               
       HCl K  10 N   4     99   2.2 N                                     
                                     29  74                               
       HNO.sub.3                                                          
           L  10 N   15    99   2.2 N                                     
                                     29.1                                 
                                         74                               
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     EXAMPLE 5 
     This example illustrates the separation and the recovery of gallium and rare earths when the dissolution is effected by nitric acid (solutions B, D, J of Example 4). 
     Separation took place in a multistage apparatus, with the aqueous and organic phases circulating countercurrently. The apparatus employed is shown schematically in the Figure of the Drawing. It comprised an extraction section E comprising 7 stages, a wash section L with 6 stages and a regeneration section with 4 stages. 
     The solvent used was tributylphosphate (TBP) diluted 50% by volume in kerosene. 
     The results of the separation are tabulated below in Table V, together with the flow rates employed. 
     
                       TABLE V                                                     
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              Results                                                     
Solu- Flow Rates    Purified Ga.sup.3 +                                   
                                 Purified Tr.sup.3 +                      
tions V      V.sub.A                                                      
                   V.sub.L                                                
                        V.sub.R                                           
                            Solutions  Solutions                          
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B     3      1     0.1  1.3 Ga: 117.2 g/l                                 
                                       Ga ≦ 1 mg/l                 
                            Y ≦ 1 mg/l                             
                                       Y: 76.9 g/l                        
                            Flow Rates: 1.1                               
                                       Flow Rates: 1.3                    
D     2.8    1     0.13 1.2 Ga: 92.8 g/l                                  
                                       Sm: 125 g/l                        
                            Sm ≦ 1 mg/l                            
                                       Ga ≦ 1 mg/l                 
                            Flow Rates: 1.13                              
                                       Flow Rates: 1.2                    
J     2.10   1     0.20 1.3 Ga: 67.5 g/l                                  
                                       La: 115.3 g/l                      
                            La ≦ 1 mg/l                            
                                       Ga ≦ 1 mg/l                 
                            Flow Rates: 1.20                              
                                       Flow Rates: 1.3                    
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     EXAMPLE 6 
     This example illustrates the separation and recovery of gallium and rare earths when the dissolution is effected with hydrochloric acid (solutions A, C, E, G, I, K of Example 4). 
     The separation and recovery of gallium and rare earths from these solutions was effected in the multistage apparatus described in Example 5. 
     The 0.1N hydrochloric acid solution used for washing was introduced in Section E. The rare earth solution was recovered at the outlet of the extraction. 
     Extraction was effected by a weakly acidic 0.1N HCl solution recovered at the outlet of Section R. 
     Teh following table compiles the different results obtained, together with the flow rates employed. 
     The solvent used was TBP diluted 50% by volume in kerosene. 
     
                       TABLE VI                                                    
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Flow Rates     Results                                                    
Solutions                                                                 
       V     V.sub.A                                                      
                   V.sub.L                                                
                       V.sub.R                                            
                           Gallium Solution                               
                                      Tr.sup.3 + Solution                 
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A      2.2   1     0.1 2.2 Flow Rate: 2.2                                 
                                      Flow Rate: 1.1                      
                           Ga: 58.6 g/l                                   
                                      Ga ≦ 1 mg/l                  
                           Y ≦ 1 mg/l                              
                                      Y: 80.9 g/l                         
C      2.2   1     0.1 2.2 Flow Rate: 2.2                                 
                                      Flow Rate: 1.1                      
                           Ga: 47.72  Ga ≦ 1 mg/l                  
                           Sm ≦ 1 mg/l                             
                                      Sm: 136.3 g/l                       
E      2.2   1     0.1 2.2 Flow Rate: 2.2                                 
                                      Flow Rate: 1.1                      
                           Ga: 53.8 g/l                                   
                                      Ga ≦ mg/l                    
                           Gd ≦ 1 mg/l                             
                                      Gd: 92.7 g/l                        
G      2.0   1     0.1 2   Flow Rate: 2                                   
                                      Flow Rate: 1.1                      
                           Ga: 30 g/l Ga ≦ 1 mg/l                  
                           Y ≦ 1 mg/l                              
                                      Y: 90 g/l                           
I      2.0   1     0.1 2   Flow Rate: 2                                   
                                      Flow Rate: 1.1                      
                           Ga: 40.5 g/l                                   
                                      Ga ≦ 1 mg/l                  
                           La ≦ 1 mg/l                             
                                      La ≦ 147.2 g/l               
K      2.0   1     0.4 2.0 Flow Rate: 2.2                                 
                                      Flow Rate: 1.4                      
                           Ga: 14.5 g/l                                   
                                      Ga ≦1 mg/l                   
                           Y ≦ 1 mg/l                              
                                      Y: 52.85 g/l                        
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     While the invention has been described in terms of various preferred embodiments, the skilled artisan will appreciate that various modifications, substitutions, omissions, and changes may be made without departing from the spirit thereof. Accordingly, it is intended that the scope of the present invention be limited solely by the scope of the following claims.