Semi-continuous rare earth metal production

Abstract

The present disclosure relates to a low temperature, semi-continuous process for producing high purity rare earth metals and alloys in molten salts. Rare earth metals and alloys are reduced from the corresponding rare earth halide in molten salts in a semi-continuous process. An air stable pellet or ingot can be fed into molten salts and reduced through metallothermic reduction or electrolysis. The formation of an air stable feedstock minimizes handling concerns of the hygroscopic rare earth salts, allowing the reduction process to be run in a semi-continuous process. The process can optionally include the addition of alloying elements such as magnesium, iron and zinc reduce the required processing temperature.

What is claimed: 
     
         1 . A process for producing rare earth metal (RE) or an alloy of rare earth metal (RE); said process is optionally a continuous or semi-continuous process; said process includes:
 a. adding to a reaction vessel an initial charge of a eutectic-forming metal that forms a eutectic with said RE; optionally adding calcium metal to said reaction vessel; said eutectic optionally has a metaling point of less than 1000° C.;   b. adding to said reaction vessel an initial charge of anhydrous RE-chloride salt and/or RE-fluoride salt to form a charged mixture; optionally adding one or more alkali metal halides to said charged mixture; said charged mixture optionally has a melting point that is less than 1000° C.;   c. heating said charged mixture in said reaction vessel; said temperature of said charged mixture in said reaction vessel is optionally greater than 700° C. and optionally less than 1000° C.;   d. mixing said charged mixture in said reaction vessel to cause a reaction to convert the RE-chloride and/or RE-fluoride to RE metal and/or RE metal alloy and calcium chloride salt and/or calcium fluoride salt;   e. removing a portion or all of the eutectic metal, rare earth metal, and/or rare earth alloy from said reaction vessel; optionally removing some or all of a salt mixture from said reaction vessel; and   f. optionally adding additional eutectic-forming metal, alkali metal halides, calcium metal, RE-chloride salt and/or RE-fluoride salt to said reaction vessel, and then repeating the steps c-f to obtain additional amount of RE metal and/or RE metal alloy.   
     
     
         2 . A method for producing rare earth metal (RE) or an alloy of rare earth metal (RE); said process is optionally a continuous or semi-continuous process; said process includes:
 a. providing a reaction vessel;   b. providing a eutectic-forming metal;   c. providing RE-chloride salt and/or RE-fluoride salt;   d. providing a chloride and/or fluoride salt;   e. adding said eutectic-forming metal, said RE-chloride salt and/or RE-fluoride salt, and said chloride and/or fluoride salt to said reaction vessel;   f. causing said RE-chloride salt and/or RE-fluoride salt to react with other materials in said reaction vessel to form RE metal and/or RE metal alloy; and   g. removing said RE metal and/or RE metal alloy from said reaction vessel.   
     
     
         3 . The method as defined in  claim 2 , including the step of adding calcium metal to the reaction vessel. 
     
     
         4 . The method as defined in  claim 3 , wherein said eutectic-forming metal is at least partially added as a master alloy that includes calcium. 
     
     
         5 . The method as defined in  claim 3 , wherein said eutectic-forming metal is melted in said reaction vessel prior to said addition of said calcium metal to said reaction vessel. 
     
     
         6 . The method as defined in  claim 2 , wherein said step of providing RE-chloride salt and/or RE-fluoride salt includes:
 i. providing Re oxide;   ii providing a chloride and/or fluoride salt; optionally providing a chloride acid and/or a fluoride acid; optionally providing water;   iii. mixing together said RE oxide, chloride and/or fluoride salt, optional chloride acid and/or a fluoride acid, and optional water to cause said RE oxide to form said RE-chloride salt and/or RE-fluoride salt; said step of mixing optionally occurring in a vacuum to remove water byproduct and inhibit formation of RE-oxychloride and/or RE-oxyflouride; said step of mixing optionally subjected to heating to remove water byproduct and inhibit formation of RE-oxychloride and/or RE-oxyflouride;   iv. optionally condensing of chloride and/or fluoride salt and said water in an optional cold trap to recovery of said chloride and/or fluoride salt; and,   v. optionally vacuum drying said formed RE-chloride salt and/or RE-fluoride salt; said vacuum drying optionally occurs at a temperature of 100° C.-200° C.   
     
     
         7 . The method as defined in  claim 2 , wherein said eutectic-forming metal includes aluminum, iron, magnesium, zinc, and/or aluminum. 
     
     
         8 . The method as defined in  claim 2 , wherein said RE-chloride salt and/or RE-fluoride salt is in the form of a pellet or ingot and optionally includes alkali salts. 
     
     
         9 . The method as defined in  claim 8 , wherein said pellet or ingot has a melting point of no more than 1000° C. 
     
     
         10 . The method as defined in  claim 2 , wherein i) said eutectic-forming metal, ii) said RE-chloride salt and/or RE-fluoride salt, iii) said chloride and/or fluoride salt, and iv) said optional calcium in said reaction vessel are heated to a temperature of no more than 1000° C. 
     
     
         11 . The method as defined in  claim 2 , further including the step of mixing and/or agitating i) said eutectic-forming metal, ii) said RE-chloride salt and/or RE-fluoride salt, iii) said chloride and/or fluoride salt, and iv) said optional calcium in said reaction vessel. 
     
     
         12 . The method as defined in  claim 2 , further including the step of adding alkali metal chlorides, alkali metal fluorides, calcium chloride, calcium fluoride, magnesium chloride, magnesium fluoride, metal halide chlorides, and/or metal halide fluorides to said reaction vessel. 
     
     
         13 . The method as defined in  claim 2 , wherein said RE-chloride salt and/or RE-fluoride salt is in the form of pellets or ingots. 
     
     
         14 . The method as defined in  claim 13 , wherein said pellets or ingots have a) a melting point of no more than 1000° C., b) a low surface area, and/or c) reduced moisture sensitivity. 
     
     
         15 . The method as defined in  claim 13 , wherein said alkali metal chlorides, alkali metal fluorides, calcium chloride, calcium fluoride, magnesium chloride, magnesium fluoride, metal halide chlorides, and/or metal halide fluorides are included in said pellets or ingots. 
     
     
         16 . The method as defined in  claim 2 , wherein said RE metal and/or RE metal alloy is allowed to separate from other materials in said reaction vessel prior to removal of said RE metal and/or RE metal alloy from said reaction vessel. 
     
     
         17 . The method as defined in  claim 16 , wherein a time for allowing said separation of said RE metal and/or RE metal alloy from other materials in said reaction vessel is at least 10 minutes, and optionally 10-60 minutes. 
     
     
         18 . The method as defined in  claim 2 , wherein said RE metal and/or RE metal alloy and any salt compounds in said reaction vessel are removed separately from said reaction vessel. 
     
     
         19 . The method as defined in  claim 2 , wherein said RE metal and/or RE metal alloy and any salt compounds in said reaction vessel are removed simultaneously, without separation, from said reaction vessel. 
     
     
         20 . The method as defined in  claim 2 , further including the step of i) purifying said RE metal and/or RE metal alloy and/or ii) separating said RE metal and/or RE metal alloy form said salt compounds; said step of purifying and/or separating optionally includes the use of a) centrifugal force, b) gas bubbling and/or c) distillation. 
     
     
         21 . The method as defined in  claim 2 , further including the step of adding sodium to said reaction vessel to at least partially regenerate calcium metal; said regeneration of said calcium metal optionally obtained in situ by a reduction of CaCl2. 
     
     
         22 . The method as defined in  claim 2 , wherein chloride salt and/or fluoride salt is at least partially removed from said reaction vessel is at least partially purified by partial crystallization of CaCl2 to within 10 degrees of the KCl—NaCl—CaCl2 eutectic. 
     
     
         23 . The method as defined in  claim 2 , further including the step of removing aluminum, iron, magnesium, zinc, and/or aluminum from said RE metal alloy; said step of removing aluminum, iron, magnesium, zinc, and/or aluminum from said RE metal alloy is optionally conducted with use of a multi-stage system; said multi-stage system optionally includes successively higher vacuum levels that draw on each successive evaporative chamber, and/or limited additional heat is added to each successive evaporative chamber to allow for recapture and reuse of latent heat during said removal process. 
     
     
         24 . The method as defined in  claim 23 , wherein a condenser of one of said chambers acts to provide a majority of heat for a successive evaporative chamber. 
     
     
         25 . The method as defined in  claim 23 , wherein said multi-stage system includes 3-6 evaporative chamber. 
     
     
         26 . The method as defined in  claim 2 , wherein no calcium metal is added to said reaction vessel; and any calcium in said reaction vessel is optionally formed by sodium additions to said reaction vessel which causes calcium-containing salts to react with said sodium and form calcium metal in said reaction vessel. 
     
     
         27 . The method as defined in  claim 2 , wherein some or all of said RE-chloride salt is replaced with RE-oxychloride salt and/or RE-oxyfluoride salt. 
     
     
         28 . The method as defined in  claim 2 , wherein said reaction vessel is at least partially formed of iron. 
     
     
         29 . The method as defined in  claim 2 , wherein said reaction of said RE-chloride salt and/or RE-fluoride salt in said reaction vessel occurs at a temperature of no more than 1000° C., and optionally no more than 850° C. 
     
     
         30 . The method as defined in  claim 2 , wherein said reaction vessel is partially or fully coated with a ceramic coating; said ceramic coating optionally including one or more materials selected from the group of yttrium oxide, zirconium oxide, calcium oxide, and magnesium oxide. 
     
     
         31 . The method as defined in  claim 2 , wherein a time of reaction of said RE-chloride salt and/or RE-fluoride salt in said reaction vessel is at least 5 minutes, and optionally about 5-30 minutes.