Method and apparatus for enhanced purification of high-purity metals

Abstract

A 99.99% pure indium feed is charged into crucible 8 and heated to 1250° C. by upper heater 6 in a vacuum atmosphere at 1×10 −4 Torr, whereupon indium evaporates, condenses on the inner surfaces of inner tube 3 and drips to be recovered into liquid reservoir 9 in the lower part of tubular member 11 whereas impurity elements having lower vapor pressure than indium stay within crucible 8. The recovered indium mass in liquid reservoir 9 is heated to 1100° C. by lower heater 7 and the resulting vapors of impurity elements having higher vapor pressure than indium pass through diffuser plates 12 in the upper part of tubular member 11 to be discharged from the system whereas the indium vapor recondenses upon contact with diffuser plates 12 and returns to liquid reservoir 9, yielding 99.9999% pure indium while preventing the loss of indium.

What is claimed is:  
     
         1 . A method of enhanced purification of high-purity metals which comprises purifying a metal feed by distillation in a vacuum atmosphere to yield the desired metal with high purity, said method further comprising a first thermal purification step in which said metal feed in a feed crucible positioned in the upper interior of an inner tube maintaining said vacuum atmosphere is heated and the generated vapor of said desired metal is brought into contact with the inner surface of said inner tube so that it is condensed and recovered in a separate form from impurity elements that have lower vapor pressure than said desired metal and which are allowed to stay within said feed crucible, and a second thermal purification step in which said desired metal as recovered is admitted into and heated in a liquid reservoir in the lower part of a tubular member positioned in the lower interior of said inner tube and the generated vapor is passed through a diffuser positioned in the upper part of said tubular member and guided by suction so that the vapors of impurity elements having higher vapor pressure than said desired metal are solidified in a separate form in a cooling trap positioned below said tubular member and the vapor of said desired metal is brought into contact with said diffuser so that it is condensed and returned to said liquid reservoir.  
     
     
         2 . The method according to  claim 1 , wherein said diffuser plate is made of a carbonaceous material.  
     
     
         3 . The method according to  claim 1  or  2 , wherein said liquid reservoir is a recovery mold for casting said desired metal having high purity after enhanced purification.  
     
     
         4 . The method according to  claim 1  or  2 , wherein said desired metal is indium, said metal feed is heated at 1100-1300° C. in the first thermal purification step and said desired metal as recovered is heated at 900-1200° C. in the second thermal purification step.  
     
     
         5 . The method according to  claim 3 , wherein said desired metal is indium, said metal feed is heated at 1100-1300° C. in the first thermal purification step and said desired metal as recovered is heated at 900-1200° C. in the second thermal purification step.  
     
     
         6 . The method according to  claim 1  or  2 , wherein said desired metal is at least one metal selected from the group consisting of antimony, zinc, tellurium, magnesium, cadmium, bismuth and silver.  
     
     
         7 . The method according to  claim 3 , wherein said desired metal is at least one metal selected from the group consisting of antimony, zinc, tellurium, magnesium, cadmium, bismuth and silver.  
     
     
         8 . An apparatus for enhanced purification of high-purity metals, which comprises an inner tube in which a vacuum atmosphere is to be formed, a first heating chamber provided in the upper interior of said inner tube, a second heating chamber provided in the lower interior of said inner tube, said first heating chamber accommodating a feed crucible with an open top into which a metal feed is charged and the desired metal in said metal feed is evaporated for recovery while impurity elements having lower vapor pressure than said desired metal are separated by being allowed to stay within said feed crucible, said second heating chamber accommodating a tubular member having in the top an inlet for receiving said desired metal as recovered and an outlet through which impurity elements that have higher vapor pressure than said desired metal and which are evaporated in separate form upon heating are discharged, as well as a liquid reservoir for heating said desired metal which is formed in the lower part of said tubular member, and a diffuser for condensing said desired metal as evaporated which is installed across the upper part of said tubular member.  
     
     
         9 . The apparatus according to  claim 8 , wherein said inner tube is surrounded by an outer tube of a larger diameter that permits said vacuum atmosphere to communicate with said inner tube and which is generally concentric therewith, said apparatus further including an upper heater and a lower heater provided in the space between the inner surface of said outer tube and the outer surface of said inner tube, said upper heater being positioned in the upper part of said space to heat said feed crucible and said lower heater being positioned in the lower part of said space to heat said liquid reservoir.  
     
     
         10 . The apparatus according to  claim 8  or  9 , wherein said diffuser consists of a plurality of generally parallel plates each having a plurality of holes made through it.  
     
     
         11 . The apparatus according to  claim 8  or  9 , wherein at least the inner surface of the ceiling of said inner tube is domed or made conical in shape.  
     
     
         12 . The apparatus according to  claim 10 , wherein at least the inner surface of the ceiling of said inner tube is domed or made conical in shape.  
     
     
         13 . The apparatus according to  claim 8  or  9 , wherein said desired metal is at least one metal selected from the group consisting of indium, antimony, zinc, tellurium, magnesium, cadmium, bismuth and silver.  
     
     
         14 . The apparatus according to  claim 10 , wherein said desired metal is at least one metal selected from the group consisting of indium, antimony, zinc, tellurium, magnesium, cadmium, bismuth and silver.  
     
     
         15 . The apparatus according to  claim 11 , wherein said desired metal is at least one metal selected from the group consisting of indium, antimony, zinc, tellurium, magnesium, cadmium, bismuth and silver.