Recycling of superalloys with the aid of an alkali metal salt bath

Abstract

The invention relates to a process for recovering valuable metals from a superalloy which has the steps of digesting the superalloy in a salt melt. The salt melt contains 60-95% by weight of NaOH and 5-40% by weight of Na 2 SO 4 .

1 - 21 . (canceled) 
   
   
       22 . A process for recovering valuable metals from a superalloy which comprises digesting the superalloy in a salt melt containing 60-95% by weight of NaOH and 5-40% by weight of Na 2 SO 4 . 
   
   
       23 . The process according to  claim 22 , which further comprises adding sodium carbonate in an amount not to exceed 10% by weight of the salt melt. 
   
   
       24 . The process according to  claim 23 , wherein the salt melt contains 75-90% by weight of NaOH, 5-20% by weight of Na 2 SO 4  and 5-10% by weight of sodium carbonate. 
   
   
       25 . The process according to  claim 22 , wherein the superalloy contains one or more of the metals from the group consisting of Ni, Co, Cr or Al as a main component and one or more of the elements from the group consisting of Re, Mo, Ta, Nb, W, Hf or Pt as secondary component. 
   
   
       26 . The process according to  claim 25 , wherein the superalloy contains 0.5 to 12% by weight of rhenium. 
   
   
       27 . The process according to  claim 22 , wherein at least 1 kg of the salt melt is used per 1 kg of superalloy. 
   
   
       28 . The process according to  claim 22 , wherein the digesting is carried out in a moving melt. 
   
   
       29 . The process according to  claim 23 , wherein the digesting is carried out in a rotary tubular kiln operated batchwise or continuously. 
   
   
       30 . The process according to  claim 22 , which further comprises passing air and/or oxygen or a mixture thereof into the melt. 
   
   
       31 . The process according to  claim 22 , which further comprises adding oxidizing component to the melt, wherein the oxidizing component is a nitrate, peroxodisulphate, peroxide of the alkali metal and/or mixtures thereof. 
   
   
       32 . The process according to  claim 31 , wherein 5 to 25% by weight of the oxidizing component, based on the salt melt, are added to the melt. 
   
   
       33 . The process according to  claim 30 , wherein the mixture of air and oxygen consisting of 25 to 95% by volume of air and 5 to 75% by volume of oxygen is passed into the melt. 
   
   
       34 . The process according to  claim 32 , wherein the digesting is carried out at temperatures of 800 to 1200° C. 
   
   
       35 . The process according to  claim 32 , wherein the superalloy is partly oxidized. 
   
   
       36 . The process according to  claim 22 , wherein three fractions consisting of:
 water-soluble alkali metal oxometallate of the metals of the 6th and/or 7th subgroup and/or of the 3rd main group of the Periodic Table of the Elements and/or mixtures thereof;   water-insolble components from the group consisting of the metals Co, Ni, Fe, Mn or Cr and/or mixtures thereof,   oxide and/or water-insoluble alkali metal oxometallate of the metals of the 4th or 5th subgroup of the Periodic Table of the Elements and/or mixtures thereof are pre-formed in the melt.   
   
   
       37 . A process for recovering valuable metals from a superalloy comprising the following steps:
 a) converting of the melt digestion product according to  claim 36  into the solid phase by cooling to room temperature,   b) commination of the solidified melt digestion product,   c) reacting of the comminuted melt digestion product in water at temperatures of less than 80° C. and production of an aqueous suspension containing
 a solution consisting of a mixture of sodium compounds from the group consisting of NaOH, Na 2 SO 4 , NaAl(OH) 4  and/or Na 2 CO 3  and alkali metallates of the elements of the 6th and/or 7th subgroups of the Periodic Table of the Elements; 
 a solid metallic phase consisting of the group of metals Co, Ni, Fe, Mn and Cr; 
 a solid phase consisting of hydroxides and/or hydrated oxides of the metals of the 3rd main group and of metals of the 4th and/or 5th subgroup of the Periodic Table of the Elements, 
   d) removing of the aqueous fraction by filtration,   e) separating of the water-insoluble fraction by magnetic deposition of metallic components, and   f) removing the oxidic fraction.   
   
   
       38 . The process according to  claim 37 , wherein the reaction of the melt digestion product in water is carried out at temperatures of less than 60° C. 
   
   
       39 . The process according to  claim 37 , wherein the reaction of the melt digestion product in water is carried out at temperatures of less than 40° C. 
   
   
       40 . A process for obtaining rhenium from a superalloy consisting of the following steps:
 a) digesting the superalloy in a salt melt consisting essentially of 60-95% by weight of NaOH and 5-40% by weight of Na 2 SO 4 ,   b) cooling of the melt to room temperature,   c) commination of the melt digestion product,   d) reacting of the comminuted melt digestion product in water at temperatures of less than 80° C. and production of an aqueous suspension containing
 a solution consisting of a mixture of sodium compounds from the group consisting of NaOH, Na 2 SO 4 , NaAl(OH) 4  and/or Na 2 CO 3  and alkali metallates of the elements of the 6th and/or 7th subgroup of the Periodic Table of the Elements; 
 a solid metallic phase consisting of the group of metals Co, Ni, Fe, Mn and Cr; 
 a solid phase consisting of hydroxides and/or hydrated oxides of the metals of the 3rd main group and of metals of the 4th and/or 5th subgroup of the Periodic Table of the Elements, 
   e) removing of the aqueous fraction by filtration, and   f) removing of the rhenium from the aqueous fraction.   
   
   
       41 . The process according to  claim 40 , which further comprises adding sodium carbonate in an amount not to exceed 10% by weight of the salt melt. 
   
   
       42 . The process according to  claim 22 , wherein the superalloy is a superalloy scrap.