Method for recovering platinum group elements

Abstract

A method for recovering platinum group elements comprises charging an oxide raw material entraining platinum group elements, copper oxide, solid carbonaceous reducing agent and flux into a closed electric furnace equipped with at least one electrode for heating material and a roof for substantially shielding material charged into the furnace from the exterior atmosphere. The charged material is melted and reduced to form a layer of molten metal under a molten slag layer and enrich platinum group elements in this molten metal. The oxide raw material, copper oxide, solid carbonaceous reducing agent and flux are prepared as powdery or particulate materials, premixed and then charged into the electric furnace. The heat-melted material in the furnace is allowed to stand at a temperature of 1200° to 1500° C. for at least 5 hours, with the molten metal containing platinum group elements then being discharged outside the furnace.

1 . A method for recovering platinum group elements comprising: 
 charging an oxide raw material entraining platinum group elements, copper oxide, solid carbonaceous reducing agent and flux into a closed electric furnace equipped with electrodes for passing electric current through and heating material charged in the furnace and a roof for substantially shielding material charged in the furnace from the exterior atmosphere,    melting and reducing the charged material by the electric current heating with the electrode, thereby forming a layer of molten metal under a molten slag layer and enriching platinum group elements in this molten metal,    which method is characterized in that:    the oxide raw material, copper oxide, solid carbonaceous reducing agent and flux are all prepared as powdery or particulate materials;    these powdery or particulate materials are premixed and then charged into the electric furnace; and    the molten metal enriched in platinum group elements is discharged outside the furnace after undergoing a standing step in which the heat-melted material in the furnace is allowed to stand at a temperature of 1200-1500° C. for at least 5 hours.    
     
     
         2 . A method for recovering platinum group elements according to  claim 1 , wherein the slag oxides formed in the furnace are controlled to the content ranges of: Al 2 O 3 : 20-40 wt %, SiO 2 : 25-40 wt %, CaO: 20-35 wt %, and FeO: 0-35 wt %.  
     
     
         3 . A method for recovering platinum group elements according to  claim 2 , wherein the content ranges of the slag oxides are controlled by the steps of: analyzing and ascertaining beforehand the amount of at least one among the oxides of Al, Si and Fe contained in the oxide raw material entraining platinum group elements, and regulating the composition of the flux components before charging them into the furnace in accordance with the contents of said oxides.  
     
     
         4 . A method for recovering platinum group elements according to  claim 3 , wherein the flux contains at least one component selected from the group consisting of Al 2 O 3 , SiO 2 , CaO and FeO.  
     
     
         5 . A method for recovering platinum group elements according to  claim 1 , wherein the composition of the molten slag is regulated to: 
 Al: 10-22 wt %    Si: 10-16 wt %    Ca: 14-22 wt %    Fe: 27 wt % or less (including 0%)    Pt: 10 ppm or less, and    the balance substantially of oxygen.    
     
     
         6 . A method for recovering platinum group elements according to  claim 1 , wherein the molten metal discharged from the furnace is transferred to and oxidized in another furnace and separated by difference in specific gravity into an oxide layer composed mainly of copper oxide and molten metal composed mainly of metallic copper in which platinum group elements are enriched.  
     
     
         7 . A method for recovering platinum group elements according to  claim 1 , wherein the molten metal discharged from the furnace is transferred to and oxidized in another furnace and separated by difference in specific gravity into an oxide layer composed mainly of copper oxide and molten metal composed mainly of metallic copper in which platinum group elements are enriched, the oxide layer composed mainly of copper oxide obtained from the discharged molten metal being reused as the copper oxide for the charging step.  
     
     
         8 . A method for recovering platinum group elements comprising: 
 charging an oxide raw material entraining platinum group elements, copper oxide, solid carbonaceous reducing agent and flux into a closed electric furnace equipped with electrodes for passing electric current through and heating material charged into the furnace and a roof for substantially shielding material charged into the furnace from the exterior atmosphere,    melting and reducing the charged material by the electric current heating with the electrode, thereby forming a layer of molten metal under a molten slag layer and enriching platinum group elements in this molten metal,    which method is characterized in that:    as the electric furnace there is used an electric furnace whose wall enclosing up to a height level of the molten slag layer generated in the furnace is constituted of an iron shell and a sheet of flowing water is formed on the outside of the iron shell to descend in contact with its outer surface.    
     
     
         9 . A method for recovering platinum group elements according to  claim 8 , wherein a self-coating layer consisting of a solidified layer of fused substances in the furnace is produced on the inner surface of the iron shell.  
     
     
         10 . A method for recovering platinum group elements according to  claim 8 , wherein the sheet of flowing water descending in contact with the outer surface of the iron shell is formed by evenly distributing water of a prescribed water head pressure from a header installed outward of an upper part of the furnace wall toward the whole outer periphery of the iron shell at the same height level.  
     
     
         11 . A method for recovering platinum group elements according to  claim 9 , wherein the sheet of flowing water descending in contact with the outer surface of the iron shell is formed by evenly distributing water of a prescribed water head pressure from a header installed outward of an upper part of the furnace wall toward the whole outer periphery of the iron shell at the same height level.