Leach column and method for metal recovery

Abstract

A leach column ( 10 ) and method for the separation and recovery of metals from mixtures. The column ( 10 ) is adapted to be electrically charged to enhance metal recovery. Particularly, a pair of electrical connections ( 20 ), ( 22 ) are positioned in the column ( 10 ) to create an electrical charge in the presence of a leaching solution ( 18 ) and a metal-containing mixture ( 26 ) to enhance leaching of the metal from the mixture. In an exemplary embodiment, the leach column ( 10 ) is used for the recovery of platinum from platinum-containing coatings on jet engine components.

What is claimed is:  
     
         1 . A leach column comprising: 
 a tube adapted to support therein a mixture containing a metal to be leached and adapted to pass a leaching solution therethrough; and    a pair of electrical connections at spaced apart locations along the tube and configured to induce an electric current therebetween in the presence of the leaching solution.    
     
     
         2 . The column of  claim 1  wherein the pair of electrical connections comprise a first electrode and a second electrode adapted to pass an electric current therebetween.  
     
     
         3 . The column of  claim 2  wherein the first electrode and the second electrode are positioned at opposing ends of the leach column.  
     
     
         4 . The column of  claim 2  wherein the first electrode and the second electrode comprise a material selected from the group consisting of graphite, nickel-base alloys, chromium-based alloys, nickel-chromium-molybdenum alloys, platinum, platinized titanium, niobium expanded mesh coated with platinum, and palladium.  
     
     
         5 . The column of  claim 2  wherein the first electrode and the second electrode comprise graphite.  
     
     
         6 . A system for leaching platinum from a platinum-containing particulate mixture, the system comprising: 
 a leach column adapted to support the platinum-containing particulate mixture therein and to pass a leaching solution therethrough;    a leaching solution for passage through the platinum-containing particulate mixture, the leaching solution comprising at least one acid capable of leaching platinum from the particulate mixture; and    a pair of electrical connections at spaced apart locations along the column and configured to induce an electric current between the electrical connections in the presence of the leaching solution.    
     
     
         7 . The system of  claim 6  wherein the pair of electrical connections comprise a first electrode and a second electrode adapted to induce an electric current therebetween.  
     
     
         8 . The system of  claim 7  wherein the first electrode and the second-electrode are positioned at opposing ends of the leach column.  
     
     
         9 . The system of  claim 7  wherein the first electrode and the second electrode comprise a material selected from the group consisting of graphite, nickel-base alloys, chromium-based alloys, nickel-chromium-molybdenum alloys, and palladium.  
     
     
         10 . The system of  claim 7  wherein the first electrode and the second electrode comprise graphite.  
     
     
         11 . The system of  claim 6  wherein the platinum containing particulate mixture comprises platinum-containing particles and inert particles.  
     
     
         12 . The system of  claim 11  wherein the inert particles are sand.  
     
     
         13 . A system for recovering platinum comprising: 
 a platinum-containing particulate mixture comprising platinum-containing particles and inert particles;    a leaching solution adapted to leach platinum from the platinum-containing particulate mixture;    at least one leach column adapted to support therein the platinum-containing particulate mixture and adapted to pass the leaching solution therethrough;    a first electrode and a second electrode spaced apart within each column, the first and second electrodes configured to induce an electric current therebetween in the presence of the leaching solution; and    an external source of electricity for inducing the electric current in each column.    
     
     
         14 . The system of  claim 13  further comprising a reservoir for containment of the leaching solution.  
     
     
         15 . The system of  claim 13  further comprising a tank for collection of leachate formed from the leaching solution after passage through the platinum-containing particulate mixture.  
     
     
         16 . The system of  claim 13  further comprising a distillation apparatus for recovery of the leaching solution from the leachate.  
     
     
         17 . The system of  claim 13  further comprising a collection box for containment of the inert particles.  
     
     
         18 . The system of  claim 13  wherein the external source of electricity is a generator.  
     
     
         19 . The system of  claim 13  wherein the leaching solution comprises one or more acids selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, phosphoric acid, sulfamic acid, citric acid, oxalic acid, and peroxide.  
     
     
         20 . A method of leaching a metal from a metal-containing particulate mixture comprising: 
 placing a metal-containing particulate mixture within a leach column;    passing a leaching solution through the particulate mixture within the column whereby to leach the metal from the particulate mixture; and    inducing an electric current through the leaching solution while leaching the metal from the particulate mixture.    
     
     
         21 . The method of  claim 20  wherein the metal leached from the metal-containing particulate mixture is selected from the group consisting of platinum, gold, silver, palladium, nickel, copper, zinc, cadmium, rhodium, and combinations thereof.  
     
     
         22 . The method of  claim 20  further comprising positioning a pair of electrical connections at spaced apart locations within the leach column for inducing the electrical current therein.  
     
     
         23 . The method of  claim 22  further comprising connecting the pair of electrical connections to an external source of electricity for inducing the electric current.  
     
     
         24 . The method of  claim 23  wherein the pair of electrical connections comprise a first electrode and a second electrode, and inducing the electric current is by passing electricity between the first and second electrodes in the presence of the leaching solution.  
     
     
         25 . The method of  claim 24  wherein the first and second electrodes are positioned at opposing ends of the leach column.  
     
     
         26 . The method of  claim 24  wherein the first electrode and the second electrode comprise a material selected from the group consisting of graphite, nickel-base alloys, chromium-based alloys, nickel-chromium-molybdenum alloys, platinum, platinized titanium, niobium expanded mesh coated with platinum, and palladium.  
     
     
         27 . The method of  claim 24  wherein the first electrode and the second electrode comprise graphite.  
     
     
         28 . The method of  claim 20  wherein the leaching solution comprises one or more acids selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, phosphoric acid, sulfamic acid, citric acid, oxalic acid, and peroxide.  
     
     
         29 . The method of  claim 20  further comprising removing a metal-containing coating from a jet engine component to produce metal-containing particles that form at least a portion of the metal-containing particulate mixture for placement within the leach column.  
     
     
         30 . The method of  claim 20  wherein the metal leached from the metal-containing particulate mixture is platinum.  
     
     
         31 . A method of recovering platinum from a platinum-containing coating on a jet engine component, the method comprising: 
 exposing the jet engine component to a stripping solution whereby a platinum-containing residue is formed on a surface of the component;    removing the platinum-containing residue from the surface of the component;    placing the platinum-containing residue within a leach column;    passing a leaching solution through the platinum-containing residue within the column; and    inducing an electric current through the leaching solution while leaching platinum from the platinum-containing residue.    
     
     
         32 . The method of  claim 31  wherein removing the platinum-containing residue from the component surface comprises blasting the component with grit, and wherein the grit is placed in the leach column with the particulate-containing residue removed thereby.  
     
     
         33 . The method of  claim 31  wherein the grit is selected from the group consisting of aluminum oxide and silicon dioxide.  
     
     
         34 . The method of  claim 31  wherein the grit is beads selected from the group consisting of ballotini beads and silicon dioxide glass beads.  
     
     
         35 . The method of  claim 31  wherein the stripping solution comprises one or more acids selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid.  
     
     
         36 . The method of  claim 31  wherein the leaching solution comprises one or more acids selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, phosphoric acid, sulfamic acid, citric acid, oxalic acid, and peroxide.  
     
     
         37 . The method of  claim 31  further comprising providing a pair of electrical connections at spaced apart locations within the leach column for inducing the electrical current therein.  
     
     
         38 . The method of  claim 37  further comprising attaching the electrical connections to an external source of electricity.  
     
     
         39 . The method of  claim 37  wherein the pair of electrical connections comprise a first electrode and a second electrode, and inducing the electric current is by passing electricity between the first and second electrodes in the presence of the leaching solution.  
     
     
         40 . The method of  claim 39  wherein the first electrode and the second electrode are positioned at opposing ends of the leach column.  
     
     
         41 . The method of  claim 39  wherein the first electrode and the second electrode comprise a material selected from the group consisting of graphite, nickel-base alloys, chromium-based alloys, nickel-chromium-molybdenum alloys, and palladium.  
     
     
         42 . The method of  claim 39  wherein the first electrode and the second electrode comprise graphite.  
     
     
         43 . The method of  claim 32  further comprising collecting the grit removed from the leach column during leaching for reclassification and reuse.  
     
     
         44 . The method of  claim 43  further comprising washing the collected grit for separation from the leaching solution.  
     
     
         45 . The method of  claim 44  further comprising drying the washed grit for reclassification and reuse.  
     
     
         46 . A method of recovering platinum from a platinum-containing coating on a jet engine component, the method comprising: 
 stripping the platinum-containing coating on the jet engine component with a stripping solution comprising one or more acids selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and phosphoric acid, whereby a platinum-containing residue is formed on a surface of the component;    blasting the surface of the component with grit to remove the platinum-containing residue and thereby form a mixture of grit and the platinum-containing residue;    placing the mixture within a leach column;    passing a leaching solution through the mixture within the column; and    inducing an electric current through the leaching solution while leaching platinum from the mixture.    
     
     
         47 . The method of  claim 46  wherein the grit comprises a material selected from the group consisting of aluminum oxide and silicon dioxide.  
     
     
         48 . The method of  claim 46  wherein the grit is selected from the group consisting of ballotini beads and silicon dioxide glass beads.  
     
     
         49 . The method of  claim 46  further comprising positioning a first electrode and a second electrode at spaced apart locations within the column, the first and second electrodes configured to induce the electric current therebetween in the presence of the leaching solution.  
     
     
         50 . The method of  claim 49  wherein the first electrode and the second electrode comprise a material selected from the group consisting of graphite, nickel-base alloys, chromium-based alloys, nickel-chromium-molybdenum alloys, and palladium.