Metal Extraction In Liquid Or Supercritical-Fluid Solvents

Abstract

A method for separating metals from metal-containing materials by extraction without generating large quantities of liquid waste is disclosed. Also disclosed is an extractant composition for use with this method. The method comprises exposing a metal-containing material to a solvent, such as supercritical carbon dioxide, an acid-base complex, and a chelating agent that is not a component of the acid-base complex. The metal is released into the solvent by a combination of oxidation by an oxidizing agent in the acid-base complex and chelation by the chelating agent. The oxidizing agent in the acid-base complex is solubilized by a solubilizing agent. The disclosed method and composition have many applications and are particularly well suited for the extraction of transition metals, including, but not limited to, platinum group metals, nom a metals and coinage metals. Applications include the recovery of metals from scrap materials and the planarization of semiconductor structures.

1 . A method for extracting a metal, comprising:
 exposing a metal-containing material comprising the metal to a liquid or supercritical-fluid solvent, an acid-base complex comprising an oxidizing agent and a solubilizing agent, and a chelating agent that is not a component of the acid-base complex; and   extracting for an extraction time sufficient for the chelating agent to form metal-containing complexes with at least a portion of the metal.   
     
     
         2 . The method of  claim 1 , where the metal is not a lanthanide or actinide. 
     
     
         3 . The method of  claim 1 , where the metal is selected from transition metals, transition metal oxides, transition metal sulfides, zero-valent transition metals, noble metals, platinum group metals, coinage metals, or combinations thereof. 
     
     
         4 - 9 . (canceled) 
     
     
         10 . The method of  claim 1 , where the solvent is a gas at room temperature and atmospheric pressure. 
     
     
         11 . The method of  claim 1 , where the solvent is a supercritical-fluid solvent. 
     
     
         12 . The method of  claim 1 , where the solvent is carbon dioxide. 
     
     
         13 . The method of  claim 1 , where the solvent is supercritical carbon dioxide. 
     
     
         14 . The method of  claim 1 , where the oxidizing agent is selected from mineral acids, and combinations thereof. 
     
     
         15 . The method of  claim 1 , where the oxidizing agent is selected from the group consisting of nitric acid, sulfuric acid, and combinations thereof. 
     
     
         16 . (canceled) 
     
     
         17 . The method of  claim 1 , where the oxidizing agent is selected to break down into volatile and/or soluble products after oxidizing the metal. 
     
     
         18 . The method of  claim 1 , where the oxidizing agent is selected to break down into compounds that are gases at room temperature and atmospheric pressure and/or water after oxidizing the metal. 
     
     
         19 . The method of  claim 1 , where the solubilizing agent is an alkyl phosphate. 
     
     
         20 . The method of  claim 1 , where the solubilizing agent is selected from the group consisting of tri-alkylphosphates, tri-alkylphosphine oxides, and combinations thereof. 
     
     
         21 - 22 . (canceled) 
     
     
         23 . The method of  claim 1 , where the solubilizing agent is soluble in supercritical carbon dioxide. 
     
     
         24 . The method of  claim 1 , where the chelating agent is a β-diketone, a fluorinated β-diketone, or combinations thereof. 
     
     
         25 . The method of  claim 1 , where the chelating agent is fluorinated. 
     
     
         26 - 27 . (canceled) 
     
     
         28 . The method of  claim 1 , where the oxidizing agent is nitric acid and the solubilizing agent is tributylphosphate. 
     
     
         29 . The method of  claim 1 , where the acid-base complex has the formula TBP(HNO 3 ) x (H 2 O) y , in which x is greater than or equal to about 0.7 and y is less than or equal to about 0.7. 
     
     
         30 . The method of  claim 1 , where the acid-base complex has the formula TBP(HNO 3 ) x (H 2 O) y , in which x is about 1.0 and y is about 0.4. 
     
     
         31 . The method of  claim 1 , where the metal-containing material is exposed to a mixture comprising the solvent, the acid-base complex, and the chelating agent, the mixture being substantially non-aqueous, with the exception of coordinated water molecules, if present, on the acid-base complex, the chelating agent, or the metal-containing complexes, or any combination thereof 
     
     
         32 . The method of  claim 1 , where the acid-base complex is a first acid-base complex, the oxidizing agent is a first oxidizing agent, the solubilizing agent is a first solubilizing agent, and further comprising exposing the metal-containing material to a second acid-base complex comprising a second oxidizing agent and a second solubilizing agent, where the first oxidizing agent is nitric acid and the second oxidizing agent is hydrochloric acid. 
     
     
         33 . The method of  claim 1 , where the solvent is supercritical carbon dioxide, the solubility of the oxidizing agent in supercritical carbon dioxide is less than about 0.1 moles per liter at 50° C. and 100 atm, and the solubility of the acid-base complex in supercritical carbon dioxide is greater than about 0.5 moles per liter at 50° C. and 100 atm. 
     
     
         34 . The method of  claim 1 , further comprising separating the metal-containing complexes from the solvent by reducing the pressure of the solvent, increasing the temperature of the solvent, or both. 
     
     
         35 . (canceled) 
     
     
         6 . The method of  claim 1 , where the metal-containing material comprises a copper film and the copper film is dissolved at a rate greater than about 2 nmoles per second. 
     
     
         37 . The method of  claim 1 , where the metal-containing material comprises a palladium film and the amount of palladium in the metal-containing material is reduced by 99% in less than about 30 seconds. 
     
     
         38 . The method of  claim 1 , where the metal-containing material, the solvent, the acid-base complex and the chelating agent form a reaction mixture, and further comprising exposing the reaction mixture to ultrasonic energy during at least a portion of the extraction time. 
     
     
         39 . (canceled) 
     
     
         40 . The method of  claim 1 , further comprising recycling the solvent, solubilizing agent, chelating agent, or any combination thereof. 
     
     
         41 . The method of  claim 1 , where the chelating agent is a first chelating agent, and further comprising exposing the metal-containing material to a second chelating agent that is not a component of the acid-base complex for a period of time sufficient for the first chelating agent, the second chelating agent, and the metal to form adducts. 
     
     
         42 . The method of  claim 41 , where the first chelating agent and the second chelating agent are different. 
     
     
         43 . The method of  claim 1 , where the chelating agent is a first chelating agent, and further comprising exposing the metal-containing material to a second chelating agent that is not a component of the acid-base complex for a period of time sufficient for the second chelating agent to displace one or more coordinated water molecules on the metal-containing complexes. 
     
     
         44 . The method of  claim 43 , where the first chelating agent and the second chelating agent are different. 
     
     
         45 . An extraction process, comprising:
 exposing a metal-containing material comprising a metal other than a lanthanide or an actinide to a liquid or supercritical-fluid solvent that is a gas at room temperature and atmospheric pressure, an acid-base complex comprising an a mineral acid oxidizing agent, an alkyl phosphate solubilizing agent, and a β-diketone chelating agent that is not a component of the acid-base complex; and   extracting the metal from the metal-containing material for an extraction time effective for the chelating agent to form metal-containing complexes with at least a portion of the metal.   
     
     
         46 . The method of  claim 45 , where the metal is a noble metal, platinum group metal or coinage metal. 
     
     
         47 . The method of  claim 45 , where the solvent is carbon dioxide, the solubilizing agent is tributylphosphate, the oxidizing agent is nitric acid, and the chelating agent is hexafluoroacetylacetone. 
     
     
         48 . (canceled) 
     
     
         49 . The method according to  claim 45  where the metal-containing material is a semiconductor structure. 
     
     
         50 . The method of  claim 49 , where the metal is copper. 
     
     
         51 . (canceled) 
     
     
         52 . The method of  claim 49 , where the solvent is carbon dioxide, the solubilizing agent is tributylphosphate, and the oxidizing agent is nitric acid. 
     
     
         53 . The method of  claim 49 , further comprising contacting the surface of the semiconductor structure with a porous pad. 
     
     
         54 . The method according to  claim 45  where the metal-containing material comprises platinum, and the method further comprises exposing a the platinum-containing material to the liquid or supercritical-fluid solvent, a first acid-base complex comprising nitric acid and a first solubilizing agent, a second acid-base complex comprising hydrochloric acid and a second solubilizing agent, and a chelating agent that is not a component of the first acid-base complex or the second acid-base complex. 
     
     
         55 . (canceled) 
     
     
         56 . The method of  claim 54 , where the first solubilizing agent, the second solubilizing agent, or both is/are tributylphosphate. 
     
     
         57 . The method of  claim 54 , where the chelating agent is a β-diketone. 
     
     
         58 . The method according to  claim 1  where the metal-containing material is a nanostructure. 
     
     
         59 . The method of  claim 58 , where the metal is iron. 
     
     
         60 . The method of  claim 58 , where the nanostructure comprises at least one carbon nanotube. 
     
     
         61 . (canceled) 
     
     
         62 . The method of  claim 58 , where the solvent is carbon dioxide, the solubilizing agent is tributylphosphate, and the oxidizing agent is nitric acid. 
     
     
         63 . An extractant composition, comprising:
 a liquid or supercritical-fluid solvent;   an acid-base complex comprising an oxidizing agent and a solubilizing agent; and   a chelating agent that is not a component of the acid-base complex.   
     
     
         64 . The extractant composition of  claim 63 , where the solvent is a gas at room temperature and atmospheric pressure. 
     
     
         65 . The extractant composition of  claim 63 , where the solvent is a supercritical-fluid solvent. 
     
     
         66 . The extractant composition of  claim 63 , where the solvent is carbon dioxide. 
     
     
         67 . The extractant composition of  claim 63 , where the solvent is supercritical carbon dioxide. 
     
     
         68 . The extractant composition of  claim 63 , where the oxidizing agent is selected from mineral acids, and combinations thereof. 
     
     
         69 - 70 . (canceled) 
     
     
         71 . The extractant composition of  claim 63 , where the oxidizing agent is selected to break down into volatile and/or soluble products after oxidizing a metal. 
     
     
         72 . The extractant composition of  claim 63 , where the oxidizing agent is selected to break down into compounds that are gases at room temperature and atmospheric pressure and/or water after oxidizing a metal. 
     
     
         73 . The extractant composition of  claim 63 , where the solubilizing agent is an alkyl phosphate. 
     
     
         74 . The extractant composition of  claim 63 , where the solubilizing agent is selected from the group consisting of tri-alkylphosphates, tri-alkylphosphine oxides, and combinations thereof. 
     
     
         75 - 76 . (canceled) 
     
     
         77 . The extractant composition of  claim 63 , where the solubilizing agent is soluble in supercritical carbon dioxide. 
     
     
         78 . The extractant composition of  claim 63 , where the chelating agent is a β-diketone a fluorinated β-diketone, or combinations thereof. 
     
     
         79 . The extractant composition of  claim 63 , where the chelating agent is fluorinated. 
     
     
         80 - 81 . (canceled) 
     
     
         82 . The extractant composition of  claim 63 , where the oxidizing agent is nitric acid and the solubilizing agent is tributylphosphate. 
     
     
         83 . The extractant composition of  claim 63 , where the acid-base complex has the formula TBP(HNO 3 ) x (H 2 O) y , in which x is greater than or equal to about 0.7 and y is less than or equal to about 0.7. 
     
     
         84 . The extractant composition of  claim 63 , where the acid-base complex has the formula TBP(HNO 3 ) x (H 2 O) y , in which x is about 1.0 and y is about 0.4. 
     
     
         85 . The extractant composition of  claim 63 , where the acid-base complex is a first acid-base complex, the oxidizing agent is a first oxidizing agent, the solubilizing agent is a first solubilizing agent, and further comprising a second acid-base complex comprising a second oxidizing agent and a second solubilizing agent, where the first oxidizing agent is nitric acid and the second oxidizing agent is hydrochloric acid. 
     
     
         86 . The extractant composition of  claim 63 , where the chelating agent is a first chelating agent and further comprising a second chelating agent that is not a component of the acid-base complex.