Ligand assisted chromatography for metal ion separation

Abstract

A method of producing substantially pure rare earth elements (REEs) from a mixture, including the steps of dissolving a mixture containing REEs in a strong acid to result in a dissolved mixture of metal ions, including that of REEs, capturing metal ions of REEs in a first set of chromatographic columns comprising strong acid cation exchange resins, washing said first set of chromatographic columns with a salt solution to remove non-adsorbing metal ions, eluting metal ions of REES from said first set of chromatographic columns with a first ligand solution to result in a solution of enriched metal ions of REEs, loading said solution of enriched metal ions of REEs onto a second set of chromatographic columns, and eluting bound metal ions of REEs stepwise from said second set of chromatographic columns using a second ligand solution to afford a substantially pure REE. The second set of chromatographic columns comprises hydrous polyvalent metal oxide selected from the group consisting of TiO2, ZrO2, or SnO2. The ligand of the second ligand solution coordinates with said hydrous polyvalent metal oxide.

1 . A method of producing substantially pure rare earth elements (REEs) from a mixture comprising:
 a. dissolving a mixture containing REEs in a strong acid to result in a dissolved mixture of metal ions, including that of REEs;   b. capturing metal ions of REEs in a first set of chromatographic columns comprising strong acid cation exchange resins;   c. washing said first set of chromatographic columns with a salt solution to remove non-adsorbing metal ions;   d. eluting metal ions of REES from said first set of chromatographic columns with a first ligand solution to result in a solution of enriched metal ions of REEs;   e. loading said solution of enriched metal ions of REEs onto a second set of chromatographic columns; and   f. eluting bound metal ions of REEs stepwise from said second set of chromatographic columns using a second ligand solution to afford a substantially pure REE, wherein said second set of chromatographic columns comprising hydrous polyvalent metal oxide selected from the group consisting of TiO 2 , ZrO 2 , or SnO 2  and wherein ligand of said second ligand solution coordinates with said hydrous polyvalent metal oxide.   
     
     
         2 . The method of  claim 1 , wherein said salt solution is a sodium or ammonium salt solution with a counter ion selected from the group consisting of chloride (Cl − ), sulfate (SO 4   2− ), bisulfate (HSO 4   − ), and nitrate (NO 3   − ). 
     
     
         3 . The method of  claim 1 , wherein said first ligand is ethylenediaminetetraacetic acid (EDTA), pentetic acid (DTPA), 1,2-diaminocyclohexanetetraacetic acid (DCTA), N-(2-Hydroxyethyl) ethylenediamine-N,N′,N′-triacetic acid (HEDTA), iminodiacetic acid (IDA), citric acid, or any combination thereof. 
     
     
         4 . The method of  claim 1 , wherein said metal ions of REEs are eluted separately by using said first ligand solution with a linear or stepwise concentration gradient of said ligand. 
     
     
         5 . The method of  claim 1 , wherein said metal ions of REEs are eluted separately by using said first ligand solution with a linear or stepwise gradient of pH. 
     
     
         6 . The method of  claim 1 , wherein said second ligand solution is a solution of ethylenediaminetetraacetic acid (EDTA), pentetic acid (DTPA), 1,2-diaminocyclohexanetetraacetic acid (DCTA), N-(2-Hydroxyethyl) ethylenediamine-N,N′,N′-triacetic acid (HEDTA), iminodiacetic acid (IDA), citric acid, or any combination thereof. 
     
     
         7 . The method of  claim 1 , wherein metal ions of REEs are eluted separately by using said second ligand solution with a linear or stepwise concentration gradient of said ligand. 
     
     
         8 . The method of  claim 1 , wherein metal ions of REEs are eluted separately by using said second ligand solution with a linear or stepwise gradient of pH. 
     
     
         9 . The method of  claim 1 , wherein said strong acid compromises one or more acids selected from the group consisting of hydrochloric acid (HCl), sulfuric acid (H 2 SO 4 ), and nitric acid (HNO 3 ). 
     
     
         10 . A method of substantially pure praseodymium (Pr), neodymium (Nd), or samarium (Sm) of  claim 1 . 
     
     
         11 . A method for separating a mixture of metals, comprising:
 a) dissolving a mixture of metals in a strong acid to result in a dissolved mixture;   b) capturing a desired group of metal ions in a first set of chromatography columns, the first set of chromatography columns is washed in a salt solution to remove non-adsorbing species, resulting in a desired group of metal ions;   c) co-eluting the desired group of metal ions with a ligand solution to result in a further washed solution; and   d) loading the further washed solution onto a second set of chromatography columns.   
     
     
         12 . The method of  claim 11 , wherein the metal ions comprise rare earth element ions. 
     
     
         13 . The method of  claim 12 , wherein the rare earth element ions comprise lanthanide ions. 
     
     
         14 . The method of  claim 11 , wherein the salt solution is a sodium salt solution. 
     
     
         15 . The method of  claim 11 , wherein the salt solution is an ammonium salt solution. 
     
     
         16 . The method of  claim 11 , wherein the metal ions comprise at least one lanthanide ion. 
     
     
         17 . The method of  claim 11 , wherein the metal ions adsorb in the second set of chromatography columns onto a solid phase, react with the ligand in a solution phase, and are eluted separately. 
     
     
         18 . The method of  claim 11 , wherein the metal ions are eluted separately by using the ligand solution with a linear gradient of ligand concentration. 
     
     
         19 . The method of  claim 11  wherein the metal ions are eluted separately by using the ligand solution with a linear gradient of pH. 
     
     
         20 . The method of  claim 11  wherein the metal ions are eluted separately by using the ligand solution with stepwise changes in ligand concentration. 
     
     
         21 . The method of  claim 11  wherein the metal ions are eluted separately by using the ligand solution with stepwise changes in pH. 
     
     
         22 . The method of  claim 11 , wherein the mixture of metals is first dissolved in a 0.1 M-2 M strong acid solution, the strong acid has at least one of hydrochloride acid (HCl), sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ); wherein the salt solution has a concentration of about 0.01 M to about 1 M; wherein the salt solution comprises co-ions including at least one of the following chloride (Cl − ), sulfate (SO 4   2− ), bisulfate (HSO 4   − ), and nitrate (NO 3   − ); wherein the first set of chromatography columns used to capture the metal ions is packed with strong-acid cation exchange resins; wherein the ligand is configured to elute the metal ions and form at least one complex with metal ions with different equilibrium constants or stability constants; wherein the ligand comprises at least one of or a combination of ethylenediaminetetraacetic acid (EDTA), pentetic acid (DTPA), 1,2-Diaminocyclohexanetetraacetic acid (DCTA), N-(2-Hydroxyethyl) ethylenediamine-N,N′,N′-triacetic acid (HEDTA), iminodiacetic acid (IDA), or citric acid. 
     
     
         23 . The method of  claim 22 , wherein the second set of chromatography columns used to separate the lanthanides is packed with an adsorbent with a ligand immobilized by covalent attachment. 
     
     
         24 . The method of  claim 22 , wherein the second set of chromatography columns used to separate the lanthanides is packed with an adsorbent with a ligand immobilized by physical adsorption.