Patent Publication Number: US-2021172042-A1

Title: Processes for the separation of rare earth elements and non-rare earth elements into individual high purity elements

Description:
RELATED APPLICATIONS 
     This U.S. Utility patent application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Application Ser. No. 62/946,078 filed Dec. 10, 2019. The aforementioned application is expressly incorporated herein by reference in its entirety and for all purposes. 
    
    
     TECHNICAL FIELD 
     This invention generally relates to industrial rare earth recovery. In alternative embodiments, provided are processes and continuous ion exchange/continuous ion chromatography (CIX/CIC) systems for the separation of rare earth elements and non-rare earth elements, including metals, into individual high purity elements. 
     BACKGROUND 
     Current methods used to purify the rare earth elements from natural sources produce massive quantities of waste. Purifying one ton of a rare earth element creates tons of acidic and radioactive waste. The processes are also energy intensive. Clearly improved methods for separating and isolating rare earth elements are needed. 
     The rare earths tend to behave chemically in a similar manner, so that separation of the individual elements by conventional chemical methods such as fractional crystallization is very difficult. The approximately 200 year time span needed to identify all of them highlights the difficulty involved in the separation of these elements from each other using chemical methods. 
     SUMMARY 
     In alternative embodiments, provided are processes for the separation of rare earth elements and non-rare earth elements, including metals, into individual high purity elements, comprising a process as set forth in  FIG. 1  and/or  FIG. 2 , and as described herein. 
     In alternative embodiments, provided are systems, for example, multiplexed systems including pluralities of chromatography columns, for the separation of rare earth elements and non-rare earth elements, including metals, into individual high purity elements, comprising a process as set forth in  FIG. 1  and/or  FIG. 2 , and as described herein. 
     In alternative embodiments, provided are continuous ion exchange/continuous ion chromatography (CIX/CIC) systems for the separation of rare earth elements and non-rare earth elements, including metals, into individual high purity elements, comprising a process as set forth in  FIG. 1  and/or  FIG. 2 . 
     In alternative embodiments, provided are processes for the separation of rare earth elements (REE) and non-rare earth elements into individual high purity elements, comprising: 
     (a) providing a starting material comprising at least one rare earth element (REE) and at least one non-rare earth elements; 
     (b) mixing the starting material in an acid or acid chloride solution, or adding the starting material to an acid or acid chloride solution, wherein the acid or acid chloride solution has greater than about 1 molarity chloride concentration, or between about 0.01 molarity and 10 molarity chloride concentration; 
     (c) adding or loading the starting material-comprising acid or acid chloride solution of step (b) into or onto an anion exchange resin column, whereby any ferric tetrachloride anion (optionally a FeCl 4   −1  complex binds to the anion exchange resin) in the starting material-comprising acid chloride solution is retained on the anion exchange resin, and generating a ferric tetrachloride (FeCl 4   −1  complex) anion-free, cationic metal-comprising eluate, 
     and optionally any zinc, thorium and/or uranium in the starting material-comprising acid chloride solution is also retained on the anion exchange resin; 
     (d) adding or loading the ferric tetrachloride anion-free, cationic metal-comprising eluate of (c) into or onto a cationic exchange resin column, whereby REEs are retained on the cationic exchange resin; 
     (e) passing low to high gradient acid eluting solutions over or through the cationic exchange resin column, wherein the passing comprises: 
     (i) first passing an eluting solution having a low acid concentration of about 0.1 to 1 molarity, followed by an eluting solution of about 1 to 2 molarity, followed by an eluting solution of about 3 to 10 or more molarity, or 
     (ii) passing an eluting solution over or through the cationic exchange resin column that changes over time from about 0.1 to 1 molarity, to about 1 to 2 molarity, to about 3 to 10 or more molarity, and 
     at low acid concentration of about 1 molarity or less, a majority of or greater than 50%, or at least about 50%, 60%, 70%, 80%, 85%, 90% or 95%, of monovalent and/or divalent cations are eluted off the cationic exchange resin column, and 
     at acid concentrations of between about 1 to 2 molarity, a majority of or greater than 50%, or at least about 50%, 60%, 70%, 80%, 85%, 90% or 95%, of trivalent cations (optionally aluminum cations) elute off the cationic exchange resin column, and 
     at acid concentrations greater than about 3 or more molarity, a majority of or greater than 50%, or at least about 50%, 60%, 70%, 80%, 85%, 90% or 95%, of the REEs elute off the cationic exchange resin column; and 
     (f) collecting the eluted REEs. 
     In alternative embodiments, of processes as provided herein:
         the at least one REE comprises lanthanum (La); cerium (Ce); praseodymium (Pr); neodymium (Nd); samarium (Sm); europium (Eu); gadolinium (Gd); terbium (Tb); dysprosium (Dy); holmium (Ho); erbium (Er); thulium (Tm); ytterbium (Yb); lutetium (Lu); yttrium (Y), scandium (Sc) or any combination thereof;   the non-rare earth elements comprise metals or metal oxides, and optionally the metals comprise iron or iron oxides, or aluminum or aluminum oxides (aluminum (Al) does not always separate easily from the REEs, but it can be done with multiple passes, it is not necessary that Al is 100% removed, and small amounts can be separated in further downstream processes);   the starting material comprises a mining waste, an acid mine drainage (AMD), an acid rock drainage (ARD), an acid or metalliferous drainage, AMD sludge, a coal overburden, a fire clay, a fly ash, an ore or any combination thereof;   the acid chloride solution comprises: hydrochloric acid or sulfuric acid combined with a chloride salt, and optionally the chloride salt comprises sodium chloride;   the anion exchange resin comprises a polymeric matrix to which functional groups are attached,       

     and optionally the functional groups comprise: tertiary amino groups; primary amines; secondary amines; quaternary ammonium groups or a combination thereof; 
     and optionally the polymeric matrix comprises: N + (CH 3 ) 3  groups (type 1 resins); —N + (CH 3 ) 2 C 2 H 4 OH groups (type 2 resins); or, a combination thereof; 
     and optionally the polymeric matrix comprises styrene-divinylbenzene;
         the anion exchange resin is regenerated by eluting off the ferric tetrachloride anion, and any zinc, thorium and/or uranium if present, by passing a water solution over or through the anion exchange resin, and the water dilutes the FeCl 4   −1  to form FeCl 3  which is not anionic and therefore not attracted to the anion exchange resin, and optionally collecting and recycling the elution solution, wherein optionally the elution solution comprises an FeCl 3  solution, and if present, the zinc, thorium and/or uranium;   the low to high gradient acid eluting solutions comprise hydrochloric acid or sulfuric acid; and/or   the cationic exchange resin comprises crosslinked polystyrene, divinylbenzene or a combination thereof, or comprises sulfonic acid groups, carboxylic acid groups or a combination thereof.       

     In alternative embodiments, provided are continuous ion chromatography (CIC) processes for the separation of rare earth elements (REE) and non-rare earth elements into individual high purity elements, comprising: 
     (a) providing a starting material comprising at least one rare earth element (REE) and at least one non-rare earth elements; 
     (b) mixing the starting material in an acid or acid chloride solution, or adding the starting material to an acid or acid chloride solution, wherein the acid or acid chloride solution has greater than about 1 molarity chloride concentration, or between about 0.1 molarity and 10 molarity chloride concentration; 
     (c) adding or loading the starting material-comprising acid or acid chloride solution of step (b) into or onto a continuous ion chromatography (CIC) column comprising a strong cation (optionally Dowex 650C™ or Purolite SSTC60™ or equivalents) or strong anion (optionally Dowex 1™, Amberlite HPR550 OH™) resin, whereby the REEs are retained on the CIC column; 
     (d) adding to or passing through the CIC column of (c) an eluting solution comprising a chelating material, thereby eluting the REEs off the CIC column; and 
     (f) collecting the eluted REEs. 
     In alternative embodiments of the CIC processes:
         the chelating material comprises: ethylenediamine, ethylenediaminetetraacetic acid (EDTA), lactic acid, glycolic acid, citric acid, acetic acid, ascorbic acid, and/or a sodium, a potassium or an ammonium salt thereof;   the at least one REE comprises lanthanum (La); cerium (Ce); praseodymium (Pr); neodymium (Nd); samarium (Sm); europium (Eu); gadolinium (Gd); terbium (Tb); dysprosium (Dy); holmium (Ho); erbium (Er); thulium (Tm); ytterbium (Yb); lutetium (Lu); yttrium (Y), scandium (Sc) or any combination thereof;   the starting material comprises a mining waste, an acid mine drainage (AMD), an acid rock drainage (ARD), an acid or metalliferous drainage, AMD sludge, a coal overburden, a fire clay, a fly ash, an ore or any combination thereof;   the eluted solution comprising the at least one REE comprises a minimum of 300 ppm REE and less than three times the REE concentration of non-REEs into multiple fractions of similar molecular mass REEs, or light, mid and heavy REE fractions;       

     In alternative embodiments, provided are continuous ion exchange/continuous ion chromatography (CIX/CIC) systems configured to practice methods as provided herein. 
     The details of one or more exemplary embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     All publications, patents, patent applications cited herein are hereby expressly incorporated by reference in their entireties for all purposes. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
       The drawings set forth herein are illustrative of exemplary embodiments provided herein and are not meant to limit the scope of the invention as encompassed by the claims. 
         FIG. 1  illustrates an exemplary process for isolating REEs and metals as provided herein. 
         FIG. 2  illustrates an exemplary process, an exemplary continuous ion exchange/continuous ion chromatography (CIX/CIC) system, for isolating REEs and metals as provided herein. 
         FIG. 3  graphically illustrates an elution stage of an exemplary continuous ion exchange/continuous ion chromatography (CIX/CIC) system for sodium (Na) using 0.25 M acid, as discussed in detail, below. 
         FIG. 4  illustrates graphically illustrates an elution stage of an exemplary continuous ion exchange/continuous ion chromatography (CIX/CIC) system for magnesium (Mg) using 0.25 M acid, as discussed in detail, below. 
         FIG. 5  illustrates graphically illustrates an elution stage of an exemplary continuous ion exchange/continuous ion chromatography (CIX/CIC) system for lanthanum (La) using 0.25 M acid, as discussed in detail, below. 
         FIG. 6  illustrates an exemplary continuous ion exchange/continuous ion chromatography (CIX/CIC) system for isolating REEs and metals as provided herein. 
         FIG. 7  illustrates an exemplary continuous ion exchange/continuous ion chromatography (CIX/CIC) system for isolating REEs and metals as provided herein. 
         FIG. 8  illustrates mono and divalent metals found in pregnated leach solutions (PLS), as discussed in detail, below. 
         FIG. 9  schematically illustrates the elution order from an exemplary CIX Stage 1 system as provided herein, as discussed in detail, below. 
         FIG. 10  graphically illustrates elution data from an exemplary Stage 1 cation CIX of  FIG. 9 . 
         FIG. 11  illustrates schematically illustrates an exemplary small element bench test configuration, as discussed in detail, below. 
         FIG. 12  graphically illustrates a feed analyses for an exemplary modified RO, APE, Membrane, as discussed in detail, below. 
         FIG. 13  graphically illustrates a membrane permeate analyses of an exemplary modified RO, APE, Membrane, as discussed in detail, below. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     In alternative embodiments, provided are processes for the separation of rare earth elements and non-rare earth elements, including metals, into individual high purity elements. 
     In alternative embodiments, processes as provided herein comprise use of any rare earth element-comprising material as a starting material; for example, a starting material for a process as provided herein can comprise a mining waste such as an acid mine drainage, or acid and metalliferous drainage, (AMD) sludge, a coal overburden, a fire clay, a fly ash, an ore or similar materials or any combination thereof. 
     In alternative embodiments, processes as provided herein are used to separate and isolate rare earth elements (REEs), or the “rare earths”, which can comprise a group of 14 elements, lanthanum (La); cerium (Ce); praseodymium (Pr); neodymium (Nd); samarium (Sm); europium (Eu); gadolinium (Gd); terbium (Tb); dysprosium (Dy); holmium (Ho); erbium (Er); thulium (Tm); ytterbium (Yb); lutetium (Lu); with similar size (atomic radius) and chemical properties. This group of chemically similar elements is called the lanthanide series by chemists and is classified by their atomic weights. Yttrium (Y) and scandium (Sc) are also usually included in the rare earth classification due to somewhat similar chemical processing responses. For the purposes of this application Sc and Y are included as REEs. 
     In alternative embodiments, processes as provided herein comprise use of one platform technology to extract and purify various feedstocks, where in alternative embodiments only using one platform technology can have the advantages of:
         1. The procedure does not require heat or excessive energy.   2. The procedure is able to recycle and recover the majority of the acids.   3. The procedure provides for the efficient recovery of iron as ferric chloride.   4. It does not use large amounts of toxic solvents.   5. The footprint of this technology is significantly smaller than competitive REE purification procedures.   6. The process is continuous.   7. The process does not use exotic equipment   8. The process yields high purity REE&#39;s and other metals of interest.       

     In alternative embodiment, processes as provided herein comprise: 
     Stage 1: Anion Exchange Resin to Remove Iron, Zinc, Thorium and Uranium. 
     In alternative embodiments, processes as provided herein subject a starting rare earth element-comprising material to an acid leaching producing a pregnated leach solution (PLS). In alternative embodiments, the acid comprises sulfuric acid, nitric acid hydrochloric acid (HCl acid) or various organic acids or mixtures thereof. In some aspects, HCl acid may be desirable because it produces chloride salts and can be recycled. Using HCl allows for easy removal of the highest contaminating metal, iron. When iron reacts with HCl in the presence of high chlorides it creates the anion complex FeCl 4   −1 . This FeCl 4   −1  complex will bind with an anion exchange resin. Greater than 99.8% of the iron can be removed with this technique. Once the FeCl 4   −1  complex is bound to the anion exchange resin it can be released easily by just passing water over it. This water dilutes the FeCl 4   −1  to form FeCl 3  which is not anionic and therefore not attracted to the anion exchange resin. The FeCl 3  solution can be recycled, as it is a popular water flocculating agent used all over the world for water purification. 
     A similar anionic chloride complex occurs with zinc and the actinides thorium and uranium. Therefore, they will come out of the anion exchange resin at this stage too. This solution can later be further oxidized with air bubbling to ensure that these actinides are in their fully oxidized stated. Thorium has an oxidation state of +4 and uranium will be at +4, +5, +6. The iron is at +3 and Zn at +2. These different oxidations states and the tendency of larger atoms to have higher affinities on IX resins enables the separation of iron and zinc from solution. 
     Stage 2: Cation Chromatographic Resin (CIC) 
     In alternative embodiments, for the next stage, processes as provided herein comprise removing the cation exchange resin and replacing it with a chromatographic resin. This allows for tighter separations. In this section the goal is to generate a light, mid, and heavy cut. This section also removes any other non-REEs that are present. 
     In alternative embodiments, the cation exchange resin is not removed. In alternative embodiments, processes and systems as provided herein comprise use of multiple columns, e.g., cation exchange resin comprising columns, where each column has its own dedicated resin (which need not ever be removed from that column). 
     Stage 3: Batch Chromatography Column or a Flash Chromatography Column 
     As an example, at this stage our volume and masses have become too small to run on the continuous system. Therefore, for the next stage, processes as provided herein comprise use of a batch chromatography column or a flash chromatography column. This column was packed with a stationary phase and eluted with a chelating agent in the mobile phase. 
     Multipurpose Facilities 
     In alternative embodiments, provided are multi-purpose facilities as schematically illustrated in  FIG. 1  and  FIG. 2 . 
     In alternative embodiments, processes as provided herein comprise use of multipurpose facilities that can process all coal biproducts. 
     In alternative embodiments, these include: 
     1. clays that can easily be leached with ion exchange or acid; 
     2. Hard mineral deposits that can be leached with high pressure acid digestion; 
     3. Fly ash can be leached in the high pressure acid digestion reactor. 
     4. Acid mine drainage, or acid and metalliferous drainage, (AMD) sludge is a high source of REE&#39;s and can easily be dissolved to form a pregnant leach solution. 
     In alternative embodiments, processes as provided herein comprise the recycling of acids. 
       FIG. 1  schematically illustrates an exemplary process and facility as provided herein that can handle, for example, coal overburden, AMD sludge and fly ash. This part of the process can extract the REE&#39;s from the matrix. The result leaving this part of the system is an REE containing pregnated leach solution (PLS) that can now be separated. Not shown are acid recycling streams that make this process more efficient. 
       FIG. 2  schematically illustrates an exemplary process comprising use of a CIX/CIC separation system and a separation design. This exemplary process comprises having the pregnated leach solution (PLS) coming into the CIX/CIC separation system. This exemplary design can handle any PLS. There is no need for special designs for specific feedstocks. The first step is iron removal on the continuous anion exchange unit. 
     The next step (Stage 1) comprises use of a continuous ion exchange to remove non-REE from the REE&#39;s. The enriched REE fraction is again processed to enrich it further. 
     Aluminum is a valuable product that can be produced in this process. It will elute as aluminum chloride. In alternative embodiments, this is converted to alumina and HCl. 
     The enriched REE fraction can then be separated into fractions of light, mid and heavy REE fractions (Stage 2). Each fraction can then campaigned to isolate individual REE&#39;s. (Stage 3). 
     Hydrometallurgy 
     We have conducted several tests with pressurized acid leaching systems. We have restricted ourselves to using only HCl, HNO 3  and H 2 SO 4 . So far, the results for acid leaching on mineralized rock follow this pattern: 
       HCl(conc)&gt;Aqua Regia&gt;HCl(dil)&gt;H 2 SO 4 (dil)&gt;H 2 SO 4 (conc). 
     Bench Scale Separation Testing. 
     The data graphically illustrated in  FIG. 3 ,  FIG. 4 ,  FIG. 5 , was obtained from a single column, not continuous. This is the Stage 1 IX separation conducted on AMD sludge from Pennsylvania. The goal of this stage 1 is to separate the non-REE&#39;s from the REE&#39;s. For simplicity of this report we chose to present a monovalent (sodium), divalent (magnesium) and trivalent REE (lanthanum) cations. All other cations exhibited a similar valence number performance. For brevity reasons we are only presenting 1 plot of each valence and not the whole Cation analysis conducted. 
     The data graphically illustrated in  FIG. 3  is for sodium; it is monovalent; all the monovalent cations exhibited a similar graph, and the majority of the monovalent cations elute with a low 0.25M solution of acid. 
     The data graphically illustrated in  FIG. 4  is for magnesium. It is divalent. All the divalent cations exhibited a similar graph. The majority of the divalent cations elute with an acid concentration of 1.0M or less. 
     The data graphically illustrated in  FIG. 5  is for Lanthanum. It is a trivalent REE. All the trivalent REE cations exhibited a similar graph. Unlike the other non-REE cations, the majority of the trivalent REE cations do not elute with acid concentrations at 1.0 M or less. These large trivalent cations have a higher affinity for the IX resin and require a higher acid strength to elute them. 
     Hydrometallurgy 
     In alternative embodiments for processes as provided herein, HCl is the acid of choice. One of the advantages of using HCl is it allows for easy removal of the highest contaminating metal, iron. When iron reacts with HCl in the presence of high chlorides it creates the anion complex FeCl 4   −1 . This FeCl 4   −1  complex will bind with an anion exchange resin. As shown in Table 1, below, greater than 99.8% of the iron is removed with this technique. Once the FeCl 4   −1  complex is bound to the anion exchange resin it can be released easily by just passing water over it. This water dilutes the FeCl 4   −1  to form FeCl 3  which is not anionic and therefore not attracted to the anion exchange resin. The FeCl 3  solution is a popular water flocculating agent used all over the world for water purification. 
     In this embodiment, as illustrated in  FIG. 6  and  FIG. 7 , the PLS solution enters the top of the 1 st  Iron Removal Column. It exits the bottom of the 1 st  column and enters the top of the 2 nd  Iron Removal Column. It exits the bottom of the 2 nd  column and enters the top of the 3 rd  Iron Removal Column. The solution that exits the bottom of the 3 rd  column is collected. After 5 minutes the columns are rotated so that column 3 becomes column 2 and column 2 becomes column 1 and column 1 goes to water washing. This is type of counter current loading. The column 1 has now been fully spent with iron loading and after the 5 minutes rotates to the water wash column that will release all of the absorbed iron. 
     As can be seen in the below table the iron content was reduced from an initial 1556.7 ppm to 3.6 ppm. A 99.8% reduction in iron. The iron has been concentrated and is fully released with the water washing. This counter current loading over 3 columns results in an iron solution coming out that is higher than the iron concentration entering in the FEED. Notice the green FeCl 4   −1  complex that results from it absorbing onto the resin. Notice the water washing column turns brown after the FeCl 4   −1  is washed off 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Iron 
                 REE 
               
               
                 Sample Name 
                 (ppm) 
                 (ppm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 PLS CIX FEED 
                 1566.7 
                 150.3 
               
               
                 PLS Solution exiting the Iron Removal Column 
                 3.6 
                 126.6 
               
               
                 Iron Exiting the Iron Water Wash Column 
                 2412.0 
                 19.9 
               
               
                   
               
            
           
         
       
     
       FIG. 8  top row illustrates some common mono and divalent metals found in the PLS. The bottom row shows some common REE&#39;s found in the PLS. Notice that the mono and divalent cations are found in our fractions  1 , 2 , and  3  but very little in fraction  4 . The opposite is true for the REE&#39;s. They are found predominantly in fractions  3  and  4 . 
     Stage 1 Separations. 
     As discussed above, exemplary CIX systems as provided herein comprise a continuous ion exchange process. In alternative embodiments, the first stage is the separation of the non-REEs from the REEs. This is accomplished because the REEs are relatively larger than most of the non-REEs and typically have higher oxidation states (+3) than the non-REEs. We have a schematic of the Stage 1 process. In this step all the elements stick onto the column. However, as the columns are rinsed with various concentrations of acids different elements come off. In alternative embodiments, monovalent elements such as sodium and potassium elute off the column with a 1M HCl solution. In alternative embodiments, divalent elements such as calcium and magnesium do not elute until a 2M HCl solution is passed over the columns. In alternative embodiments, the trivalent elements (REEs) are not eluted until a much higher concentrated acid is passed of the columns. Iron is also a trivalent, but, In alternative embodiments, it was removed in a prior anion exchange system. Aluminum is trivalent too, but it is much smaller than the REE atoms and, In alternative embodiments, elutes near the end of the 2 M HCl with the divalents. 
       FIG. 9  illustrates schematically the elution order from this exemplary CIX Stage 1 system.  FIG. 10  graphically illustrates elution data from Stage 1 cation CIX. This shows that metals (Sodium, Na shown here) come out of the columns at a 1 M acid solution and the REEs don&#39;t come out until a 6M HCl. 
     Stage 2 Separations. 
     In alternative embodiments, following stage 1 we have (greater than 70%) REEs that have eluted off in the 6M HCl section of the stage 1 scheme. In alternative embodiments, the next stage 2 process is the separate these REEs into 3 different fractions. A light, mid and heavy fraction. 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                 Lights 
                 Mids 
                 Heavies 
               
               
                   
                 Individual REE, 
                 Individual REE, 
                 Individual REE 
               
               
                   
                 314.88 ppm 
                 107.56 ppm 
                 33.06 ppm 
               
               
                   
                   
               
             
            
               
                   
                 SC - 29.76 
                 Pr - 9.63 
                 Tb - 1.95 
               
               
                   
                 Y- 8.05 
                 Nd - 63.29 
                 Dy - 8.05 
               
               
                   
                 La - 62.92 
                 Sm - 13.66 
                 Ho - 10.24 
               
               
                   
                 Ce - 214.15 
                 Eu - 4.27 
                 Er - 5.85 
               
               
                   
                   
                 Gd -16.71 
                 Tm - 1.46 
               
               
                   
                   
                   
                 Yb - 4.51 
               
               
                   
                   
                   
                 Lu - 1.00 
               
               
                   
                   
               
               
                   
                 The results after Stage 2 that show the REE&#39;s divided up into three fractions. 
               
               
                   
                 Lights, Mids, Heavies. 
               
            
           
         
       
     
     Stage 3 Separations. 
     In alternative embodiments, this column is packed with an absorbent stationary phase and the mobile phase comprises chelating agents. In alternative embodiments, this stage of separations is reserved for production of REE and REE derivatives (such as REE-oxalate, REE-glycolate, REE-lactate, REE-EDTA) in purities of 95% or greater. In an example, five elements were chosen and purified to higher than 95% purity as shown by our internal testing. 
     Reagent Recycle. 
     In alternative embodiments, the leaching and Stage 1 CIX system require that a significant amount of acid be present but not necessarily consumed. In order to recover and recycle this acid in the process we have used pressurized membrane systems. 
     In an example, a sample of REE leached from coal overburden with hydrochloric acid was put onto an acid stable membrane to concentrate REE from the acid solution into a small volume thereby improving extraction of REE&#39;s and simultaneously permeate clean HCl acid for reuse in the leaching process. In alternative embodiments, The simultaneous upgrading of the REE concentration and purification of HCl has the potential to improve and reduce the entire cost of REE extraction. 
     REE Concentration and Acid Purification Process Description 
     A small volume, 7 liters, was passed through an acid stable NF/RO membrane. The membrane rejects REE there by concentrating the REE&#39;s but permeates HCl acid for reuse in the leaching process and operating at 1500 psig. 
     Bench Test Process Set-Up 
     An exemplary bench unit set-up P+I diagram is schematically illustrated in  FIG. 11 . The system uses a small spiral wound special modified RO module to purify the processed REE acid. 
     Although the feed acid was quite clean, the actual industrial process can use a polymeric hollow fiber UF as pretreatment, hence this feed water was pretreated with UF and then transferred to the feed tank. In order to achieve maximum recovery in our bench test the concentrate is returned back to the feed tank until we had recovered about 40% of feed as clean permeate. To insure recovery was mass balanced properly the initial feed, final permeate, and concentrate were weighed. 
     The modified acid RO element was base line tested on tap water test solution to make sure it had proper flux and rejection based MDS specifications. The modified RO, referred to as APE, is the only membrane capable of permeating HCl, but rejecting REE&#39;s. 
     The Pass 1 tests for APE membrane were run at 50° C. to 60° C. and 800 psig but normalized to 1500 psig to reflect the flux at elevated pressures needed to overcome the osmotic pressure of the sample. The membrane flux data being expressed as LMH (liters/meter/hour). 
       FIG. 12  (Feed) and  FIG. 13  (membrane permeate) illustreat an analyses of the Feed and Permeate for the exemplary modified reverse osmosis (RO), APE, Membrane. These data are consistent with other REE tests we have run on the modified RO acid stable microfluidic diffusional sizing (MDS) membrane, APE. The overall REE rejection is 96.2% and based on past experience the heavy REE&#39;s (the most valuable) are rejected at 98.5% to 99% be the membrane. 
     Any of the above aspects and embodiments can be combined with any other aspect or embodiment as disclosed here in the Summary, Figures and/or Detailed Description sections. 
     As used in this specification and the claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. 
     Unless specifically stated or obvious from context, as used herein, the term “or” is understood to be inclusive and covers both “or” and “and”. 
     Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. About can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.” 
     Unless specifically stated or obvious from context, as used herein, the terms “substantially all”, “substantially most of”, “substantially all of” or “majority of” encompass at least about 90%, 95%, 97%, 98%, 99% or 99.5%, or more of a referenced amount of a composition. 
     The entirety of each patent, patent application, publication and document referenced herein hereby is incorporated by reference. Citation of the above patents, patent applications, publications and documents is not an admission that any of the foregoing is pertinent prior art, nor does it constitute any admission as to the contents or date of these publications or documents. Incorporation by reference of these documents, standing alone, should not be construed as an assertion or admission that any portion of the contents of any document is considered to be essential material for satisfying any national or regional statutory disclosure requirement for patent applications. Notwithstanding, the right is reserved for relying upon any of such documents, where appropriate, for providing material deemed essential to the claimed subject matter by an examining authority or court. 
     Modifications may be made to the foregoing without departing from the basic aspects of the invention. Although the invention has been described in substantial detail with reference to one or more specific embodiments, those of ordinary skill in the art will recognize that changes may be made to the embodiments specifically disclosed in this application, and yet these modifications and improvements are within the scope and spirit of the invention. The invention illustratively described herein suitably may be practiced in the absence of any element(s) not specifically disclosed herein. Thus, for example, in each instance herein any of the terms “comprising”, “consisting essentially of”, and “consisting of” may be replaced with either of the other two terms. Thus, the terms and expressions which have been employed are used as terms of description and not of limitation, equivalents of the features shown and described, or portions thereof, are not excluded, and it is recognized that various modifications are possible within the scope of the invention. Embodiments of the invention are set forth in the following claims. 
     A number of embodiments of the invention have been described. Nevertheless, it can be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.