Systems and processes for recovery of high-grade rare earth concentrate from acid mine drainage

Abstract

In one aspect, the disclosure relates to a continuous process for treating acid mine drainage while simultaneously recovering a high-grade rare earth preconcentrate suitable for extraction of commercially valuable rare earth oxides. In a further aspect, the preconcentrate is from about 0.1% to 5% rare earth elements on a dry weight basis. In another aspect, the disclosure relates to a method for processing the preconcentrate to generate a pregnant leach solution that does not form gels or emulsions and is suitable for processing via solvent extraction. In another aspect, the disclosure relates to a system and plant for carrying out the disclosed process. In still another aspect, the disclosure relates to a composition containing rare earth elements produced by the process disclosed herein. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present disclosure.

1 - 19 . (canceled) 
     
     
         20 . A composition comprising a pregnant leach solution (PLS) made by the method comprising the following steps:
 a. contacting a raw material containing REEs with a first base to form waste solids and an aqueous phase and discarding the waste solids;   b. contacting the aqueous phase with a second base to form an REE-enriched preconcentrate and an effluent and discharging the effluent;   c. contacting the REE-enriched preconcentrate with an acid to form an acidic preconcentrate;   d. filtering the acidic preconcentrate to form an acidic filtrate; and   e. contacting the acidic filtrate with a third base and filtering to form a pregnant leach solution;   wherein the pregnant leach solution is enriched in REEs and essentially free of solids.   
     
     
         21 . The composition of  claim 20 , wherein the raw material is raw acid mine drainage (AMD), an AMD precipitate (AMDp), or an enriched AMD precipitate (eAMDp). 
     
     
         22 . The composition of  claim 20 , wherein contacting the raw material with the first base changes the pH of the aqueous phase to about 4.0 to about 4.5. 
     
     
         23 . The composition of  claim 20 , wherein the first base comprises NaOH, KOH, ammonia, ammonium hydroxide, quicklime, lime slurry, or a combination thereof. 
     
     
         24 . The composition of  claim 20 , wherein contacting the aqueous phase with the second base changes the pH of the aqueous phase to about 8.0 to about 8.5. 
     
     
         25 . The composition of  claim 20 , wherein the second base comprises NaOH, KOH, ammonia or an ammonium compound, quicklime, lime slurry, or a combination thereof. 
     
     
         26 . The composition of  claim 20 , wherein the contacting the REE-enriched preconcentrate with the acid changes the pH of the REE-enriched preconcentrate to about 0.7 to about 3.0. 
     
     
         27 . The composition of  claim 20 , wherein the acid comprises hydrochloric acid, nitric acid, sulfuric acid, or a combination thereof. 
     
     
         28 . The composition of  claim 20 , wherein contacting the acidic filtrate with the third base changes the pH of the acidic filtrate to about 2.8 to about 3.0. 
     
     
         29 . The composition of  claim 20 , wherein the third base comprises MgO, NaOH, KOH, ammonia or ammonium hydroxide, quicklime, lime slurry, or a combination thereof. 
     
     
         30 . The composition of  claim 20 , wherein step (e) further comprises oxidizing the acidic filtrate. 
     
     
         31 . The composition of  claim 30 , wherein the acidic filtrate is oxidized mechanically, electrochemically, with an oxidizing agent, or a combination thereof. 
     
     
         32 . The composition of  claim 31 , wherein the oxidizing agent is hydrogen peroxide. 
     
     
         33 . The composition of  claim 20 , further comprising a step for recovering scandium between steps (a) and (b), the step for recovering scandium comprising contacting the aqueous phase with a fourth base, thereby forming a scandium-enriched solid concentrate, and removing the scandium-enriched solid concentrate from the aqueous phase. 
     
     
         34 . The composition of  claim 33 , wherein contacting the aqueous phase with a fourth base changes the pH of the aqueous phase to about 4.9 to about 5.1. 
     
     
         35 . The composition of  claim 33 , wherein the fourth base comprises NaOH, KOH, ammonia or an ammonium compound, quicklime, lime slurry, or a combination thereof. 
     
     
         36 . The composition of  claim 20 , further comprising adding a flocculating agent, a coagulating agent, or both in any of steps (a), (b), or (c). 
     
     
         37 . The composition of  claim 20 , wherein following step (e), the method further comprises subjecting the pregnant leach solution to solvent extraction to produce a refined rare earth resource comprising at least 50% REEs. 
     
     
         38 . The composition of  claim 20 , wherein the pregnant leach solution comprises one or more of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, or yttrium. 
     
     
         39 . The composition of  claim 38 , wherein, when present, the lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, or yttrium are present in the following amounts in μg/L: 
       
         
           
                 
                 
                 
                 
               
                     
                     
                 
                     
                   Element 
                   Minimum 
                   Maximum 
                 
                     
                     
                 
                     
                 
                 
                 
                 
                 
               
                     
                   Y 
                   7151 
                   111,224 
                 
                     
                   La 
                   1477 
                   32,650 
                 
                     
                   Ce 
                   4906 
                   86,414 
                 
                     
                   Pr 
                   782 
                   10,803 
                 
                     
                   Nd 
                   3688 
                   48,145 
                 
                     
                   Sm 
                   1133 
                   12,001 
                 
                     
                   Eu 
                   302 
                   3,223 
                 
                     
                   Gd 
                   1820 
                   18,229 
                 
                     
                   Tb 
                   339 
                   3,021 
                 
                     
                   Dy 
                   1995 
                   18,229 
                 
                     
                   Ho 
                   354 
                   3639 
                 
                     
                   Er 
                   908 
                   10,032 
                 
                     
                   Tm 
                   112 
                   1291 
                 
                     
                   Yb 
                   638 
                   7380 
                 
                     
                   Lu 
                   91 
                   1100 
                 
                     
                   Th 
                   0.06 
                   322 
                 
                     
                   U 
                   198 
                   1205 
                 
                     
                     
                 
             
                
                
                
               
               
                
               
            
             
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         40 . The composition of  claim 20 , wherein the pregnant leach solution comprises iron present in an amount less than or equal to about 5 mg/L. 
     
     
         41 . The composition of  claim 39 , wherein, when present, the lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, or yttrium are present in the following amounts in μg/L: 
       
         
           
                 
                 
                 
                 
               
                     
                     
                 
                     
                   Element 
                   Minimum 
                   Maximum 
                 
                     
                     
                 
                     
                 
                 
                 
                 
                 
               
                     
                   Y 
                   7151 
                   111,224 
                 
                     
                   La 
                   1477 
                   32,650 
                 
                     
                   Ce 
                   4906 
                   86,414 
                 
                     
                   Pr 
                   782 
                   10,803 
                 
                     
                   Nd 
                   3688 
                   48,145 
                 
                     
                   Sm 
                   1133 
                   12,001 
                 
                     
                   Eu 
                   302 
                   3,223 
                 
                     
                   Gd 
                   1820 
                   18,229 
                 
                     
                   Tb 
                   339 
                   3,021 
                 
                     
                   Dy 
                   1995 
                   18,229 
                 
                     
                   Ho 
                   354 
                   3639 
                 
                     
                   Er 
                   908 
                   10,032 
                 
                     
                   Tm 
                   112 
                   1291 
                 
                     
                   Yb 
                   638 
                   7380 
                 
                     
                   Lu 
                   91 
                   1100 
                 
                     
                   Th 
                   0.06 
                   322 
                 
                     
                   U 
                   198 
                   1205 
                 
                     
                     
                 
             
                
                
                
               
               
                
               
            
             
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         42 . The composition of  claim 20 , wherein the pregnant leach solution comprises iron present in an amount less than or equal to about 5 mg/L.