Extraction of metals from metallic compounds

Abstract

Methods for the extraction of metals such as rare earth metals and thorium from metal compounds and solutions. The methods may include the selective precipitation of rare earth elements from pregnant liquor solutions as rare earth oxalates. The rare earth oxalates are converted to rare earth carbonates in a metathesis reaction before being digested in an acid and treated for the extraction of thorium. A two-step extraction method may be applied to precipitate thorium as thorium hydroxide under controlled pH conditions such that pure thorium precipitate is recovered from a first step and a thorium-free rare earth solution is recovered at the subsequent step. The resulting rare earth solutions are of extremely high purity and may be processed directly in a solvent extraction circuit for the separation of rare earth elements, or may be processed for the direct production of a 99.9% bulk rare earth hydroxide/oxide concentrate.

1 . (canceled) 
     
     
         2 . A method for the extraction of thorium from an acidic solution containing solubilized thorium, the method comprising the steps of:
 first contacting the acidic solution with a hydroxide precipitant at a first pH of at least about pH 2.8 and not greater than about pH 3.9 to precipitate thorium as thorium hydroxide and form an intermediate thorium depleted solution and a first thorium hydroxide product;   separating at least a portion of the first thorium hydroxide product from the intermediate thorium depleted solution;   second contacting the intermediate thorium depleted solution with the hydroxide precipitant at a second pH of at least about pH 3 and not greater than about pH 4, wherein the second pH is greater than the first pH, to precipitate additional solubilized thorium as thorium hydroxide and form a thorium depleted solution and a second thorium hydroxide product; and   separating at least a portion of the second thorium hydroxide product from the thorium depleted solution.   
     
     
         3 . (canceled) 
     
     
         4 . The method recited in  claim 2 , wherein at least one of the first and second contacting steps comprises contacting the acidic solution or the intermediate thorium depleted solution with the hydroxide precipitant at a pH of at least about pH 3.2. 
     
     
         5 . The method recited in  claim 2 , wherein at least one of the first and second contacting steps comprises contacting the acidic solution or the intermediate thorium deleted solution with the hydroxide precipitant at a pH of at least about pH 3.3. 
     
     
         6 . The method recited in  claim 2 , wherein at least one of the first and second contacting steps comprises contacting the acidic solution or the intermediate thorium deleted solution with the hydroxide precipitant at a pH of at least about pH 3.4. 
     
     
         7 . The method recited in  claim 2 , wherein at least one of the first and second contacting steps comprises contacting the acidic solution or the intermediate thorium deleted solution with the hydroxide precipitant at a pH of at least about pH 3.5. 
     
     
         8 . The method recited in  claim 2 , wherein at least one of the first and second contacting steps comprises contacting the acidic solution or the intermediate thorium deleted solution with the hydroxide precipitant at a pH of at least about pH 3.7. 
     
     
         9 . The method recited in  claim 2 , wherein at least one of the first and second contacting steps comprises contacting the acidic solution or the intermediate thorium deleted solution with the hydroxide precipitant at a pH of not greater than pH 3.9. 
     
     
         10 . The method recited in  claim 2 , wherein the hydroxide precipitant is selected from the group consisting of sodium hydroxide and ammonium hydroxide. 
     
     
         11 . The method recited in  claim 2 , wherein the hydroxide precipitant comprises ammonium hydroxide. 
     
     
         12 . The method recited in  claim 2 , wherein the concentration of solubilized thorium in the acidic solution is at least about 50 mg/l and is not greater than about 2000 mg/l. 
     
     
         13 . The method recited in  claim 2 , wherein the concentration of solubilized thorium in the acidic solution is at least about 100 mg/l and is not greater than about 1600 mg/l. 
     
     
         14 . The method recited in  claim 2 , wherein the acidic solution comprises solubilized rare earth elements. 
     
     
         15 . The method recited in  claim 2 , wherein the acidic solution is a nitric acid solution. 
     
     
         16 . The method recited in  claim 15 , further comprising the step of:
 leaching, before the contacting step, a rare earth containing product to form the acidic solution, the leaching comprising the step of contacting the rare earth containing product with nitric acid to solubilize rare earth elements as rare earth nitrates and solubilize thorium as thorium nitrate.   
     
     
         17 . The method recited in  claim 16 , wherein the rare earth containing product comprises at least one rare earth compound selected from the group consisting of rare earth oxides, rare earth hydroxides, rare earth carbonates and mixtures thereof. 
     
     
         18 . The method recited in  claim 16 , wherein the rare earth containing product comprises rare earth carbonates. 
     
     
         19 . The method recited in  claim 2 , wherein the acidic solution comprises at least two different rare earth elements. 
     
     
         20 . The method recited in  claim 2 , wherein the acidic solution comprises at least three different rare earth elements. 
     
     
         22 . The method recited in  claim 2 , wherein the rare earth elements comprise at least three different rare earth elements selected from the group consisting of cerium, dysprosium, europium, terbium, lanthanum, neodymium, praseodymium and yttrium. 
     
     
         23 . The method recited in  claim 19 , wherein the rare earth elements comprise at least one rare earth element selected from the group consisting of neodymium, europium, praseodymium and terbium. 
     
     
         24 . The method recited in  claim 2 , wherein at least about 95% of the thorium in the acidic solution is precipitated as thorium hydroxide in the thorium hydroxide product. 
     
     
         25 . The method recited in  claim 2 , wherein at least about 98% of the thorium in the acidic solution is precipitated as thorium hydroxide in the thorium hydroxide product. 
     
     
         26 . The method recited in  claim 2 , wherein the thorium depleted solution comprises not greater than about 0.01 at. % thorium. 
     
     
         27 . The method recited in  claim 2 , wherein the thorium depleted solution comprises not greater than about 0.005 at. % thorium. 
     
     
         28 . The method recited in  claim 2 , wherein metals solubilized in the thorium depleted solution comprise at least about 99% solubilized rare earth metals. 
     
     
         29 . The method recited in  claim 2 , wherein at least about 99% of rare earth metals solubilized in the acidic solution are solubilized in the thorium depleted solution. 
     
     
         30 - 47 . (canceled) 
     
     
         48 . The method recited in  claim 2 , wherein the first pH is from about pH 3.0 to about pH 3.3. 
     
     
         49 . The method recited in  claim 2 , wherein the second pH is from about pH 3.5 to about pH 4.0. 
     
     
         50 . The method recited in  claim 2 , wherein the first pH is from about pH 3.0 to about pH 3.3 and the second pH is from about pH 3.5 to about pH 4.0. 
     
     
         51 . The method recited in  claim 2 , further comprising the step of recycling at least a portion of the second thorium hydroxide product to the first contacting step. 
     
     
         52 . The method recited in  claim 51 , wherein the second thorium hydroxide product comprises at least about 20 at. % rare earth elements.