Separation of radium and rare earth elements from monazite

Abstract

A method of chemically extracting radium-228, rare earth metals, thorium, the decay products of thorium, and phosphates from thorium-containing ores. The method involves breaking thorium-containing ore into fragments, wetting the fragments with a concentrated strong acid to make a slurry, heating the slurry, passing the heated solution through a first anion exchange column, retaining metals and radium-228 captured on the resin, allowing the radium-228 ions to decay to actinium-228, purifying the actinium-228 fraction, sending the actinium-228 fraction through a capture column, eluting the captured thorium-228 with acid, removing radium from the solution, retaining the radium-228 fraction for isomer in-growth, retaining decay products from the radium-228, separating the REEs from the process stream; and eluting and retaining the REEs.

1 . A chemical separation process for removing radium-228, from materials containing thorium-232 to make “neutralized thorium”, and to separate rare earth elements from common thorium ores or mining waste streams, comprising the steps of:
 (a) breaking concentrated monazite or other thorium-containing ore into small fragments;   (b) wetting the fragments with a concentrated strong acid to make a slurry, wherein the slurry contains, among other things, rare earth elements (REE), actinium and radium ions;   (c) heating the slurry made in step (b);   (d) filtering and passing the heated solution through a first anion exchange column having an anion exchange resin;   (e) retaining metals on the resin the first anion exchange column;   (f) allowing the radium ions to decay to actinium-228;   (g) purifying the actinium-228 fraction;   (h) sending the actinium-228 fraction through a final thorium-228 capture column;   (i) eluting the captured thorium-228 with 1M HNOsub.3;   (j) removing radium from the solution;   (k) retaining the radium-228 fraction for isotope in-growth;   (l) retaining decay products from the radium-228 fraction for use as alpha-emitter used in medical isotope generators;   (m) separating the each individual REEs from the process stream; and   (n) eluting and retaining the separated REEs.   
   
   
       2 . The process of  claim 1 , wherein step (a) comprises pulverizing or comminuting. 
   
   
       3 . The process of  claim 2 , wherein step (a) comprises passing the concentrated monazite or other thorium-containing ore through a mesh screen. 
   
   
       4 . The process of  claim 4 , wherein the mesh screen used in step (a) is between 10 and 200 mesh. 
   
   
       5 . The process of  claim 1 , wherein the strong acid used in step (b) is 8M nitric acid. 
   
   
       6 . The process of  claim 1 , further including the step of removing and recovering the metals retained in step (e) by using a 90% methanol-10% nitric acid solution. 
   
   
       7 . The process of  claim 6 , wherein the metals retained include, Th, Fe, Co Ni, Cu Ag Sn Zn Ce A. Sc Te Zr Hf Cr Mo Mn and U. 
   
   
       8 . The process of  claim 1 , further including the step of eluting thorium from the resin in the first anion exchange column using 1 M HNOsub.3. 
   
   
       9 . The process of  claim 8 , further including the step of further purifying the captured thorium-228. 
   
   
       10 . The process of  claim 1 , further including the step of passing the solution over at least one additional anion exchange resin column. 
   
   
       11 . The process of  claim 1 , wherein step (j) involves removing radium from the solution via co-precipitation with barium nitrate 
   
   
       12 . The process of  claim 11 , further including the step of secondarily and tertiary co-precipitating barium nitrate to ensure complete separation of the radium-228 fraction. 
   
   
       13 . The process of  claim 1 , wherein step (m) involves separating each REE in order of the size of the rare earth metal ions, with the smallest separated first and the largest last. 
   
   
       14 . The process of  claim 1 , wherein step (m) involves separating each REE lanthanides using reversed-phased partition chromatograph. 
   
   
       15 . The process of  claim 14 , wherein the stationary phase of the reversed-phased partition chromatograph employs an organic phosphorous compound. 
   
   
       16 . The process of  claim 15 , wherein the organic phosphorous compound of the stationary phase is selected from the group consisting of bis-(2-ethylhexyl)-o-phosphoric acid (HDEHP), and tri-n-butylphosphate (TBP), bis(di-n-hexyl-phosphinyl)methane (HDPM), and di-n-butylphosphate. 
   
   
       17 . The process of  claim 14 , wherein the stationary phase uses a long-chain amine. 
   
   
       18 . The process of  claim 17 , wherein the long-chain amine is selected from the group consisting of tri-octyl-amine and di-nonyl-naphalene-sulphonic acid in heptane. 
   
   
       19 . The process of  claim 14 , further including the step of using a support for the stationary phase. 
   
   
       20 . The process of  claim 19 , wherein the support is selected from the group consisting of Corvic (poly(vinyl chloride-vinyl acetate) co-polymers), siliconized kieselguhy or silica gel, Kel-F, (polychlorotrifluoroethane), and filter paper. 
   
   
       21 . The process of  claim 14 , wherein the mobile phases are substantially pure aqueous solutions containing strong acids. 
   
   
       22 . The process of  claim 21 , wherein the strong acids are selected from the group consisting of nitric acid, hydrochloric acid, and perchloric acid. 
   
   
       23 . The process of  claim 1 , wherein step (n) involves eluting each REE in order of increasing atomic number. 
   
   
       24 . The process of  claim 1 , further including the step of recovering phosphates as phosphoric acid. 
   
   
       25 . The process of  claim 1 , further including the step of distilling nitric acid from the process stream and placing the distillate back in the process stream for use in an earlier method step. 
   
   
       26 . The process of  claim 1 , further including the step of reserving thorium-232 depleted of radium-228.