Process for solubilizing, reducing and fixing hexavalent chromium contained in chromite ore processing residue into trivalent chromium

Abstract

A process for reducing hexavalent chromium, Cr(VI), contained within a chromite ore processing residue matrix comprising the sequential steps of providing a chromite ore processing residue matrix containing Cr(VI), solubilizing the matrix to release Cr(VI), reducing the Cr(VI) to Cr(III) using Fe(II), and, fixing the residual Fe(II) using a effective amount of a Fe(II) precipitating agent to make a Fe(II) precipitate.

1 . A process for reducing hexavalent chromium, Cr(VI), contained within a chromite ore processing residue matrix comprising the sequential steps of:
 providing a chromite ore processing residue matrix having a particle size containing Cr(VI),   solubilizing the matrix using a dissolution effective amount of FeSO 4 ,   reducing the Cr(VI) to Cr(III) using Fe(II), and,   fixing the Fe(II) using a fixation effective amount of a Fe(II) precipitating agent to make a Fe(II) precipitate.   
   
   
       2 . The process of  claim 1 , further comprising the step of reducing the particle size of the matrix to less than 25 mm in diameter. 
   
   
       3 . The process of  claim 1 , wherein the dissolution effective amount of FeSO 4  is at least about two times the stoichiometric requirement for Fe(II) based on the Cr(VI) concentration of anhydrous FeSO 4  or an equivalent amount of hydrated FeSO 4  solids. 
   
   
       4 . The process of  claim 1 , wherein the dissolution effective amount of FeSO 4  is at least 5% w/w of anhydrous FeSO 4  or an equivalent amount of hydrated FeSO 4  solids. 
   
   
       5 . The process of  claim 1 , wherein the Fe(II) precipitating agent is a sulfide containing compound. 
   
   
       6 . The process of  claim 1 , wherein the Fe(II) precipitating agent is an alkali metal sulfide. 
   
   
       7 . The process of  claim 1  wherein the Fe(II) precipitating agent is an alkaline earth metal sulfide. 
   
   
       8 . The process of  claim 1 , wherein the Fe(II) precipitating agent is sodium sulfide, sodium bisulfide, or calcium polysulfide. 
   
   
       9 . The process of  claim 1 , wherein the fixation effective amount is at least about one half the stoichiometric requirement of the Fe(II). 
   
   
       10 . The process of  claim 1 , where the Fe(II) precipitating agent is an orthophosphate containing compound. 
   
   
       11 . The process of  claim 1 , wherein the Fe(II) precipitating agent is phosphoric acid. 
   
   
       12 . A process for reducing hexavalent chromium, Cr(VI), contained within a chromite ore processing residue matrix, the process comprising:
 providing a chromite ore processing residue matrix having a particle size containing Cr(VI),   solubilizing the Cr(VI) to trivalent chromium, Cr(III), using at least about two times the stoichiometric requirement for Fe(II) based on the Cr(VI) concentration of anhydrous FeSO 4  or an equivalent amount of hydrated FeSO 4  solids, and   reducing the Cr(VI) to Cr(III) using Fe(II).   
   
   
       13 . The process of  claim 12  further comprising:
 fixing the Fe(II) using a fixation effective amount of a Fe(II) precipitating agent to make a Fe(II) precipitate.   
   
   
       14 . The process of  claim 12  further comprising the step of reducing the particle size of the matrix to less than 25 mm and preferably less than 2 mm. 
   
   
       15 . The process of  claim 12 , wherein the Fe(II) precipitating agent is a sulfide containing compound. 
   
   
       16 . The process of  claim 12 , wherein the Fe(II) precipitating agent is an alkali metal sulfide. 
   
   
       17 . The process of  claim 12 , wherein the Fe(II) precipitating agent is an alkaline earth metal sulfide. 
   
   
       18 . The process of  claim 12 , wherein the Fe(II) precipitating agent is sodium sulfide, sodium bisulfide, or calcium polysulfide. 
   
   
       19 . The process of  claim 12 , wherein the fixation effective amount is at least about one half the stoichiometric requirement of the Fe(II). 
   
   
       20 . The process of  claim 12 , wherein the Fe(II) precipitating agent is an orthophosphate containing compound.