Method for nickel and cobalt recovery from laterite ores by combination of atmospheric and moderate pressure leaching

Abstract

A process for leaching laterite ores containing limonite and saprolite. Sufficient mineral acid is added to a slurry of limonite which is leached at atmospheric pressure to dissolve most of the soluble non-ferrous metals and soluble iron. After adding saprolite the slurry is further leached at a temperature above the normal boiling point and at a pressure above atmospheric pressure for a time sufficient to leach most of the contained nickel in the saprolite and to precipitate most of the iron in solution. The pressure of the slurry is then reduced, and nickel and/or cobalt is subsequently recovered from the leach solution by solvent extraction, resin-in-pulp or other ion exchange, sulfide or hydroxide precipitation, or other recovery method.

1 . A process for leaching laterite ores containing limonite and saprolite, comprising the following steps: 
 (a) adding sufficient mineral acid to a slurry of limonite ore and leaching at atmospheric pressure to dissolve most of the soluble non-ferrous metals and soluble iron in the ore;    (b) adding saprolite ore to the leach slurry produced in (a) and leaching at a temperature above the normal boiling point of the leach solution and at a pressure above atmospheric pressure in an autoclave for a time sufficient to leach most of the contained nickel in the saprolite ore and to precipitate most of the iron in solution;    (c) reducing the pressure of the leach slurry produced in (b) to atmospheric pressure; and    (d) recovering at least one of either nickel or cobalt compounds from the leach solution.    
   
   
       2 . A process as recited in  claim 1 , in which the limonite ore slurry is prepared at as high a solids concentration as possible consistent with good mixing.  
   
   
       3 . A process as recited in  claim 1 , in which step (a) is carried out at a temperature in the range of approximately 95 to 105° C.  
   
   
       4 . A process as recited in  claim 2 , in which step (b) is carried out at a temperature high enough to achieve a rapid rate of reaction and satisfactory nickel (and cobalt) extraction, but low enough that the resulting working pressure is within the tolerance of a simple, low cost autoclave.  
   
   
       5 . A process as recited in  claim 3 , in which step (b) is carried out at a temperature in the range of approximately 120 to 160° C.  
   
   
       6 . A process as recited in  claim 4 , in which step (b) is carried out at a temperature of approximately 150° C.  
   
   
       7 . A process as recited in  claim 4 , in which the mineral acid is selected from the group of sulfuric, hydrochloric, and nitric acid, or mixtures thereof.  
   
   
       8 . A process as recited in  claim 5 , in which the mineral acid is sulfuric acid.  
   
   
       9 . A process as recited in any of claims  1 ,  3 ,  5  or  8 , in which said recovery of at least one of either nickel or cobalt compounds from the leach solution includes adding an ion exchange resin to the leach solution without prior solid/liquid separation.  
   
   
       10 . A process as recited in any of claims  1 ,  3 ,  5 , or  8 , in which the leach solution is first separated from the precipitate prior to said recovery of at least one of either nickel or cobalt compounds from the leach solution.  
   
   
       11 . A process as recited in claims  1  or  8 , in which a reductant is added during step (a) to enhance the dissolution of cobalt from the ore.  
   
   
       12 . A process as recited in  claim 11 , in which the reductant is selected from the group of sulfur dioxide, hydrogen sulfide, soluble bisulfite and sulfite compounds, or soluble ferrous iron compounds.  
   
   
       13 . A process as recited in claims  1  or  8 , in which iron-bearing seed material is added in step (b) to enhance the precipitation of iron.  
   
   
       14 . A process as recited in  claim 13 , in which the seed material is a portion of the final leach residue produced in step (c).