Solvent extraction process for recovering nickel and cobalt from each solutions

Abstract

A method of separating nickel, cobalt or both from other cations contained in a leach solution, the method including the steps of subjecting the leach solution to separate solvent extraction steps using an organophosphinic acid, a carboxylic acid and an organophosphinic acid.

1 . A method of separating nickel, cobalt or both from other cations contained in a leach solution, the method including the steps of subjecting the leach solution to separate solvent extraction steps using an organophosphoric acid, a carboxylic acid and an organophosphinic acid.  
     
     
         2 . The method as claimed in  claim 1 , wherein the carboxylic acid extraction step is conducted with a mixture of carboxylic acid and a synergist that is capable of increasing the pH gap, ΔpH 50 , between isotherms for nickel and cobalt and those for manganese and calcium, wherein the pH 50  value is the pH at which 50% metal extraction is achieved.  
     
     
         3 . The method as claimed in  claim 2 , wherein the synergist is selected from the group consisting of pyridine carboxylate esters, phosphine oxides and oximes.  
     
     
         4 . The method as claimed in any one of the preceding claims, wherein the carboxylic acids is the formula RCOOH, in which R represents any optionally substituted aliphatic or aromatic group, or a combination of these groups.  
     
     
         5 . The method as claimed in  claim 4 , wherein R contains at least 4 carbon atoms.  
     
     
         6 . The method as claimed in  claim 4 , wherein R contains between 4 and 18 carbon atoms.  
     
     
         7 . The method as claimed in any one of the preceding claims, wherein the carboxylic acid is 2-hexyl, 2-methyl octacarboxylic acid or a carboxylic acid having extraction characteristics similar to or the same as 2-hexyl, 2-methyl octacarboxylic acid.  
     
     
         8 . The method as claimed in any one of the preceding claims, wherein the organophosphoric acid is of the formula (RO) 2 PO 2 H, in which each R group, which may be the same or different, is an optionally substituted branched, straight chained or cyclic alkyl, alkenyl or alkynyl group.  
     
     
         9 . The method as claimed in  claim 8 , wherein each R group has a minimum of 4 carbon atoms.  
     
     
         10 . The method as claimed in  claim 8 , wherein each R group has between 6 to 18 carbon atoms.  
     
     
         11 . The method as claimed in  claim 8 , wherein R is n-octyl, cyclooctyl or 2-ethylhexyl.  
     
     
         12 . The method as claimed in any one of  claims 1  to  7 , wherein the organophosphoric acid is di-2-ethylhexyl phosphoric acid, or an organophosphoric acid having extraction characteristics similar to or the same as di-2-ethylhexyl phosphoric acid.  
     
     
         13 . The method as claimed in any one of the preceding claims, wherein the organophosphinic acid is of the formula R 2 PO 2 H, in which the two R groups, which may be the same or different, are selected from optionally substituted branched, straight chained or cyclic alkyl, alkenyl or alkynyl groups.  
     
     
         14 . The method as claimed in  claim 13 , wherein the two R groups each contain a minimum of 4 carbon atoms.  
     
     
         15 . The method as claimed in  claim 13 , wherein the two R groups each contain from 6 to 18 carbon atoms.  
     
     
         16 . The method as claimed in any one of  claims 1  to  12 , wherein the organophosphinic acid is di-2,4,4-trimethylpentyl phosphinic acid or an organophosphinic acid having extraction characteristics similar to or the same as di-2,4,4-trimethylpentyl phosphinic acid.  
     
     
         17 . The method as claimed in any one of the preceding claims, wherein a modifier is used in the organophosphoric and organophosphinic acid solvent extraction stages to facilitate phase separation of the aqueous and organic phases.  
     
     
         18 . The method as claimed in  claim 17 , wherein the modifier is tri n-butyl phosphate.  
     
     
         19 . The method as claimed in any one of the preceding claims, wherein the organic solvent used in the carboxylic acid, organophosphoric acid and organophosphinic acid solvent extraction stages is kerosene.  
     
     
         20 . The method as claimed in any one of the preceding claims, wherein the loaded organic phase resulting from solvent extraction with organophosphoric acid is scrubbed with an aqueous scrub solution containing manganese and copper, which aqueous scrub solution is obtained by conducting a selective strip on a scrubbed loaded organic solution produced in the scrubbing step, and recycling the manganese and copper-containing aqueous solution back to the scrubbing stage to be used as the aqueous scrub solution.  
     
     
         21 . The method as claimed in  claim 20 , wherein a spent aqueous scrub solution generated in the scrubbing step is then recycled to the leach solution of the organophosphoric acid extraction step to maximise the recovery of cobalt (and nickel, if present), and the selectively stripped organic is subjected to bulk stripping to remove a large proportion of the cations remaining therein to be recycled for use as the organic phase for the organophosphoric solvent extraction.  
     
     
         22 . The method as claimed in  claim 20  or  claim 21 , wherein the mole ratio of (Mn+Cu)/(Co+Ni) in the aqueous scrub solution is at least 1.5.  
     
     
         23 . The method as claimed in any one of the preceding claims, wherein the method does not include a sulphide precipitation stage for separating cobalt from manganese.  
     
     
         24 . A method for separating nickel, cobalt or both from other cations contained in a leach solution, the method involving subjecting the leach solution to separate solvent extraction steps using: 
 (a) an organophosphinic acid; and    (b) a carboxylic acid in combination with a synergist that is capable of increasing the pH gap, ΔpH 50 , between isotherms for nickel and cobalt and those for manganese and calcium.    
     
     
         25 . A plant for conducting the method as claimed in any one of  claims 1  to  23 , the plant including, in any order: 
 a carboxylic acid solvent extraction circuit including a carboxylic acid solvent extractor and a carboxylic acid stripper;  
 an organophosphoric acid solvent extraction circuit including an organophosphoric acid solvent extractor and an organophosphoric acid stripper; and  
 an organophosphinic acid solvent extraction circuit including an organophosphinic acid solvent extractor and an organophosphinic acid stripper.  
 
     
     
         26 . The plant as claimed in  claim 25 , wherein the organophosphoric acid extraction circuit includes: 
 a scrubber for scrubbing the loaded organic solution generated in solvent extractor;    a selective stripper in which the scrubbed organic solution generated in the scrubber is subjected to selective stripping to generate the aqueous scrub solution for use in the scrubber;    a scrubbed organic solution conduit for conducting the scrubbed organic solution to the selective stripper;    an aqueous scrub solution conduit for conducting the aqueous scrub solution from the selective stripper to the scrubber; and    a spent aqueous scrub solution conduit for conducting the spent aqueous scrub solution from the scrubber to the organophosphoric acid solvent extractor.    
     
     
         27 . The plant as claimed in  claim 26 , wherein the plant further includes an organic solution recycle conduit for conducting the partially stripped scrubbed solution from the stripper to the organophosphoric acid solvent extractor.  
     
     
         28 . The plant as claimed in  claim 27 , wherein a bulk stripper is located in the recycle conduit, in which the partially stripped scrubbed solution is stripped of remaining impurities before-being conducted to the solvent extractor.  
     
     
         29 . The plant as claimed in any one of  claims 25  to  28 , the plant including cobalt and nickel recovery stages for recovering cobalt and nickel.