Solvent extraction process for separating cobalt from nickel in aqueous solution

Abstract

A process for separating Co from Ni in an aqueous solution comprises subjecting the solution to extraction and using kinetic differences between Ni and Co in the extraction for achieving at least a partial separation of Co from Ni. This is effected by controlling the duration of the extraction so that a major portion of Co and a minor portion of Ni is extracted from the solution to produce a loaded extractant, enriched in Co and depleted in Ni compared to the feed solution, and a Co-depleted raffinate containing Ni. In a further embodiment, the invention utilizes kinetic differences between Ni and Co during striping for effecting separation of Ni and Co. The loaded extractant can be subjected to a bulk stripping or a selective stripping operation to obtain Co and Ni solutions from which Ni and Co can be recovered. The process may be incorporated in a hydrometallurgical process for the extraction of Ni and/or Co from an ore or concentrate containing Ni and Co.

What is claimed is: 
     
         1 . A process for separating and recovering Co from Ni in an aqueous feed solution comprising sulphates, comprising:
 subjecting the feed solution comprising the sulphates and containing Ni and Co and impurities comprising Mg and Mn to extraction with an extractant and using kinetic differences between Ni and Co in the extraction by controlling duration of the extraction, thereby separating the Co from the Ni, and from the Mg and the Mn, whereby a major portion of Co and a minor portion of Ni is extracted from the feed solution to produce a loaded extractant and a Co-depleted raffinate containing Ni wherein the loaded extractant is enriched in Co and depleted in Ni compared to the feed solution, wherein the concentration of Ni in the feed solution is greater than the concentration of Co, and wherein the duration of extraction is about 30 to 240 seconds, wherein the molar ratio of (Mg+Mn):Co in the feed solution is at least 6:1.   
     
     
         2 . The process of  claim 1 , wherein the feed solution is acidic. 
     
     
         3 . The process of  claim 1 , wherein the feed solution is derived from leaching of ores or concentrates containing Ni and Co. 
     
     
         4 . The process of  claim 1 , wherein the duration of the extraction is controlled by limiting the duration of the extraction to a period wherein a maximum ratio of Co:Ni has been extracted. 
     
     
         5 . The process of  claim 1 , wherein the duration of the extraction is controlled by limiting the duration of the extraction to a period wherein a maximum ratio of Ni:Co remains unextracted. 
     
     
         6 . The process of  claim 1 , comprising a plurality of extractions, wherein the duration of each of the extractions is about 30 to 240 seconds. 
     
     
         7 . The process of  claim 1 , wherein the extraction is carried out at a temperature of about 15° C. to 50° C. 
     
     
         8 . The process of  claim 1 , wherein the extraction is carried out at an organic to aqueous ratio of about 0.5:1 to 4:1. 
     
     
         9 . The process of  claim 1 , further comprising controlling pH of the extraction by adding an alkali. 
     
     
         10 . The process of  claim 9 , wherein the alkali is added to the extractant in an amount of about 0.01 to 0.3 grammole per litre. 
     
     
         11 . The process of  claim 1 , wherein the extraction is carried out at a pH of about 2.5 to 5.5. 
     
     
         12 . The process of  claim 1 , further comprising subjecting the extractant to saponification prior to contact with the aqueous feed solution, wherein the extractant is contacted with an alkali to pre-neutralize or saponify the extractant. 
     
     
         13 . The process of  claim 1 , wherein the extractant comprises a mixture of at least two extractants and one of the two extractants is a carboxylic acid and the other of the two extractants is a hydroxyoxime. 
     
     
         14 . The process of  claim 13 , wherein the carboxylic acid comprises 2-methyl, 2-ethyl heptanoic acid and the carboxylic acid extractant percentage is about 2 to 20 v/v % with reference to total volume of the extractants and a diluent. 
     
     
         15 . The process of  claim 14 , wherein the hydroxyoxime comprises 5,8-diethyl-7-hydroxy-6-dodecanone oxime and the hydroxyoxime extractant percentage is about 4 to 40 v/v % with reference to total volume of the extractants and a diluent. 
     
     
         16 . The process of  claim 1 , wherein the extraction is carried out in two or more successive stages and raffinate from the first stage is contacted by fresh or recycled stripped extractant in the second stage to extract more Co, thereby to further improve the Ni:Co ratio in raffinate produced by the second stage. 
     
     
         17 . The process of  claim 1 , further comprising stripping the Co and Ni from the loaded extractant with an acidic strip solution having a pH of about 1.5 to about 2.5 to produce a Co and Ni product solution and a stripped extractant which is recycled to the extraction, wherein the stripping is carried out a temperature of about 30° C. to 60° C., in 2 to 4 stages, and for a duration of about 3 to 15 minutes per stage. 
     
     
         18 . The process of  claim 1 , wherein the loaded extractant is subjected to stripping with an acidic solution to produce an aqueous product solution containing Ni and Co and further comprising subjecting the aqueous product solution to a further extraction stage to produce a Co-loaded extractant, which is subjected to further stripping to produce a Co product solution, and a second Ni raffinate which is combined with the Co-depleted raffinate from the Ni and Co extraction to produce a Ni product solution. 
     
     
         19 . The process of  claim 1 , further comprising selectively stripping Co from the loaded extractant with a dilute acidic strip solution to produce a Co solution having a pH of about 1 to 2.5 and a partially stripped extractant and then subjecting the Co solution to a second Co extraction to produce a Co-loaded extractant and a second Ni raffinate,
 wherein the selective stripping is carried out a temperature of about 20 to 40° C., in 1 or 2 stages, and for a duration of about 1 to 10 minutes per stage.   
     
     
         20 . The process of  claim 19 , further comprising stripping Ni from the partially stripped extractant with a stronger acidic strip solution to produce a Ni solution having a pH of about 1.0 to 2.0 and a stripped extractant and recycling the stripped extractant to the extraction, wherein the stripping is carried out a temperature of about 30° C. to 60° C., in 1 to 6 stages, and for a duration of about 3 to 15 minutes per stage. 
     
     
         21 . The process of  claim 20  further comprising subjecting the Ni-solution to a third Co-extraction with stripped extractant from the second Co-extraction to produce a further Co-loaded extractant and a third Ni raffinate which is combined with both the Co-depleted raffinate from the extraction and the second Ni raffinate to produce a Ni product solution. 
     
     
         22 . The process of  claim 1 , further comprising scrubbing any Mn present from the loaded extractant with a scrub aqueous solution comprising part of the solution enriched in Co or a part of the raffinate, the scrub aqueous solution having a cobalt to manganese ratio of about 10:1 to 0.75:1, wherein the scrubbing is carried out at a temperature of about 20° C. to 40° C. 
     
     
         23 . The process of  claim 1 , wherein the extraction is carried out using an inline mixer or pipe mixer for mixing the feed solution and the extractant. 
     
     
         24 . A hydrometallurgical process for the recovery of Ni or Co or both Ni and Co from a feed material containing Ni and Co, comprising subjecting the feed material to acid leaching to obtain a resultant acid leach solution and treating the acid leach solution according to the process of  claim 1 .