Method for producing nickel powder

Abstract

Provided is a method for producing coarse particles of so-called high purity nickel powder containing a small amount of impurities and particularly having a low sulfur content from a nickel ammine sulfate complex solution using fine nickel powder. The method for producing nickel powder from a nickel sulfate solution includes the treatment steps of: (1) a hydroxylation step of producing a precipitate of nickel hydroxide; (2) a complexing step of forming a mixture slurry containing a nickel ammine sulfate complex solution, seed crystals, and the nickel hydroxide; (3) a reduction step of forming a reduced slurry containing the nickel powder formed by precipitation of a nickel component on the seed crystals: and (4) a solid-liquid separation step of subjecting the reduced slurry formed in the reduction step (3) to solid-liquid separation to separately recover the nickel powder and a post-reduction solution.

1 . A method of producing nickel powder containing a small amount of impurities from a nickel sulfate solution containing the impurities, comprising the process steps of:
 (1) a hydroxylation step of adding an alkali to the nickel sulfate solution containing the impurities to produce a precipitate of nickel hydroxide having a decreased concentration of the impurities contained therein;   (2) a complexing step of adding a post-reduction solution obtained in a solid-liquid separation step (4) and nickel powder as seed crystals to the precipitate of nickel hydroxide having the decreased concentration of the impurities contained therein and produced in the hydroxylation step (1), and dissolving the precipitate of nickel hydroxide, to form a mixture slurry containing a nickel ammine sulfate complex solution, seed crystals, nickel hydroxide and the impurities contained in the precipitate of nickel hydroxide;   (3) a reduction step of blowing hydrogen gas into the mixture slurry formed in the complexing step (2) to form a reduced slurry containing nickel powder formed by precipitation of a nickel component in the mixture slurry on the seed crystals; and   (4) a solid-liquid separation step of   subjecting the reduced slurry formed in the reduction step (3) to solid-liquid separation to separately recover the nickel powder and a post-reduction solution,   repeatedly sieving the recovered nickel powder by particle size and subjecting a nickel powder having particles smaller than a predetermined size as seed crystals to either or both of the complexing step (2) and the reduction step (3), and, repeatedly subjecting the recovered post-reduction solution to the complexing step (2).   
     
     
         2 . The method of producing nickel powder according to  claim 1 , wherein repeated operation of sieving the nickel powder recovered in the solid-liquid separation step (4) by particle size, and adding a nickel powder having particles smaller than a predetermined size as seed crystals to either or both of the complexing step (2) and the reduction step (3) provides a nickel powder coarser than the nickel powder of seed crystals. 
     
     
         3 . The method of producing nickel powder according to  claim 2 , wherein seed crystals to be added to either or both of the complexing step (2) and the reduction step (3) have an average particle size of 0.1 to 100 μm. 
     
     
         4 . The method of producing nickel powder according to  claim 1 , wherein, in the complexing step (2), when the mixture slurry containing the nickel ammine sulfate complex solution, the seed crystals, and nickel hydroxide is formed, a dispersant is further added to the mixture slurry. 
     
     
         5 . The method of producing nickel powder according to  claim 1 , wherein, in the complexing step (2), an amount of the seed crystals added is 1 to 100% based on the weight of nickel in the nickel ammine sulfate complex solution. 
     
     
         6 . The method of producing nickel powder according to  claim 1 , wherein the reduced slurry is sieved, and undersize nickel powder and undersize reduced slurry of the resulting post-reduction solution are repeatedly used as parts of the nickel powder as seed crystals and the post-reduction solution in the complexing step (2). 
     
     
         7 . The method of producing nickel powder according to  claim 6 , wherein the complexing step (2) is composed of two steps:
 a dissolution step of adding the post-reduction solution to obtain the nickel ammine sulfate complex solution; and   a seed crystal addition step of adding the mixture slurry containing either nickel powder or nickel powder and the post-reduction solution.   
     
     
         8 . The method of producing nickel powder according to  claim 1 , wherein the nickel sulfate solution is obtained by dissolving, in a sulfuric acid solution, at least one of nickel and cobalt mixed sulfide, nickel sulfide, crude nickel sulfate, nickel oxide, nickel hydroxide, nickel carbonate, and metallic nickel powder which is recovered by leaching a nickel oxide ore. 
     
     
         9 . The method of producing nickel powder according to  claim 1 , wherein the nickel sulfate solution is obtained by:
 a leaching step of dissolving a nickel-containing material having cobalt as an impurity; and   a solvent extraction step of adjusting pH of the leachate containing nickel and cobalt obtained in the leaching step and then separating the leachate into a nickel sulfate solution and a cobalt-recovering solution by solvent extraction.   
     
     
         10 . The method of producing nickel powder according to  claim 1 , wherein a concentration of ammonium sulfate in the nickel ammine sulfate complex solution is 100 to 500 g/L, and an ammonium concentration is 1.9 or more in a molar ratio based on a nickel concentration in the nickel ammine sulfate complex solution. 
     
     
         11 . The method of producing nickel powder according to  claim 1 , wherein, in the reduction step (3), hydrogen gas is blown while maintaining the temperature in the range of 100 to 200° C. and the pressure in the range of 0.8 to 4.0 MPa. 
     
     
         12 . The method of producing nickel powder according to  claim 4 , wherein the dispersant contains a polyacrylate salt. 
     
     
         13 . The method of producing nickel powder according to  claim 1 , comprising:
 a nickel powder briquetting step of processing the nickel powder obtained in the reduction step (3) into nickel briquettes in a block form using a briquetting machine; and   a briquette sintering step of subjecting the resulting nickel briquettes in the block form to sintering treatment under holding conditions at a temperature of 500 to 1200° C. in a hydrogen atmosphere to form nickel briquettes as a sintered compact.   
     
     
         14 . The method of producing nickel powder according to  claim 1 , comprising an ammonium sulfate recovery step of concentrating the post-reduction solution from the solid-liquid separation step (4) to crystallize ammonium sulfate and recovering ammonium sulfate crystals. 
     
     
         15 . The method of producing nickel powder according to  claim 1 , comprising an ammonia recovery step of adding an alkali to the post-reduction solution from the solid-liquid separation step (4), heating the resulting mixture to volatilize ammonia gas and recovering the ammonia gas.