Method for producing nickel powder

Abstract

Provided is a method for producing coarse particles of high purity nickel powder from a nickel ammine sulfate complex solution using industrially-inexpensive hydrogen gas and fine nickel powder. The method for producing nickel powder, including performing the following processes (1) to (5), wherein a sulfuric acid solution containing nickel and cobalt is subjected to (1) a pH adjusting step, (2) a solvent extraction step, (3) a complexing step for obtaining a nickel ammine sulfate complex solution, (4) a reduction step for obtaining a reduced slurry containing nickel powder, and (5) a solid-liquid separation step of performing solid-liquid separation to obtain nickel powder and a solution after reduction, and solution after reduction repeatedly using the solution after reduction in either or both of (2) the solvent extraction step and (3) the complexing step.

1 . A method of producing nickel powder, comprising performing processes (1) to (5) on a sulfuric acid solution containing nickel and cobalt:
 (1) a pH adjusting step of adding an alkali hydroxide to the sulfuric acid solution containing nickel and cobalt to obtain a pH-adjusted solution;   (2) a solvent extraction step of bringing the pH-adjusted solution obtained in the pH adjusting step into contact with an extractant to separate into a raffinate and an organic phase after extraction, and then bringing the organic phase after extraction into contact with a solution after reduction which mainly contains sodium ions, magnesium ions, sulfate ions, and ammonium ions as impurities and is obtained in a subsequent solid-liquid separation step to separate into an aqueous phase after exchange containing nickel and an organic phase after exchange containing cobalt and the impurities;   (3) a complexing step of adding ammonium sulfate or a solution after reduction obtained in a solid-liquid separation step described below and ammonium sulfate to the aqueous phase after exchange obtained in the solvent extraction step to obtain a nickel ammine sulfate complex solution;   (4) a reduction step of blowing hydrogen gas into a mixture slurry prepared by adding seed crystals to the nickel ammine sulfate complex solution obtained in the complexing step, to form a nickel powder by precipitation of nickel on a surface of the seed crystals to obtain a reduced slurry containing the nickel powder; and   (5) the solid-liquid separation step of subjecting the reduced slurry obtained in the reduction step to solid-liquid separation to obtain a nickel powder and the solution after reduction which mainly contains sodium ions, magnesium ions, sulfate ions, and ammonium ions as impurities, and then recycling the resulting solution after reduction in either or both of the solvent extraction step and the complexing step, and repeatedly operating sieve of the resulting nickel powder by particle size and addition of a nickel powder having a particle size smaller than a predetermined particle size to either or both of the complexing step and the reduction step as seed crystals to obtain a coarse nickel powder.   
     
     
         2 . The method of producing nickel powder according to  claim 1 , wherein in the solvent extraction step, the resulting organic phase after exchange is brought into contact with water to separate into a cobalt-recovering solution and an organic phase after stripping, and then the organic phase after stripping is recycled as the extractant. 
     
     
         3 . (canceled) 
     
     
         4 . The method of producing nickel powder according to  claim 1 , wherein the nickel powder being sieved to have the particle size smaller than the predetermined particle size has an average particle size of 0.1 to 100 μm. 
     
     
         5 . The method of producing nickel powder according to  claim 1 , wherein, in the reduction step, a dispersant containing one or more selected from polyacrylic acid, acrylate salts, and sulfonate salts is further added during the preparation of the mixture slurry. 
     
     
         6 . The method of producing nickel powder according to  claim 1 , wherein, in the reduction step, an amount of the seed crystals added is 1 to 100% based on the weight of nickel in the nickel ammine sulfate complex solution. 
     
     
         7 . The method of producing nickel powder according to  claim 1 , wherein the sulfuric acid solution containing nickel and cobalt includes at least one of nickel and cobalt mixed sulfide, crude nickel sulfate, nickel oxide, nickel hydroxide, nickel carbonate, and metal nickel powder. 
     
     
         8 . The method of producing nickel powder according to  claim 1 , wherein the extractant is 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester or di-(2,4,4-trimethylpentyl)phosphinic acid. 
     
     
         9 . The method of producing nickel powder according to  claim 1 , wherein a concentration of the ammonium sulfate in the nickel ammine sulfate complex solution is in a range of 100 to 500 g/L, and a molar ratio of the ammonium concentration to the concentration of nickel in the complex solution is 2.0 or higher. 
     
     
         10 . The method of producing nickel powder according to  claim 1 , wherein the reduction step is performed while maintaining a temperature in a range of 150 to 200° C. and a pressure in a range of 1.0 to 4.0 MPa. 
     
     
         11 . The method of producing nickel powder according to  claim 1 , comprising:
 a nickel powder briquetting step of processing the nickel powder obtained through the reduction step and the solid-liquid separation step 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.   
     
     
         12 . The method of producing nickel powder according to  claim 1 , comprising an ammonium sulfate recovery step of concentrating the solution after reduction obtained in the solid-liquid separation step to crystallize ammonium sulfate and recovering ammonium sulfate crystals. 
     
     
         13 . The method of producing nickel powder according to  claim 1 , comprising an ammonia recovery step of adding an alkali to the solution after reduction obtained in the solid-liquid separation step, heating the resulting mixture to volatilize ammonia gas and recovering the ammonia gas.