the method for producing nickel powder according to the present invention will be described with reference to the production flow chart of the nickel powder of the present invention shown in fig1 . note that examples of the method for obtaining a nickel sulfate solution before the complexing step include a method comprising subjecting nickel oxide ore to pressure leach by a known method , neutralizing the resulting leachate to remove impurities , adding a sulfurizing agent to the solution after removing impurities to precipitate nickel as a sulfide , then dissolving the sulfide containing nickel with sulfuric acid or the like , and separating nickel from other impurities by a method such as known solvent extraction to prepare the nickel sulfate solution . this is a step of adding ammonia gas or aqueous ammonia ( nh 4 oh ) to a nickel sulfate ( niso 4 ) solution to form an ammine complex of nickel . in doing so , ammonia is added so that the molar ratio of the ammonium concentration to the nickel concentration in the solution is 1 . 9 or more . if the molar ratio is less than 1 . 9 , a part of nickel in solution will not form an ammine complex but produce a precipitate of nickel hydroxide . further , ammonium sulfate may be added in this step in order to adjust the ammonium sulfate concentration . the ammonium sulfate concentration at that time is preferably 100 to 500 g / l . if ammonium sulfate is added in an amount exceeding an ammonium sulfate concentration of 500 g / l , the solubility will be exceeded to precipitate crystals , and an ammonium sulfate concentration of less than 100 g / l will be difficult to be achieved in terms of the metal balance of the process . in this step , to the nickel ammine sulfate complex solution obtained in the “ complexing step ” ( 1 ), is added a seed crystal slurry containing nickel powder having an average particle size of 10 to 200 μm serving as seed crystals , and then thereto is added a surfactant for smoothing the surface in an amount of 1 to 20 % by weight based on the weight of the nickel powder in the seed crystal slurry to form a mixed slurry . as the surfactant to be added , at least one of polyethylene glycol and polyvinyl alcohol each having a nonionic functional group can be used , or sodium polyacrylate having an anionic functional group can be used . if the amount of the surfactant added is as small as less than 1 % by weight , the effect of smoothing is small , and if the amount of the surfactant added is as large as more than 20 % by weight , the amount is not desirable in terms of impurities and the cost of the chemical . in this step , hydrogen gas is blown into the mixed slurry obtained in the “ seed crystal and surfactant addition step ” ( 2 ) to precipitate nickel from solution into the voids of the seed crystals to form a reduced slurry containing reduced nickel powder , and then the reduced slurry is subjected to solid - liquid separation treatment to produce pre - growth nickel powder which is reduced nickel powder . in doing so , reaction temperature is preferably 150 to 200 ° c . if the reaction temperature is less than 150 ° c ., reduction efficiency will be reduced , and even if it exceeds 200 ° c ., the reaction will not be affected , but the loss of thermal energy will increase . further , the pressure during the reaction is preferably 1 . 0 to 4 . 0 mpa . if the pressure is less than 1 . 0 mpa , reaction efficiency will be reduced , and even if it is higher than 4 . 0 mpa , the reaction will not be affected , but the loss of hydrogen gas will increase . in this step , the nickel ammine sulfate complex solution obtained in the “ complexing step ” ( 1 ) is added to the “ pre - growth nickel powder ” which has been recovered by subjecting the reduced slurry produced in the “ reduction step ” ( 3 ) to solid - liquid separation treatment to form a nickel complex slurry , which is fed again as the “ mixed slurry ” in the “ reduction step ” ( 3 ). the nickel complex slurry is subjected to reduction treatment by hydrogen gas to grow the “ pre - growth nickel powder ” in the nickel complex slurry into “ post - growth nickel powder ” to produce “ product nickel powder ”. the growth step ( 4 ) is repeated at least once to thereby grow nickel powder and densely smooth the surface thereof . a complexing treatment was performed to prepare a solution containing a nickel ammine sulfate complex , by adding 191 ml of 25 % aqueous ammonia to a solution containing 336 g of nickel sulfate and 330 g of ammonium sulfate and adjusting the total volume of the resulting solution to 1000 ml . the seed crystal and surfactant addition step was performed to prepare a mixed slurry , by adding a seed crystal slurry containing 75 g of seed crystals to the above solution and further adding thereto 2 . 5 g ( 3 % by weight ) of polyethylene glycol “ peg - 20000 ” ( manufactured by nof corporation ) as a nonionic surfactant . next , the reduction treatment was performed by charging an autoclave as a high pressure vessel with the mixed slurry , heating the mixed slurry to 185 ° c . with stirring , then blowing hydrogen gas as a reducing agent into the mixed slurry , and feeding hydrogen gas so as to maintain the pressure in the autoclave at 3 . 5 mpa . after a lapse of one hour from the start of the feeding of hydrogen gas , the feeding of hydrogen gas was stopped , and the autoclave was cooled . the reduced slurry obtained after cooling was subjected to solid - liquid separation by washing and filtration to recover pre - growth nickel powder . the recovered pre - growth nickel powder was again added to the solution containing a nickel ammine complex prepared through complexing treatment by adding 191 ml of 25 % aqueous ammonia to a solution containing 336 g of nickel sulfate and 330 g of ammonium sulfate and adjusting the total volume of the resulting solution to 1000 ml , and the reaction was repeated to obtain product nickel powder having a smooth surface . further , an increase in the bulk density was also observed with an increase in the reduction treatment ( the number of times of the reaction ) in the growth step . furthermore , when a 50 - cc shipping container was filled with the nickel powder , the powder did not scatter , and the operation was able to be performed without running a local exhaust ventilation . a complexing treatment was performed to prepare a solution containing a nickel ammine complex , by adding 191 ml of 25 % aqueous ammonia to a solution containing 336 g of nickel sulfate and 330 g of ammonium sulfate and adjusting the total volume of the resulting solution to 1000 ml . the seed crystal and surfactant addition step was performed to prepare a mixed slurry , by adding a seed crystal slurry containing 75 g of seed crystals to the above solution and further adding thereto 5 . 0 g ( 7 % by weight ) of polyvinyl alcohol “ pva - 2000 ” ( manufactured by kanto chemical co ., inc .) as a nonionic surfactant . next , the reduction treatment was performed by charging an autoclave as a high pressure vessel with the mixed slurry , heating the mixed slurry to 185 ° c . with stirring , then blowing hydrogen gas as a reducing agent into the mixed slurry , and feeding hydrogen gas so as to maintain the pressure in the autoclave at 3 . 5 mpa . after a lapse of one hour from the start of the feeding of hydrogen gas , the feeding of hydrogen gas was stopped , and the autoclave was cooled . the reduced slurry obtained after cooling was subjected to solid - liquid separation by washing and filtration to recover pre - growth nickel powder . the recovered pre - growth nickel powder was again added to the solution containing a nickel ammine complex prepared through complexing treatment by adding 191 ml of 25 % aqueous ammonia to a solution containing 336 g of nickel sulfate and 330 g of ammonium sulfate and adjusting the total volume of the resulting solution to 1000 ml , and the reaction was repeated to obtain product nickel powder having a smooth surface . further , an increase in the bulk density was also observed with an increase in the reduction treatment ( the number of times of the reaction ) in the growth step . furthermore , when a 50 - cc shipping container was filled with the nickel powder , the powder did not scatter , and the operation was able to be performed without running a local exhaust ventilation . the complexing treatment was performed to prepare a solution containing a nickel ammine complex , by adding 191 ml of 25 % aqueous ammonia to a solution containing 336 g of nickel sulfate and 330 g of ammonium sulfate and adjusting the total volume of the resulting solution to 1000 ml . the seed crystal and surfactant addition step was performed to prepare a mixed slurry , by adding a seed crystal slurry containing 75 g of seed crystals to the above solution and further adding thereto 3 . 73 g ( 2 % by weight ) of na polyacrylate “ paa - 6000 ” ( t - 50 manufactured by toagosei co ., ltd . : having a solid content of 40 %) as an anionic surfactant . next , the reduction treatment was performed by charging an autoclave as a high pressure vessel with the mixed slurry , heating the mixed slurry to 185 ° c . with stirring , then blowing hydrogen gas as a reducing agent into the mixed slurry , and feeding hydrogen gas so as to maintain the pressure in the autoclave at 3 . 5 mpa . after a lapse of one hour from the start of the feeding of hydrogen gas , the feeding of hydrogen gas was stopped , and the autoclave was cooled . the reduced slurry obtained after cooling was subjected to solid - liquid separation by washing and filtration to recover pre - growth nickel powder . the recovered pre - growth nickel powder was again added to the solution containing a nickel ammine complex prepared through complexing treatment by adding 191 ml of 25 % aqueous ammonia to a solution containing 336 g of nickel sulfate and 330 g of ammonium sulfate and adjusting the total volume of the resulting solution to 1000 ml , and the reaction was repeated to obtain product nickel powder having a smooth surface as shown in fig2 . further , as shown in fig3 , an increase in the bulk density was observed by the reduction treatment in the growth step . the complexing treatment was performed to prepare a solution containing a nickel ammine complex , by adding 191 ml of 25 % aqueous ammonia to a solution containing 336 g of nickel sulfate and 330 g of ammonium sulfate and adjusting the total volume of the resulting solution to 1000 ml . a mixed slurry was prepared by adding only a seed crystal slurry containing 75 g of seed crystals to the above solution . next , the reduction treatment was performed by charging an autoclave as a high pressure vessel with the prepared mixed slurry , heating the mixed slurry to 185 ° c . with stirring , blowing hydrogen gas as a reducing agent into the mixed slurry , and feeding hydrogen gas so as to maintain the pressure in the autoclave at 3 . 5 mpa . after a lapse of one hour from the start of the feeding of hydrogen gas , the feeding of hydrogen gas was stopped , and the autoclave was cooled . then , the slurry obtained after cooling was subjected to washing and filtration to recover nickel powder . the recovered nickel powder was nickel powder in which the outside surface thereof had the same unevenness as the seed crystals . further , a 50 - cc shipping container was intended to be filled with the resulting nickel powder , but dust scattered when a local exhaust ventilation was not run .