Hydrometallurgical pathway has a high potential for the extraction of nickel from primary and secondary resources, such as spent catalysts. The purpose of this research is to recover nickel from the spent catalysts from the steel industry and to produce nickel sulfate. in this regard, chemical leaching processes, conventional crystallization and sonocrystallization were utilized to achieve the desired product. Initially, the effect of different parameters of sulfuric acid concentration, solid content and the amount of ammonium persulfate at 80 °C and the stirring rate of 500 rpm in 2 hours was investigated. The concentration of sulfuric acid in the range of 0.5 to 1 molar, the solid content between 15 to 35 percent and the amount of ammonium persulfate were changed from 1 to 4 grams. Using statistical analysis of variance, the results of the experiments were analyzed and a model was developed for the leaching process. The highest recovery rate of nickel was 99.67% under conditions of 1.2 molar acid concentration, 2.5 g increase of ammonium persulfate and solid content of 25%. . For extraction of metal as sulfate salt, the leach solution was isolated in two separate parts without applying ultrasonic waves and ultrasonic waves were subjected to cooling the crystallization experiments. Conventional crystallization experiments at concentrations between 75 and 136 g / L, with volumes of 0 to 35% vol / vol of organic material, including ethylene glycol, isopropanol and n-butanol, at 15 °C with 30 rpm agitated in Shaker incubator was performed for 24 hours. The highest nickel recovery was obtained by adding 15% ethylene glycol and a solution concentration of 100 g / L of nickel, which was 79.7%. Sonocrystallization experiments were carried out at 5 °C, 100 g / L Ni concentration and for 10 hours at 10 to 40% in the organic phase and at 45 to 400 W ultrasonic waves in different amplitudes. The results showed that the highest recovery of nickel was in the presence of 40% isopropanol and 150 watts, which was equal to 29.2%. In the case of ultrasonic waves, the number of water in crystals reduce from six to one, and in a period of 2 hours, a more uniform product than crystals was obtained with less recovery than ordinary crystallization