A method for preparing crystalline cobalt nitrate. The method includes: 1) calcining a spent Co/SiO2 catalyst, cooling the calcined material to room temperature, and grinding it to yield a powder; 2) heating the powder in a fluidized bed reactor; 3) adding the heated powder into excess dilute nitric acid solution and filtering to obtain a cobalt nitrate solution; 4) adjusting the pH value of the cobalt nitrate solution to 1.5, adding a preheated oxalic acid solution, adjusting a pH value of the resulting solution to 1.5, immediately filtering the resulting solution to yield a precipitate of cobalt oxalate, washing the precipitate of cobalt oxalate to yield a neutral filtrate; 5) drying the precipitate and calcining to yield cobalt oxide; 6) dissolving the cobalt oxide in nitric acid to yield a second cobalt nitrate solution; and 7) evaporating the second cobalt nitrate solution to obtain crystalline cobalt nitrate.