The nichel values from the fuel oil ash could be efficiently recovered as double salt, nickel ammounium sulfate hexabhydrated crystal（NAS）, by the addition of ammounum sulfate to the nickel prefnant liquor from the vanadium recovery process.
The amount of ammounium sulfate added has little effect on the crystal suze characterisiics, but the yield of crystalline precipitate was greatly increased by the addition of ammonium sulfate in excess because of the sharp decrease in solubility of NAS.
The recovery of nickel valuse as NAS was ranged 220 to 230 kg per ton of the fuel oil ash.
The nucleation rate was studied in a mixed suspension-mixed product removal cooling crystallizer, which was found to correlate with power-lqw kinetics of the form B^o=kMG^2.0 The constant k is a function of operation conditions that include temperature, degree of agitation and fluid characteristics. The value of k was 1.47×10¹² under the experimental conditions in this investigation.