Kinetics of and preparation of nickel by Ni3S2?NiO reaction under reduced pressure

The reaction between Ni₃S₂ (liquid) and NiO (solid) resulting in the formation of Ni and SO₂ was investigated in the temperature range 800° to 1200°C under a reduced pressure of <0.1 mm Hg. From the kinetic studies in the temperature range 950° to 1150°C, the reaction was found to proceed in three stages: i) Up to about 25 pct reduction, the rate of reaction was high and followed approximately a cubic rate law. During this stage, the reaction is thought to be under mixed control. Activation energy for the first 10 pct reduction was found to be approximately 45 kcal per mole. ii) From about 25 to 90 pct reduction, it obeyed the parabolic rate law, with an activation energy of 86±6 kcal per mole. This value is in agreement with the activation energy reported in the literature for the diffusion of sulfur in nickel. iii) Beyond 90 pct reduction, the reaction was very sluggish owing to the poor availability of the reactants. Optimum conditions for preparing nickel sponge by the above reaction and its processing into thin strips have been standardized. Some of the properties of the metal thus produced have also been incorporated.