In the current investigation, the difference in dissolution behaviour between metallic nickel and copper powders under the condition of ammonia pressure leaching has been studied. The leaching rates were determined at the NH3 concentration of 1 or 1.5 mol/L and over the (NH4)2SO4 concentration range from 0 to 1.5 mol/L, the temperature range from 15° to 200°C, the agitation range from 400 to 1200 rev/min and oxygen partial pressure range from 0.5 to 10 atmospheres. The solubility of nickel ammine sulphate in the H2O-NH3-(NH4)2SO4 system was also measured in the present work. The experimental results obtained under these conditions are summarized as follows. The leaching of the nickel powder is shown to be a reaction of the zero-th order, indicating that the leaching time curve is a linear relation. But the leaching of the copper powder is an autocatalytic reaction, showing an extended S-shaped curve with a certain incubation period. The average leaching rate of the nickel powder is directly proportional to the oxygen partial pressure, and that of the copper powder to the square root of the oxygen partial pressure. The leaching amount of the nickel powder in solutions containing both ammonia and ammonium sulphate in the presence of oxygen is very small compared with that of the copper powder. This fact is independent of the difference in solubility between the Ni(NH3)6SO4 and Cu(NH3)4SO4·H2O in the H2O-NH3-(NH4)2SO4 systems.
(Received January 7, 1971)
* Department of Metallurgy, Faculty of Engineering, Tohoku University, Sendai, Japan.
© 2002 The Japan Institute of Metals
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