STUDIES ON THE KINETICS OF Ni DISSOLUTION IN AQUEOUS AMMONIACAL SOLUTION

Studies have been carried out on the kinetics of Ni dissolution in aqueoussolution of NH_3 and (NH_4)_2CO_3 with O_2 present. It is shown that the NH_3 andNH_4~+ salt dissolution of Ni is an electrochemical reaction accompanied by surfaceoxidation of Ni by O_2. The reaction rate may be either in the NH_3 concentrationcontrol region or in the O_2 concentration control region depending on the ratio ofthe concentration of NH_3 and that of O_2. In the NH_3 controlling region, the surface of Ni will be passivated rathereasily with the formation of oxide film. The dissolution reaction will then beinterrupted. In the O_2 controlling region, the rate of reaction will be controlled bythe rate of O_2 transfer through the liquid film around the Ni surface. It can becorrelated with the equation of the rate of O_2 mass transfer.