PRELIMINARY STUDIES ON KINETICS OF HIGH PRESSURE HYDROGEN REDUCTION OF NICKEL ION IN AQUEOUS SOLUTION TO METALLIC NICKEL

Studies were made on high pressure hydrogen reduction of Ni ammoniacal solution to metallic Ni with fine Ni powder, which was also prepared by hydrogen reduction with Cr~(2+) as nucleating agent, added as solid seed. Results indicate that the reduction was carried out under chemical reaction rate control region. The rate of reduction is proportional to the amount of Ni powder as solid seed added,and to the square root of partial pressure of hydrogen and is not influenced by the concentration of Ni ion in solution up to most of Ni reduced. Both activation of hydrogen molecules and phase transformation of Ni are believed to proceed on the surface of Ni powder added. Reaction can be considered to proceed according to the following scheme with reaction 4 as the rate controlling step:(5) 2H~++2NH_3=2NH_4~+ fast