Abstract
This work is devoted to a kinetic and mass transfer study of simultaneous cementation of nickel and cobalt on zinc powder through stirred tank reactor. The influence of different parameters (stirring rate, temperature, zinc dust quantity, concentration of zinc and copper) on the process of cementation of cobalt and nickel in similar conditions to those of industrial zinc sulphate solution was experimentally determined. These parameters were studied for their effect on the rate of simultaneous cementation represented by the product k ¯ a e , of the overall mass transfer coefficient k ¯ and the effective surface area a e . Some of the significant results are the following: (1) The cementation reaction of nickel was found to proceed with two different rates: an initial fast rate followed by a final slower one. The product k ¯ a e was calculated and the values increased with stirring rate and less affected by temperature. Mechanistic study of the reaction through activation energy determination (13 kJ mol −1 ) showed that the cementation of nickel on zinc is a diffusion controlled reaction. (2) The temporal evolution of the cobalt concentration has revealed that the re-dissolution of cobalt occurred after about 50 min. The reaction of cobalt was found under chemical control.
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