アンモニア性硫酸ニッケル水溶液からのニッケルの水素ガス還元

水溶液からの金属のガス還元に関する研究 (第3報)

抄録

Hydrogen reduction of nickel from an aqueous ammoniacal solution was studied kinetically. The rate curves of the reductive reactions seemed to essentially consist of three distinctstages. The reaction rate of the first stage, which was characteristic of the reaction when small amounts of ferrous sulfate or nickel seed are used, was of the first order with respect to both the partial pressure of hydrogen gas and the concentration of ferrous sulfate added. This reaction was controlled by a chemical reaction having an activation energy of 22.2 kcal/mol. When larger amounts of nickel seed or ferrous sulfate together with anthraquinone were used, the first stage became extremely short. Consequently the reaction seemed to begin with the second stage. This second stage was characterized by a zeroth order reaction with respect to the concentration of nickel. The reaction rate of this stage was of the first order with respect to the partial pressure of hydrogen, having an activation energy of 4.2 kcal/mol. The reaction during this stage may have been controlled by the absorption of hydrogen gas through the boundary layer between the gaseous and liquid phases. The activation energy of the third stage was found to be 11.3 kcal/mol. From observations with a scanning electron microscope during this stage, the increased particle size of reduced nickel may have led to insufficient active sites on the nickel particles, resulting inadecline in the reaction rate.