On the Behavior of Cobalt Ions in the Aqueous Solution of Cobalt Nitrate

Consideration was made on the chemical species of cobalt ions in aqueous solution, which are necessary for reproducing experiments on the hydrolysis of cobalt nitrate and on the neutralizaion of cobalt nitrate solution with sodium hydroxide. Model analysis based on the chemical equilibria among these species was carried out, to obtain concentrations of these species as a function of the concentrations of cobalt nitrate for the hydrolysis experiment and of the concentrations of sodium hydroxide for the neutralization experiment. A general feature of the data both on the hydrolysis of cobalt nitrate and the neutralization can qualitatively be reproduced, by assuming chemical species of Co2+, CoOH+, Co (OH) 2, Co(OH) 3-, Co(OH) 42- and Co20H3+. A quantitative agreement between data and calculations, however, is not satisfactory, which suggests the necessity to further take into account of the existence of polynuclear complex ions of cobalt in the aqueous solution.