Dissolution Velocity of Zinc Ferrite in Acids

Abstract

Wlodzimierz Wolski and Irena Okonska Kozlowska: Dissolution Velocity of Zinc Ferrite in Acids
The kinetics of the system ZnFe₂O₄/H⁺ has been examined in various concentrations of hydrochloric and nitric acids separately and in their mixtures. It was found that in nitric acid independent of its concentration the process is non-stoichiometric one, giving after the same lapse of time more zinc cations to the solution than the stoichiometricity requires. This behaviour can be observed in both dilute and concentrated HNO₃.
In the presence of hydrochloric acid the same ferrite displays quite different way of dissolution ; here according to the analytical data, the amounts of ferric and zinc ions do indicate the molar solubility. Rather surprisingly, however, the best conditions in order to dissolve stoichiometrically this compound in acids under investigation, have been achieved for the mixture of 2N HNO₃ and 2N HCl even, when. the proportion of HCl:HNO₃ had been as small as 1:20.
The results of temperature effects examination |20°, 40°, 60°C| upon this reaction showed, as to be expected, much more greater rate of dissolution in higher temperatures. The findings allowed to establish the kinetic equation and calculate the rate constants K and k. The most accurately they fit when put in the following equation : dx/dt=s₀k(1-x)³;K=1/t[1/(1-x)²-1];K=2ks₀, where s₀ is the specific area.