Troilite oxidation by hydrogen peroxide.
The kinetics and mechanism of troilite oxidation by H(2)O(2) was studied at temperatures of 25 and 45 degrees C. Solutions within the range 0.1-0.85 mol L(-1) H(2)O(2) in HClO(4) (0.01-0.1 mol L(-1)) were used as dissolution media. The experimental amount of dissolved iron was plotted versus t(n), with n ranging from 0.25 to 1.55. The theoretical interpretation of this dependence suggests that the troilite oxidation involves several processes: Both experimental results and theoretical considerations illustrate the importance of temperature, pH, and [H(2)O(2)] for the kinetics and mechanisms of troilite oxidation. The amounts of dissolved iron strongly increase with temperature and [H(+)], whereas an increase of H(2)O(2) concentration seems to reduce the troilite oxidation. The reaction orders with respect to [H(+)] are variable, pointing out notable modifications of reaction mechanism with experimental conditions. The estimated value E(a)=25.4+/-0.9 k J mol(-1) ([H(2)O(2)]=0.4 mol L(-1) and pH 1) points to dissolution kinetics controlled by a mix regime of surface reaction and diffusion.