A kinetic model of the dissolution of magnetite (Fe3O4) in EDTA solutions

Magnetite, an iron oxide present under reducing conditions,is a component of soils, iron ores, corrosion scales on iron and steels, and others. For a wet analysis of magnetite in samples, magnetite is preliminarily dissolved; the precision and accuracy of the final analytical results are greatly influenced by the dissolution process. A dissolution model would be useful in the design of dissolution processes and control of the optimum dissolution conditions for particular analytical purposes. Here, modeling was made for the kinetics of the dissolution of magnetite in EDTA (H4Y) solutions by assuming the following successive reactions: 1) chelation of the Fe ion sites on Fe3O4 with HnY(4-n-), and the transfer of Fe chelates to the solution; 2) the reaction of the oxide ion sites left behind on Fe3O4 with protons, and the transfer of the formed water to the solution. The derived rate equation reproduced the time-course of the dissolved Fe concentration and the Fe concentration peaks at pH 2.3. For five EDTA species with different proton numbers (n = 0 similar to 4), the resulting model parameters (rate constants) were examined in the pH range 1.5 similar to 3.3. From the pH dependence of the model parameters, H2Y2- was estimated to be the most likely dissolving EDTA species in solution.