A KINETIC-MODEL OF THE DISSOLUTION OF MAGNETITE (FE3O4) IN EDTA SOLUTIONS

Magnetite, an iron oxide present under reducing conditions,is a compon ent of soils, iron ores, corrosion scales on iron and steels, and othe rs. For a wet analysis of magnetite in samples, magnetite is prelimina rily dissolved; the precision and accuracy of the final analytical res ults are greatly influenced by the dissolution process. A dissolution model would be useful in the design of dissolution processes and contr ol of the optimum dissolution conditions for particular analytical pur poses. 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 th e oxide ion sites left behind on Fe3O4 with protons, and the transfer of the formed water to the solution. The derived rate equation reprodu ced the time-course of the dissolved Fe concentration and the Fe conce ntration peaks at pH 2.3. For five EDTA species with different proton numbers (n = 0 similar to 4), the resulting model parameters (rate con stants) 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.