A Theoretical Study on the Inclusion of Fe, Cu, and Zn in Illite Clays

The inclusion of Fe, Cu, and Zn in (1, 0, 0), (0, 0.5, 0), and (0.5, 0.5, 0.5) sites of an illite with the KAl2Si4O12H2 structure has been studied. For the inclusion of the metals, their common oxidation states were chosen, that is, 0, +2, +3 and 0, +1, +2, for Fe and Cu, respectively, while 0 and +2 for Zn. Periodic DFT calculations were performed to know the most favourable site of incorporation of the ions. Energetically the most favourable site for the inclusion corresponds to the (1, 0, 0) coordinate for all the ions independently of their oxidation state. However, the highest oxidation state of the metals (Fe3+, Cu2+, and Zn2+) was the most favoured for being incorporated into the illite structure and was the selected ion for the discussion. In those structures, metal oxygen interaction plays an important role in stabilizing the systems. Structural and energetic results indicate that illite presents good adsorption characteristic of those Fe3+, Cu2+, and Zn2+ in the (1, 0, 0) site. Thus, those ions may be available for plants for its extraction by phytoextraction techniques and the consequent soil regeneration. The inclusion of a second metallic ion revealed the most favourable inclusion corresponding to the inclusion of Fe3+ ion. The inclusion of this ion modifies the coordination sphere around the first metal being available for subsequent extraction by phytoremediation or other techniques for clean-up of the soil and its regeneration.