Mechanism of dissolution of different species of iron contained in kaolin Bycitrate-Bisulphite

The mechanism of dissolution of iron species contained in kaolinitic clay from the Guadalupe mine in Huayacocotla ejido El Carbonero, Veracruz, Mexico was investigated, using the synergistic effect of bisulfite as the reducing agent and citrate as complexing agent. The clay was dry screened, yielding particle sizes of -100 +250 mesh. Kaolin was characterized by X-ray diffraction (DRX) and atomic absorption (AA), identifying magnetite, ilmenite and greigite as the prevalent iron phases. Dissolution experiments were carried out in solutions of 0.5 M of sodium thiosulfate, 0.9 M of citric acid, at 90 ° C and pH 3, controlling the latter parameter with sodium hydroxide. The reactions involved in the dissolution of the different iron species were proposed. Since the iron in magnetite and greigite is present as Fe(III), a reducing agent (bisulfite) is required to liberate it from these phases, whereas in ilmenite, iron is present as Fe(II) and is dissolved employing a complexing ligand