Carbonization of mixtures of coal tar pitch and graphite FeCl3 compounds: A Mossbauer study

Mixtures of coal tar pitch (CTP) and first-stage FeCl3-graphite intercalation compounds (GIC) have been synthesized with different GIC concentrations, then pyrolysed at different final temperatures and at several heating rates. Mossbauer spectroscopy has been used to characterize the iron states after these thermal treatments. The initial GIC is characterized by a typical singlet of high-spin Fe(III) and we have studied the thermal stability of the GIC under nitrogen flow by X-ray measurements: FeCl3 is progressively reduced to FeCl2 and reduction is complete at 500 degrees C. At 750 degrees C, all iron has been removed from the graphene layers. After pyrolysis of the CTP and GIC mixture, different phases are identified in the resulting green-coke: metallic iron (alpha-Fe), which is present in greater quantities at high GIC concentrations and at higher pyrolysis temperatures, ferrous chloride, iron sulfide (FeS, troilite), nonstoichiometric Fe(1-)xS (pyrrhotite), and a not-well-determined fourth phase that could be austenitic iron (gamma-Fe). After steam activation of the green-coke at 750 degrees C, most of the iron is oxidized into magnetite as confirmed by X-ray measurements and Mossbauer spectroscopy.