EPR and FTIR characterization of paramagnetic transition metal ions in fossil fuels: tar sands

Abstract

The techniques of EPR and FTIR spectroscopy have been applied to the bitumen and mineral fractions of a tar sand sample originating from Circle Cliffs, Utah to detect and identify paramagnetic transition metal ions present, indicate whether or not they are organically bound, and determine the identities of the complexes in which they occur. An EPR spectrum of the bitumen reveals the presence of V('4+) at a site of axial symmetry. Fitting the spectrum to the second order perturbation solution of the spin Hamiltonian indicates that the spectrum originates from vanadyl etioporphyrin. An EPR spectrum characteristic of Mn('2+) in a carbonate lattice was observed for the mineral component. A quantitative analysis of the mineral components, conducted using FTIR spectroscopy, shows the tar sand mineral fraction consists of the two clays, kaolinite and illite, quartz, gypsum, and one carbonate, dolomite. A computer simulation of the EPR spectrum positively identifies the Mn('2+) host as polycrystalline dolomite, shows the ions are at two crystallographically distinct sites in the dolomite lattice, and gives the relative population at each site. A second feature observed in the EPR spectrum of the mineral fraction is a broad line at g = 4.2 which is attributed to Fe('3+) in kaolinite. A third and final feature observed in the EPR spectrum of the tar sand mineral fraction is a broad line at g = 2. The temperature-dependent behavior of this line suggests that it is due to Fe('3+) in amorphous iron oxides and wustite, two compounds that commonly coat kaolinite surfaces.