Analytical electron microscopy of carbon-rich mineral aggregates in solvent-diluted bitumen products from mined Alberta oil sands

Contaminant solids in solvent-diluted bitumen product obtained by solvent extraction and solids agglomeration (SESA) of Alberta oil sands are characterized using aberration-corrected scanning transmission electron microscopy (STEM). In particular, the distribution of carbon present in these contaminant solids is determined from spatially resolved spectroscopy. Three distinct types of carbon-rich particles are identified and consist of carbonate minerals, micrometer-sized particles of toluene-insoluble organic carbon, and clay aggregates containing toluene-insoluble organic carbon. Energy-dispersive X-ray spectroscopy (EDX) maps confirm the presence of carbonates, in addition to other minerals, whose abundances are determined by a recently developed quantitative phase analysis methodology. Carbonaceous micrometer-sized particles with detectable amounts of oxygen and sulfur also appear in the elemental maps and suggest the presence of bitumen-unrelated organic materials. Finally, EDX maps also suggest an intricate sub-micrometer association of carbon with clay minerals. To map the distribution of light elements and transition metals in these clay aggregates, electron energy-loss spectroscopy (EELS) analysis has been carried out at the nanometer scale. In addition to carbon-rich regions, sub-10-nm titanium and iron oxide particles are often found dispersed on the clay surfaces. By observing clay platelets in orientations both parallel and perpendicular to the electron beam, EELS maps confirm that the carbon is present on the surface of the clays, rather than intercalated between individual clay mineral layers within the crystal structure. Furthermore, the organic coating is not uniform, displaying carbon-rich features with dimension on the order of a few nanometers, while leaving some regions of the clay mineral surface exposed. Partial nanometer-scale organic coverage has been proposed to result in a biwettable character for clay platelets that will influence the bitumen extraction process, and such coverage has been shown here directly for the first time using spatially resolved spectroscopic microscopy observations.Peer reviewed: YesNRC publication: Ye