Bitumen Emulsion—Mineral Surface Interactions: An NMR Study on the Interface Layer Composition

Compositions containing bitumen emulsions and solids have many applications, such as soil stabilization, cold mix asphalt preparation, dust binding, surface dressing and slurry sealing. Therefore, the interaction of bitumen with minerals is of great interest in science and applications. In the interaction of bitumen emulsion with a mineral surface, one of the processes that influence the properties of the bitumen-mineral composition is the formation of interface layers. Nuclear magnetic resonance can provide insights into the interactions of bitumen and minerals at the molecular level. However, the presence of magnetic constituents in most solids as well as the background magnetic field gradients at the interface does not allow the use of NMR to its full potential. In this work, we describe a ¹H NMR approach to study the interface layer formed by a specified bitumen emulsion in the presence of non-magnetic as well as magnetic minerals. This approach is based on the consecutive flushing off of "bulky" components of the bitumen emulsion and the following extraction of the surface layer material, which can then be analyzed by NMR spectroscopy. As a proof of concept, this technique was tested on samples prepared using a bitumen emulsion and four different silicate minerals. The ¹H NMR study showed that interfacial layers may accumulate asphaltenes adsorbed to mineral surfaces to a different extent depending on the specific elemental composition of minerals. More asphaltenes were detected in the interfacial layers on surfaces of studied minerals with a higher content of calcium.