Heavy mineral-asphaltene interactions governing the stability and destabilization of water-in-oil emulsions

Persistent water-in-oil emulsions stabilized by asphaltenes represent a major challenge in crude oil production and tailings management, contributing to environmental risks associated with inefficient phase separation and wastewater treatment. While mineral-asphaltene interactions are known to influence emulsion stability, the role of heavy minerals has remained largely unexplored. In this work, we have systematically investigated the interactions between pyrite, a representative heavy mineral commonly present in crude oil and oil sands, and asphaltenes in toluene and heptol systems. Oxygen-containing asphaltene subfractions selectively adsorb onto pyrite through interactions with oxidized iron sites. Although pristine pyrite exhibits negligible intrinsic interfacial activity at the toluene-water interface, the presence of pyrite markedly reduces interfacial tension in asphaltene-stabilized systems, particularly at low pyrite loadings (e.g., 10 mg L^-1 pyrite in 1000 mg L^-1 asphaltenes). At higher pyrite concentrations, however, emulsion stability decreases under centrifugation due to the high density of pyrite. In mixed solvents of reduced aromaticity (heptol), enhanced asphaltene adsorption onto pyrite leads to the formation of dense pyrite-asphaltene complexes that promote droplet coalescence and demulsification. The proposed mechanism was further validated using industrial emulsions derived from Steam-Assisted Gravity Drainage (SAGD) operations. These findings elucidate how the coupling of surface chemistry and particle density governs emulsion stability and destabilization, providing mechanistic insight relevant to the mitigation of asphaltene-related environmental challenges in heavy oil production.