High mineral content is one of the most striking characteristics of brown coals, but little is known about the effects of minerals on the rheological behaviors of brown coal-oil slurries. In this work, two Chinese brown coals with different concentrations of mineral matters were selectively demineralized in HF and/ or HCl aqueous solutions and then mixed with hydrogenated aromatic oil to prepare brown coal-oil slurries. Afterward, the viscosity of the brown coal-oil slurries was measured at low temperatures and atmospheric pressure. Swelling and extraction experiments were conducted to understand the reason for the influences of different minerals on the rheological behaviors of brown coal-oil slurries. Compared with the corresponding brown coal-oil slurries prepared by the brown coals without mineral matters, the viscosity of brown coal-oil slurries relatively decreased and increased under the influence of clays and cationic components, respectively. The variation in viscosity is mainly ascribed to the difference in extracting characteristics of brown coals with different mineral matters. Additionally, we found that the thixotropic structure of the brown coal-oil slurries may be formed by OHA-pi hydrogen bonding between aromatic molecules in solvents and hydroxyl groups on the surface of coal particles, and mineral matters may affect the viscosity of brown coal-oil slurries by changing the amounts of the OH-pi hydrogen bonds. (C) 2014 Elsevier Ltd. All rights reserved.