Protic ionic liquids reshape tailings filtration and accelerate its dewatering

Pressure-driven filtration is widely used for solid–liquid separation, yet its efficiency is limited by the low permeability and high compressibility of filter cakes formed from fine, clay-rich suspensions. These cake properties arise from interfacial interactions that govern particle aggregation, hydration, and wetting. However, chemical strategies to deliberately tune cake structure under pressure remain scarce. Here, we show that protic ionic liquids (ILs) based on octylammonium oleate significantly enhance the dewatering of oil sands tailings by acting as tunable surface-active modifiers of cake formation and consolidation. Across mature and fluid fine tailings, IL treatment accelerates early drainage and produces cohesive, homogeneous cakes with substantially higher net water release than untreated samples. Dewatering performance depends strongly on the IL stoichiometry: amine-rich formulations outperform neat and acid-rich variants, achieving clearer phase separation and improved permeability retention even at reduced dosages. Analysis of the aqueous filtrate reveals minimal loss of IL components and stoichiometry-dependent ion-exchange effects, including displacement of Na⁺ and K⁺ and selective retention of Ca²⁺ and Mg²⁺, consistent with IL-mediated modification of clay–water interfacial environments. Similar trends in diluted tailings confirm that the enhanced dewatering arises from interfacial control. Because a large fraction of process water remains trapped in fine tailings after bitumen extraction, dewatering efficiency directly limits water reuse and tailings management in oil sands operations. By establishing IL stoichiometry as a molecular design lever for permeability-limited filtration, this work positions amine-rich ILs as a versatile platform for improving water recovery from challenging industrial clay-rich slurries.