Because of their ionic nature, ILs have an affinity for minerals surfaces, which also have a charge. As a result, in the presence of an IL, the energy of adhesion between bitumen and oil is close to an order of magnitude smaller than in water, facilitating separation.
Using water instead of an IL results in poor separation and emulsified mineral particles in the separated oil. Illustrated below is the separation of oil sands using an IL and a hydrocarbon solvent as a diluent. Note that in this application, ILs are used as a separating fluid, not as a solvent. They are immiscible with hydrocarbons. Because of density differences, a separation into three layers is achieved upon standing using gravity. Centrifugation speeds the separation significantly. At about 75% IL (right-hand vial in this example), clean sand and solvent-diluted bitumen are readily obtained.
Some water is used to remove IL from extracted sand, but both water and IL are easily separated and recycled through a closed system. For oil sands extractions, there is no need for tailings ponds. Clean minerals and oil are obtained from various types of sludge, remediating a significant environmental problem while providing recyclable materials with economic value.
