The present invention provides a method of removing spectator ions and contaminants from aqueous suspensions of solid particles. In accordance with the method of the invention, the solid particles are transported across a phase boundary into a non-polar organic solvent, leaving the spectator ions and contaminants in the aqueous phase. To facilitate the efficient transportation of the solid particles across the phase boundary, the surface of the solid particles is coated with an amphiphilic polyelectrolyte. If desired, the solid particles can be recovered from the organic phase by evaporating the organic solvent.