The motion of binary mixtures of solids in a cylindrical three-phase fluidized bed has been examined using a non-invasive gamma-ray emission particle tracking technique. Bubble wake motion and emulsion compensatory descending motion are seen to be the major factors affecting the solids mixing. Bubble rise velocities are found to follow a log-normal distribution and are shown to be weak functions of the degree of mixing of the solids. The mean solids flow patterns reveal a complex gulf streaming with a systematic strong vortex ring in the entrance region rising close to the vessel walls and descending in the centre.