Particle dynamics of a three-phase fluidized bed are characterized using radioactive particle tracking (RPT). Solid-liquid mass transfer measurements were performed using a benzoic acid particle on a flexible tether. Columns with 12.7 cm inner diameter and 160-200 cm in length were used. The fluids used are water and air, and the solids are spherical polycarbonate particles 6.35 mm in diameter with a density of 1160 kg/m(3). All experiments are conducted at atmospheric pressure and room temperature. Analysis of RPT data, for free and tethered particles, shows that tethering does not affect particle velocities in the main bed region.