Studies were carried out on the fluidized bed conversion of high-level radioactive liquid wastes into compact granular solids and on their growth rate. A calciner of 4-inch diameter provided with a projecting beak two-fluid atomizing nozzle were used with ferric sulfate solution as feed. The total weight of fluidized bed, as well as the rates of product withdrawal from the overflow pipe and of solid elutriation in the off-gas, were nearly constant throughout a run. The main source of the solids elutriated in the off gas is considered to be contributed by solidification through drying and calcination of the spray droplets while suspended without depositing on bed particle surface. A convenient equation has been obtained which permits prediction of the growth rate of particles in a fluidized bed calcination process with a reasonable degree of accuracy.