Rates of liquid-solid mass transfer at a packed bed of Raschig rings fixed to the wall of a stirred tank were measured by a technique which involves the diffusion-controlled dissolution of copper in acidified dichromate. Variables studied were impeller rotation speed, impeller geometry, Raschig ring diameter, bed thickness, presence of baffles, physical properties of the solution, and effect of superimposed flow. Mass transfer data for the batch reactor were correlated by a dimensionless equation. For a given set of conditions, the radial-flow impeller was found to produce higher rates of mass transfer than the axial-flow impeller. The presence of baffles increased the rate of mass transfer inside the bed. Applications of the suggested reactor in conducting different diffusion-controlled liquid-solid reactions were evaluated.