In order to investigate the relationship between the pore diameter and the rate of uptake of U(VI) ions and Ce(III) ions, N,N,N',N'-tetramethylmalonamide (TMMA) chelating resins with different pore diameters were synthesized, using different pore producing solvents. The batch technique was used to study the kinetics of the adsorption U(VI) and Ce(III) ions from 3 M HNO3, acid, and 3 M NaNO3+0.05 M HNO3, salt, media. The process was found to be controlled by the particle diffusion model. The calculated values for the diffusion coefficient were found to be directly proportional to the pore diameter, i.e. the resin with the largest pore diameter showed the fastest rate of uptake. (C) 2002 Elsevier Science B.V. All rights reserved.