The reaction kinetics of the mesoporous powder, MCM-TP, anchored with synergistic extractant TOPO-P204, with Pd2+ in spent fuels have been investigated. The results showed that the reaction rate was independent of pellet size, which suggested that the powder pellet was highly porous and was composed of plate-like “grains”. This analysis was confirmed by observing the surface and cross section of the pellet with SEM. It provided the physical basis for establishing the liquid-solid reaction model of mesoporous powders: P-G* model. The calculated curves from the model were in good agreement with the experimental results.