Powder-activated carbons have a fine granulometry of less than 100 ums with a large average diameter between 15 & 25 um. Thus, they present a large external surface and a small diffusion distance. The rate of adsorption is very high and the problems related to the mass transfer rate are very low. They are thus preferably used for adsorption from the solution phase because of their low diffusion rates. The carbon is added to the solution directly, agitated, and left in contact for short time (5 - 30 min) and then separated by filtration. This group of carbons includes decolorization and medicinal carbons. Powdered carbon in a batch-type process may be used advantageously in systems where the extreme temperatures and pressures required would make continuous treatment in a column system impractical, in cases where exceptional purity is required and a polish filtration step after Granular carbon treatment is necessary, or in installations where relatively small batches of many different products or grades are being processed.