Anomalous transport in activated carbon porous samples: power-law trapping-time distributions

We present experimental solute desorption measurements in porous packings o f activated carbon grains. In desorption experiments a tagged NaI solution initially saturating the medium is replaced by water. The solute concentrat ion, obtained at different cross sections of the porous sample, follows a p ower-law decay for long times. We experimentally observe a constant power-l aw exponent as we modify the injection rate and the distance from the inlet section. We reobtain this behavior within a continuous-time random-walk ap proach, establishing a relation between the waiting time distribution anti the adsorption isotherm determined experimentally. The obtained waiting tim e distribution with a divergent first moment is characteristic of anomalous mixing zone broadening. (C) 2000 Elsevier Science B.V. All rights reserved .