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

We present experimental solute desorption measurements in porous packings of activated carbon grains. In desorption experiments a tagged NaI solution initially saturating the medium is replaced by water. The solute concentration, obtained at different cross sections of the porous sample, follows a power-law decay for long times. We experimentally observe a constant power-law exponent as we modify the injection rate and the distance from the inlet section. We reobtain this behavior within a continuous-time random-walk approach, establishing a relation between the waiting time distribution and the adsorption isotherm determined experimentally. The obtained waiting time distribution with a divergent first moment is characteristic of anomalous mixing zone broadening.