Fractal approach for the description of liquid-phase adsorption dynamics: the case study of the reuse of coal combustion ash as adsorbent

In this work, we validated the superior accuracy of fractal-like kinetic models with respect to their classical counterparts in interpreting cadmium adsorption dynamics on both raw and beneficiated combustion fly ashes. Results showed that classical and fractal-like kinetic models produce comparable outputs only for low fractional degrees of adsorption; this was ascribed to a likely more homogeneous pollutant concentration in the particle outer shells. For longer adsorption times a less random pollutant intraparticle distribution should be responsible for a fractal-like behaviour. Microstructural characteristics of the different ash-based adsorbents have been used to explain the observed behaviour, and extensions to other cases have been proposed as well.