Ash from Biomass Thermoconversion Processes, and Its Reuse as Adsorbent Material

Biomass thermoconversion residues can have a fate other than landfilling. In this chapter, it is presented the case in which the ash can be used as an adsorbent material towards pollutants from fluid phases, thus contributing to increasing the “sustainable circularity” nature of the proposal (a residue is reused for purification operations). The ashes are discussed in their main characteristics, together with possible activation processes aimed at increasing their sorbent capacities. This is then followed by a general discussion on the fluid–solid adsorption process, and by an in-depth analysis of the thermodynamic and kinetic aspects, with the appropriate constitutive equations and methods for obtaining, from experimental data, the kinetic and diffusive parameters of the process. The chapter then continues with an extension in which the concepts of fractal dynamics are applied to the constitutive equations of adsorption kinetics.