Minimization and beneficiation of fly ashes of the combustion of forest biomass. Silica is the predominant component in the inorganic fraction of the fly ashes. Adsorbent/catalyst materials from the fly ashes of the fluidized bed combustion. Micro-mesoporous silica activated from fly ash by KOH chemical activation. Fly ash can be used as precursor of adsorbent materials or catalyst support.