This article reports a research aimed at investigating agglomeration phenomena during fluidized-bed thermochemical processing of olive husk biomass and their mitigation, taking into account both combustion and gasification conditions. Agglomeration is due to the presence of alkalis in fuel ash producing low-melting compounds in combination with SiO2 present in common bed materials (e.g., silica sand). The use of kaolin and fireclay as additives and in some cases as bed materials for inhibiting bed agglomeration was investigated. Experiments were carried out in an alumina crucible and a fluidized bed at 900 degrees C and were complemented by scanning electronic microscopy (SEM) and X-ray diffraction (XRD) analyses of the collected samples. Fireclay proved to be mechanically resistant to abrasion and not prone to forming low-melting-temperature compounds. As in the case of kaolin, which has a similar composition, the mechanism of alkali neutralization has been attributed to the formation of K2O Al2O3-2SiO(2) and K2O- 3CaO-6SiO(2) ternary compounds having a higher melting point with respect to that of the K2O-4SiO(2) binary compound. For the investigated biomass, the minimum amount of fireclay needed to prevent agglomeration was around 16 mg/g(fuel).