Fabrication and characterization of macroporous flyash ceramic pellets

Macroporous ceramic pellets (MCPs) were prepared from industrial waste flyash via a mechanical foaming and pseudo-double-emulsion (PDE) method. The MCPs with different relative densities (ρr) were characterized in terms of total and open porosities (εt and εo), average pore size (davg), specific surface area (Sp), surface roughness, and microstructure. The inner and outer pore structure of the MCPs was found to be composed of interconnected circular pores. The average size of the MCPs was controlled over the range of 2.0–3.0 mm by varying the solid loading ratio of slurries. Increasing the slurry loading led to increasing viscosity of the slurry and consequently greater size of the MCPs. The physical properties of the MCPs investigated herein (i.e., εt, εo, davg, Sp, and surface roughness) increased with decreasing ρr (i.e., increasing foaming ratio). It was found that the degree of pore connectivity can be controlled by the ρr of the MCPs. Heavy metal leaching test results showed that the amount of heavy metals released from the MCPs was much lower than that from flyash powders. The results were attributed to melting and subsequent immobilization of the heavy metals as well as their partial sublimation during the sintering process.

Research Highlights
► Macroporous ceramic pellets were successfully fabricated from industrial waste flyash.
► Average size of macroporous flyash pellets increased with increasing solid loading ratio.
► Physical properties of macroporous flyash pellets were controlled as a function of the relative density of the pellets.
► The amount of heavy metals released from macroporous flyash pellets was considerably lower than that for flyash powders.