Synthesis of fly ash-based self-supported zeolites foam geopolymer via saturated steam treatment

It is reported the synthesis of self-supported zeolite foam geopolymers (ZFG) from fly ash (FA) using saturated steam. These materials could be used as porous bulk-type solid adsorbents. Characterization analyses show that the alkaline activator (AA) modulus affects the structural unit distribution in foam geopolymer (FG), which ultimately provides different chemical compositions for the nucleation of zeolites resulting in different types of zeolites. Furthermore, the pore structure of ZFGs range from micro- to the macro-range and combine the functional micro-porosity of the zeolites, the meso-porosity and the macro-porosity of the foam geopolymer. ZFGs exhibit low apparent density (approximately 355 Kg/m³) and higher compressive strength (ranging from 1.03 MPa to 2.96 MPa). The possibility of using these innovative materials as heavy metal (Pb²⁺) adsorbents was then evaluated. The results show that they have a great capacity for the removal of the Pb²⁺ (as high as 123.2 mg g^-1) and high adsorption efficiency (equilibration time as fast as 60 min). The lightweight bulk-type ZFGs could be used in packed beds as membranes for easy collection, unlike granular adsorbents. Moreover, their production contributes to the elimination of polluting FA solid wastes, mitigating the environmental impact associated with this waste disposal, while decreasing production costs.