Biomass fly ash geopolymer monoliths for effective methylene blue removal from wastewaters

For the first time biomass fly ash geopolymer monoliths were used as adsorbents for the removal of methylene blue from synthetic wastewaters. Highly porous and lightweight fly ash-based geopolymers were produced and then evaluated as methylene blue adsorbents. The geopolymers’ porosity strongly affects the dye extraction, a threefold increase (from 5.4 to 15.4 mg/g) being observed when the porosity rises from 40.7 to 80.6%. The maximum uptake reported here (15.4 mg/g) surpasses several other powdered adsorbents, which demonstrates the interesting potential of this innovative adsorbent. Moreover, these monolithic adsorbents can be used directly in packed beds as membranes, this being a major advantage over powdered adsorbents. Furthermore, these adsorbents were successfully regenerated and reused (up to five cycles) without compromising the performances. In fact, enhanced methylene blue uptake (up to 20.5 mg/g) was observed after regeneration. Additionally, an unexplored waste stream was used as raw material which mitigates the waste environmental footprint contributing towards a circular economy.