A comparative study on fly ash, geopolymer and faujasite block for Pb removal from aqueous solution

•Geopolymer and its deriving zeolite–faujasite–was prepared from fly ash.•Both geopolymer and its deriving faujasite can effectively remove Pb.•Geopolymer has the same adsorption mechanisms as faujasite or zeolite materials.•Shows geopolymer technology is a feasible process in adsorbent manufacturing.

This work aims to evaluate the efficiencies of fly ash, fly ash-based geopolymer and faujasite block, which is transformed from geopolymer, as sorbents for lead (Pb) from aqueous solutions. Comparative experiments were performed to examine the mineralogical features of the fly ash, geopolymer and faujasite block and their adsorption capacities. Equilibrium isotherms and thermodynamic parameters were obtained through systematic investigation of parameters including pH, initial Pb concentration, temperature and contact time. The adsorption kinetics of geopolymer and faujasite block fit well to the pseudo-second-order kinetic model, while the adsorption of fly ash fit to the pseudo-first-order kinetic model. The adsorption equilibrium data of fly ash, geopolymer and faujasite can be expressed using Langmuir model. The maximum adsorption capacities of fly ash, geopolymer and faujasite block at pH = 3 were determined to be 49.8, 118.6 and 143.3 mg/g, respectively. Through this study we demonstrate that both geopolymer and faujasite can effectively remove Pb from wastewater. Most importantly, we prove that geopolymer has the same adsorption mechanisms as faujasite or similar zeolite materials. This finding suggests geopolymer technology being an energy-saving, low cost and environmentally friendly process in adsorbent manufacturing.

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