Potential of ammonium adsorption of coal fly ash-based porous geopolymer granules

Porous geopolymer materials have been recently used in environmental remediation applications as adsorbents. This study is to investigate the NH 4 + adsorption capacity of geopolymer activated from coal fly ash mixing with NaOH, Na 2 SiO 3 , and H 2 O 2 . The H 2 O 2 with various ratios (0%, 4.5%, and 8.5%) were added into the fly ash pastes as blowing agents. The NH 4 + adsorption capacity of these materials was examined concerning the effects of NaOH concentration, H 2 O 2 contents, adsorbent particle sizes, dosages, and NH 4 + concentration by batch adsorption test. The results show that adding 4.5% (G45) and 8.5% (G85) of H 2 O 2 developed porous structures in geopolymer granules and their NH 4 + adsorption capacity depends on their particle sizes and pore structures. In particular, geopolymer granules with 8.5% H 2 O 2 exhibited higher NH 4 + adsorption capacity than lower content of H 2 O 2 in case of particle size of 3.0-8.0 mm. However, pulverized geopolymer still demonstrated the greatest NH 4 + adsorption capacity. In addition, both granules G45 and G85 demonstrated a well-fit (R 2 = 0.97-0.99) with Langmuir and Freundlich isotherms. The maximum NH 4 + adsorption capacity of G85 was 19.86 mg/g, which indicated the NH 4 + adsorption potential of porous geopolymer granules generated from waste materials such as coal fly ash.