Arsenic adsorption from aqueous solution on synthetic zeolites

The adsorption of arsenic from aqueous solution on synthetic zeolites H-MFI-24 (H24) and H-MFI-90 (H90) with MFI topology has been investigated at room temperature (r.t) applying batch equilibrium techniques. The influences of different sorption parameters such as contact time, solution pH, initial arsenic concentration and temperature were also studied thoroughly in order to optimize the reaction conditions. The adsorption of arsenic on to H24 and H90 follows the first-order kinetics and equilibrium time was about 100 min for both the adsorbents. The first-order rate constant (k), 4.7 × 10−3 min−1 for H90 is more than two times higher in magnitude compared to 2.1 × 10−3 min−1 for H24. Adsorption performance of H90 is higher compared to H24 due to it's highly mesoporous nature which in turn accelerates the diffusion process during adsorption. As(V) sorption capacity derived from Langmuir isotherm for H24 and H90 are 0.0358 and 0.0348 g g−1, respectively. Arsenic uptake was also quantitatively evaluated using the Freundlich and Dubinin-Kaganer-Radushkevich (DKR) isotherm models. Ion exchange between adsorbent's terminal aluminol groups with different predominant forms of arsenate in solution is one of the various important reactions occurred during adsorption process.