Synthesis of Na-X zeolite from low aluminum coal fly ash: Characterization and high efficient As(V) removal

Abstract

Na-X zeolite was successfully prepared from low aluminum coal fly ash (LACFA) via fusion-hydrothermal treatment. The influence of various synthesis parameters was investigated, including aluminum additives (AlCl3·6H2O, Al(NO3)3·9H2O, AlF3·3H2O and NaAlO2), dosages of NaAlO2, weight ratio of LACFA/NaOH, crystallization temperature and time. The results indicated that the addition of Al species played a key role in the synthesis process of purity Na-X zeolite, and the corresponding relative crystallinity of the obtained samples was in the order of Na-X zeolite(Al) ≫ Na-X zeolite(Cl) > Na-X zeolite(N) > Na-X zeolite(F) (Here, “Al”, “Cl”, “N” and “F” represent NaAlO2, AlCl3·6H2O, Al(NO3)3·9H2O and AlF3·3H2O, respectively). And the optimal operating conditions were: the weight ratio of LACFA/NaOH = 0.83, short crystallization time 360 min, low crystallization temperature 90 °C and 0.038 mol NaAlO2. Additionally, X-ray fluorescence (XRF), X-ray powder diffraction (XRD), Fourier Transforms Infrared (FT-IR) and Scanning Electron Microscopy (SEM) were employed to determine the resultant samples. Based on the results of As(V) adsorption experiment, the experimental data was suitable fitted by Freundlich adsorption isotherm model, and the theoretical maximum adsorption capacity was 27.79 mg/g at pH = 2.14. The kinetics studies suggested that “surface reaction” was the rate-determining step of adsorption process, and the thermodynamics studies indicated that the adsorption process was spontaneous and endothermic. These results deemed that the LACFA was suitable for preparing Na-X zeolite(Al), and the obtained Na-X zeolite(Al) was served as a promising adsorbent to remove As(V) from acid wastewater.