In‐situ synthesis of NaP zeolite doped with transition metals using fly ash

Abstract Here, a novel approach has been proposed to synthesize NaP zeolite adsorbents doped with transition metals (M‐NaP) using the Na 2 SiO 3 and NaAlO 2 compounds extracted from fly ash via activation and stage treatment. The preparation process of M‐NaP employed the in‐situ synthesis in combination with organic complexation method. The effects of the addition amounts and valence state of transition metals on the zeolite products were investigated. The crystalline phase, morphology, and particle size of M‐NaP were characterized using X‐ray diffractometry (XRD), Scanning electron microscopy (SEM), and Laser particle size analyzer (PSD). The doping process was investigated using X‐ray photoelectron spectroscopy (XPS) and Materials Studio. The adsorption performance of M‐NaP was tested by the adsorption of Zn 2+ . The optimal molar ratio of n(Al 2 O 3 )/n(M) was identified as 8:1 for Co–NaP, Ni–NaP, and Fe–NaP, compared with 6:1 for Ti–NaP. The influence of transition metals on adsorption was: Co–NaP > Ni–NaP > Ti–NaP > Fe‐NaP. Due to largest surface area of Co–NaP (162.5 m 2 /g, five times than that of NaP‐RAW), the maximum removal rate of Zn 2+ was above 99.50% at 25°C. The existence state of transition metals in M‐NaP primarily included: isomorphous substitution and balance of the skeletal charge, with the latter in majority. The simulation of Materials Studio indicates that Si at T4 was first substituted and then, Si at T3 opposite T4 was replaced when the replacement of Si in different sites occurred.