Stabilization of lead in waste water and farmland soil using modified coal fly ash

As a by-product of coal-fired power plants, fly ash has attracted widespread attention because of its heavy metal adsorption potential. In this study, two fly ashes from different power plants were re-used through modification to adsorb Pb(Ⅱ) from aqueous solution and field soil. The physicochemical properties of adsorbents were characterized by X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), the X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), as well as the X-ray photoelectron spectroscopy (XPS). In addition, batch sorption experiments and field study were conducted to investigate their adsorption capacity on Pb(Ⅱ). The results demonstrated that, the surface area of modified fly ash-2 (MFA-2) has increased 25 times. The kinetic study illustrated that the adsorption process on both modified fly ash-1 (MFA-1) and MFA-2 were more suitable for pseudo-second-order model. Nevertheless, MFA-2 took less time to reach adsorption equilibrium. Compared with the raw fly ashes, the prepared MFAs had stronger affinities to Pb(II). When used as adsorbents, more than 146 and 165 mg of Pb(II) could be adsorptively stabilized by per gram of MFA-1 and MFA-2 at 318 K from waste water, respectively; when employed as amendments, the addition of MFA-1 and MFA-2 into soil could reduce Pb accumulation in rice, with the total Pb content in rice grains is lower than the level of natural standard. The investigation declared that the MFAs were promising materials which had great potentials on adsorptive stabilization of Pb(II) from waste water and contaminated soil, which also realizes the recycling of resources and cleaner production.