低温碱熔-晶化SiO2/Al2O3复合物合成沸石及其对Cd2+的吸附

Adsorption of Zeolite on Cd2+ by Low-temperature and Alkali-fusion-crystallization Synthesis of SiO2/Al2O3 Compound

摘要:

以SiO2/Al2O3含量较高的粉煤灰(FA)为原料，NaOH为改性剂，采用低温碱熔-水热晶化法合成沸石(ZE)。通过SEM-EDS、XRD、XRF、XPS、FTIR和BET对ZE进行了物相表征，通过静态吸附实验考察了ZE对Cd2+的吸附性能及机理。结果表明：经NaOH改性，FA中Si—O—Si和Si—O—Al 键断裂形成[SiO4]4-和[AlO6]5-单体，ZE比表面积增至21.54m2/g。当ZE投加量为0.1g、Cd2+初始质量浓度为100 mg/L、吸附时间为30min时，平衡吸附量为49.38mg/g，比FA提高57.29%。在pH=4~9时，ZE对Cd2++的去除率在90%以上。在35℃条件下，ZE对Cd2+吸附符合准二级动力学方程，速率常数为0.0586g/(mg·min)；ZE对Cd2+的吸附过程符合Langmiur等温模型，1/n为0.4324；热力学实验表明，△G在-20~0 kJ/mol，吸附过程为自发的吸热反应；D-R模型中吸附能均大于16 kJ/mol，ZE对Cd2+吸附过程是物理吸附和化学吸附共同作用的结果。

Abstract:

Abstract: Zeolite (ZE) was synthesized in low-temperature and alkali-fusion-hydrothermal crystallization process with fly ash (FA) containing high SiO2 and Al2O3 content as raw materials, NaOH as modifier. ZE was characterized by scanning electron microscope coupled with energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET). The adsorption properties and mechanism of synthetic zeolite for Cd2+ were investigated by static adsorption experiment. The results showed that the Si-O-Si and Si-O-Al bonds in FA fractured to form [SiO4]4- and [AlO6]5- monomers after NaOH modification. The surface area of ZE increased to 21.54 m2/g. The equilibrium adsorption capacity of the Cd2+ on ZE was 49.38 mg.g-1 under the conditions of the ZE dosage of 0.1 g, Cd2+ initial concentration of 100 mg/L and adsorption time of 30 min, which more than 57.29% FA reaction. ZE adsorption of the Cd2+ removal efficiency was more 90% at pH=4~9. At 35℃, the adsorption kinetics of ZE for Cd2+ followed the pseudo-two-order kinetic equation model with rate constant of 0.0586g/(mg.min). The Cd2+ adsorption isotherm is accorded with Langmiur model, 1/n was 0.4324. The thermodynamic experiments revealed that the Gibbs free energy change △G was between -20 and 0 kJ/mol, indicating that the adsorption was a spontaneous and endothermic process. From the D-R isotherm model, the adsorption energy was more than 16 KJ/mol, which demonstrated that the adsorption of Cd2+ was a combination of physical adsorption and chemical adsorption.