低温碱熔-晶化SiO2/Al2O3复合物合成沸石及其对Cd2+的吸附

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

以SiO2/Al2O3含量较高的粉煤灰(FA)为原料,Na OH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断裂形成[SiO4]4-和[AlO6]5-单体,ZE比表面积增至21.54 m2/g。当ZE投加量为0.1 g、Cd2+初始质量浓度为100 mg/L、吸附时间为30 min时,平衡吸附量为49.38 mg/g。在p H=4~9时,ZE对Cd2+的去除率在90%以上。在35℃下,ZE对Cd2+吸附符合准二级动力学方程,速率常数为0.0586 g/(g·min);ZE对Cd2+的吸附过程符合Fredunlich等温模型,拟合指数(1/n)为0.4324;热力学实验表明,(35)G在-20~0k J/mol,吸附过程为自发的吸热反应;D-R模型中吸附能均大于16k J/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。

Zeolite(ZE) was synthesized in low-temperature and alkali-fusion-hydrothermal crystallization process with flyash(FA) containing high SiO2 and Al2 O3 content as raw materials, Na OH 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 under the conditions of the ZE dosage of 0.1 g, Cd2+initial concentration of 100 mg/L and adsorption time of 30 min. ZE adsorption of the Cd2+ removal efficiency was more than90% 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 0.0586 g/(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(35)G was between-20 and 0 kJ/mol,indicating that the adsorption was a spontaneous and endothermicprocess. 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.