Preparation And Adsorption Of Recyclable Magnetically Modified Natural Zeolites

In recent years, with the rapid development of social economy, plenty of industrial wastes and sanitary sewages were poured into natural water, of which subsistent heavy metal ions can affect human health seriously. Given this problem, researchers resolve the worsening pollution caused by the heavy metal ions using different adsorbents and processing methods.In this paper, the clinoptilolite produced in Jinyun county of Zhejiang province as an object, which was modified by traditional methods in order to obtain the modified natural zeolite with high adsorption capacity. Then, on the basis of magnetic carrier technology, different magnetically modified zeolites (MMZ) were prepared by combining the modified zeolite with Fe₃O₄ via chemical co-precipitation method and physical adhesion process. The optimal MMZ was characterized by XRD, SEM, FT-IR, TG-DSC, N₂ adsorption isotherms and magnetization measurements. The adsorption of the MMZ for heavy metal ions was studied, and the optimal adsorption conditions, adsorption capacity and adsorption mechanism were also explored.Through the experiments of modification for the natural zeolite and of adsorption for Pb²⁺ on the modified zeolite, the conclusion can be drawn that the modified zeolite by NaCl (Na-zeolite) has the optimal adsorption for Pb²⁺. The adsorption of Pb²⁺ on the Na-zeolite is dependent on pH, and the maximum adsorption capacity of Pb in the initial concentration range studied reaches 66.99 mg/g.For the magnetically modified natural zeolites by chemical method: N₂ adsorption analysis shows that the specific surface areas of the MMZ (Ammonia), MMZ (NaOH) and the Na-zeolite are 100.90 m²/g, 64.02 m²/g and 25.13 m²/g, respectively. According to the FT-IR spectra, the prepared MMZ (Ammonia) cause shift of the Si-0 (Si or Al) at 1054.5 cm^-1 to 1039.3 cm^-1, and the shift indicates that the Fe³⁺ cations similar with Al³⁺ cations embed into the framework of the Na-zeolite during preparation process. In different initial concentration, the adsorption tests of the MMZ and Na-zeolite for Pb²⁺, Cu²⁺ and Cd²⁺ shows that the adsorption is dependent on pH, and the equilibrium adsorbance increases with the increase of initial concentration. According to the general models of liquid phase adsorption, the data of adsorption isotherms is linear fitted, and the fitted curves and the lineared Langmuir curves are basically in coincidence. The fact shows that the adsorption process belonged with the monolayer Langmuir adsorption, and the maximum amount of adsorbed Pb²⁺ per mg of the MMZ (Ammonia), MMZ (NaOH) and the Na-zeolite are 130.72 mg/g, 88.18 mg/g and 65.92 mg/g, respectively.For the magnetically modified natural zeolites by physical process: the structure of MMZ is not manifestly changed along with Fe₃O₄ coated the surface of Na-zeolite, but the specific area increases. The magnetization measurements confirm that the bulk magnetization of the MMZ (Urethane) and Fe₃O₄are 11.7 emu/g and 39.8 emu/g. In different initial concentration, the adsorption tests of the MMZ (Urethane), MMZ (CMC) and Na-zeolite for Pb show that the equilibrium adsorbance increases with the increase of initial concentration, and the maximum amount of adsorbed are 54.53 mg/g, 84.00 mg/g and 66.99 mg/g, respectively.The use of the MMZ developed here offers a unique advantage in separation science and technology. The separation and recovery of heavy metal ions from a complex multiphase system can be accomplished without pretreatment, as the saturated MMZ can be isolated with an external magnetic field.