School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China.
Water Sci Technol. 2010;62(4):937-46. doi: 10.2166/wst.2010.301.
Zeolite X was successfully synthesized from natural halloysite mineral by hydrothermal method. The synthesized zeolite X was characterized by XRD, SEM, TEM and HRTEM. The characterization indicated that zeolite X had high crystallinity together with symmetrical and uniform pore channels. Ammonium (NH₄+) adsorption properties of zeolite X were studied using batch experiments. The results revealed that high initial concentration and low temperature favored NH₄+ adsorption on zeolite X. Both Langmuir and Freundlich isotherms fit well with the equilibrium data. Kinetic studies showed that the adsorption followed pseudo-second-order model. Intra-particle diffusion analysis demonstrated that NH₄+ diffused quickly among the particles at the initial 20 min of the adsorption process, and then the diffusion slowed down and stabilized. Thermodynamic parameters such as change in free energy (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) indicated that the adsorption was spontaneous and exothermic at ambient conditions. The reusable ability of zeolite X was also evaluated. Due to its low cost, high adsorption capacity and fast adsorption rate, zeolite X synthesized from halloysite could be used as an effective and environmental-friendly adsorbent for NH₄+ removal.
沸石 X 由天然埃洛石矿物通过水热法成功合成。合成的沸石 X 通过 XRD、SEM、TEM 和 HRTEM 进行了表征。表征表明，沸石 X 具有高结晶度以及对称且均匀的孔道。通过批量实验研究了沸石 X 对铵（NH₄+）的吸附性能。结果表明，高初始浓度和低温有利于 NH₄+在沸石 X 上的吸附。Langmuir 和 Freundlich 等温线都很好地拟合了平衡数据。动力学研究表明，吸附过程遵循拟二级动力学模型。内扩散分析表明，在吸附过程的最初 20 分钟内，NH₄+在颗粒间快速扩散，然后扩散速度减慢并稳定下来。自由能（ΔG⁰）、焓（ΔH⁰）和熵（ΔS⁰）等热力学参数表明，在环境条件下，吸附是自发的和放热的。还评估了沸石 X 的可重复使用能力。由于其成本低、吸附容量大和吸附速率快，由埃洛石合成的沸石 X 可用作去除 NH₄+的有效且环保的吸附剂。
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