Abstract:

Fluoride removal is an urgent water treatment problem worldwide. In this paper, Magnesium oxide adsorbents were synthesized through a simple precipitation-calcination method and applied to the study of wastewater defluorination. The pH had a great influence on the specific surface area of the synthesized magnesium oxide material, and the specific surface area of the synthesized material was the largest (101.1—154.8m²/g) when the pH was in the range of 10—10.5. The maximum adsorption capacity was 61.337mg/g through batch adsorption experiment and isotherm study. This process conformed to the Freundlich model, which proved that the adsorption process was based on the heterogeneous adsorption. Through kinetic studies, the adsorption process conformed to the pseudo-second-order kinetic model, which proved that the adsorption process included chemisorption. The adsorption mechanism over MgO was deduced to be electrostatic interaction and ion exchange mechanism by characterization results of XRD, SEM, FTIR and XPS. In the range of pH 2—10, magnesium oxide can effectively remove fluoride from water. Among the common competitive anions, only CO${}_{\mathrm{3}}^{\mathrm{2}-}$ and PO${}_{\mathrm{4}}^{\mathrm{3}-}$ had adverse effects on the adsorption of fluoride. The cyclic adsorption test showed that the magnesium oxide adsorbent had the potential of renewable utilization. Therefore, through the batch adsorption test of the synthesized magnesium oxide material and the exploration of the adsorption mechanism, the theoretical accumulation of the industrial application of wastewater defluorination was provided.

Key words: magnesium oxide, precipitation, fluoride, adsorption, kinetic

摘要：

氟化物移除是全世界范围内急需解决的水处理问题。本文通过一种简单的沉淀-煅烧法合成了氧化镁吸附剂并将其应用于废水除氟研究。pH对合成的氧化镁材料比表面积影响较大，pH在10~10.5时合成的材料比表面积最大（101.1~154.8m²/g）。通过批量吸附实验及等温线研究，发现最大吸附容量为61.337mg/g；该过程符合Freundlich模型，说明吸附过程为非均相吸附；通过动力学研究，发现吸附过程符合拟二级动力学模型，说明吸附过程包含化学吸附。通过X射线衍射（XRD）、扫描电子显微镜（SEM）、傅里叶变换红外光谱（FTIR）、X射线光电子能谱（XPS）等表征结果推断出氧化镁的吸附机理为静电相互作用、离子交换机制。在pH为2~10时氧化镁能有效去除水中的氟化物；常见竞争阴离子中仅有CO₃^2-、PO₄^3-对氟化物的吸附有不利影响；循环吸附实验表明氧化镁吸附剂具有可再生利用的潜力。因此，通过对合成的氧化镁材料进行批次吸附实验及吸附机理的探究，为废水除氟的工业应用提供一定的理论积累。

关键词: 氧化镁, 沉淀, 氟化物, 吸附, 动力学