Abstract:

High-fluoride water is widely distributed in China. As removing fluorine from water is urgent, it is imperative to develop effective and inexpensive absorbent materials for the removal of fluoride. The reserves of diatomite in China are very rich, ranking second in the world. Due to the unique physical and chemical properties of diatomite, it has been widely used as a new type of adsorption and environmental protection materials in the industry in recent years. In this study, diatomite was used as an adsorbent to study the adsorption of fluoride (F^-) in the water. The structural characteristics of diatomite are analyzed by using SEM, XRD and FTIR. Different experimental conditions of diatomite (i.e., dosage, pH, and solution concentration) were identified to study the adsorption of F^- onto diatomite. In addition, kinetic fitting and an orthogonal experiment were used for identifying optimal conditions and combinations. The results show that the surface of diatomaceous earth has a rich pore structure with clear pores, large specific surface area, high silica content, and rich oxygen-containing functional groups. The adsorption process of fluoride ions by diatomaceous earth can be represented by the Freundlich model where r can reach 0.993, indicating that the process of adsorbing F^- onto diatomite is an adsorption-complex interaction, belonging to surface adsorption and multi-molecular layer adsorption. The quasi-second-order kinetic model is the process of adsorbing F^- onto diatomite. This model's fitting effect is better than that of the quasi-first-order kinetic model and the W-M kinetic model, as the r for the quasi-second-order kinetic model can reach 0.999. This finding indicates that the process of adsorbing F^- onto diatomite is a chemical adsorption. The maximum adsorption capacity can reach 32.2 mg·g^-1 and the order of the influencing factors is: dosage>concentration>pH, according to the orthogonal experiment. When the fluoride concentration is 100 mg∙L^-1, pH is 6.0, and dosage is 4 g∙L^-1, the removal rate of F^- can reach 91.8%. Therefore, diatomite can be used as a highly efficient, low-cost, and environmental friendly fluoride-removing adsorbent. The current study can provide a theoretical basis for the future treatment of fluorine-containing water bodies.

Key words: diatomite, fluoride, adsorption, kinetics, removal rate, characterization

摘要：

中国高浓度含氟水分布广泛且危害严重,水体除氟迫在眉睫。研发除氟效果好、价格便宜的吸附材料是一项艰巨的任务,对水体除氟具有重大的意义。硅藻土（Diatomite）因其特有的物理和化学性质,作为一种新型的吸附型、环保型材料近年来在工业中已经得到了普遍的应用。以硅藻土作为吸附剂对水体中的氟化物（F^-）进行吸附研究,采用了SEM、XRD、FTIR对其进行表征,分析其结构特性;探究了投加量、溶液pH、溶液初始质量浓度对硅藻土吸附F^-的影响,对其进行吸附和动力学拟合,并设计正交实验,得出最优条件以及最优组合。结果表明：硅藻土表面具有丰富的孔隙结构且孔洞清晰,比表面积大,二氧化硅含量较高,且含有丰富的含氧官能团;硅藻土对氟离子的吸附过程能够更好的符合Freundlich模型,r值可达0.993,说明硅藻土对F^-的吸附过程是吸附-络合相互作用,为表面吸附和多分子层吸附;准二级动力学模型对硅藻土吸附F^-的过程拟合效果优于准一级动力学模型、W-M动力学模型,r值为0.999,表明硅藻土对F^-的吸附过程是化学吸附作用。其中最大吸附量可达到32.2 mg∙g^-1,根据正交实验得出各影响因素大小依次为：投加量>质量浓度>pH;当氟化物质量浓度为100 mg∙L^-1,pH值为6.0,投加量为4.0 g∙L^-1时,硅藻土对F^-的去除率可达到91.8%。因此,硅藻土可作为高效、廉价、环保的除氟吸附剂,可为以后的含氟水体治理提供理论依据。

关键词: 硅藻土, 氟化物, 吸附, 动力学, 去除率, 表征