腐植酸改性强化磁铁矿吸附水体中铅镉的实验研究

磁铁矿是一种绿色廉价的矿物材料,对水体中重金属离子具有良好的吸附性,但吸附容量低,选择性差,易团聚,通过改性可以克服该缺点并提高其吸附性能。本文以腐植酸为改性剂,采用常温水相反应制备了腐植酸改性磁铁矿吸附材料。通过傅里叶红外光谱(FTIR)、扫描电镜(SEM)和X射线光电子能谱(XPS)表征研究其表面形貌和微观结构。采用静态平衡实验考察了pH、吸附时间等因素对铅、镉吸附性能的影响,探讨了吸附动力学规律,拟合了吸附等温线。结果表明:腐植酸上的羧基、羟基被成功地接枝到了磁铁矿表面。在室温下,溶液初始pH对Pb~(2+)的吸附率几乎无影响,对Cd~(2+)的影响较大,当pH=7时,Pb~(2+)和Cd~(2+)吸附率均达到了95%。对初始质量浓度为10mg/L的Pb~(2+)、Cd~(2+)最佳吸附平衡时间为360min,吸附过程符合准二级动力学方程。吸附等温线实验得到的竞争吸附顺序为Pb~(2+)Cd~(2+),由Langmuir等温吸附模型得到Pb~(2+)、Cd~(2+)饱和吸附容量分别为39.27mg/g、28.95mg/g,显著大于磁铁矿的饱和吸附容量,表明磁铁矿经腐植酸改性后增强了对水中铅镉的吸附能力。

Enhancement of Pb and Cd Adsorption in Water Samples by Magnetite Using Humic Acid as Modifier

BACKGROUND: Magnetite is widely used as a green and cheap mineral material to adsorb heavy metals in water samples, but it has the disadvantages of low adsorption capacity, poor selectivity and easy reunion. Surface modification of magnetite could overcome these problems and improve its adsorption properties.
OBJECTIVES: To enhance the adsorption properties of magnetite by using a humic acid modifier.
METHODS: The morphology and structure of magnetite and humic acid-modified magnetite were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The effect of conditions such as optimal pH and adsorption time on Pb²⁺ and Cd²⁺ adsorption rate were investigated by static equilibrium experiment.
RESULTS: Carboxyl and hydroxyl groups in humic acid were successfully absorbed onto the surface of magnetite. At room temperature, the initial pH of the solution had little effect on the adsorption rate of Pb²⁺, but had a greater influence on Cd²⁺. When pH=7, the adsorption rates of Pb²⁺ and Cd²⁺ reached 95%. The optimal adsorption equilibrium time of Pb²⁺ and Cd²⁺ with initial mass concentration of 10mg/L was 360 minutes, and the adsorption process accords with the quasi-second-order kinetic equation. The order of competitive adsorption was Pb²⁺ followed by Cd²⁺. The Langmuir isothermal adsorption model yielded maximum adsorption capacity of Pb²⁺ and Cd²⁺ of 39.27mg/g and 28.95mg/g, respectively.
CONCLUSIONS: The adsorption capacity of humic acid-modified magnetite was higher than that of magnetite, indicating that the ability of humic acid-modified magnetite was enhanced to adsorb Pb²⁺ and Cd²⁺ in water samples.