纳米铁去除水体中镉的反应动力学、吸附平衡和影响因素

Removal of Cadmium Ion from Aqueous Solution by Nano Zero-valent Iron: Kinetics, Equilibrium and Impact Factors

镉(Cd)具有致癌、无生物降解性和生物累积性特点,日益严重的镉环境污染问题已引起人们广泛关注。纳米铁是一种能有效去除多种有机和无机污染物的吸附剂。采用批实验方式研究纳米铁(nZVI)吸附镉的动力学和去除效率,可为深入研究纳米铁在重金属Cd污染修复的可行性方面提供理论支撑。利用透射电镜和扫描电镜等对实验室合成的纳米铁颗粒进行了表征,结果表明,纳米铁颗粒平均BET比表面积为49.16 m2·g^-1,粒径为20-40 nm。探讨了多种影响因素对纳米铁颗粒吸附镉的影响,如溶液pH、反应时间、初始浓度和纳米铁投加量。同时研究了Cd2+的准一级和二级反应动力学,应用Freundlich、Langmuir和Temkin等温吸附模型进行平衡吸附研究。结果表明,纳米铁对水溶液中镉吸附是化学吸附。颗粒内扩散模型表明粒内扩散不是控制反应速率的唯一步骤。吸附动力学研究表明,nZVI吸附Cd2+过程符合准二级反应动力学模型。平衡吸附数据能够很好地符合Langmuir、Freundlich和Temkin模型(r2>0.95)。通过Langmuir模型获得室温下吸附剂单层Cd吸附量为256.4 mg·g^-1。在pH 7和(25±1)℃条件下,纳米铁能够有效吸附镉。当nZVI颗粒投加量为1.00 g·L^-1,Cd2+初始质量浓度为74.51 mg·L^-1时,24 h之内,Cd2+去除率达到98.62%。纳米铁可作为一种用于水体镉去除的非常有应用前景的材料。

The increase in environmental pollution caused by cadmium is of great concern because of its carcinogenic properties, non-biodegradability and bio-accumulation. Nano zerovalent iron(nZVI) is an effective adsorbent for removing various organic and inorganic contaminants. Batch experiments were conducted to investigate adsorption kinetics and efficiency of cadmium removal with NZVI. These results would provide theoretical support for in-depth studies on the feasibility of remediation using nZVI for Cd pollution.The synthesized nZVI particles in the laboratory were characterized with different methods such as Brunauer-Emmett-Teller(BET), transmission electron microscopy(TEM), and scanning electron microscope(SEM). Average BET surface area of the synthesized particles was 49.16 m2·g^-1, with diameter range of 20–40 nm. The effects of various parameters, such as solution pH, contact time, initial concentration and nZVI dosage were studied. The adsorption feature of Cd2+ ions was studied in terms of pseudo-first-and-second-order kinetics, and the Freundlich, Langmuir and Temkin isotherms models had also been used to simulate the equilibrium adsorption. The adsorption of cadmium onto nZVI particles was a chemisorption process. The intraparticle diffusion model described that the intraparticle diffusion was not the only rate-limiting step. The adsorption kinetic studies indicated that the sorption process was well fitted by the pseudo-second-order kinetic. The equilibrium data were fitted to Langmuir, Freundlich and Temkin isotherm adsorption models(r2>0.95).The monolayer adsorption capacity of the sorbent, as obtained from the Langmuir isotherm, is 256.4 mg·g^-1 at room temperature. The results showed that cadmium could be removed efficiently by NZVI at pH 7,(25±1) ℃. About 98.62% cadmium ion were removed within 24 h in a concentration of 74.51 mg·L^-1, with a 1.00 g·L^-1 dose of nZVI particles. nZVI appears to be a promising material for the removal of cadmium from contaminated water sources.