纳米铁快速去除地下水中多种重金属研究

摘要

重金属污染的地下水治理不断面临着挑战，尤其是在一些发展中国家。纳米铁颗粒代表新一代环境治理技术，面对最具挑战的环境治理问题能够提供有效的解决办法。在实验室制得纳米铁颗粒，粒径为20~40 nm，比表面积（BET）为49.16 m2·g-1。通过考察纳米铁对多种重金属共存水体的去除情况，包括As(III)、As(V)、Cd(II)、Pb(II)、Cr(VI)、Cu(II)和Mn(II)，实验结果表明，重金属的去除效果与重金属类型，纳米铁投加量和反应时间有关。通常当纳米铁投加量为1.25 g·L-1时，反应时间在30 min内，纳米铁对水体中质量浓度范围为0.1~1.0 mg·L-1的重金属离子As(III)、As(V)、Cd(II)、Pb(II)、Cr(VI)、Cu(II)和Mn(II)去除率达90%以上，还可获得以下结论：1）纳米铁能同时对As(III)和As(V)去除，而不需要将As(III)预先氧化成As(V)；2）纳米铁对重金属去除速率快慢为Cu(Ⅱ)> Pb(Ⅱ)>Cr(Ⅵ)>Cd(Ⅱ)；3）纳米铁对重金属去除由刚开始快速消失，到后期缓慢去除的2个步骤组成；4）纳米铁对实际水样中重金属都有很好的去除效果，尤其是对高浓度Mn去除效果更明显，可通过延长处理时间或增加纳米铁的投加量方式，去除率能达99%以上。纳米铁对重金属的去除机理取决于重金属的标准电势，纳米铁对As和Cd(Ⅱ)的去除主要是通过吸附沉淀作用，而对Cu(Ⅱ)、Pb(Ⅱ)和Cr(Ⅵ)去除以还原为主。纳米铁因具有高的比表面积和高的反应活性，更重要的是，它在现场应用时具有很好的灵活性，故可通过高压喷射方式直接注入到地下水中用于多种污染物治理。%Remediation of groundwater contaminated by heavy metal is a recurring challenge, especially in developing countries. Nanoscale iron particles represent a new generation of environmental remediation technologies that could provide cost-effective solutions to some of the most challenging environmental cleanup problems. This study investigated the use of nZVI particles with the particle size of 20-40 nm and specific surface area (BET) of 49.16 m2·g-1 in removing mixed heavy metal contaminants including As(III), As(V), Cd(II), Pb(II), Cr(VI), Cu(II) and Mn(II) from groundwater. Results showed that the removal efficiencies of heavy metals varied with the metal species, nZVI loading, and reaction time. In most cases, use of 1.25 g·L-1 nZVI resulted in removal efficiencies of more than 90% for Cr(VI), Cu(II), Cd(II), Pb(II), Mn(II), As(III), and As(V) with different concentration levels (0.1-1.0 mg·L-1) in 30 min. The following points may be concluded: 1) Both As(III) and As(V) from aqueous solution were removed effectively using NZVI without additional oxidant for oxidizing As(III) to As(V). 2) The removal rate of the heavy metals by nZVI particles followed the sequence Cu(Ⅱ)> Pb(Ⅱ) >Cr(Ⅵ) >Cd(Ⅱ). 3) Batch studies indicate that the removal of heavy metals is a two-step reaction with a fast initial reaction which remove heavy metals to a near-disappearance (or very low) level followed by a slow subsequent removal process. 4) This study demonstrated the efficacy of nZVI particles for the rapid removal of mixed heavy metals, especially for high level Mn(II) from groundwater. 99% for Mn(II) can be removed by prolonging reaction time or increasing the nZVI loading. Depending on the standard potential E0of the heavy metals, the removal mechanisms of Cd(Ⅱ) and As(III) by nZVI is due to sorption or coprecipitation while that of Cu(Ⅱ), Pb(Ⅱ) or Cr(Ⅵ) is mainly redox processes. Due to their small particle size and reactivity, the nanosacle particles may be useful in wide array of environmental applications including subsurface injection for groundwater treatment.