RCEES OpenIR  > 环境水质学国家重点实验室
纳米零价铁除砷效果及氧气强化除砷作用机制
Alternative TitleArsenic Removal Performance of Nano Zero-Valent Iron and the Mechanism of Oxygen Enhanced Arsenic Removal
孙路静
Subtype硕士
Thesis Advisor栾富波
2020-09
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name工学博士
Degree Discipline环境工程
Keyword纳米零价铁,As(Iii)/As(v),氧气含量,强化去除,作用机制 Nano Zero-valent Iron, As(Iii)/As(v), Oxygen Content, Enhanced Removal, Reaction Mechanism
Abstract

     地下水砷(As)污染已经成为一个全球性的环境问题,严重威胁着生态环境和人类的健康。地下水中As 主要以无机的As(III)和As(V)两种形态赋存。纳米零价铁(nZVI)对地下水中重金属具有较好的去除效果,也是高效去除地下水中As 的潜在材料之一。本论文分别研究了nZVI 去除As(III)和As(V)的效果,重点考察反应时间、As 初始浓度、nZVI 投加量等因素对nZVI 去除水中As(III)和As(V)的影响,并利用动力学模型(准一级、准二级)、吸附等温线模型和Werber-Morris 粒子内扩散模型对nZVI 吸附AsIII)/As(V)的过程进行拟合分析。针对地下水随水位变化而出现的厌氧、好氧波动现象以及异位泵出处理时地下水中氧含量变化的问题,对不同氧含量(厌氧、低氧、中氧和高氧)条件下nZVI 去除As(III)/As(V)的过程进行了对比分析,并对固体产物进行SEM、XRD 和XPS 表征,探讨了氧气促进nZVI 除As(III)/As(V)效果的作用机制。结果表明:
     (1)在nZVI 去除As(III)的过程中,As(III)的去除率随反应时间增加逐渐升高并趋于稳定,但随着As(III)初始浓度增加去除率逐渐降低。As(III)在nZVI 上的吸附符合准二级动力学模型(R2>0.990),其吸附速率常数k2 最大为0.304g·mg-1·min-1。Werber-Morris 粒子内扩散模型表明nZVI 吸附As(III)的过程可分为外扩散、内扩散、吸附平衡3 个阶段,且由外扩散和颗粒内扩散共同控制,其中外扩散速率常数可达36.041 mg·g-1·min-0.5。Langmiur 等温吸附模型能够很好地描述As(III)在nZVI 上的吸附,饱和吸附量为148.81 mg·g-1。As(III)的去除率随nZVI投加量的增大而升高,当投加量大于0.4 g·L-1 时去除率可达100%(As(III)初始浓度为50 mg·L-1)。氧气可明显促进nZVI 对As(III)的去除效果,不同氧含量对nZVI 除As 效果有不同程度的促进作用,随着氧含量的增加在整体上As(III)的去除率呈现先升高后降低再升高的趋势。O2/nZVI 摩尔比等于0.5 时As(III)的去除效果最好,总As 去除率为96.41%,比厌氧条件下提高了35.04%。
     (2)在nZVI 去除As(V)的过程中,各影响因素对As(V)的去除率的影响趋势及模型拟合结果与As(III)体系大致相同,但吸附速率常数、扩散速率常数(kid)和Langmiur 等温吸附模型所计算饱和吸附量(68.97 mg·g-1)均小于As(III)体系,说明nZVI 对As(V)的吸附速率慢于As(III),且As(V)在nZVI 表面更难扩散。与As(III)相比,nZVI 投加量为1.0 g·L-1 时仍未能完全去除(As(V)初始浓度为50mg·L-1),说明As(V)需要更多的nZVI 才能达到有效去除的目的。O2/nZVI 摩尔比等于0.5 时As(V)的去除率最高,为51.75%,比厌氧条件下提高了27.14%。在相同的实验条件下,nZVI 对As(III)的去除率均大于As(V),可实现As(III)的直接高效去除。因此,将nZVI 应用于以As(III)为主要污染物的地下水修复中更具优势。
     (3)在nZVI 去除As(III)/As(V)的机制研究中,固相表征结果表明nZVI 去除As 的作用机制包括吸附、氧化、还原等,且以吸附作用为主。氧气含量条件显著影响着nZVI 的氧化程度及nZVI 除As 效果。低氧条件下,nZVI 少量氧化生成无定型铁矿物促进了As 的吸附;中氧条件下,nZVI 被大量氧化为溶解态铁,As 的去除率降低;高氧条件下,溶解态铁被进一步氧化为铁矿物,提高了As 的去除率。
     本论文研究结果表明,nZVI 对As(III)和As(V)均具有较好的去除效果,且对As(III)去除效果明显优于As(V)。适量氧气存在可明显促进nZVI 对As(III)和As(V)的去除效果,且nZVI 大量氧化后仍能保持较高的As(III)和As(V)去除效率。研究结果可为开发nZVI 除As(III)/As(V)技术提供数据支持,同时也为人为强化nZVI 除As 效果提供理论依据。
 

Other Abstract

       Arsenic (As) contamination in groundwater has been recognized as a global environmental problem, severely threatening the ecological environment and human health. As is mainly appeared in groundwater as inorganic As(III) and As(V) forms. Nano zero-valent iron (nZVI) can effectively remove the heavy metals in groundwater,and it is also one of the potential materials to control As contamination in groundwater. This study evaluated the effects of nZVI on removing As(III) and As(V), where in the influences of reaction time, initial concentration of arsenic and nZVI dosage on the As removal were investigated. Pseudo-first/second order kinetic, Langmuir/Freundlich isotherm and Werber-Morris intra-particle diffusion model were applied to simulate the adsorption kinetic process of As(III)/As(V). As regard to anaerobic and aerobic fluctuation in groundwater with the change of water level and the change of
groundwater oxygen content during ex-situ treatment, comparative analysis was carried out to evaluate the effects of Arsenic removal by nZVI under different oxygen content conditions (anaerobic, low, medium and high oxygen). Additionally, the mechanism of oxygen promoting the removal of arsenic by nZVI was analyzed based on the characterization results (SEM, XRD and XPS). The findings in present study were concluded as follows:
      (1) In the process of As(III) removal by nZVI, the removal efficiency of As(III)gradually increased and stabilized with the increase of reaction time, but decreased with the increase of initial concentration of As(III). The results of model fitting showed that the adsorption of As(III) on nZVI conformed to the pseudo-second order kinetic model (R2>0.990), and the maximum adsorption rate constant k2 was 0.304 g·mg-1·min-1. The fitting result of Werber-Morris intra-particle diffusion model suggested that the adsorption process included external diffusion, internal diffusion and adsorption equilibrium, controlling by external and internal diffusion processes, where in the maximum external diffusion rate constant reached to 36.041 mg·g-1·min-0.5. Langmuir isotherm model well fitted the adsorption process of As(III) on nZVI (R2>0.900), and the saturation adsorption capacity was 148.81 mg·g-1. The As(III) removal efficiency elevated with the increase of nZVI dosage, and reached 100% when the dosage was higher than 0.4 g·L-1 (As(III) initial concentration was 50 mg·L-1). It was observed that the presence of oxygen significantly promoted the removal of As(III) by nZVI, whereas the removal efficiencies was different with changing oxygen contents. The As(III) removal efficiency was increased initially, followed by a decrease, but then raised again with increasing of oxygen content. The maximum removal efficiency of As(III) was 96.47% when the molar ratio of O2/nZVI was 0.5, 35.04% higher than that of under anaerobic condition.
      (2) In the process of As(V) removal by nZVI, the influence trend of various factors on the removal efficiency of As(V) and the results of model fitting were approximately the same as that of As(III) system. However, the adsorption rate constant, diffusion coefficient (kid) and saturation adsorption capacity (68.97 mg·g-1) of Langmuir isotherm model were all less than that of in As(III) system, indicating that the adsorption of As(V) by nZVI was much slower and As(V) was hard to diffuse on the surface of nZVI.Compared with As(III), it was not completely removed when the dosage was 1.0 g·L-1 (As(V) initial concentration was 50 mg·L-1), indicating that more nZVI was needed to achieve effective removal. The maximum removal efficiency of As(V) was 51.75% when the molar ratio of O2/nZVI was 0.5, 27.14% higher than that of under anaerobic condition. The removal efficiency of As(III) by nZVI was higher than that of As(V) under the same experimental conditions, and nZVI can directly and efficiently remove As(III). Therefore, applying nZVI to remedy As(III) contaminated groundwater was more effecient.
      (3) Solid phase characterizations were carried out to study the mechanism of removing As(III)/As(V) by nZVI. The results indicated that mechanism for removing As included adsorption, reduction, oxidation and so on. Adsorption as the main removal mechanism took place in two reaction system. In addition, it was observed that oxygen can significantly affect the oxidation extent of nZVI and the performance of arsenic removal by nZVI. Under low oxygen condition, nZVI was slightly oxidized to amorphous iron oxides which could enhance the arsenic removal efficiency. Under medium oxygen condition, nZVI was oxidized to a large amount of dissolved iron, resulting in a decline of arsenic removal efficiency. In terms of high oxygen condition, dissolved iron were further oxidized to form new amorphous iron minerals which could further enhance the arsenic removal efficiency.
      The above results verified that nZVI had certain removal effect on both As(III) and As(V), and removal effect of As(III) was significantly better than that of As(V). Adequate oxygen can significantly enhance the effect of arsenic removal by nZVI, and high removal efficiency of As(III) and As(V) can be maintained after massive oxidation of nZVI. The results can afford data support for evaluating the effect of removing As(III)/As(V) by nZVI with different oxygen content conditions, and provide a theoretical support for the effect of removing arsenic artificial enhancement by nZVI.

Pages104
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/43649
Collection环境水质学国家重点实验室
Recommended Citation
GB/T 7714
孙路静. 纳米零价铁除砷效果及氧气强化除砷作用机制[D]. 北京. 中国科学院生态环境研究中心,2020.
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