In situ removal of arsenic from groundwater by using permeable reactive barriers of organic matter/limestone/zero-valent iron mixtures

In this study, two mixtures of municipal compost, limestone and, optionally, zero-valent iron were assessed in two column experiments on acid mine treatment. The effluent solution was systematically analysed throughout the experiment and precipitates from both columns were withdrawn for scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry analysis and, from the column containing zero-valent iron, solid digestion and sequential extraction analysis. The results showed that waters were cleaned of arsenic, metals and acidity, but chemical and morphological analysis suggested that metal removal was not due predominantly to biogenic sulphide generation but to pH increase, i.e. metal (oxy)hydroxide and carbonate precipitation. Retained arsenic and metal removal were clearly associated to co-precipitation with and/or sorption on iron and aluminum (oxy)hydroxides. An improvement on the arsenic removal efficiency was achieved when the filling mixture contained zero-valent iron. Values of arsenic concentrations were then always below 10 μg/L.     

Degradation of chlorinated phenols by nanoscale zero-valent iron

Chlorophenols (CPs), as important contaminants in groundwater, are toxic and difficult to biodegrade. Recently nanoscale zero-valent iron received a great deal of attention because of its excellent performance in treating recalcitrant compounds. In this study, nanoscale zero-valent iron particles were prepared using chemical reduction, and the reductive transformations of three kinds of chlorinated phenols (2-CP, 3-CP, and 4-CP) by nanoscale zero-valent iron under different conditions were investigated. The transformation process of the CPs was shown to be dechlorination first, then cleavage of the benzene ring. The removal efficiency of the CPs varied as follows: 2-CP > 3-CP > 4-CP. The reactivity of CPs was associated with their energy of lowest unoccupied molecular orbit (E _LUMO). With the increase in initial concentrations of CPs, removal efficiency decreased a little. But the quantities of CPs reduced increased evidently. Temperature had influence on not only the removal efficiency, but also the transformation pathway. At higher temperatures, dechlorination occurred prior to benzene ring cleavage. At lower temperatures, however, the oxidation product was formed more easily.     

壳聚糖稳定纳米铁去除地表水中Cr(Ⅵ)污染的影响因素

以壳聚糖为稳定剂,制备纳米零价铁颗粒,TEM表征结果显示:其粒径分布范围为20—150 nm,平均粒径为82.4 nm.研究表明,壳聚糖稳定的纳米铁去除Cr(Ⅵ)的还原反应符合一级反应动力学方程.溶液中投加稳定剂壳聚糖,当壳聚糖浓度为150 mg.l-1时,80 min内表观一级动力学常数kobs约为空白溶液的2倍;干扰离子Ca2+,Mg2+,HCO3-和CO32-对壳聚糖稳定纳米铁去除Cr(Ⅵ)的批试验结果显示,Ca2+和Mg2+在80 min内使壳聚糖稳定纳米铁对Cr(Ⅵ)去除率分别降低了约20%和10%;HCO3-和CO32-的存在使去除率降低了约10%.     

膨润土负载纳米铁用于降解水体中阿莫西林

采用液相还原法合成膨润土负载纳米铁(B-nZVI)和纳米铁(nZVI)并用于降解水中的阿莫西林.实验结果表明,无论是单独nZVI还是B-nZVI都能有效降解阿莫西林.在25 mL浓度为20 mg.L-1的阿莫西林溶液中加入0.1 g的B-nZVI(其中nZVI的含量为0.05 g),溶液的初始pH值为6.65,摇床的振荡速率为250 r.min-1,反应温度为25℃,反应时间为120 min的条件下,B-nZVI对阿莫西林的降解效率高达93.1%,在此实验条件下,单独nZVI(0.05 g)对阿莫西林的降解效率只有82.3%,这是由于膨润土对nZVI起到分散作用,从而使B-nZVI的反应活性得到提高.降解动力学研究表明,B-nZVI对阿莫西林的降解过程符合表观一级反应动力学规律,相关系数R2均大于0.945.B-nZVI可多次重复用于降解阿莫西林.     

Rapid degradation of carbon tetrachloride by commercial micro-scale zinc powder assisted by citric acid

We developed an effective method for degradation of carbon tetrachloride (CT) in contaminated water. Zinc metal as a reducing agent for CT in aqueous solutions has been previously studied in some detail, but the rapid corrosion of zinc surface usually reduces its efficiency in removing CT. We assumed that citric acid could enhance the degradation of CT by zinc powder due to the elimination of a passivation layer of Zn(II) (hydr)oxides on the surface of zinc powder through chelating of organic ligands with Zn(II) produced from the reaction and keeping the exposure of active sites to targets. Here the influence of citric acid on the decomposing of CT by commercial micro-scale zinc powder was investigated in a pH range of 3.5–7.5 at 25°C in batch experiments. Reaction mixtures were analysed by gas chromatography/headspace analysis, and Cl⁻ concentration was determined by turbidimetry. The results demonstrate that the degradation of CT by zinc metal alone is very weak, but the addition of citric acid can assist zinc powder to decompose CT more completely and rapidly at all pHs. Degradation of CT took place mainly in the first 10 min of reaction, coupled with 75–95% of CT removal. Maximum dechlorination percentage (82.4%) of CT was obtained at pH 5.5. In that case, chloroform and dichloromethane, as main intermediates, were found at low levels during the whole reaction, suggesting that CT may be sequentially and multiply degraded so quickly that methane is yielded before the intermediates can be desorbed and released to aqueous solution. When compared with the current methods of nano-scale zinc and bimetallic systems, the application of commercial micro-scale zinc particles assisted by organic ligands is of environmental significance since it allows decontamination of aqueous chlorinated organic compounds at low cost and with high efficiency.     

Nanoscale zero-valent iron supported on biochar for the highly efficient removal of nitrobenzene

• Biochar supported nanoscale zero-valent iron composite (nZVI/BC) was synthesized. • nZVI/BC quickly and efficiently removed nitrobenzene (NB) in solution. • NB removal by nZVI/BC involves simultaneous adsorption and reduction mechanism. • nZVI/BC exhibited better catalytic activity, stability and durability than nZVI. The application of nanoscale zero-valent iron (nZVI) in the remediation of contaminated groundwater or wastewater is limited due to its lack of stability, easy aggregation and iron leaching. To address this issue, nZVI was distributed on oak sawdust-derived biochar (BC) to obtain the nZVI/BC composite for the highly efficient reduction of nitrobenzene (NB). nZVI, BC and nZVI/BC were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). For nZVI/BC, nZVI particles were uniformly dispersed on BC. nZVI/BC exhibited higher removal efficiency for NB than the simple summation of bare nZVI and BC. The removal mechanism was investigated through the analyses of UV-Visible spectra, mass balance and XPS. NB was quickly adsorbed on the surface of nZVI/BC, and then gradually reduced to aniline (AN), accompanied by the oxidation of nZVI to magnetite. The effects of several reaction parameters, e.g., NB concentration, reaction pH and nZVI/BC aging time, on the removal of NB were also studied. In addition to high reactivity, the loading of nZVI on biochar significantly alleviated Fe leaching and enhanced the durability of nZVI.     

Effects of different types of biochar on the properties and reactivity of nano zero-valent iron in soil remediation

• Biochar enhanced the mobility and stability of zero-valent iron nanoparticles. • Particle performance was best when the BC:nZVI mass ratio was 1:1. • Bagasse-BC@nZVI removed 66.8% of BDE209. The addition of nano zero-valent iron (nZVI) is a promising technology for the in situ remediation of soil. Unfortunately, the mobility and, consequently, the reactivity of nZVI particles in contaminated areas decrease due to their rapid aggregation. In this study, we determined how nZVI particles can be stabilized using different types of biochar (BC) as a support (BC@nZVI). In addition, we investigated the transport behavior of the synthesized BC@nZVI particles in a column filled with porous media and their effectiveness in the removal of BDE209 (decabromodiphenyl ether) from soil. The characterization results of N₂ Brunauer–Emmett–Teller (BET) surface area analyses, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) indicated that nZVI was successfully loaded into the BC. The sedimentation test results and the experimental breakthrough curves indicated that all of the BC@nZVI composites manifested better stability and mobility than did the bare-nZVI particles, and the transport capacity of the particles increased with increasing flow velocity and porous medium size. Furthermore, the maximum concentrations of the column effluent for bagasse–BC@nZVI (B–BC@nZVI) were 19%, 37% and 48% higher than those for rice straw–BC@nZVI (R–BC@nZVI), wood chips–BC@nZVI (W–BC@nZVI) and corn stalks–BC@nZVI (C–BC@nZVI), respectively. A similar order was found for the removal and debromination efficiency of decabromodiphenyl ether (BDE209) by the aforementioned particles. Overall, the attachment of nZVI particles to BC significantly increased the reactivity, stability and mobility of B–BC@nZVI yielded, and nZVI the best performance.     

两种土壤中对硝基氯苯被Fe~0还原的对比研究

利用零价铁(Fe~0)还原技术修复受对氯硝基苯(p-CNB)污染的土壤,研究常温常压下松砂土和中壤土两种不同土壤的理化性质对还原反应的影响.结果表明:Fe0能有效还原松砂土和中壤土中的p-CNB,生成对应的苯胺化合物,降低毒性;当土壤中p-CNB的含量约为2.5×10~(-6)mol·g~(-1),Fe~0用量为25 mg·g~(-1),反应体系中水分含量为0.75 mL·g~(-1)时,于25℃反应2 h后,松砂土和中壤土中p-CNB的还原率均超过93%;还原反应在中壤土中进行得较快.污染物在土壤中的老化时间对Fe~0还原降解效果影响很小,而土壤粒径、土壤是否灭菌以及土壤有机质含量等因素则对还原有较明显影响;还原降解反应在没有灭菌、有机质含量较高且粒径偏小的壤土中进行得最彻底.     

纳米Fe0对Cr（VI）的还原及其影响因素

采用纳米Fe0还原水溶液中的Cr（Ⅵ）,考察纳米Fe0投加量、Cr（Ⅵ）初始浓度、溶液pH值和有机酸等因素对cr（Ⅵ）还原的影响。结果表明,纳米Fe。对Cr（Ⅵ）的还原效果明显,其对Cr（Ⅵ）的还原率分别是铁粉和铁屑的7和13倍。Cr（Ⅵ）溶液初始质量浓度为20mg·L-1、Fe。投加量为5g·L“条件下,反应24h时纳米Fe0对Cr（Ⅵ）的还原率达82．7％。溶液低pH值可以促进Fe。的腐蚀速度,提高反应速率,当pH值为3．0时还原效果最好。草酸、丙二酸和丁二酸对纳米Fe。还原Cr（Ⅵ）均有明显的促进作用,3种有机酸对Cr（Ⅵ）还原率的提高幅度由高到低依次为草酸、丙二酸和丁二酸。     

中性条件下超声波/零价铁协同降解活性艳红X-3B

考察了中性条件下超声波降解、零价铁还原及超声波-零价铁联用对活性艳红X-3B模拟废水的降解效果,通过对比降解过程中UV-Vis光谱的变化,探讨了超声波-零价铁协同处理活性艳红X-3B的可行性.结果表明,在中性条件下超声波对活性艳红X-3B降解缓慢,经过25min辐射后,活性艳红X-3B的分解率不足7.5%;零价铁直接还原速率较慢,反应25min后,活性艳红X-3B的分解率仅为48.82%;"超声波/零价铁"对降解活性艳红X-3B有明显的协同效应,25min后分解率达99.42%(600W),反应符合准一级动力学过程.与零价铁直接还原相比,在200W,400W和600W超声波的协同作用下,X-3B降解的表观反应速率常数分别提高了2.12,2.76和4.00倍,半衰期相应缩短.另外,添加H2O2会抑制协同效应.     

纳米零价铁颗粒去除水中重金属的研究进展

重金属是毒性大、难降解、易累积的环境污染物,纳米零价铁作为一种新型功能修复材料在去除水体和土壤中重金属方面有着广阔的应用前景.本文综述了纳米零价铁颗粒去除水中重金属的研究进展,包括纳米零价铁的常用制备方法及特性、去除效能、对不同重金属的去除机理以及发展前景和今后的研究方向,以期为该领域的深入研究提供借鉴并拓展新的思路.     

Removing polybrominated diphenyl ethers in pure water using Fe/Pd bimetallic nanoparticles

Polybrominated diphenyl ethers (PBDEs) have been widely used as fire-retardants. Due to their high production volume, widespread usage, and environmental persistence, PBDEs have become ubiquitous contaminants in various environments.Nanoscale zero-valent iron (ZVI) is an effective reductant for many halogenated organic compounds. To enhance the degradation efficiency, ZVI/Palladium bimetallic nanoparticles (nZVI/Pd) were synthesized in this study to degrade decabromodiphenyl ether (BDE209) in water. Approximately 90% of BDE209 was rapidly removed by nZVI/Pd within 80 min, whereas about 25% of BDE209 was removed by nZVI. Degradation of BDE209 by nZVI/Pd fits pseudo-first-order kinetics. An increase in pH led to sharply decrease the rate of BDE209 degradation. The degradation rate constant in the treatment with initial pH at 9.0 was more than 6.8 × higher than that under pH 5.0. The degradation intermediates of BDE209 by nZVI/Pd were identified and the degradation pathways were hypothesized. Results from this study suggest that nZVI/Pd may be an effective tool for treating polybrominated diphenyl ethers (PBDEs) in water.     

纳米Fe~0协同微生物对PCB77的降解研究

研究了纳米零价铁协同微生物降解水溶液中的PCB77。从污染土样中分离出一株多氯联苯（PCBs）降解菌,对其进行革兰氏染色形态观察,并用降解菌降解PCB77。结果表明：培养温度30℃、溶液pH 7.0、微生物接种量109 cfu·mL-1、PCB77初始质量浓度1.0 mg·L-1时,降解菌对PCB77的降解率为58.63%。纳米零价铁对PCB77的降解是一个还原脱氯过程,7 d时的降解率为82.99%。采用纳米零价铁/微生物联合体系降解水溶液中PCB77,降解率显著高于微生物和纳米零价铁单一体系,降解率可达93.30%。研究结果将为环境中PCBs残留提供了一种高效去除的方法,并为PCBs污染土壤的修复提供理论依据。     

UV light induces Ag nanoparticle formation: roles of natural organic matter,iron, and oxygen

Nanoparticles occurring in the environment originate either from engineered, synthetically produced nanoparticles, or from naturally produced nanoparticles. The latter can be formed in natural media by light-induced reduction of metal ions in presence of natural organic matter, such as humic substances occurring widely in waters, soils and sediments. There is actually few knowledge on the effect of sunlight and of the nature of organic matter on nanoparticle formation. Therefore, we studied here the photoreduction of silver(I) ion to silver nanoparticles with and without ferrous ion under oxic and anoxic conditions, using humic and fulvic acids as proxies of natural organic matter. UV light-induced formation of silver nanoparticles was monitored up to 60 min by measuring surface plasmon resonance in air-saturated mixture and nitrogen-saturated mixture of silver(I) ion–organic matter. Results show that the surface plasmon resonance intensity was about 2.5 times higher in the nitrogen-purged solution mixture than the air-saturated solution. This finding suggests the oxygen-containing species had no major role in forming silver nanoparticles. Therefore, photo-driven formation of silver nanoparticles most likely involved photoactivation of silver(I) ion and natural organic matter complexes. We observed also that both iron(II) and iron(III) ions highly modified the surface plasmon resonance spectra of the particles with broader features. Results also reveal that in the presence of humic acid, the intensity of the surface plasmon resonance peak decreased by at least 50 %, while almost no change in the intensity was seen when fulvic acid was used. Overall, our findings demonstrate that the ligand–metal charge transfer process, affected by the nature of organic matter, i.e., humic acid versus fulvic acid, was influenced by redox iron species.     

零价铁还原和过硫酸盐氧化联合降解水中硝基苯

将零价铁(Fe0)的还原和过硫酸盐(persulfate,PS)的高级氧化技术结合用于水中难降解有机污染物硝基苯的去除.研究结果表明,Fe0在常温常压下可将硝基苯还原生成苯胺,随着Fe0投加量的增加,硝基苯还原为苯胺的速率逐渐增大.PS本身对硝基苯氧化作用不明显,但在Fe0与PS二者联合体系中,硝基苯和苯胺同时被去除,而且随着PS投加量的增加二者被去除的速度也随之增加.在Fe0还原和PS氧化联合处理硝基苯的体系中可能存在两个过程,一是Fe0还原硝基苯产生苯胺和二价铁离子Fe2+,二是Fe2+催化PS产生强氧化性的硫酸根自由基将苯胺氧化降解.     

Removal of decabromodiphenyl ether (BDE-209) by sepiolite-supported nanoscale zerovalent iron

Nanoscale zerovalent iron (nZVI) synthesized using sepiolite as a supporter was used to investigate the removal kinetics and mechanisms of decabromodiphenyl ether (BDE-209). BDE-209 was rapidly removed by the prepared sepiolite-supported nZVI with a reaction rate that was 5 times greater than that of the conventionally prepared nZVI because of its high surface area and reactivity. The degradation of BDE-209 occurred in a stepwise debromination manner, which followed pseudo-first-order kinetics. The removal efficiency of BDE-209 increased with increasing dosage of sepiolite-supported nZVI particles and decreasing pH, and the efficiency decreased with increasing initial BDE-209 concentrations. The presence of tetrahydrofuran (THF) as a cosolvent at certain volume fractions in water influenced the degradation rate of sepiolite-supported nZVI. Debromination pathways of BDE-209 with sepiolite-supported nZVI were proposed based on the identified reaction intermediates, which ranged from nona- to mono-brominated diphenylethers (BDEs) under acidic conditions and nona- to penta-BDEs under alkaline conditions. Adsorption on sepiolite-supported nZVI particles also played a role in the removal of BDE-209. Our findings indicate that the particles have potential applications in removing environmental pollutants, such as halogenated organic contaminants.     

Human lung injury following exposure to humic substances and humic-like substances

Among the myriad particles the human respiratory tract is exposed to, a significant number are distinctive in that they include humic substances (HS) and humic-like substances (HULIS) as organic components. HS are heterogeneous, amorphous, organic materials which are ubiquitous occurring in all terrestrial and aqueous environments. HULIS are a complex class of organic, macromolecular compounds initially extracted from atmospheric aerosol particles which share some features with HS including an aromatic, polyacidic nature. As a result of having a variety of oxygen-containing functional groups, both HS and HULIS complex metal cations, especially iron. Following particle uptake by cells resident in the lung, host iron will be sequestered by HS- and HULIS-containing particles initiating pathways of inflammation and subsequent fibrosis. It is proposed that (1) human exposures to HS and HULIS of respirable size (<10 µm diameter) are associated with inflammatory and fibrotic lung disease and (2) following retention of particles which include HS and HULIS, the mechanism of cell and tissue injury involves complexation of host iron. Human inflammatory and fibrotic lung injuries following HS and HULIS exposures may include coal workers’ pneumoconiosis, sarcoidosis, and idiopathic pulmonary fibrosis as well as diseases associated with cigarette smoking and exposures to emission and ambient air pollution particles.     

In-situ electrochemical measurements of total concentration and speciation of heavy metals in acid mine drainage (AMD): assessment of the use of anodic stripping voltammetry

We assessed the use of anodic stripping voltammetry (ASV) for in-situ determinations of both total concentration and speciation of dissolved heavy metals (Cd, Cu, Pb and Zn) in acid mine drainage (AMD). In the Kwangyang Au–Ag mine area of South Korea, different sites with varying water chemistry within an AMD were studied with a field portable anodic stripping voltammeter. Anodic stripping voltammetry after wet oxidation (acidification) was very sensitive enough to determine total concentration of dissolved Cd because Cd was dominantly present as ‘labile’ species, whilst the technique was not so effective for determining total Cu especially in the downstream sites from the retention pond, due to its complexation with organic matter. For dissolved Pb, the concentrations determined by ASV after wet oxidation generally agreed with those by ICP-AES. In the downstream samples (pH>5), however, ASV data after wet oxidation were lower than ICP-AES data because a significant fraction of dissolved Pb was present in those samples as ‘inert’ species associated with colloidal iron oxide particles. The determination of total dissolved Zn by ASV after wet oxidation appeared to be unsatisfactory for the samples with high Cu content, possibly due to the interference by the formation of Zn–Cu intermetallic compounds on the mercury coated electrode. In AMD samples with high dissolved iron, use of ultraviolet irradiation was not effective for determining total concentrations because humate destruction by UV irradiation possibly resulted in the removal of a part of dissolved heavy metals from waters through the precipitation of iron hydroxides.     

Effect of humic acid and metal ions on the debromination of BDE209 by nZVM prepared from steel pickling waste liquor

As a promising in situ remediation technology, nanoscale zero-valent iron (nZVI) can remove polybrominated diphenyl ethers such as decabromodiphenyl ether (BDE209) effectively, However its use is limited by its high production cost. Using steel pickling waste liquor as a raw material to prepare nanoscale zero-valent metal (nZVM) can overcome this deficiency. It has been shown that humic acid and metal ions have the greatest influence on remediation. The results showed that nZVM and nZVI both can effectively remove BDE209 with little difference in their removal efficiencies, and humic acid inhibited the removal efficiency, whereas metal ions promoted it. The promoting effects followed the order Ni²⁺>Cu²⁺>Co²⁺ and the cumulative effect of the two factors was a combination of the promoting and inhibitory individual effects. The major difference between nZVM and nZVI lies in their crystal form, as nZVI was found to be amorphous while that of nZVM was crystal. However, it was found that both nZVM and nZVI removed BDE209 with similar removal efficiencies. The effects and cumulative effects of humic acid and metal ions on nZVM and nZVI were very similar in terms of the efficiency of the BDE209 removal.     

零价铁降解氯代有机污染物的QSPR研究

利用密度泛函理论B3IYP/6-31G(d)水平计算氯代有机污染物绝热电子亲合能(EAad)、垂直电子亲合能(EAvert)及C-Cl键键离解能(BDE),据此研究零价铁对该类化合物脱氯降解的定量结构-性质关系(QSPR).结果表明,描述符EAad和BDE所建QSPR模型效果均较好,同时EAad可以很好地体现还原过程,BDE则对于降解途径预测具有较大价值.