Synthesis of clay-supported nanoscale zero-valent iron using green tea extract for the removal of phosphorus from aqueous solutions

This study addresses the synthesis of nanoscale zero-valent iron(n ZVI) in the presence of natural bentonite(B-n ZVI) using green tea extract. The natural bentonite and B-n ZVI were then applied for the removal of phosphorus from aqueous solutions at various concentrations, p H levels and contact time. The desorption of phosphorus(P) from adsorbents was done immediately after sorption at the maximum initial concentration using the successive dilution method. The characterization of FTIR, SEM, and XRD indicated that n ZVI was successfully loaded to the surface of natural bentonite. The sorption of phosphorus on B-n ZVI was observed to be p H-dependent, with maximum phosphorus removal occurring at the p H range of 2 to 5. The results demonstrate that the maximum sorption capacities of natural bentonite and B-n ZVI were 4.61 and 27.63 mg·g^(-1), respectively.Langmuir, Freundlich, and Redlich–Peterson models properly described the sorption isotherm data. For either adsorbent, desorption isotherms did not coincide with their corresponding sorption isotherms, suggesting the occurrence of irreversibility and hysteresis. The average percentages of retained phosphorus released from natural bentonite and B-n ZVI were 80% and 9%, respectively. The results indicated that sorption kinetics was best described by the pseudo-second-order model. The present study suggests that B-n ZVI could be used as a suitable adsorbent for the removal of phosphorus from aqueous solutions.

Synthesis of nanoscale zero-valent iron supported on exfoliated graphite for removal of nitrate

Nano ZVI particles supported on micro-scale exfoliated graphite were prepared by using KBH4 as reducing agent in the H2O/ethanol system. The supported ZVI materials generally have higher activity and greater flexibility for environmental remediation applications. The exfoliated graphite as the support was treated beforehand to hydrophilic material. Nano iron particles are deposited onto the rough graphite surface while those were formed by borohydride reduction. The possible nitrate reduction pathways were proposed. The TEM image shows that iron particles are highly dispersed on the surface of graphite and several of iron particles are imbedded in the pit of support surface. In this synthesis, iron particles have a nearly spherical shape with a grain size of 50?100 nm. The surface areas of materials with different iron loadings of 3.5%, 7.0%, 10.0%, 15.0% and 20.0%(mass fraction) are 2.89, 9.55, 8.45, 23.8 and 6.18 m2·g?1 by BET surface analyzer. The chemical reduction of nitrate by supported nano ZVI in aqueous solution were tested in series batch experiments. Experiment results suggest that NO3? can be more rapidly reduced to NH4+ at neutral pH and anaerobic conditions by supported nano ZVI than unsupported nano ZVI or ZVI scraps. The 15% nano Fe/graphite shows the best reduction efficiency contrasted with other Fe loading particles.

Treatment of simulated wastewater containing Reactive Red 195 by zero-valent iron/activated carbon combined with microwave discharge electrodeless lamp/sodium hypochlorite

A comparative study of treatment of simulated wastewater containing Reactive Red 195 using zero-valent iron/activated carbon （ZVI/AC）, microwave discharge electrodeless lamp/sodium hypochlorite （MDEL/NaCIO） and the combination of ZVI/AC- MDEL/NaCIO was conducted. The preliminary results showed the two steps method of ZVI/AC-MDEL/NaCIO had much higher degradation efficiency than both single steps. The final color removal percentage was nearly up to 100% and the chemical oxygen demand reduction percentage was up to approximately 82%. The effects of operational parameters, including initial pH value of simulated wastewater, ZVI/AC ratio and particle size of ZVI were also investigated. In addition, from the discussion of synergistic effect between ZVI/AC and MEDL/NaCIO, we found that in the ZVI/AC-MEDL/NaCIO process, ZVI/AC could break the azo bond firstly and then MEDLfNaCIO degraded the aromatic amine products effectively. Reversing the order would reduce the degradation efficiency.

Advanced treatment of biologically pretreated coking wastewater by intensified zero-valent iron process(IZVI) combined with anaerobic filter and biological aerated filter(AF/BAF)

Experiments were conducted to investigate the behavior of the sequential system of intensified zero-valent iron process(IZVI) and anaerobic filter and biological aerated filter(AF/BAF) reactors for advanced treatment of biologically pretreated coking wastewater. Particular attention was paid to the performance of the integrated system for the removal of chemical oxygen demand(COD), ammonia nitrogen(NH3-N) and total nitrogen(TN). The average removal efficiencies of COD, NH3-N and TN were 76.28%, 96.76% and 59.97%, with the average effluent mass concentrations of 56, 0.53 and 18.83 mg/L, respectively, reaching the first grade of the national discharge standard. Moreover, the results of gas chromatography/mass spectrum(GC/MS) and gel permeation chromatography(GPC) analysis demonstrated that the refractory organic compounds with high relative molecular mass were partly removed in IZVI process by the function of oxidation-reduction, flocculation and adsorption which could also enhance the biodegradability of the system effluent. The removal efficiencies of NH3-N and TN were achieved mainly in the subsequent AF/BAF reactors by nitrification and denitrification. Overall, the results obtained show that the application of IZVI in combination with AF/BAF is a promising technology for advanced treatment of biologically pretreated coking wastewater.

Degradation of nitrobenzene-containing wastewater by sequential nanoscale zero valent iron-persulfate process

As nitrobenzene(NB)is structurally stable and difficult to degrade due to the presence of an electron withdrawing group(nitro group).The sequential nanoscale zero valent iron-persulfate(NZVI-Na_(2)S_(2)O_(8))process was proposed in this study for the degradation NB-containing wastewater.The results showed that the NB degradation efficiency and the total organic carbon removal efficiency in the sequential NZVINa_(2)S_(2)O_(8)process were 100%and 49.25%,respectively,at a NB concentration of 200 mg L^(-1),a NZVI concentration of 0.75 g L^(-1),a Na_(2)S_(2)O_(8)concentration of 26.8 mmol L^(-1),an initial pH of 5,and a reaction time of 30 min,which were higher than those(88.53%and 35.24%,respectively)obtained in the NZVI/Na_(2)S_(2)O_(8)process.Sulfate radicals(SO_(4)·-)and hydroxyl radicals(·OH)generated in the reaction were identified directly by electron paramagnetic resonance spectroscopy and indirectly by radical capture experiments,and it was shown that both SO_(4)^(·-)and·OH played a major role in the sequential NZVI-Na_(2)S_(2)O_(8)process.The possible pathways involved in the reduction of NB to aniline(AN)and the further oxidative degradation of AN were determined by gas chromatography-mass spectrometry.

Sorption Kinetic of Arsenate as Water Contaminant on Zero Valent Iron

This study investigates the sorption of arsenate from water using zero-valent iron ZVI as sorbent. Batch experiments were carried out to study the sorption kinetics of arsenate under different concentrations of arsenate varies from 0.5 to 200 mg/l. A kinetic model was considered to describe the arsenates sorption on ZVI material. The kinetics of the arsenate sorption processes were described by the Langmuir kinetic model. The sorption capacity increases with high initial concentration which obtained the maximum sorption 2.1 mg/g at 200 mg/l of arsenate initial concentration. The results show that the rapid initial sorption rates of arsenate were occurred at the beginning of experiments running time, followed by a slower removal that gradually approaches an equilibrium condition. The data from laboratory batch experiments were used to verify the simulation results of the kinetic model resulting in good agreement between measured and modeled results. The results indicate that ZVI could be employed as sorbent materials to enhance the sorption processes and increase the removal rate of arsenate from water.

Enhanced degradation of carbon tetrachloride by surfactant-modified zero-valent iron

Sorption of carbon tetrachloride (CT) by zero-valent iron (ZVI) is the rate-limiting step in the degradation of CT, so the sorption capacity of ZVI is of great importance. This experiment was aimed at enhancing the sorption of CT by ZVI and the degradation rate of CT by modification of surfactants. This study showed that ZVI modified by cationic surfactants has favorable synergistic effect on the degradation of CT. The CT degradation rate of ZVI modified by cetyl pyridinium bromide (CPB) was higher than that of the unmodified ZVI by 130%, and the CT degradation rate of ZVI modified by cetyl trimethyl ammonium bromide (CTAB) was higher than that of the unmodified ZVI by 81%. This study also showed that the best degradation effect is obtained at the near critical micelle concentrations (CMC) and that high loaded cationic surfactant does not have good synergistic effect on the degradation due to its hydrophilicity and the block in surface reduction sites. Furthermore degradation of CT by ZVI modified by nonionic surfactant has not positive effect on the degradation as the ionic surfactant and the ZVI modified by anionic surfactant has hardly any obvious effects on the degradation.

Remediation of Malathion Contaminated Soil Using Zero Valent Iron Nano-Particles

In this study, iron nano-particles were used to remediate malathion contaminated soil in the concentration range of 1 - 10 μg?g–1. The zero valent iron nano-particles were prepared by reducing ferric chloride solution with sodium boro- hydride for remediation of the soil. The optimized quantity of iron nano particles was found to be 0.1 g?kg–1 of soil con- taminated with 10 μg?g–1 of malathion. Malathion was determined in the soil after leaching to water at pH 8.2 and fol- lowed by its oxidation with slight excess of N-bromosuccinimide (NBS). The unconsumed NBS was estimated by measuring the decrease in the color intensity of rhodamine B. Degradation product formed during the oxidation of ma-lathion by zero valent iron was monitored by the Attenuated Total Reflectance Fourier Transform Infrared Spectros- copy (ATR-FTIR). The results clearly showed that quantitative oxidation of malathion was achieved within eight min- utes after the addition of zero valent iron nano particles.

H₂Gas Charging of Zero-Valent Iron and TCE Degradation

Granular zero-valent iron (ZVI) has been widely used to construct permeable reactive barriers (PRB) for the in situ remediation of groundwater contaminated with halogenated hydrocarbons. In the anaerobic condition of most groundwater flow systems, iron undergoes corrosion by water and results in hydrogen gas generation. Several studies have shown that some of the hydrogen gas generated at the iron/water interface can diffuse into the iron lattice. Hydrogen gas also can be an electron donor for dechlorination of chlorinated compounds. In this study, the possibility of hydrogen gas bound in the lattice of ZVI playing a role in dehalogenation and improving the degradation efficiency of ZVI was evaluated. Two different granular irons were tested: one obtained from Quebec Metal Powders Ltd (QMP) and the other from Connelly-GPM. Ltd. For each type of iron, two samples were mixed with water and sealed in testing cells. Since the rate of hydrogen entry varies directly with the square root of the hydrogen pressure, one sample was maintained for several weeks under near-vacuum conditions to minimize the amount of hydrogen entering the iron lattice. The other sample was maintained for the same period at a hydrogen pressure of over 400 kPa to maximize the amount of hydrogen entering the iron lattice. The degradation abilities of the reacted ironsand the original iron materials were tested by running several sets of batch tests. The results of this study show little to no improvement of inorganic TCE degradation reactions due to the presence of lattice-stored hydrogen in iron material. This is probably due to the high energiesrequired to release hydrogen trapped in the iron lattice. However, there are certain chemical compounds that can promote hydrogen release from the iron lattice, and there may be bacteria that can utilize lattice-bound hydrogen to carry out dechlorination reactions.

Evaluating Effectiveness and Permanence of Selenium Treatment in a Solid Matrix via Aqueous-Mediated Zero Valent Iron Reaction

Increasingly, as regulatory limits become more stringent, selenium has become a parameter of concern. Selenium is a naturally occurring element that is largely mobilized by anthropogenic activity such as mining for fuel and subsequent combustion, metal ore refining and processing, and agricultural irrigation. Of concern is removing selenium liquid matrices and immobilizing it from leachable solid matrices. Chemical reduction and stabilization using zero valent iron (ZVI) is applicable to both concerns. The solid matrix case study is applicable to ash ponds solids or industrial bag house dust solids. This paper presents data for treatment and stabilization of selenium within a solid matrix using ZVI. The methodology uses an aqueous mediate reaction to promote a stable solid matrix of non-leachable selenium. The paper describes matrix challenges and key variables that effected successful treatment. Testing with simulated and real bag house dust solids were used to establish data to support the permeance of the reaction. The data show that ZVI converts ionic selenium to a zero valent state in the solid matrix. It was also recognized that a fraction of ionic selenium may fail to react with the ZVI, but the results show that despite the presence of the unreacted ionic selenium, the toxicity characteristic leachate procedure (TCLP) results following treatment do not exceed the 1 mg/L hazardous waste criteria.

Application of Iron Nanoparticles Synthesized by Green Tea for the Removal of Hexavalent Chromium in Column Tests

Nano zero valent iron particles (nZVI) are popular the last few years because of the numerous applications in remediation of a wide range of pollutants in contaminated soils and aquifers. The nZVI particles can be 10 - 1000 times more reactive than granular or micro-scale ZVI particles due to the small particle size, large specific surface area and high reactivity. An alternative green synthesis procedure was used for the production of nano zero valent iron particles (nZVI) using green tea (GT) extract, which is characterized by its high antioxidant content. Polyphenols in green tea extract possess double role in the synthesis of nZVI, because they not only reduce ferric cations, but also protect nZVI from oxidation and agglomeration as capping agents. The objective of current study was to simulate ata laboratory scale the attachment of GT-nZVI particles on soil material and study the effectiveness of attached nanoparticles for removing hexavalent chromium (Cr(VI)) from contaminated groundwater flowing through the porous soil bed. Column tests were carried out with various flowrates in order to examine the effect of contact time between the attached on porous medium nZVI and the flow-through solution on Cr(VI) reduction. After the completion of column tests the soil material in each column was split in 5 vertical sections, which were further subjected to chemical analyses and leaching tests. According to the results of the study increasing the contact time favors the reduction and removal of Cr(VI) from the aqueous phase. The reductive precipitation of Cr can be described as a reaction that follows a pseudo-first order kinetic law, with rate constant equal to k = 0.0243 ± 0.0011 min-1. Leaching tests indicated that precipitated chromium is not soluble. In the examined soil material, the total amount of precipitated Cr was found to range between 280 and 890 mg/(kg soil), while soluble Cr was less than 1.4 mg/kg and most probably it was due to the presence of residual Cr(VI) solution in the porosity of soil.

铁基双金属催化剂活化过硫酸单盐(PMS)去除诺氟沙星性能研究

采用过渡金属Cu、Co和Mn对纳米零价铁(nZVI)掺杂改性,制备铁基双金属nZVI/Cu、nZVI/Co和nZVI/Mn催化剂,用于活化过氧单硫酸盐(PMS),研究了不同过渡金属、催化体系和过渡金属掺杂量对催化降解诺氟沙星(NOR)性能的影响。结果表明,当Co的掺杂量为5%时,nZVI/Co-5%/PMS活化体系在120 min内实现了84.4%的NOR去除。优异的活化降解性能主要得益于过渡金属Co的引入抑制了nZVI的钝化和团聚。

纳米零价铁复合材料对污染土壤修复的最新进展

土壤污染严重威胁农产品的安全和人类健康。近几年来纳米零价铁(nZVI)复合材料由于环境友好、易于制备、价格低廉、优异化学活性等特点广泛地应用于污染土壤修复,但是对土壤中不同污染类型修复的调研较少。综述主要调研nZVI复合材料修复污染土壤中重金属、有机污染物和石油有机物的最新进展。重点评述nZVI复合材料的不同性质对污染土壤中各种污染物修复效果的影响,最后对n ZVI铁复合材料修复污染土壤得出结论并对未来方向进行展望。该综述为更好地应用nZVI复合材料对污染土壤的修复提供理论依据和指导。

碳改性纳米零价铁对水中六价铬的强化吸附还原研究

纳米零价铁材料因其还原性强的特点而多用于水中Cr(Ⅵ)污染治理。以葡萄糖和氯化铁为原料,通过碳化煅烧还原,制备碳改性纳米零价铁复合材料(nZVI@GC)。材料形貌及结构性质的分析显示,nZVI@GC上纳米零价铁为体心立方的α-Fe^(0),且颗粒分散均匀,平均粒径为32 nm。批处理试验显示,24 h内nZVI@GC对水体中Cr(Ⅵ)的吸附还原质量比为178.6 mg/g,是纳米零价铁(nZVI)的5.7倍,且吸附还原反应符合准二级动力学模型(R^(2)=0.9993)。其中,在pH值为2~3,Cr(Ⅵ)的初始质量浓度为50 mg/L,纳米零价铁的投加质量浓度为0.5 g/L的条件下,nZVI@GC可在30 min内完全吸附还原水中的Cr(Ⅵ)。在干燥空气中无保护存放nZVI@GC时,复合材料上的碳可以有效抑制氧气对纳米零价铁的侵蚀。与新制备材料相比,30 d后nZVI@GC对水中Cr(Ⅵ)的吸附还原率仅下降3.4%。nZVI@GC为材料高效、经济地吸附还原水中Cr(Ⅵ)提供了一种选择。

生物炭改性及其对除草剂污染水体和土壤修复的研究进展

除草剂已被大量使用于现代农业生产,而长期使用除草剂可能造成其在土壤中大量残留,或通过降水、淋溶和径流污染水体,因此引发环境污染问题和食品安全问题。生物炭作为一种绿色、高效的吸附剂已被广泛用于修复有机物污染水体和土壤。本文介绍了酸碱、有机物和金属盐浸渍改性,纳米零价铁和微生物负载改性等生物炭改性方法;综述了改性生物炭在除草剂污染修复中的应用情况,对比分析了生物炭改性前后的修复效果;探讨了改性生物炭自身特性、环境条件对改性生物炭修复除草剂污染的影响及机制。未来仍需对改性生物炭在除草剂污染修复过程中的稳定性、长效性和安全性等方面开展研究。

硫化纳米零价铁活化过二硫酸盐降解废水中四环素

硫化零价铁(S-nZVI)因其电子传递效率高、选择性好,近年来在水处理领域应用广泛。将S-nZVI与高级氧化技术结合,可发挥材料优异的催化性能,实现对污染物的高效降解。本文以硫脲为硫源制备高活性S-nZVI,构建S-nZVI活化过二硫酸盐(PDS)高级氧化体系实现对四环素(TC)的高效降解。采用扫描电子显微镜(SEM)、X射线衍射(XRD)、比表面积(BET)、X射线光电子能谱仪(XPS)等表征方法分析S-nZVI的组成结构和表面形貌,考察硫铁物质的量的比(S/Fe)、硫化时间、S-nZVI投加量、PDS浓度、溶液初始pH和共存离子对TC降解的影响作用,通过活性物种淬灭实验和电子顺磁共振实验(EPR)探究自由基和非自由基活性物质对TC的降解作用,利用液相色谱-质谱联用(LC-MS)分析TC降解的可能路径。结果表明:纳米零价铁(nZVI)经硫化改性后,比表面积增大,Fe和S均匀地分布在材料表面;S/Fe对TC降解的影响作用较小,TC降解率与S-nZVI投加量和PDS浓度呈正相关,但随着硫化时间增加呈现降低趋势;S-nZVI/PDS体系在较宽pH范围(pH=5~9)内均具有较优的TC降解效果;反应溶液中存在不同阴离子时,TC降解率受到不同程度抑制作用,其中HCO_(3)^(-)抑制作用最为显著;当S/Fe为0.028、硫化时间为2h、S-nZVI投加量为1g/L、PDS浓度为2mmolL,不调节初始溶液pH时,反应120min后TC降解率可达94.6%;S-nZVI/PDS体系的活性物种除常见自由基(SO_(4)^(·-)和HO^(·))外,还包括非自由基活性物质Fe(Ⅳ),但Fe(Ⅳ)对TC的降解作用较小;TC降解主要通过特定官能团裂解和开环反应进行,最终氧化降解成CO_(2)和H_(2)O。

零价铁活化过氧乙酸降解水中双酚A的效果与机制

双酚A(BPA)是含酚工业废水中代表性污染物,采用零价铁(ZVI)活化过氧乙酸(PAA)去除水中BPA,探究了ZVI和PAA投量、pH以及工业废水中典型共存阴离子对PAA活化和BPA降解的影响,并通过探究反应活性物种和活性位点解析了ZVI活化PAA的反应机制。在投加50 mg/L ZVI,1.00 mmol/L PAA和初始pH为3.4的最优工艺条件下,ZVI/PAA体系反应30 min可去除水中99.24%的BPA;HCO_(3)^(-)和SO_(4)^(2-)对BPA降解具有抑制作用,Cl^(-)(0~20.0 mmol/L)则加速BPA降解。反应中ZVI及其表面氧化层分别释放溶解性Fe(Ⅱ)和Fe(Ⅲ),溶出的Fe(Ⅱ)活化PAA贡献26.46%的BPA降解,非均相ZVI活化PAA对BPA降解起主要作用;淬灭实验表明,ZVI/PAA体系存在CH_(3)C(O)OO·、CH_(3)C(O)O·、·OH和FeⅣO^(2+),其中CH_(3)C(O)OO·和FeⅣO^(2+)是降解BPA的主要活性物种。本研究可为工业废水中双酚A的有效去除提供理论和数据支撑。

纳米铁改性生物炭载体强化厌氧氨氧化菌富集与脱氮效果研究

为实现厌氧氨氧化菌(AnAOB)在载体生物膜中快速富集,本文采用液相还原方法制备了纳米铁改性生物炭(nZVI@BC)载体,并设置两组相同的厌氧氨氧化(ANAMMOX)富集装置(R_(1)、R_(2)),通过对R_(1)、R_(2)装置添加不同载体(分别为BC和nZVI@BC),考察在富集过程中ANAMMOX装置的脱氮性能、载体表面特征和微生物群落结构差异.结果表明:①BC表面成功负载nZVI,nZVI@BC载体比BC载体具有更高的比表面积,改性后载体的比表面积从47.17 m^(2)/g增至210.82 m^(2)/g,可为微生物提供更多的附着位点.②R_(2)装置NH_(4)^(+)-N和NO_(2)^(−)-N去除率稳定达到90%所需时间均比R_(1)装置短,且稳定运行后,R_(1)、R_(2)装置的TN去除率最高分别为86.99%、89.65%.③nZVI@BC载体表面颜色由黑色变为红褐色,表明红色的ANAMMOX生物膜初步形成,且其表面生物量比BC载体表面生物量高23倍.④第20天,R_(1)、R_(2)装置中AnAOB的相对丰度分别为10.47%和29.15%;R_(1)、R_(2)装置载体表面主要的AnAOB属均为Candidatus Kuenenia,其相对丰度分别为7.49%和23.76%.研究显示,改性的nZVI@BC载体显著促进了ANAMMOX生物膜的快速形成和AnAOB的高效富集,提升了ANAMMOX过程的脱氮性能.

不同粒径零价铁对微氧脱氮系统的影响

构建了部分硝化反硝化厌氧氨氧化(SNAD)微氧体系,并定期向体系内投加120 mg不同粒径的零价铁(ZVI),从反应器运行情况、微生物性能以及群落结构来探究不同粒径ZVI对微氧系统的影响。研究结果表明,在50 nm粒径ZVI(50 nZVI)的介导下,系统的TIN去除率最终稳定在83.591%,电子传递活性(ETSA)是接种污泥的1.48倍,均高于其他粒径ZVI的影响。越小粒径ZVI越能促进胞外聚合物的产生,有利于活性污泥结构稳定。这都源于粒径越小的ZVI更容易被微生物吸附、利用。微生物群落结构与功能分析结果表明,在粒径越小的ZVI介导下的微生物群落多样性越高,群落结构也越复杂。ZVI介导会促进对氧需求不敏感的微生物的富集,样品中主要检测出Candidatus_Brocadia和Candidatus_Kuenenia两种厌氧氨氧化菌(AnAOB),且在50 nZVI影响下丰度最高,分别为4.650%和0.692%。nZVI介导下,AnAOB与Gemmobacter和norank_f_Comamonadaceae两种兼性厌氧型反硝化菌共同作用构成SNAD的脱氮途径。而在mZVI介导下,兼性厌氧型反硝化为主要脱氮途径。