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.

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.

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.

Characterization of the adsorption behavior of aqueous cadmium on nanozero-valent iron based on orthogonal experiment and surface complexation modeling

Polyvinylpyrrolidone K-30(PVP) was introduced into the preparation of nanozero-valent iron(n ZVI) and the traditional liquid-phase reduction was improved. The introduction of PVP simplified the traditional method.The n ZVI prepared with this new approach showed excellent surface characters and high performance on the removal of cadmium. TEM results showed that the aggregates of n ZVI can reach to several micrometers in length but less than 100 nm in diameter. The iron particles that were enclosed by a layer of oxide film that is less than10 nm, demonstrated that the n ZVI possesses a core–shell structure. BET results indicate that the specific surface area of the n ZVI was 20.3159 m^2g^(-1). A three factor and three level orthogonal experiment was employed to find out the dominant factor that affects the removal rate of cadmium by n ZVI. Based on the range values, the prominence order of each factor was: initial p H of the solution N initial concentration of cadmium N dosage of n ZVI, the range was 96.453, 3.294 and 1.747, respectively. A simulation was performed under the same condition and a same conclusion was derived, this consistence confirmed the validity of the conclusion that p H is the most significant factor that affects the adsorption efficiency.

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.

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.

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.

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.

Effect of sub-zero cooling on microstructure and mechanical properties of a low alloyed austempered ductile iron

The effect of sub-zero cooling on microstructure and mechanical properties of a low alloyed austempered ductile iron has been investigated. Austempering of samples was performed at 325℃and 400℃after austenitizing at 875℃and 950℃. The sub-zero treatments were carried out by cooling down the samples to -30℃, -70℃and -196℃. The changes in volume fraction of austenite and mechanical properties were determined after cooling to each temperature. The austenite volume fraction of samples which were austenitized at 875℃and austempered at 325℃remained unchanged, whilst it reduced in samples austenitized at 950℃and 875℃for austempering temperature of 400℃. In these specimens, some austenite transformed to martensite after subzero cooling. Mechanical property measurements showed a slight increase in strength and hardness and decrease in elongation and toughness due to this transformation behavior.

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。

零价铝还原联合过硫酸盐氧化高效处理DDNP工业废水

二硝基重氮酚(DDNP)是一种应用广泛的高效引发炸药,生产单位质量的DDNP便会产生200~300倍的含DDNP及其衍生物的工业废水。DDNP毒性大且十分稳定,难以生物降解,而且由于其结构中存在强吸电子的硝基结构,具有抗氧化性,单一高级氧化技术也难以将其彻底降解。利用改性微米零价铝(C@mZVAl)联合过硫酸钠(Na_(2)S_(2)O_(8))构建先还原后氧化体系,考察耦合体系对DDNP的降解性能。结果表明,无需进行额外稀释或调pH等预处理,C@mZVAl联合Na_(2)S_(2)O_(8)便可实现对实际DDNP工业废水〔DDNP(1 050±15) mg/L〕的高效处理,处理效果明显优于单独的氧化或还原处理体系。增加C@mZVAl的投加量可以加快还原阶段的反应速率,增加Na_(2)S_(2)O_(8)的投加量可进一步提高DDNP和COD的去除率,当DDNP初始质量浓度为(1 050±15) mg/L时,还原阶段投加8 g/L C@mZVAl联合氧化阶段投加10 mmol/L Na_(2)S_(2)O_(8)进行反应,废水中DDNP降解率达96.81%,COD去除率达81.20%,出水清澈。相较于目前其他的DDNP处理工艺,改性微米零价铝(C@mZVAl)联合过硫酸钠(Na_(2)S_(2)O_(8))工艺具有效率高、操作简单、药剂消耗少等特点,为DDNP及其他类型抗氧化有机工业废水的治理提供新的思路。

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。

磷酸铁废水零排放及资源化处理技术分析

目前,磷酸铁锂是锂电池的主要正极材料,而磷酸铁是制备磷酸铁锂的关键前驱体。磷酸铁生产过程产生大量废水,其酸性强、盐分高,处理难度大,现已成为制约磷酸铁生产企业发展的瓶颈。磷酸铁废水含有高浓度磷酸根、硫酸根、氨根及金属离子,废水经预处理+膜浓缩+蒸发结晶处理后可获得硫酸铵、磷酸二氢铵等副产品,处理后的废水可回用于生产环节,因而磷酸铁废水具有良好的资源化回收价值。本文综述磷酸铁废水处理技术现状,分析磷酸铁废水处理存在的问题,然后提出磷酸铁废水零排放处理技术思路,以实现磷酸铁废水的资源化利用,保护生态环境。